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Linux/kernel/cgroup/cgroup.c

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  1 /*
  2  *  Generic process-grouping system.
  3  *
  4  *  Based originally on the cpuset system, extracted by Paul Menage
  5  *  Copyright (C) 2006 Google, Inc
  6  *
  7  *  Notifications support
  8  *  Copyright (C) 2009 Nokia Corporation
  9  *  Author: Kirill A. Shutemov
 10  *
 11  *  Copyright notices from the original cpuset code:
 12  *  --------------------------------------------------
 13  *  Copyright (C) 2003 BULL SA.
 14  *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
 15  *
 16  *  Portions derived from Patrick Mochel's sysfs code.
 17  *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 18  *
 19  *  2003-10-10 Written by Simon Derr.
 20  *  2003-10-22 Updates by Stephen Hemminger.
 21  *  2004 May-July Rework by Paul Jackson.
 22  *  ---------------------------------------------------
 23  *
 24  *  This file is subject to the terms and conditions of the GNU General Public
 25  *  License.  See the file COPYING in the main directory of the Linux
 26  *  distribution for more details.
 27  */
 28 
 29 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 30 
 31 #include "cgroup-internal.h"
 32 
 33 #include <linux/cred.h>
 34 #include <linux/errno.h>
 35 #include <linux/init_task.h>
 36 #include <linux/kernel.h>
 37 #include <linux/magic.h>
 38 #include <linux/mutex.h>
 39 #include <linux/mount.h>
 40 #include <linux/pagemap.h>
 41 #include <linux/proc_fs.h>
 42 #include <linux/rcupdate.h>
 43 #include <linux/sched.h>
 44 #include <linux/sched/task.h>
 45 #include <linux/slab.h>
 46 #include <linux/spinlock.h>
 47 #include <linux/percpu-rwsem.h>
 48 #include <linux/string.h>
 49 #include <linux/hashtable.h>
 50 #include <linux/idr.h>
 51 #include <linux/kthread.h>
 52 #include <linux/atomic.h>
 53 #include <linux/cpuset.h>
 54 #include <linux/proc_ns.h>
 55 #include <linux/nsproxy.h>
 56 #include <linux/file.h>
 57 #include <net/sock.h>
 58 
 59 #define CREATE_TRACE_POINTS
 60 #include <trace/events/cgroup.h>
 61 
 62 #define CGROUP_FILE_NAME_MAX            (MAX_CGROUP_TYPE_NAMELEN +      \
 63                                          MAX_CFTYPE_NAME + 2)
 64 
 65 /*
 66  * cgroup_mutex is the master lock.  Any modification to cgroup or its
 67  * hierarchy must be performed while holding it.
 68  *
 69  * css_set_lock protects task->cgroups pointer, the list of css_set
 70  * objects, and the chain of tasks off each css_set.
 71  *
 72  * These locks are exported if CONFIG_PROVE_RCU so that accessors in
 73  * cgroup.h can use them for lockdep annotations.
 74  */
 75 DEFINE_MUTEX(cgroup_mutex);
 76 DEFINE_SPINLOCK(css_set_lock);
 77 
 78 #ifdef CONFIG_PROVE_RCU
 79 EXPORT_SYMBOL_GPL(cgroup_mutex);
 80 EXPORT_SYMBOL_GPL(css_set_lock);
 81 #endif
 82 
 83 /*
 84  * Protects cgroup_idr and css_idr so that IDs can be released without
 85  * grabbing cgroup_mutex.
 86  */
 87 static DEFINE_SPINLOCK(cgroup_idr_lock);
 88 
 89 /*
 90  * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
 91  * against file removal/re-creation across css hiding.
 92  */
 93 static DEFINE_SPINLOCK(cgroup_file_kn_lock);
 94 
 95 struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
 96 
 97 #define cgroup_assert_mutex_or_rcu_locked()                             \
 98         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
 99                            !lockdep_is_held(&cgroup_mutex),             \
100                            "cgroup_mutex or RCU read lock required");
101 
102 /*
103  * cgroup destruction makes heavy use of work items and there can be a lot
104  * of concurrent destructions.  Use a separate workqueue so that cgroup
105  * destruction work items don't end up filling up max_active of system_wq
106  * which may lead to deadlock.
107  */
108 static struct workqueue_struct *cgroup_destroy_wq;
109 
110 /* generate an array of cgroup subsystem pointers */
111 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
112 struct cgroup_subsys *cgroup_subsys[] = {
113 #include <linux/cgroup_subsys.h>
114 };
115 #undef SUBSYS
116 
117 /* array of cgroup subsystem names */
118 #define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
119 static const char *cgroup_subsys_name[] = {
120 #include <linux/cgroup_subsys.h>
121 };
122 #undef SUBSYS
123 
124 /* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
125 #define SUBSYS(_x)                                                              \
126         DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);                 \
127         DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);                  \
128         EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);                      \
129         EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
130 #include <linux/cgroup_subsys.h>
131 #undef SUBSYS
132 
133 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
134 static struct static_key_true *cgroup_subsys_enabled_key[] = {
135 #include <linux/cgroup_subsys.h>
136 };
137 #undef SUBSYS
138 
139 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
140 static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
141 #include <linux/cgroup_subsys.h>
142 };
143 #undef SUBSYS
144 
145 static DEFINE_PER_CPU(struct cgroup_cpu_stat, cgrp_dfl_root_cpu_stat);
146 
147 /*
148  * The default hierarchy, reserved for the subsystems that are otherwise
149  * unattached - it never has more than a single cgroup, and all tasks are
150  * part of that cgroup.
151  */
152 struct cgroup_root cgrp_dfl_root = { .cgrp.cpu_stat = &cgrp_dfl_root_cpu_stat };
153 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
154 
155 /*
156  * The default hierarchy always exists but is hidden until mounted for the
157  * first time.  This is for backward compatibility.
158  */
159 static bool cgrp_dfl_visible;
160 
161 /* some controllers are not supported in the default hierarchy */
162 static u16 cgrp_dfl_inhibit_ss_mask;
163 
164 /* some controllers are implicitly enabled on the default hierarchy */
165 static u16 cgrp_dfl_implicit_ss_mask;
166 
167 /* some controllers can be threaded on the default hierarchy */
168 static u16 cgrp_dfl_threaded_ss_mask;
169 
170 /* The list of hierarchy roots */
171 LIST_HEAD(cgroup_roots);
172 static int cgroup_root_count;
173 
174 /* hierarchy ID allocation and mapping, protected by cgroup_mutex */
175 static DEFINE_IDR(cgroup_hierarchy_idr);
176 
177 /*
178  * Assign a monotonically increasing serial number to csses.  It guarantees
179  * cgroups with bigger numbers are newer than those with smaller numbers.
180  * Also, as csses are always appended to the parent's ->children list, it
181  * guarantees that sibling csses are always sorted in the ascending serial
182  * number order on the list.  Protected by cgroup_mutex.
183  */
184 static u64 css_serial_nr_next = 1;
185 
186 /*
187  * These bitmasks identify subsystems with specific features to avoid
188  * having to do iterative checks repeatedly.
189  */
190 static u16 have_fork_callback __read_mostly;
191 static u16 have_exit_callback __read_mostly;
192 static u16 have_free_callback __read_mostly;
193 static u16 have_canfork_callback __read_mostly;
194 
195 /* cgroup namespace for init task */
196 struct cgroup_namespace init_cgroup_ns = {
197         .count          = REFCOUNT_INIT(2),
198         .user_ns        = &init_user_ns,
199         .ns.ops         = &cgroupns_operations,
200         .ns.inum        = PROC_CGROUP_INIT_INO,
201         .root_cset      = &init_css_set,
202 };
203 
204 static struct file_system_type cgroup2_fs_type;
205 static struct cftype cgroup_base_files[];
206 
207 static int cgroup_apply_control(struct cgroup *cgrp);
208 static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
209 static void css_task_iter_advance(struct css_task_iter *it);
210 static int cgroup_destroy_locked(struct cgroup *cgrp);
211 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
212                                               struct cgroup_subsys *ss);
213 static void css_release(struct percpu_ref *ref);
214 static void kill_css(struct cgroup_subsys_state *css);
215 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
216                               struct cgroup *cgrp, struct cftype cfts[],
217                               bool is_add);
218 
219 /**
220  * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
221  * @ssid: subsys ID of interest
222  *
223  * cgroup_subsys_enabled() can only be used with literal subsys names which
224  * is fine for individual subsystems but unsuitable for cgroup core.  This
225  * is slower static_key_enabled() based test indexed by @ssid.
226  */
227 bool cgroup_ssid_enabled(int ssid)
228 {
229         if (CGROUP_SUBSYS_COUNT == 0)
230                 return false;
231 
232         return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
233 }
234 
235 /**
236  * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
237  * @cgrp: the cgroup of interest
238  *
239  * The default hierarchy is the v2 interface of cgroup and this function
240  * can be used to test whether a cgroup is on the default hierarchy for
241  * cases where a subsystem should behave differnetly depending on the
242  * interface version.
243  *
244  * The set of behaviors which change on the default hierarchy are still
245  * being determined and the mount option is prefixed with __DEVEL__.
246  *
247  * List of changed behaviors:
248  *
249  * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
250  *   and "name" are disallowed.
251  *
252  * - When mounting an existing superblock, mount options should match.
253  *
254  * - Remount is disallowed.
255  *
256  * - rename(2) is disallowed.
257  *
258  * - "tasks" is removed.  Everything should be at process granularity.  Use
259  *   "cgroup.procs" instead.
260  *
261  * - "cgroup.procs" is not sorted.  pids will be unique unless they got
262  *   recycled inbetween reads.
263  *
264  * - "release_agent" and "notify_on_release" are removed.  Replacement
265  *   notification mechanism will be implemented.
266  *
267  * - "cgroup.clone_children" is removed.
268  *
269  * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
270  *   and its descendants contain no task; otherwise, 1.  The file also
271  *   generates kernfs notification which can be monitored through poll and
272  *   [di]notify when the value of the file changes.
273  *
274  * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
275  *   take masks of ancestors with non-empty cpus/mems, instead of being
276  *   moved to an ancestor.
277  *
278  * - cpuset: a task can be moved into an empty cpuset, and again it takes
279  *   masks of ancestors.
280  *
281  * - memcg: use_hierarchy is on by default and the cgroup file for the flag
282  *   is not created.
283  *
284  * - blkcg: blk-throttle becomes properly hierarchical.
285  *
286  * - debug: disallowed on the default hierarchy.
287  */
288 bool cgroup_on_dfl(const struct cgroup *cgrp)
289 {
290         return cgrp->root == &cgrp_dfl_root;
291 }
292 
293 /* IDR wrappers which synchronize using cgroup_idr_lock */
294 static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
295                             gfp_t gfp_mask)
296 {
297         int ret;
298 
299         idr_preload(gfp_mask);
300         spin_lock_bh(&cgroup_idr_lock);
301         ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
302         spin_unlock_bh(&cgroup_idr_lock);
303         idr_preload_end();
304         return ret;
305 }
306 
307 static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
308 {
309         void *ret;
310 
311         spin_lock_bh(&cgroup_idr_lock);
312         ret = idr_replace(idr, ptr, id);
313         spin_unlock_bh(&cgroup_idr_lock);
314         return ret;
315 }
316 
317 static void cgroup_idr_remove(struct idr *idr, int id)
318 {
319         spin_lock_bh(&cgroup_idr_lock);
320         idr_remove(idr, id);
321         spin_unlock_bh(&cgroup_idr_lock);
322 }
323 
324 static bool cgroup_has_tasks(struct cgroup *cgrp)
325 {
326         return cgrp->nr_populated_csets;
327 }
328 
329 bool cgroup_is_threaded(struct cgroup *cgrp)
330 {
331         return cgrp->dom_cgrp != cgrp;
332 }
333 
334 /* can @cgrp host both domain and threaded children? */
335 static bool cgroup_is_mixable(struct cgroup *cgrp)
336 {
337         /*
338          * Root isn't under domain level resource control exempting it from
339          * the no-internal-process constraint, so it can serve as a thread
340          * root and a parent of resource domains at the same time.
341          */
342         return !cgroup_parent(cgrp);
343 }
344 
345 /* can @cgrp become a thread root? should always be true for a thread root */
346 static bool cgroup_can_be_thread_root(struct cgroup *cgrp)
347 {
348         /* mixables don't care */
349         if (cgroup_is_mixable(cgrp))
350                 return true;
351 
352         /* domain roots can't be nested under threaded */
353         if (cgroup_is_threaded(cgrp))
354                 return false;
355 
356         /* can only have either domain or threaded children */
357         if (cgrp->nr_populated_domain_children)
358                 return false;
359 
360         /* and no domain controllers can be enabled */
361         if (cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
362                 return false;
363 
364         return true;
365 }
366 
367 /* is @cgrp root of a threaded subtree? */
368 bool cgroup_is_thread_root(struct cgroup *cgrp)
369 {
370         /* thread root should be a domain */
371         if (cgroup_is_threaded(cgrp))
372                 return false;
373 
374         /* a domain w/ threaded children is a thread root */
375         if (cgrp->nr_threaded_children)
376                 return true;
377 
378         /*
379          * A domain which has tasks and explicit threaded controllers
380          * enabled is a thread root.
381          */
382         if (cgroup_has_tasks(cgrp) &&
383             (cgrp->subtree_control & cgrp_dfl_threaded_ss_mask))
384                 return true;
385 
386         return false;
387 }
388 
389 /* a domain which isn't connected to the root w/o brekage can't be used */
390 static bool cgroup_is_valid_domain(struct cgroup *cgrp)
391 {
392         /* the cgroup itself can be a thread root */
393         if (cgroup_is_threaded(cgrp))
394                 return false;
395 
396         /* but the ancestors can't be unless mixable */
397         while ((cgrp = cgroup_parent(cgrp))) {
398                 if (!cgroup_is_mixable(cgrp) && cgroup_is_thread_root(cgrp))
399                         return false;
400                 if (cgroup_is_threaded(cgrp))
401                         return false;
402         }
403 
404         return true;
405 }
406 
407 /* subsystems visibly enabled on a cgroup */
408 static u16 cgroup_control(struct cgroup *cgrp)
409 {
410         struct cgroup *parent = cgroup_parent(cgrp);
411         u16 root_ss_mask = cgrp->root->subsys_mask;
412 
413         if (parent) {
414                 u16 ss_mask = parent->subtree_control;
415 
416                 /* threaded cgroups can only have threaded controllers */
417                 if (cgroup_is_threaded(cgrp))
418                         ss_mask &= cgrp_dfl_threaded_ss_mask;
419                 return ss_mask;
420         }
421 
422         if (cgroup_on_dfl(cgrp))
423                 root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
424                                   cgrp_dfl_implicit_ss_mask);
425         return root_ss_mask;
426 }
427 
428 /* subsystems enabled on a cgroup */
429 static u16 cgroup_ss_mask(struct cgroup *cgrp)
430 {
431         struct cgroup *parent = cgroup_parent(cgrp);
432 
433         if (parent) {
434                 u16 ss_mask = parent->subtree_ss_mask;
435 
436                 /* threaded cgroups can only have threaded controllers */
437                 if (cgroup_is_threaded(cgrp))
438                         ss_mask &= cgrp_dfl_threaded_ss_mask;
439                 return ss_mask;
440         }
441 
442         return cgrp->root->subsys_mask;
443 }
444 
445 /**
446  * cgroup_css - obtain a cgroup's css for the specified subsystem
447  * @cgrp: the cgroup of interest
448  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
449  *
450  * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
451  * function must be called either under cgroup_mutex or rcu_read_lock() and
452  * the caller is responsible for pinning the returned css if it wants to
453  * keep accessing it outside the said locks.  This function may return
454  * %NULL if @cgrp doesn't have @subsys_id enabled.
455  */
456 static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
457                                               struct cgroup_subsys *ss)
458 {
459         if (ss)
460                 return rcu_dereference_check(cgrp->subsys[ss->id],
461                                         lockdep_is_held(&cgroup_mutex));
462         else
463                 return &cgrp->self;
464 }
465 
466 /**
467  * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem
468  * @cgrp: the cgroup of interest
469  * @ss: the subsystem of interest
470  *
471  * Find and get @cgrp's css assocaited with @ss.  If the css doesn't exist
472  * or is offline, %NULL is returned.
473  */
474 static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
475                                                      struct cgroup_subsys *ss)
476 {
477         struct cgroup_subsys_state *css;
478 
479         rcu_read_lock();
480         css = cgroup_css(cgrp, ss);
481         if (!css || !css_tryget_online(css))
482                 css = NULL;
483         rcu_read_unlock();
484 
485         return css;
486 }
487 
488 /**
489  * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
490  * @cgrp: the cgroup of interest
491  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
492  *
493  * Similar to cgroup_css() but returns the effective css, which is defined
494  * as the matching css of the nearest ancestor including self which has @ss
495  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
496  * function is guaranteed to return non-NULL css.
497  */
498 static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
499                                                 struct cgroup_subsys *ss)
500 {
501         lockdep_assert_held(&cgroup_mutex);
502 
503         if (!ss)
504                 return &cgrp->self;
505 
506         /*
507          * This function is used while updating css associations and thus
508          * can't test the csses directly.  Test ss_mask.
509          */
510         while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
511                 cgrp = cgroup_parent(cgrp);
512                 if (!cgrp)
513                         return NULL;
514         }
515 
516         return cgroup_css(cgrp, ss);
517 }
518 
519 /**
520  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
521  * @cgrp: the cgroup of interest
522  * @ss: the subsystem of interest
523  *
524  * Find and get the effective css of @cgrp for @ss.  The effective css is
525  * defined as the matching css of the nearest ancestor including self which
526  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
527  * the root css is returned, so this function always returns a valid css.
528  * The returned css must be put using css_put().
529  */
530 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
531                                              struct cgroup_subsys *ss)
532 {
533         struct cgroup_subsys_state *css;
534 
535         rcu_read_lock();
536 
537         do {
538                 css = cgroup_css(cgrp, ss);
539 
540                 if (css && css_tryget_online(css))
541                         goto out_unlock;
542                 cgrp = cgroup_parent(cgrp);
543         } while (cgrp);
544 
545         css = init_css_set.subsys[ss->id];
546         css_get(css);
547 out_unlock:
548         rcu_read_unlock();
549         return css;
550 }
551 
552 static void cgroup_get_live(struct cgroup *cgrp)
553 {
554         WARN_ON_ONCE(cgroup_is_dead(cgrp));
555         css_get(&cgrp->self);
556 }
557 
558 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
559 {
560         struct cgroup *cgrp = of->kn->parent->priv;
561         struct cftype *cft = of_cft(of);
562 
563         /*
564          * This is open and unprotected implementation of cgroup_css().
565          * seq_css() is only called from a kernfs file operation which has
566          * an active reference on the file.  Because all the subsystem
567          * files are drained before a css is disassociated with a cgroup,
568          * the matching css from the cgroup's subsys table is guaranteed to
569          * be and stay valid until the enclosing operation is complete.
570          */
571         if (cft->ss)
572                 return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
573         else
574                 return &cgrp->self;
575 }
576 EXPORT_SYMBOL_GPL(of_css);
577 
578 /**
579  * for_each_css - iterate all css's of a cgroup
580  * @css: the iteration cursor
581  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
582  * @cgrp: the target cgroup to iterate css's of
583  *
584  * Should be called under cgroup_[tree_]mutex.
585  */
586 #define for_each_css(css, ssid, cgrp)                                   \
587         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
588                 if (!((css) = rcu_dereference_check(                    \
589                                 (cgrp)->subsys[(ssid)],                 \
590                                 lockdep_is_held(&cgroup_mutex)))) { }   \
591                 else
592 
593 /**
594  * for_each_e_css - iterate all effective css's of a cgroup
595  * @css: the iteration cursor
596  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
597  * @cgrp: the target cgroup to iterate css's of
598  *
599  * Should be called under cgroup_[tree_]mutex.
600  */
601 #define for_each_e_css(css, ssid, cgrp)                                 \
602         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
603                 if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
604                         ;                                               \
605                 else
606 
607 /**
608  * do_each_subsys_mask - filter for_each_subsys with a bitmask
609  * @ss: the iteration cursor
610  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
611  * @ss_mask: the bitmask
612  *
613  * The block will only run for cases where the ssid-th bit (1 << ssid) of
614  * @ss_mask is set.
615  */
616 #define do_each_subsys_mask(ss, ssid, ss_mask) do {                     \
617         unsigned long __ss_mask = (ss_mask);                            \
618         if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */ \
619                 (ssid) = 0;                                             \
620                 break;                                                  \
621         }                                                               \
622         for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {       \
623                 (ss) = cgroup_subsys[ssid];                             \
624                 {
625 
626 #define while_each_subsys_mask()                                        \
627                 }                                                       \
628         }                                                               \
629 } while (false)
630 
631 /* iterate over child cgrps, lock should be held throughout iteration */
632 #define cgroup_for_each_live_child(child, cgrp)                         \
633         list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
634                 if (({ lockdep_assert_held(&cgroup_mutex);              \
635                        cgroup_is_dead(child); }))                       \
636                         ;                                               \
637                 else
638 
639 /* walk live descendants in preorder */
640 #define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)          \
641         css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))  \
642                 if (({ lockdep_assert_held(&cgroup_mutex);              \
643                        (dsct) = (d_css)->cgroup;                        \
644                        cgroup_is_dead(dsct); }))                        \
645                         ;                                               \
646                 else
647 
648 /* walk live descendants in postorder */
649 #define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)         \
650         css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
651                 if (({ lockdep_assert_held(&cgroup_mutex);              \
652                        (dsct) = (d_css)->cgroup;                        \
653                        cgroup_is_dead(dsct); }))                        \
654                         ;                                               \
655                 else
656 
657 /*
658  * The default css_set - used by init and its children prior to any
659  * hierarchies being mounted. It contains a pointer to the root state
660  * for each subsystem. Also used to anchor the list of css_sets. Not
661  * reference-counted, to improve performance when child cgroups
662  * haven't been created.
663  */
664 struct css_set init_css_set = {
665         .refcount               = REFCOUNT_INIT(1),
666         .dom_cset               = &init_css_set,
667         .tasks                  = LIST_HEAD_INIT(init_css_set.tasks),
668         .mg_tasks               = LIST_HEAD_INIT(init_css_set.mg_tasks),
669         .task_iters             = LIST_HEAD_INIT(init_css_set.task_iters),
670         .threaded_csets         = LIST_HEAD_INIT(init_css_set.threaded_csets),
671         .cgrp_links             = LIST_HEAD_INIT(init_css_set.cgrp_links),
672         .mg_preload_node        = LIST_HEAD_INIT(init_css_set.mg_preload_node),
673         .mg_node                = LIST_HEAD_INIT(init_css_set.mg_node),
674 
675         /*
676          * The following field is re-initialized when this cset gets linked
677          * in cgroup_init().  However, let's initialize the field
678          * statically too so that the default cgroup can be accessed safely
679          * early during boot.
680          */
681         .dfl_cgrp               = &cgrp_dfl_root.cgrp,
682 };
683 
684 static int css_set_count        = 1;    /* 1 for init_css_set */
685 
686 static bool css_set_threaded(struct css_set *cset)
687 {
688         return cset->dom_cset != cset;
689 }
690 
691 /**
692  * css_set_populated - does a css_set contain any tasks?
693  * @cset: target css_set
694  *
695  * css_set_populated() should be the same as !!cset->nr_tasks at steady
696  * state. However, css_set_populated() can be called while a task is being
697  * added to or removed from the linked list before the nr_tasks is
698  * properly updated. Hence, we can't just look at ->nr_tasks here.
699  */
700 static bool css_set_populated(struct css_set *cset)
701 {
702         lockdep_assert_held(&css_set_lock);
703 
704         return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
705 }
706 
707 /**
708  * cgroup_update_populated - update the populated count of a cgroup
709  * @cgrp: the target cgroup
710  * @populated: inc or dec populated count
711  *
712  * One of the css_sets associated with @cgrp is either getting its first
713  * task or losing the last.  Update @cgrp->nr_populated_* accordingly.  The
714  * count is propagated towards root so that a given cgroup's
715  * nr_populated_children is zero iff none of its descendants contain any
716  * tasks.
717  *
718  * @cgrp's interface file "cgroup.populated" is zero if both
719  * @cgrp->nr_populated_csets and @cgrp->nr_populated_children are zero and
720  * 1 otherwise.  When the sum changes from or to zero, userland is notified
721  * that the content of the interface file has changed.  This can be used to
722  * detect when @cgrp and its descendants become populated or empty.
723  */
724 static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
725 {
726         struct cgroup *child = NULL;
727         int adj = populated ? 1 : -1;
728 
729         lockdep_assert_held(&css_set_lock);
730 
731         do {
732                 bool was_populated = cgroup_is_populated(cgrp);
733 
734                 if (!child) {
735                         cgrp->nr_populated_csets += adj;
736                 } else {
737                         if (cgroup_is_threaded(child))
738                                 cgrp->nr_populated_threaded_children += adj;
739                         else
740                                 cgrp->nr_populated_domain_children += adj;
741                 }
742 
743                 if (was_populated == cgroup_is_populated(cgrp))
744                         break;
745 
746                 cgroup1_check_for_release(cgrp);
747                 cgroup_file_notify(&cgrp->events_file);
748 
749                 child = cgrp;
750                 cgrp = cgroup_parent(cgrp);
751         } while (cgrp);
752 }
753 
754 /**
755  * css_set_update_populated - update populated state of a css_set
756  * @cset: target css_set
757  * @populated: whether @cset is populated or depopulated
758  *
759  * @cset is either getting the first task or losing the last.  Update the
760  * populated counters of all associated cgroups accordingly.
761  */
762 static void css_set_update_populated(struct css_set *cset, bool populated)
763 {
764         struct cgrp_cset_link *link;
765 
766         lockdep_assert_held(&css_set_lock);
767 
768         list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
769                 cgroup_update_populated(link->cgrp, populated);
770 }
771 
772 /**
773  * css_set_move_task - move a task from one css_set to another
774  * @task: task being moved
775  * @from_cset: css_set @task currently belongs to (may be NULL)
776  * @to_cset: new css_set @task is being moved to (may be NULL)
777  * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
778  *
779  * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
780  * css_set, @from_cset can be NULL.  If @task is being disassociated
781  * instead of moved, @to_cset can be NULL.
782  *
783  * This function automatically handles populated counter updates and
784  * css_task_iter adjustments but the caller is responsible for managing
785  * @from_cset and @to_cset's reference counts.
786  */
787 static void css_set_move_task(struct task_struct *task,
788                               struct css_set *from_cset, struct css_set *to_cset,
789                               bool use_mg_tasks)
790 {
791         lockdep_assert_held(&css_set_lock);
792 
793         if (to_cset && !css_set_populated(to_cset))
794                 css_set_update_populated(to_cset, true);
795 
796         if (from_cset) {
797                 struct css_task_iter *it, *pos;
798 
799                 WARN_ON_ONCE(list_empty(&task->cg_list));
800 
801                 /*
802                  * @task is leaving, advance task iterators which are
803                  * pointing to it so that they can resume at the next
804                  * position.  Advancing an iterator might remove it from
805                  * the list, use safe walk.  See css_task_iter_advance*()
806                  * for details.
807                  */
808                 list_for_each_entry_safe(it, pos, &from_cset->task_iters,
809                                          iters_node)
810                         if (it->task_pos == &task->cg_list)
811                                 css_task_iter_advance(it);
812 
813                 list_del_init(&task->cg_list);
814                 if (!css_set_populated(from_cset))
815                         css_set_update_populated(from_cset, false);
816         } else {
817                 WARN_ON_ONCE(!list_empty(&task->cg_list));
818         }
819 
820         if (to_cset) {
821                 /*
822                  * We are synchronized through cgroup_threadgroup_rwsem
823                  * against PF_EXITING setting such that we can't race
824                  * against cgroup_exit() changing the css_set to
825                  * init_css_set and dropping the old one.
826                  */
827                 WARN_ON_ONCE(task->flags & PF_EXITING);
828 
829                 rcu_assign_pointer(task->cgroups, to_cset);
830                 list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
831                                                              &to_cset->tasks);
832         }
833 }
834 
835 /*
836  * hash table for cgroup groups. This improves the performance to find
837  * an existing css_set. This hash doesn't (currently) take into
838  * account cgroups in empty hierarchies.
839  */
840 #define CSS_SET_HASH_BITS       7
841 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
842 
843 static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
844 {
845         unsigned long key = 0UL;
846         struct cgroup_subsys *ss;
847         int i;
848 
849         for_each_subsys(ss, i)
850                 key += (unsigned long)css[i];
851         key = (key >> 16) ^ key;
852 
853         return key;
854 }
855 
856 void put_css_set_locked(struct css_set *cset)
857 {
858         struct cgrp_cset_link *link, *tmp_link;
859         struct cgroup_subsys *ss;
860         int ssid;
861 
862         lockdep_assert_held(&css_set_lock);
863 
864         if (!refcount_dec_and_test(&cset->refcount))
865                 return;
866 
867         WARN_ON_ONCE(!list_empty(&cset->threaded_csets));
868 
869         /* This css_set is dead. unlink it and release cgroup and css refs */
870         for_each_subsys(ss, ssid) {
871                 list_del(&cset->e_cset_node[ssid]);
872                 css_put(cset->subsys[ssid]);
873         }
874         hash_del(&cset->hlist);
875         css_set_count--;
876 
877         list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
878                 list_del(&link->cset_link);
879                 list_del(&link->cgrp_link);
880                 if (cgroup_parent(link->cgrp))
881                         cgroup_put(link->cgrp);
882                 kfree(link);
883         }
884 
885         if (css_set_threaded(cset)) {
886                 list_del(&cset->threaded_csets_node);
887                 put_css_set_locked(cset->dom_cset);
888         }
889 
890         kfree_rcu(cset, rcu_head);
891 }
892 
893 /**
894  * compare_css_sets - helper function for find_existing_css_set().
895  * @cset: candidate css_set being tested
896  * @old_cset: existing css_set for a task
897  * @new_cgrp: cgroup that's being entered by the task
898  * @template: desired set of css pointers in css_set (pre-calculated)
899  *
900  * Returns true if "cset" matches "old_cset" except for the hierarchy
901  * which "new_cgrp" belongs to, for which it should match "new_cgrp".
902  */
903 static bool compare_css_sets(struct css_set *cset,
904                              struct css_set *old_cset,
905                              struct cgroup *new_cgrp,
906                              struct cgroup_subsys_state *template[])
907 {
908         struct cgroup *new_dfl_cgrp;
909         struct list_head *l1, *l2;
910 
911         /*
912          * On the default hierarchy, there can be csets which are
913          * associated with the same set of cgroups but different csses.
914          * Let's first ensure that csses match.
915          */
916         if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
917                 return false;
918 
919 
920         /* @cset's domain should match the default cgroup's */
921         if (cgroup_on_dfl(new_cgrp))
922                 new_dfl_cgrp = new_cgrp;
923         else
924                 new_dfl_cgrp = old_cset->dfl_cgrp;
925 
926         if (new_dfl_cgrp->dom_cgrp != cset->dom_cset->dfl_cgrp)
927                 return false;
928 
929         /*
930          * Compare cgroup pointers in order to distinguish between
931          * different cgroups in hierarchies.  As different cgroups may
932          * share the same effective css, this comparison is always
933          * necessary.
934          */
935         l1 = &cset->cgrp_links;
936         l2 = &old_cset->cgrp_links;
937         while (1) {
938                 struct cgrp_cset_link *link1, *link2;
939                 struct cgroup *cgrp1, *cgrp2;
940 
941                 l1 = l1->next;
942                 l2 = l2->next;
943                 /* See if we reached the end - both lists are equal length. */
944                 if (l1 == &cset->cgrp_links) {
945                         BUG_ON(l2 != &old_cset->cgrp_links);
946                         break;
947                 } else {
948                         BUG_ON(l2 == &old_cset->cgrp_links);
949                 }
950                 /* Locate the cgroups associated with these links. */
951                 link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
952                 link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
953                 cgrp1 = link1->cgrp;
954                 cgrp2 = link2->cgrp;
955                 /* Hierarchies should be linked in the same order. */
956                 BUG_ON(cgrp1->root != cgrp2->root);
957 
958                 /*
959                  * If this hierarchy is the hierarchy of the cgroup
960                  * that's changing, then we need to check that this
961                  * css_set points to the new cgroup; if it's any other
962                  * hierarchy, then this css_set should point to the
963                  * same cgroup as the old css_set.
964                  */
965                 if (cgrp1->root == new_cgrp->root) {
966                         if (cgrp1 != new_cgrp)
967                                 return false;
968                 } else {
969                         if (cgrp1 != cgrp2)
970                                 return false;
971                 }
972         }
973         return true;
974 }
975 
976 /**
977  * find_existing_css_set - init css array and find the matching css_set
978  * @old_cset: the css_set that we're using before the cgroup transition
979  * @cgrp: the cgroup that we're moving into
980  * @template: out param for the new set of csses, should be clear on entry
981  */
982 static struct css_set *find_existing_css_set(struct css_set *old_cset,
983                                         struct cgroup *cgrp,
984                                         struct cgroup_subsys_state *template[])
985 {
986         struct cgroup_root *root = cgrp->root;
987         struct cgroup_subsys *ss;
988         struct css_set *cset;
989         unsigned long key;
990         int i;
991 
992         /*
993          * Build the set of subsystem state objects that we want to see in the
994          * new css_set. while subsystems can change globally, the entries here
995          * won't change, so no need for locking.
996          */
997         for_each_subsys(ss, i) {
998                 if (root->subsys_mask & (1UL << i)) {
999                         /*
1000                          * @ss is in this hierarchy, so we want the
1001                          * effective css from @cgrp.
1002                          */
1003                         template[i] = cgroup_e_css(cgrp, ss);
1004                 } else {
1005                         /*
1006                          * @ss is not in this hierarchy, so we don't want
1007                          * to change the css.
1008                          */
1009                         template[i] = old_cset->subsys[i];
1010                 }
1011         }
1012 
1013         key = css_set_hash(template);
1014         hash_for_each_possible(css_set_table, cset, hlist, key) {
1015                 if (!compare_css_sets(cset, old_cset, cgrp, template))
1016                         continue;
1017 
1018                 /* This css_set matches what we need */
1019                 return cset;
1020         }
1021 
1022         /* No existing cgroup group matched */
1023         return NULL;
1024 }
1025 
1026 static void free_cgrp_cset_links(struct list_head *links_to_free)
1027 {
1028         struct cgrp_cset_link *link, *tmp_link;
1029 
1030         list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
1031                 list_del(&link->cset_link);
1032                 kfree(link);
1033         }
1034 }
1035 
1036 /**
1037  * allocate_cgrp_cset_links - allocate cgrp_cset_links
1038  * @count: the number of links to allocate
1039  * @tmp_links: list_head the allocated links are put on
1040  *
1041  * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1042  * through ->cset_link.  Returns 0 on success or -errno.
1043  */
1044 static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1045 {
1046         struct cgrp_cset_link *link;
1047         int i;
1048 
1049         INIT_LIST_HEAD(tmp_links);
1050 
1051         for (i = 0; i < count; i++) {
1052                 link = kzalloc(sizeof(*link), GFP_KERNEL);
1053                 if (!link) {
1054                         free_cgrp_cset_links(tmp_links);
1055                         return -ENOMEM;
1056                 }
1057                 list_add(&link->cset_link, tmp_links);
1058         }
1059         return 0;
1060 }
1061 
1062 /**
1063  * link_css_set - a helper function to link a css_set to a cgroup
1064  * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1065  * @cset: the css_set to be linked
1066  * @cgrp: the destination cgroup
1067  */
1068 static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1069                          struct cgroup *cgrp)
1070 {
1071         struct cgrp_cset_link *link;
1072 
1073         BUG_ON(list_empty(tmp_links));
1074 
1075         if (cgroup_on_dfl(cgrp))
1076                 cset->dfl_cgrp = cgrp;
1077 
1078         link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1079         link->cset = cset;
1080         link->cgrp = cgrp;
1081 
1082         /*
1083          * Always add links to the tail of the lists so that the lists are
1084          * in choronological order.
1085          */
1086         list_move_tail(&link->cset_link, &cgrp->cset_links);
1087         list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1088 
1089         if (cgroup_parent(cgrp))
1090                 cgroup_get_live(cgrp);
1091 }
1092 
1093 /**
1094  * find_css_set - return a new css_set with one cgroup updated
1095  * @old_cset: the baseline css_set
1096  * @cgrp: the cgroup to be updated
1097  *
1098  * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1099  * substituted into the appropriate hierarchy.
1100  */
1101 static struct css_set *find_css_set(struct css_set *old_cset,
1102                                     struct cgroup *cgrp)
1103 {
1104         struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1105         struct css_set *cset;
1106         struct list_head tmp_links;
1107         struct cgrp_cset_link *link;
1108         struct cgroup_subsys *ss;
1109         unsigned long key;
1110         int ssid;
1111 
1112         lockdep_assert_held(&cgroup_mutex);
1113 
1114         /* First see if we already have a cgroup group that matches
1115          * the desired set */
1116         spin_lock_irq(&css_set_lock);
1117         cset = find_existing_css_set(old_cset, cgrp, template);
1118         if (cset)
1119                 get_css_set(cset);
1120         spin_unlock_irq(&css_set_lock);
1121 
1122         if (cset)
1123                 return cset;
1124 
1125         cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1126         if (!cset)
1127                 return NULL;
1128 
1129         /* Allocate all the cgrp_cset_link objects that we'll need */
1130         if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1131                 kfree(cset);
1132                 return NULL;
1133         }
1134 
1135         refcount_set(&cset->refcount, 1);
1136         cset->dom_cset = cset;
1137         INIT_LIST_HEAD(&cset->tasks);
1138         INIT_LIST_HEAD(&cset->mg_tasks);
1139         INIT_LIST_HEAD(&cset->task_iters);
1140         INIT_LIST_HEAD(&cset->threaded_csets);
1141         INIT_HLIST_NODE(&cset->hlist);
1142         INIT_LIST_HEAD(&cset->cgrp_links);
1143         INIT_LIST_HEAD(&cset->mg_preload_node);
1144         INIT_LIST_HEAD(&cset->mg_node);
1145 
1146         /* Copy the set of subsystem state objects generated in
1147          * find_existing_css_set() */
1148         memcpy(cset->subsys, template, sizeof(cset->subsys));
1149 
1150         spin_lock_irq(&css_set_lock);
1151         /* Add reference counts and links from the new css_set. */
1152         list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1153                 struct cgroup *c = link->cgrp;
1154 
1155                 if (c->root == cgrp->root)
1156                         c = cgrp;
1157                 link_css_set(&tmp_links, cset, c);
1158         }
1159 
1160         BUG_ON(!list_empty(&tmp_links));
1161 
1162         css_set_count++;
1163 
1164         /* Add @cset to the hash table */
1165         key = css_set_hash(cset->subsys);
1166         hash_add(css_set_table, &cset->hlist, key);
1167 
1168         for_each_subsys(ss, ssid) {
1169                 struct cgroup_subsys_state *css = cset->subsys[ssid];
1170 
1171                 list_add_tail(&cset->e_cset_node[ssid],
1172                               &css->cgroup->e_csets[ssid]);
1173                 css_get(css);
1174         }
1175 
1176         spin_unlock_irq(&css_set_lock);
1177 
1178         /*
1179          * If @cset should be threaded, look up the matching dom_cset and
1180          * link them up.  We first fully initialize @cset then look for the
1181          * dom_cset.  It's simpler this way and safe as @cset is guaranteed
1182          * to stay empty until we return.
1183          */
1184         if (cgroup_is_threaded(cset->dfl_cgrp)) {
1185                 struct css_set *dcset;
1186 
1187                 dcset = find_css_set(cset, cset->dfl_cgrp->dom_cgrp);
1188                 if (!dcset) {
1189                         put_css_set(cset);
1190                         return NULL;
1191                 }
1192 
1193                 spin_lock_irq(&css_set_lock);
1194                 cset->dom_cset = dcset;
1195                 list_add_tail(&cset->threaded_csets_node,
1196                               &dcset->threaded_csets);
1197                 spin_unlock_irq(&css_set_lock);
1198         }
1199 
1200         return cset;
1201 }
1202 
1203 struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1204 {
1205         struct cgroup *root_cgrp = kf_root->kn->priv;
1206 
1207         return root_cgrp->root;
1208 }
1209 
1210 static int cgroup_init_root_id(struct cgroup_root *root)
1211 {
1212         int id;
1213 
1214         lockdep_assert_held(&cgroup_mutex);
1215 
1216         id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1217         if (id < 0)
1218                 return id;
1219 
1220         root->hierarchy_id = id;
1221         return 0;
1222 }
1223 
1224 static void cgroup_exit_root_id(struct cgroup_root *root)
1225 {
1226         lockdep_assert_held(&cgroup_mutex);
1227 
1228         idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1229 }
1230 
1231 void cgroup_free_root(struct cgroup_root *root)
1232 {
1233         if (root) {
1234                 idr_destroy(&root->cgroup_idr);
1235                 kfree(root);
1236         }
1237 }
1238 
1239 static void cgroup_destroy_root(struct cgroup_root *root)
1240 {
1241         struct cgroup *cgrp = &root->cgrp;
1242         struct cgrp_cset_link *link, *tmp_link;
1243 
1244         trace_cgroup_destroy_root(root);
1245 
1246         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1247 
1248         BUG_ON(atomic_read(&root->nr_cgrps));
1249         BUG_ON(!list_empty(&cgrp->self.children));
1250 
1251         /* Rebind all subsystems back to the default hierarchy */
1252         WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1253 
1254         /*
1255          * Release all the links from cset_links to this hierarchy's
1256          * root cgroup
1257          */
1258         spin_lock_irq(&css_set_lock);
1259 
1260         list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1261                 list_del(&link->cset_link);
1262                 list_del(&link->cgrp_link);
1263                 kfree(link);
1264         }
1265 
1266         spin_unlock_irq(&css_set_lock);
1267 
1268         if (!list_empty(&root->root_list)) {
1269                 list_del(&root->root_list);
1270                 cgroup_root_count--;
1271         }
1272 
1273         cgroup_exit_root_id(root);
1274 
1275         mutex_unlock(&cgroup_mutex);
1276 
1277         kernfs_destroy_root(root->kf_root);
1278         cgroup_free_root(root);
1279 }
1280 
1281 /*
1282  * look up cgroup associated with current task's cgroup namespace on the
1283  * specified hierarchy
1284  */
1285 static struct cgroup *
1286 current_cgns_cgroup_from_root(struct cgroup_root *root)
1287 {
1288         struct cgroup *res = NULL;
1289         struct css_set *cset;
1290 
1291         lockdep_assert_held(&css_set_lock);
1292 
1293         rcu_read_lock();
1294 
1295         cset = current->nsproxy->cgroup_ns->root_cset;
1296         if (cset == &init_css_set) {
1297                 res = &root->cgrp;
1298         } else {
1299                 struct cgrp_cset_link *link;
1300 
1301                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1302                         struct cgroup *c = link->cgrp;
1303 
1304                         if (c->root == root) {
1305                                 res = c;
1306                                 break;
1307                         }
1308                 }
1309         }
1310         rcu_read_unlock();
1311 
1312         BUG_ON(!res);
1313         return res;
1314 }
1315 
1316 /* look up cgroup associated with given css_set on the specified hierarchy */
1317 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1318                                             struct cgroup_root *root)
1319 {
1320         struct cgroup *res = NULL;
1321 
1322         lockdep_assert_held(&cgroup_mutex);
1323         lockdep_assert_held(&css_set_lock);
1324 
1325         if (cset == &init_css_set) {
1326                 res = &root->cgrp;
1327         } else if (root == &cgrp_dfl_root) {
1328                 res = cset->dfl_cgrp;
1329         } else {
1330                 struct cgrp_cset_link *link;
1331 
1332                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1333                         struct cgroup *c = link->cgrp;
1334 
1335                         if (c->root == root) {
1336                                 res = c;
1337                                 break;
1338                         }
1339                 }
1340         }
1341 
1342         BUG_ON(!res);
1343         return res;
1344 }
1345 
1346 /*
1347  * Return the cgroup for "task" from the given hierarchy. Must be
1348  * called with cgroup_mutex and css_set_lock held.
1349  */
1350 struct cgroup *task_cgroup_from_root(struct task_struct *task,
1351                                      struct cgroup_root *root)
1352 {
1353         /*
1354          * No need to lock the task - since we hold cgroup_mutex the
1355          * task can't change groups, so the only thing that can happen
1356          * is that it exits and its css is set back to init_css_set.
1357          */
1358         return cset_cgroup_from_root(task_css_set(task), root);
1359 }
1360 
1361 /*
1362  * A task must hold cgroup_mutex to modify cgroups.
1363  *
1364  * Any task can increment and decrement the count field without lock.
1365  * So in general, code holding cgroup_mutex can't rely on the count
1366  * field not changing.  However, if the count goes to zero, then only
1367  * cgroup_attach_task() can increment it again.  Because a count of zero
1368  * means that no tasks are currently attached, therefore there is no
1369  * way a task attached to that cgroup can fork (the other way to
1370  * increment the count).  So code holding cgroup_mutex can safely
1371  * assume that if the count is zero, it will stay zero. Similarly, if
1372  * a task holds cgroup_mutex on a cgroup with zero count, it
1373  * knows that the cgroup won't be removed, as cgroup_rmdir()
1374  * needs that mutex.
1375  *
1376  * A cgroup can only be deleted if both its 'count' of using tasks
1377  * is zero, and its list of 'children' cgroups is empty.  Since all
1378  * tasks in the system use _some_ cgroup, and since there is always at
1379  * least one task in the system (init, pid == 1), therefore, root cgroup
1380  * always has either children cgroups and/or using tasks.  So we don't
1381  * need a special hack to ensure that root cgroup cannot be deleted.
1382  *
1383  * P.S.  One more locking exception.  RCU is used to guard the
1384  * update of a tasks cgroup pointer by cgroup_attach_task()
1385  */
1386 
1387 static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1388 
1389 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1390                               char *buf)
1391 {
1392         struct cgroup_subsys *ss = cft->ss;
1393 
1394         if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1395             !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
1396                 snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
1397                          cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1398                          cft->name);
1399         else
1400                 strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1401         return buf;
1402 }
1403 
1404 /**
1405  * cgroup_file_mode - deduce file mode of a control file
1406  * @cft: the control file in question
1407  *
1408  * S_IRUGO for read, S_IWUSR for write.
1409  */
1410 static umode_t cgroup_file_mode(const struct cftype *cft)
1411 {
1412         umode_t mode = 0;
1413 
1414         if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1415                 mode |= S_IRUGO;
1416 
1417         if (cft->write_u64 || cft->write_s64 || cft->write) {
1418                 if (cft->flags & CFTYPE_WORLD_WRITABLE)
1419                         mode |= S_IWUGO;
1420                 else
1421                         mode |= S_IWUSR;
1422         }
1423 
1424         return mode;
1425 }
1426 
1427 /**
1428  * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1429  * @subtree_control: the new subtree_control mask to consider
1430  * @this_ss_mask: available subsystems
1431  *
1432  * On the default hierarchy, a subsystem may request other subsystems to be
1433  * enabled together through its ->depends_on mask.  In such cases, more
1434  * subsystems than specified in "cgroup.subtree_control" may be enabled.
1435  *
1436  * This function calculates which subsystems need to be enabled if
1437  * @subtree_control is to be applied while restricted to @this_ss_mask.
1438  */
1439 static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1440 {
1441         u16 cur_ss_mask = subtree_control;
1442         struct cgroup_subsys *ss;
1443         int ssid;
1444 
1445         lockdep_assert_held(&cgroup_mutex);
1446 
1447         cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1448 
1449         while (true) {
1450                 u16 new_ss_mask = cur_ss_mask;
1451 
1452                 do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1453                         new_ss_mask |= ss->depends_on;
1454                 } while_each_subsys_mask();
1455 
1456                 /*
1457                  * Mask out subsystems which aren't available.  This can
1458                  * happen only if some depended-upon subsystems were bound
1459                  * to non-default hierarchies.
1460                  */
1461                 new_ss_mask &= this_ss_mask;
1462 
1463                 if (new_ss_mask == cur_ss_mask)
1464                         break;
1465                 cur_ss_mask = new_ss_mask;
1466         }
1467 
1468         return cur_ss_mask;
1469 }
1470 
1471 /**
1472  * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1473  * @kn: the kernfs_node being serviced
1474  *
1475  * This helper undoes cgroup_kn_lock_live() and should be invoked before
1476  * the method finishes if locking succeeded.  Note that once this function
1477  * returns the cgroup returned by cgroup_kn_lock_live() may become
1478  * inaccessible any time.  If the caller intends to continue to access the
1479  * cgroup, it should pin it before invoking this function.
1480  */
1481 void cgroup_kn_unlock(struct kernfs_node *kn)
1482 {
1483         struct cgroup *cgrp;
1484 
1485         if (kernfs_type(kn) == KERNFS_DIR)
1486                 cgrp = kn->priv;
1487         else
1488                 cgrp = kn->parent->priv;
1489 
1490         mutex_unlock(&cgroup_mutex);
1491 
1492         kernfs_unbreak_active_protection(kn);
1493         cgroup_put(cgrp);
1494 }
1495 
1496 /**
1497  * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1498  * @kn: the kernfs_node being serviced
1499  * @drain_offline: perform offline draining on the cgroup
1500  *
1501  * This helper is to be used by a cgroup kernfs method currently servicing
1502  * @kn.  It breaks the active protection, performs cgroup locking and
1503  * verifies that the associated cgroup is alive.  Returns the cgroup if
1504  * alive; otherwise, %NULL.  A successful return should be undone by a
1505  * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1506  * cgroup is drained of offlining csses before return.
1507  *
1508  * Any cgroup kernfs method implementation which requires locking the
1509  * associated cgroup should use this helper.  It avoids nesting cgroup
1510  * locking under kernfs active protection and allows all kernfs operations
1511  * including self-removal.
1512  */
1513 struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
1514 {
1515         struct cgroup *cgrp;
1516 
1517         if (kernfs_type(kn) == KERNFS_DIR)
1518                 cgrp = kn->priv;
1519         else
1520                 cgrp = kn->parent->priv;
1521 
1522         /*
1523          * We're gonna grab cgroup_mutex which nests outside kernfs
1524          * active_ref.  cgroup liveliness check alone provides enough
1525          * protection against removal.  Ensure @cgrp stays accessible and
1526          * break the active_ref protection.
1527          */
1528         if (!cgroup_tryget(cgrp))
1529                 return NULL;
1530         kernfs_break_active_protection(kn);
1531 
1532         if (drain_offline)
1533                 cgroup_lock_and_drain_offline(cgrp);
1534         else
1535                 mutex_lock(&cgroup_mutex);
1536 
1537         if (!cgroup_is_dead(cgrp))
1538                 return cgrp;
1539 
1540         cgroup_kn_unlock(kn);
1541         return NULL;
1542 }
1543 
1544 static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1545 {
1546         char name[CGROUP_FILE_NAME_MAX];
1547 
1548         lockdep_assert_held(&cgroup_mutex);
1549 
1550         if (cft->file_offset) {
1551                 struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1552                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
1553 
1554                 spin_lock_irq(&cgroup_file_kn_lock);
1555                 cfile->kn = NULL;
1556                 spin_unlock_irq(&cgroup_file_kn_lock);
1557         }
1558 
1559         kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1560 }
1561 
1562 /**
1563  * css_clear_dir - remove subsys files in a cgroup directory
1564  * @css: taget css
1565  */
1566 static void css_clear_dir(struct cgroup_subsys_state *css)
1567 {
1568         struct cgroup *cgrp = css->cgroup;
1569         struct cftype *cfts;
1570 
1571         if (!(css->flags & CSS_VISIBLE))
1572                 return;
1573 
1574         css->flags &= ~CSS_VISIBLE;
1575 
1576         list_for_each_entry(cfts, &css->ss->cfts, node)
1577                 cgroup_addrm_files(css, cgrp, cfts, false);
1578 }
1579 
1580 /**
1581  * css_populate_dir - create subsys files in a cgroup directory
1582  * @css: target css
1583  *
1584  * On failure, no file is added.
1585  */
1586 static int css_populate_dir(struct cgroup_subsys_state *css)
1587 {
1588         struct cgroup *cgrp = css->cgroup;
1589         struct cftype *cfts, *failed_cfts;
1590         int ret;
1591 
1592         if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1593                 return 0;
1594 
1595         if (!css->ss) {
1596                 if (cgroup_on_dfl(cgrp))
1597                         cfts = cgroup_base_files;
1598                 else
1599                         cfts = cgroup1_base_files;
1600 
1601                 return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1602         }
1603 
1604         list_for_each_entry(cfts, &css->ss->cfts, node) {
1605                 ret = cgroup_addrm_files(css, cgrp, cfts, true);
1606                 if (ret < 0) {
1607                         failed_cfts = cfts;
1608                         goto err;
1609                 }
1610         }
1611 
1612         css->flags |= CSS_VISIBLE;
1613 
1614         return 0;
1615 err:
1616         list_for_each_entry(cfts, &css->ss->cfts, node) {
1617                 if (cfts == failed_cfts)
1618                         break;
1619                 cgroup_addrm_files(css, cgrp, cfts, false);
1620         }
1621         return ret;
1622 }
1623 
1624 int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1625 {
1626         struct cgroup *dcgrp = &dst_root->cgrp;
1627         struct cgroup_subsys *ss;
1628         int ssid, i, ret;
1629 
1630         lockdep_assert_held(&cgroup_mutex);
1631 
1632         do_each_subsys_mask(ss, ssid, ss_mask) {
1633                 /*
1634                  * If @ss has non-root csses attached to it, can't move.
1635                  * If @ss is an implicit controller, it is exempt from this
1636                  * rule and can be stolen.
1637                  */
1638                 if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1639                     !ss->implicit_on_dfl)
1640                         return -EBUSY;
1641 
1642                 /* can't move between two non-dummy roots either */
1643                 if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1644                         return -EBUSY;
1645         } while_each_subsys_mask();
1646 
1647         do_each_subsys_mask(ss, ssid, ss_mask) {
1648                 struct cgroup_root *src_root = ss->root;
1649                 struct cgroup *scgrp = &src_root->cgrp;
1650                 struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1651                 struct css_set *cset;
1652 
1653                 WARN_ON(!css || cgroup_css(dcgrp, ss));
1654 
1655                 /* disable from the source */
1656                 src_root->subsys_mask &= ~(1 << ssid);
1657                 WARN_ON(cgroup_apply_control(scgrp));
1658                 cgroup_finalize_control(scgrp, 0);
1659 
1660                 /* rebind */
1661                 RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1662                 rcu_assign_pointer(dcgrp->subsys[ssid], css);
1663                 ss->root = dst_root;
1664                 css->cgroup = dcgrp;
1665 
1666                 spin_lock_irq(&css_set_lock);
1667                 hash_for_each(css_set_table, i, cset, hlist)
1668                         list_move_tail(&cset->e_cset_node[ss->id],
1669                                        &dcgrp->e_csets[ss->id]);
1670                 spin_unlock_irq(&css_set_lock);
1671 
1672                 /* default hierarchy doesn't enable controllers by default */
1673                 dst_root->subsys_mask |= 1 << ssid;
1674                 if (dst_root == &cgrp_dfl_root) {
1675                         static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1676                 } else {
1677                         dcgrp->subtree_control |= 1 << ssid;
1678                         static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1679                 }
1680 
1681                 ret = cgroup_apply_control(dcgrp);
1682                 if (ret)
1683                         pr_warn("partial failure to rebind %s controller (err=%d)\n",
1684                                 ss->name, ret);
1685 
1686                 if (ss->bind)
1687                         ss->bind(css);
1688         } while_each_subsys_mask();
1689 
1690         kernfs_activate(dcgrp->kn);
1691         return 0;
1692 }
1693 
1694 int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1695                      struct kernfs_root *kf_root)
1696 {
1697         int len = 0;
1698         char *buf = NULL;
1699         struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1700         struct cgroup *ns_cgroup;
1701 
1702         buf = kmalloc(PATH_MAX, GFP_KERNEL);
1703         if (!buf)
1704                 return -ENOMEM;
1705 
1706         spin_lock_irq(&css_set_lock);
1707         ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1708         len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1709         spin_unlock_irq(&css_set_lock);
1710 
1711         if (len >= PATH_MAX)
1712                 len = -ERANGE;
1713         else if (len > 0) {
1714                 seq_escape(sf, buf, " \t\n\\");
1715                 len = 0;
1716         }
1717         kfree(buf);
1718         return len;
1719 }
1720 
1721 static int parse_cgroup_root_flags(char *data, unsigned int *root_flags)
1722 {
1723         char *token;
1724 
1725         *root_flags = 0;
1726 
1727         if (!data)
1728                 return 0;
1729 
1730         while ((token = strsep(&data, ",")) != NULL) {
1731                 if (!strcmp(token, "nsdelegate")) {
1732                         *root_flags |= CGRP_ROOT_NS_DELEGATE;
1733                         continue;
1734                 }
1735 
1736                 pr_err("cgroup2: unknown option \"%s\"\n", token);
1737                 return -EINVAL;
1738         }
1739 
1740         return 0;
1741 }
1742 
1743 static void apply_cgroup_root_flags(unsigned int root_flags)
1744 {
1745         if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
1746                 if (root_flags & CGRP_ROOT_NS_DELEGATE)
1747                         cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE;
1748                 else
1749                         cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;
1750         }
1751 }
1752 
1753 static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
1754 {
1755         if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
1756                 seq_puts(seq, ",nsdelegate");
1757         return 0;
1758 }
1759 
1760 static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1761 {
1762         unsigned int root_flags;
1763         int ret;
1764 
1765         ret = parse_cgroup_root_flags(data, &root_flags);
1766         if (ret)
1767                 return ret;
1768 
1769         apply_cgroup_root_flags(root_flags);
1770         return 0;
1771 }
1772 
1773 /*
1774  * To reduce the fork() overhead for systems that are not actually using
1775  * their cgroups capability, we don't maintain the lists running through
1776  * each css_set to its tasks until we see the list actually used - in other
1777  * words after the first mount.
1778  */
1779 static bool use_task_css_set_links __read_mostly;
1780 
1781 static void cgroup_enable_task_cg_lists(void)
1782 {
1783         struct task_struct *p, *g;
1784 
1785         spin_lock_irq(&css_set_lock);
1786 
1787         if (use_task_css_set_links)
1788                 goto out_unlock;
1789 
1790         use_task_css_set_links = true;
1791 
1792         /*
1793          * We need tasklist_lock because RCU is not safe against
1794          * while_each_thread(). Besides, a forking task that has passed
1795          * cgroup_post_fork() without seeing use_task_css_set_links = 1
1796          * is not guaranteed to have its child immediately visible in the
1797          * tasklist if we walk through it with RCU.
1798          */
1799         read_lock(&tasklist_lock);
1800         do_each_thread(g, p) {
1801                 WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1802                              task_css_set(p) != &init_css_set);
1803 
1804                 /*
1805                  * We should check if the process is exiting, otherwise
1806                  * it will race with cgroup_exit() in that the list
1807                  * entry won't be deleted though the process has exited.
1808                  * Do it while holding siglock so that we don't end up
1809                  * racing against cgroup_exit().
1810                  *
1811                  * Interrupts were already disabled while acquiring
1812                  * the css_set_lock, so we do not need to disable it
1813                  * again when acquiring the sighand->siglock here.
1814                  */
1815                 spin_lock(&p->sighand->siglock);
1816                 if (!(p->flags & PF_EXITING)) {
1817                         struct css_set *cset = task_css_set(p);
1818 
1819                         if (!css_set_populated(cset))
1820                                 css_set_update_populated(cset, true);
1821                         list_add_tail(&p->cg_list, &cset->tasks);
1822                         get_css_set(cset);
1823                         cset->nr_tasks++;
1824                 }
1825                 spin_unlock(&p->sighand->siglock);
1826         } while_each_thread(g, p);
1827         read_unlock(&tasklist_lock);
1828 out_unlock:
1829         spin_unlock_irq(&css_set_lock);
1830 }
1831 
1832 static void init_cgroup_housekeeping(struct cgroup *cgrp)
1833 {
1834         struct cgroup_subsys *ss;
1835         int ssid;
1836 
1837         INIT_LIST_HEAD(&cgrp->self.sibling);
1838         INIT_LIST_HEAD(&cgrp->self.children);
1839         INIT_LIST_HEAD(&cgrp->cset_links);
1840         INIT_LIST_HEAD(&cgrp->pidlists);
1841         mutex_init(&cgrp->pidlist_mutex);
1842         cgrp->self.cgroup = cgrp;
1843         cgrp->self.flags |= CSS_ONLINE;
1844         cgrp->dom_cgrp = cgrp;
1845         cgrp->max_descendants = INT_MAX;
1846         cgrp->max_depth = INT_MAX;
1847 
1848         for_each_subsys(ss, ssid)
1849                 INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1850 
1851         init_waitqueue_head(&cgrp->offline_waitq);
1852         INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
1853 }
1854 
1855 void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts)
1856 {
1857         struct cgroup *cgrp = &root->cgrp;
1858 
1859         INIT_LIST_HEAD(&root->root_list);
1860         atomic_set(&root->nr_cgrps, 1);
1861         cgrp->root = root;
1862         init_cgroup_housekeeping(cgrp);
1863         idr_init(&root->cgroup_idr);
1864 
1865         root->flags = opts->flags;
1866         if (opts->release_agent)
1867                 strscpy(root->release_agent_path, opts->release_agent, PATH_MAX);
1868         if (opts->name)
1869                 strscpy(root->name, opts->name, MAX_CGROUP_ROOT_NAMELEN);
1870         if (opts->cpuset_clone_children)
1871                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1872 }
1873 
1874 int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags)
1875 {
1876         LIST_HEAD(tmp_links);
1877         struct cgroup *root_cgrp = &root->cgrp;
1878         struct kernfs_syscall_ops *kf_sops;
1879         struct css_set *cset;
1880         int i, ret;
1881 
1882         lockdep_assert_held(&cgroup_mutex);
1883 
1884         ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
1885         if (ret < 0)
1886                 goto out;
1887         root_cgrp->id = ret;
1888         root_cgrp->ancestor_ids[0] = ret;
1889 
1890         ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
1891                               ref_flags, GFP_KERNEL);
1892         if (ret)
1893                 goto out;
1894 
1895         /*
1896          * We're accessing css_set_count without locking css_set_lock here,
1897          * but that's OK - it can only be increased by someone holding
1898          * cgroup_lock, and that's us.  Later rebinding may disable
1899          * controllers on the default hierarchy and thus create new csets,
1900          * which can't be more than the existing ones.  Allocate 2x.
1901          */
1902         ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
1903         if (ret)
1904                 goto cancel_ref;
1905 
1906         ret = cgroup_init_root_id(root);
1907         if (ret)
1908                 goto cancel_ref;
1909 
1910         kf_sops = root == &cgrp_dfl_root ?
1911                 &cgroup_kf_syscall_ops : &cgroup1_kf_syscall_ops;
1912 
1913         root->kf_root = kernfs_create_root(kf_sops,
1914                                            KERNFS_ROOT_CREATE_DEACTIVATED |
1915                                            KERNFS_ROOT_SUPPORT_EXPORTOP,
1916                                            root_cgrp);
1917         if (IS_ERR(root->kf_root)) {
1918                 ret = PTR_ERR(root->kf_root);
1919                 goto exit_root_id;
1920         }
1921         root_cgrp->kn = root->kf_root->kn;
1922 
1923         ret = css_populate_dir(&root_cgrp->self);
1924         if (ret)
1925                 goto destroy_root;
1926 
1927         ret = rebind_subsystems(root, ss_mask);
1928         if (ret)
1929                 goto destroy_root;
1930 
1931         ret = cgroup_bpf_inherit(root_cgrp);
1932         WARN_ON_ONCE(ret);
1933 
1934         trace_cgroup_setup_root(root);
1935 
1936         /*
1937          * There must be no failure case after here, since rebinding takes
1938          * care of subsystems' refcounts, which are explicitly dropped in
1939          * the failure exit path.
1940          */
1941         list_add(&root->root_list, &cgroup_roots);
1942         cgroup_root_count++;
1943 
1944         /*
1945          * Link the root cgroup in this hierarchy into all the css_set
1946          * objects.
1947          */
1948         spin_lock_irq(&css_set_lock);
1949         hash_for_each(css_set_table, i, cset, hlist) {
1950                 link_css_set(&tmp_links, cset, root_cgrp);
1951                 if (css_set_populated(cset))
1952                         cgroup_update_populated(root_cgrp, true);
1953         }
1954         spin_unlock_irq(&css_set_lock);
1955 
1956         BUG_ON(!list_empty(&root_cgrp->self.children));
1957         BUG_ON(atomic_read(&root->nr_cgrps) != 1);
1958 
1959         kernfs_activate(root_cgrp->kn);
1960         ret = 0;
1961         goto out;
1962 
1963 destroy_root:
1964         kernfs_destroy_root(root->kf_root);
1965         root->kf_root = NULL;
1966 exit_root_id:
1967         cgroup_exit_root_id(root);
1968 cancel_ref:
1969         percpu_ref_exit(&root_cgrp->self.refcnt);
1970 out:
1971         free_cgrp_cset_links(&tmp_links);
1972         return ret;
1973 }
1974 
1975 struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
1976                                struct cgroup_root *root, unsigned long magic,
1977                                struct cgroup_namespace *ns)
1978 {
1979         struct dentry *dentry;
1980         bool new_sb;
1981 
1982         dentry = kernfs_mount(fs_type, flags, root->kf_root, magic, &new_sb);
1983 
1984         /*
1985          * In non-init cgroup namespace, instead of root cgroup's dentry,
1986          * we return the dentry corresponding to the cgroupns->root_cgrp.
1987          */
1988         if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
1989                 struct dentry *nsdentry;
1990                 struct cgroup *cgrp;
1991 
1992                 mutex_lock(&cgroup_mutex);
1993                 spin_lock_irq(&css_set_lock);
1994 
1995                 cgrp = cset_cgroup_from_root(ns->root_cset, root);
1996 
1997                 spin_unlock_irq(&css_set_lock);
1998                 mutex_unlock(&cgroup_mutex);
1999 
2000                 nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
2001                 dput(dentry);
2002                 dentry = nsdentry;
2003         }
2004 
2005         if (IS_ERR(dentry) || !new_sb)
2006                 cgroup_put(&root->cgrp);
2007 
2008         return dentry;
2009 }
2010 
2011 static struct dentry *cgroup_mount(struct file_system_type *fs_type,
2012                          int flags, const char *unused_dev_name,
2013                          void *data)
2014 {
2015         struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
2016         struct dentry *dentry;
2017         int ret;
2018 
2019         get_cgroup_ns(ns);
2020 
2021         /* Check if the caller has permission to mount. */
2022         if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
2023                 put_cgroup_ns(ns);
2024                 return ERR_PTR(-EPERM);
2025         }
2026 
2027         /*
2028          * The first time anyone tries to mount a cgroup, enable the list
2029          * linking each css_set to its tasks and fix up all existing tasks.
2030          */
2031         if (!use_task_css_set_links)
2032                 cgroup_enable_task_cg_lists();
2033 
2034         if (fs_type == &cgroup2_fs_type) {
2035                 unsigned int root_flags;
2036 
2037                 ret = parse_cgroup_root_flags(data, &root_flags);
2038                 if (ret) {
2039                         put_cgroup_ns(ns);
2040                         return ERR_PTR(ret);
2041                 }
2042 
2043                 cgrp_dfl_visible = true;
2044                 cgroup_get_live(&cgrp_dfl_root.cgrp);
2045 
2046                 dentry = cgroup_do_mount(&cgroup2_fs_type, flags, &cgrp_dfl_root,
2047                                          CGROUP2_SUPER_MAGIC, ns);
2048                 if (!IS_ERR(dentry))
2049                         apply_cgroup_root_flags(root_flags);
2050         } else {
2051                 dentry = cgroup1_mount(&cgroup_fs_type, flags, data,
2052                                        CGROUP_SUPER_MAGIC, ns);
2053         }
2054 
2055         put_cgroup_ns(ns);
2056         return dentry;
2057 }
2058 
2059 static void cgroup_kill_sb(struct super_block *sb)
2060 {
2061         struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2062         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2063 
2064         /*
2065          * If @root doesn't have any mounts or children, start killing it.
2066          * This prevents new mounts by disabling percpu_ref_tryget_live().
2067          * cgroup_mount() may wait for @root's release.
2068          *
2069          * And don't kill the default root.
2070          */
2071         if (!list_empty(&root->cgrp.self.children) ||
2072             root == &cgrp_dfl_root)
2073                 cgroup_put(&root->cgrp);
2074         else
2075                 percpu_ref_kill(&root->cgrp.self.refcnt);
2076 
2077         kernfs_kill_sb(sb);
2078 }
2079 
2080 struct file_system_type cgroup_fs_type = {
2081         .name = "cgroup",
2082         .mount = cgroup_mount,
2083         .kill_sb = cgroup_kill_sb,
2084         .fs_flags = FS_USERNS_MOUNT,
2085 };
2086 
2087 static struct file_system_type cgroup2_fs_type = {
2088         .name = "cgroup2",
2089         .mount = cgroup_mount,
2090         .kill_sb = cgroup_kill_sb,
2091         .fs_flags = FS_USERNS_MOUNT,
2092 };
2093 
2094 int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2095                           struct cgroup_namespace *ns)
2096 {
2097         struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2098 
2099         return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2100 }
2101 
2102 int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2103                    struct cgroup_namespace *ns)
2104 {
2105         int ret;
2106 
2107         mutex_lock(&cgroup_mutex);
2108         spin_lock_irq(&css_set_lock);
2109 
2110         ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2111 
2112         spin_unlock_irq(&css_set_lock);
2113         mutex_unlock(&cgroup_mutex);
2114 
2115         return ret;
2116 }
2117 EXPORT_SYMBOL_GPL(cgroup_path_ns);
2118 
2119 /**
2120  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2121  * @task: target task
2122  * @buf: the buffer to write the path into
2123  * @buflen: the length of the buffer
2124  *
2125  * Determine @task's cgroup on the first (the one with the lowest non-zero
2126  * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2127  * function grabs cgroup_mutex and shouldn't be used inside locks used by
2128  * cgroup controller callbacks.
2129  *
2130  * Return value is the same as kernfs_path().
2131  */
2132 int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2133 {
2134         struct cgroup_root *root;
2135         struct cgroup *cgrp;
2136         int hierarchy_id = 1;
2137         int ret;
2138 
2139         mutex_lock(&cgroup_mutex);
2140         spin_lock_irq(&css_set_lock);
2141 
2142         root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2143 
2144         if (root) {
2145                 cgrp = task_cgroup_from_root(task, root);
2146                 ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2147         } else {
2148                 /* if no hierarchy exists, everyone is in "/" */
2149                 ret = strlcpy(buf, "/", buflen);
2150         }
2151 
2152         spin_unlock_irq(&css_set_lock);
2153         mutex_unlock(&cgroup_mutex);
2154         return ret;
2155 }
2156 EXPORT_SYMBOL_GPL(task_cgroup_path);
2157 
2158 /**
2159  * cgroup_migrate_add_task - add a migration target task to a migration context
2160  * @task: target task
2161  * @mgctx: target migration context
2162  *
2163  * Add @task, which is a migration target, to @mgctx->tset.  This function
2164  * becomes noop if @task doesn't need to be migrated.  @task's css_set
2165  * should have been added as a migration source and @task->cg_list will be
2166  * moved from the css_set's tasks list to mg_tasks one.
2167  */
2168 static void cgroup_migrate_add_task(struct task_struct *task,
2169                                     struct cgroup_mgctx *mgctx)
2170 {
2171         struct css_set *cset;
2172 
2173         lockdep_assert_held(&css_set_lock);
2174 
2175         /* @task either already exited or can't exit until the end */
2176         if (task->flags & PF_EXITING)
2177                 return;
2178 
2179         /* leave @task alone if post_fork() hasn't linked it yet */
2180         if (list_empty(&task->cg_list))
2181                 return;
2182 
2183         cset = task_css_set(task);
2184         if (!cset->mg_src_cgrp)
2185                 return;
2186 
2187         mgctx->tset.nr_tasks++;
2188 
2189         list_move_tail(&task->cg_list, &cset->mg_tasks);
2190         if (list_empty(&cset->mg_node))
2191                 list_add_tail(&cset->mg_node,
2192                               &mgctx->tset.src_csets);
2193         if (list_empty(&cset->mg_dst_cset->mg_node))
2194                 list_add_tail(&cset->mg_dst_cset->mg_node,
2195                               &mgctx->tset.dst_csets);
2196 }
2197 
2198 /**
2199  * cgroup_taskset_first - reset taskset and return the first task
2200  * @tset: taskset of interest
2201  * @dst_cssp: output variable for the destination css
2202  *
2203  * @tset iteration is initialized and the first task is returned.
2204  */
2205 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2206                                          struct cgroup_subsys_state **dst_cssp)
2207 {
2208         tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2209         tset->cur_task = NULL;
2210 
2211         return cgroup_taskset_next(tset, dst_cssp);
2212 }
2213 
2214 /**
2215  * cgroup_taskset_next - iterate to the next task in taskset
2216  * @tset: taskset of interest
2217  * @dst_cssp: output variable for the destination css
2218  *
2219  * Return the next task in @tset.  Iteration must have been initialized
2220  * with cgroup_taskset_first().
2221  */
2222 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2223                                         struct cgroup_subsys_state **dst_cssp)
2224 {
2225         struct css_set *cset = tset->cur_cset;
2226         struct task_struct *task = tset->cur_task;
2227 
2228         while (&cset->mg_node != tset->csets) {
2229                 if (!task)
2230                         task = list_first_entry(&cset->mg_tasks,
2231                                                 struct task_struct, cg_list);
2232                 else
2233                         task = list_next_entry(task, cg_list);
2234 
2235                 if (&task->cg_list != &cset->mg_tasks) {
2236                         tset->cur_cset = cset;
2237                         tset->cur_task = task;
2238 
2239                         /*
2240                          * This function may be called both before and
2241                          * after cgroup_taskset_migrate().  The two cases
2242                          * can be distinguished by looking at whether @cset
2243                          * has its ->mg_dst_cset set.
2244                          */
2245                         if (cset->mg_dst_cset)
2246                                 *dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2247                         else
2248                                 *dst_cssp = cset->subsys[tset->ssid];
2249 
2250                         return task;
2251                 }
2252 
2253                 cset = list_next_entry(cset, mg_node);
2254                 task = NULL;
2255         }
2256 
2257         return NULL;
2258 }
2259 
2260 /**
2261  * cgroup_taskset_migrate - migrate a taskset
2262  * @mgctx: migration context
2263  *
2264  * Migrate tasks in @mgctx as setup by migration preparation functions.
2265  * This function fails iff one of the ->can_attach callbacks fails and
2266  * guarantees that either all or none of the tasks in @mgctx are migrated.
2267  * @mgctx is consumed regardless of success.
2268  */
2269 static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
2270 {
2271         struct cgroup_taskset *tset = &mgctx->tset;
2272         struct cgroup_subsys *ss;
2273         struct task_struct *task, *tmp_task;
2274         struct css_set *cset, *tmp_cset;
2275         int ssid, failed_ssid, ret;
2276 
2277         /* check that we can legitimately attach to the cgroup */
2278         if (tset->nr_tasks) {
2279                 do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2280                         if (ss->can_attach) {
2281                                 tset->ssid = ssid;
2282                                 ret = ss->can_attach(tset);
2283                                 if (ret) {
2284                                         failed_ssid = ssid;
2285                                         goto out_cancel_attach;
2286                                 }
2287                         }
2288                 } while_each_subsys_mask();
2289         }
2290 
2291         /*
2292          * Now that we're guaranteed success, proceed to move all tasks to
2293          * the new cgroup.  There are no failure cases after here, so this
2294          * is the commit point.
2295          */
2296         spin_lock_irq(&css_set_lock);
2297         list_for_each_entry(cset, &tset->src_csets, mg_node) {
2298                 list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2299                         struct css_set *from_cset = task_css_set(task);
2300                         struct css_set *to_cset = cset->mg_dst_cset;
2301 
2302                         get_css_set(to_cset);
2303                         to_cset->nr_tasks++;
2304                         css_set_move_task(task, from_cset, to_cset, true);
2305                         put_css_set_locked(from_cset);
2306                         from_cset->nr_tasks--;
2307                 }
2308         }
2309         spin_unlock_irq(&css_set_lock);
2310 
2311         /*
2312          * Migration is committed, all target tasks are now on dst_csets.
2313          * Nothing is sensitive to fork() after this point.  Notify
2314          * controllers that migration is complete.
2315          */
2316         tset->csets = &tset->dst_csets;
2317 
2318         if (tset->nr_tasks) {
2319                 do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2320                         if (ss->attach) {
2321                                 tset->ssid = ssid;
2322                                 ss->attach(tset);
2323                         }
2324                 } while_each_subsys_mask();
2325         }
2326 
2327         ret = 0;
2328         goto out_release_tset;
2329 
2330 out_cancel_attach:
2331         if (tset->nr_tasks) {
2332                 do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2333                         if (ssid == failed_ssid)
2334                                 break;
2335                         if (ss->cancel_attach) {
2336                                 tset->ssid = ssid;
2337                                 ss->cancel_attach(tset);
2338                         }
2339                 } while_each_subsys_mask();
2340         }
2341 out_release_tset:
2342         spin_lock_irq(&css_set_lock);
2343         list_splice_init(&tset->dst_csets, &tset->src_csets);
2344         list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2345                 list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2346                 list_del_init(&cset->mg_node);
2347         }
2348         spin_unlock_irq(&css_set_lock);
2349 
2350         /*
2351          * Re-initialize the cgroup_taskset structure in case it is reused
2352          * again in another cgroup_migrate_add_task()/cgroup_migrate_execute()
2353          * iteration.
2354          */
2355         tset->nr_tasks = 0;
2356         tset->csets    = &tset->src_csets;
2357         return ret;
2358 }
2359 
2360 /**
2361  * cgroup_migrate_vet_dst - verify whether a cgroup can be migration destination
2362  * @dst_cgrp: destination cgroup to test
2363  *
2364  * On the default hierarchy, except for the mixable, (possible) thread root
2365  * and threaded cgroups, subtree_control must be zero for migration
2366  * destination cgroups with tasks so that child cgroups don't compete
2367  * against tasks.
2368  */
2369 int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp)
2370 {
2371         /* v1 doesn't have any restriction */
2372         if (!cgroup_on_dfl(dst_cgrp))
2373                 return 0;
2374 
2375         /* verify @dst_cgrp can host resources */
2376         if (!cgroup_is_valid_domain(dst_cgrp->dom_cgrp))
2377                 return -EOPNOTSUPP;
2378 
2379         /* mixables don't care */
2380         if (cgroup_is_mixable(dst_cgrp))
2381                 return 0;
2382 
2383         /*
2384          * If @dst_cgrp is already or can become a thread root or is
2385          * threaded, it doesn't matter.
2386          */
2387         if (cgroup_can_be_thread_root(dst_cgrp) || cgroup_is_threaded(dst_cgrp))
2388                 return 0;
2389 
2390         /* apply no-internal-process constraint */
2391         if (dst_cgrp->subtree_control)
2392                 return -EBUSY;
2393 
2394         return 0;
2395 }
2396 
2397 /**
2398  * cgroup_migrate_finish - cleanup after attach
2399  * @mgctx: migration context
2400  *
2401  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2402  * those functions for details.
2403  */
2404 void cgroup_migrate_finish(struct cgroup_mgctx *mgctx)
2405 {
2406         LIST_HEAD(preloaded);
2407         struct css_set *cset, *tmp_cset;
2408 
2409         lockdep_assert_held(&cgroup_mutex);
2410 
2411         spin_lock_irq(&css_set_lock);
2412 
2413         list_splice_tail_init(&mgctx->preloaded_src_csets, &preloaded);
2414         list_splice_tail_init(&mgctx->preloaded_dst_csets, &preloaded);
2415 
2416         list_for_each_entry_safe(cset, tmp_cset, &preloaded, mg_preload_node) {
2417                 cset->mg_src_cgrp = NULL;
2418                 cset->mg_dst_cgrp = NULL;
2419                 cset->mg_dst_cset = NULL;
2420                 list_del_init(&cset->mg_preload_node);
2421                 put_css_set_locked(cset);
2422         }
2423 
2424         spin_unlock_irq(&css_set_lock);
2425 }
2426 
2427 /**
2428  * cgroup_migrate_add_src - add a migration source css_set
2429  * @src_cset: the source css_set to add
2430  * @dst_cgrp: the destination cgroup
2431  * @mgctx: migration context
2432  *
2433  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2434  * @src_cset and add it to @mgctx->src_csets, which should later be cleaned
2435  * up by cgroup_migrate_finish().
2436  *
2437  * This function may be called without holding cgroup_threadgroup_rwsem
2438  * even if the target is a process.  Threads may be created and destroyed
2439  * but as long as cgroup_mutex is not dropped, no new css_set can be put
2440  * into play and the preloaded css_sets are guaranteed to cover all
2441  * migrations.
2442  */
2443 void cgroup_migrate_add_src(struct css_set *src_cset,
2444                             struct cgroup *dst_cgrp,
2445                             struct cgroup_mgctx *mgctx)
2446 {
2447         struct cgroup *src_cgrp;
2448 
2449         lockdep_assert_held(&cgroup_mutex);
2450         lockdep_assert_held(&css_set_lock);
2451 
2452         /*
2453          * If ->dead, @src_set is associated with one or more dead cgroups
2454          * and doesn't contain any migratable tasks.  Ignore it early so
2455          * that the rest of migration path doesn't get confused by it.
2456          */
2457         if (src_cset->dead)
2458                 return;
2459 
2460         src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2461 
2462         if (!list_empty(&src_cset->mg_preload_node))
2463                 return;
2464 
2465         WARN_ON(src_cset->mg_src_cgrp);
2466         WARN_ON(src_cset->mg_dst_cgrp);
2467         WARN_ON(!list_empty(&src_cset->mg_tasks));
2468         WARN_ON(!list_empty(&src_cset->mg_node));
2469 
2470         src_cset->mg_src_cgrp = src_cgrp;
2471         src_cset->mg_dst_cgrp = dst_cgrp;
2472         get_css_set(src_cset);
2473         list_add_tail(&src_cset->mg_preload_node, &mgctx->preloaded_src_csets);
2474 }
2475 
2476 /**
2477  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2478  * @mgctx: migration context
2479  *
2480  * Tasks are about to be moved and all the source css_sets have been
2481  * preloaded to @mgctx->preloaded_src_csets.  This function looks up and
2482  * pins all destination css_sets, links each to its source, and append them
2483  * to @mgctx->preloaded_dst_csets.
2484  *
2485  * This function must be called after cgroup_migrate_add_src() has been
2486  * called on each migration source css_set.  After migration is performed
2487  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2488  * @mgctx.
2489  */
2490 int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
2491 {
2492         struct css_set *src_cset, *tmp_cset;
2493 
2494         lockdep_assert_held(&cgroup_mutex);
2495 
2496         /* look up the dst cset for each src cset and link it to src */
2497         list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
2498                                  mg_preload_node) {
2499                 struct css_set *dst_cset;
2500                 struct cgroup_subsys *ss;
2501                 int ssid;
2502 
2503                 dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2504                 if (!dst_cset)
2505                         goto err;
2506 
2507                 WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2508 
2509                 /*
2510                  * If src cset equals dst, it's noop.  Drop the src.
2511                  * cgroup_migrate() will skip the cset too.  Note that we
2512                  * can't handle src == dst as some nodes are used by both.
2513                  */
2514                 if (src_cset == dst_cset) {
2515                         src_cset->mg_src_cgrp = NULL;
2516                         src_cset->mg_dst_cgrp = NULL;
2517                         list_del_init(&src_cset->mg_preload_node);
2518                         put_css_set(src_cset);
2519                         put_css_set(dst_cset);
2520                         continue;
2521                 }
2522 
2523                 src_cset->mg_dst_cset = dst_cset;
2524 
2525                 if (list_empty(&dst_cset->mg_preload_node))
2526                         list_add_tail(&dst_cset->mg_preload_node,
2527                                       &mgctx->preloaded_dst_csets);
2528                 else
2529                         put_css_set(dst_cset);
2530 
2531                 for_each_subsys(ss, ssid)
2532                         if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])
2533                                 mgctx->ss_mask |= 1 << ssid;
2534         }
2535 
2536         return 0;
2537 err:
2538         cgroup_migrate_finish(mgctx);
2539         return -ENOMEM;
2540 }
2541 
2542 /**
2543  * cgroup_migrate - migrate a process or task to a cgroup
2544  * @leader: the leader of the process or the task to migrate
2545  * @threadgroup: whether @leader points to the whole process or a single task
2546  * @mgctx: migration context
2547  *
2548  * Migrate a process or task denoted by @leader.  If migrating a process,
2549  * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2550  * responsible for invoking cgroup_migrate_add_src() and
2551  * cgroup_migrate_prepare_dst() on the targets before invoking this
2552  * function and following up with cgroup_migrate_finish().
2553  *
2554  * As long as a controller's ->can_attach() doesn't fail, this function is
2555  * guaranteed to succeed.  This means that, excluding ->can_attach()
2556  * failure, when migrating multiple targets, the success or failure can be
2557  * decided for all targets by invoking group_migrate_prepare_dst() before
2558  * actually starting migrating.
2559  */
2560 int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2561                    struct cgroup_mgctx *mgctx)
2562 {
2563         struct task_struct *task;
2564 
2565         /*
2566          * Prevent freeing of tasks while we take a snapshot. Tasks that are
2567          * already PF_EXITING could be freed from underneath us unless we
2568          * take an rcu_read_lock.
2569          */
2570         spin_lock_irq(&css_set_lock);
2571         rcu_read_lock();
2572         task = leader;
2573         do {
2574                 cgroup_migrate_add_task(task, mgctx);
2575                 if (!threadgroup)
2576                         break;
2577         } while_each_thread(leader, task);
2578         rcu_read_unlock();
2579         spin_unlock_irq(&css_set_lock);
2580 
2581         return cgroup_migrate_execute(mgctx);
2582 }
2583 
2584 /**
2585  * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2586  * @dst_cgrp: the cgroup to attach to
2587  * @leader: the task or the leader of the threadgroup to be attached
2588  * @threadgroup: attach the whole threadgroup?
2589  *
2590  * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2591  */
2592 int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
2593                        bool threadgroup)
2594 {
2595         DEFINE_CGROUP_MGCTX(mgctx);
2596         struct task_struct *task;
2597         int ret;
2598 
2599         ret = cgroup_migrate_vet_dst(dst_cgrp);
2600         if (ret)
2601                 return ret;
2602 
2603         /* look up all src csets */
2604         spin_lock_irq(&css_set_lock);
2605         rcu_read_lock();
2606         task = leader;
2607         do {
2608                 cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
2609                 if (!threadgroup)
2610                         break;
2611         } while_each_thread(leader, task);
2612         rcu_read_unlock();
2613         spin_unlock_irq(&css_set_lock);
2614 
2615         /* prepare dst csets and commit */
2616         ret = cgroup_migrate_prepare_dst(&mgctx);
2617         if (!ret)
2618                 ret = cgroup_migrate(leader, threadgroup, &mgctx);
2619 
2620         cgroup_migrate_finish(&mgctx);
2621 
2622         if (!ret)
2623                 trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
2624 
2625         return ret;
2626 }
2627 
2628 struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
2629         __acquires(&cgroup_threadgroup_rwsem)
2630 {
2631         struct task_struct *tsk;
2632         pid_t pid;
2633 
2634         if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2635                 return ERR_PTR(-EINVAL);
2636 
2637         percpu_down_write(&cgroup_threadgroup_rwsem);
2638 
2639         rcu_read_lock();
2640         if (pid) {
2641                 tsk = find_task_by_vpid(pid);
2642                 if (!tsk) {
2643                         tsk = ERR_PTR(-ESRCH);
2644                         goto out_unlock_threadgroup;
2645                 }
2646         } else {
2647                 tsk = current;
2648         }
2649 
2650         if (threadgroup)
2651                 tsk = tsk->group_leader;
2652 
2653         /*
2654          * kthreads may acquire PF_NO_SETAFFINITY during initialization.
2655          * If userland migrates such a kthread to a non-root cgroup, it can
2656          * become trapped in a cpuset, or RT kthread may be born in a
2657          * cgroup with no rt_runtime allocated.  Just say no.
2658          */
2659         if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) {
2660                 tsk = ERR_PTR(-EINVAL);
2661                 goto out_unlock_threadgroup;
2662         }
2663 
2664         get_task_struct(tsk);
2665         goto out_unlock_rcu;
2666 
2667 out_unlock_threadgroup:
2668         percpu_up_write(&cgroup_threadgroup_rwsem);
2669 out_unlock_rcu:
2670         rcu_read_unlock();
2671         return tsk;
2672 }
2673 
2674 void cgroup_procs_write_finish(struct task_struct *task)
2675         __releases(&cgroup_threadgroup_rwsem)
2676 {
2677         struct cgroup_subsys *ss;
2678         int ssid;
2679 
2680         /* release reference from cgroup_procs_write_start() */
2681         put_task_struct(task);
2682 
2683         percpu_up_write(&cgroup_threadgroup_rwsem);
2684         for_each_subsys(ss, ssid)
2685                 if (ss->post_attach)
2686                         ss->post_attach();
2687 }
2688 
2689 static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
2690 {
2691         struct cgroup_subsys *ss;
2692         bool printed = false;
2693         int ssid;
2694 
2695         do_each_subsys_mask(ss, ssid, ss_mask) {
2696                 if (printed)
2697                         seq_putc(seq, ' ');
2698                 seq_printf(seq, "%s", ss->name);
2699                 printed = true;
2700         } while_each_subsys_mask();
2701         if (printed)
2702                 seq_putc(seq, '\n');
2703 }
2704 
2705 /* show controllers which are enabled from the parent */
2706 static int cgroup_controllers_show(struct seq_file *seq, void *v)
2707 {
2708         struct cgroup *cgrp = seq_css(seq)->cgroup;
2709 
2710         cgroup_print_ss_mask(seq, cgroup_control(cgrp));
2711         return 0;
2712 }
2713 
2714 /* show controllers which are enabled for a given cgroup's children */
2715 static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
2716 {
2717         struct cgroup *cgrp = seq_css(seq)->cgroup;
2718 
2719         cgroup_print_ss_mask(seq, cgrp->subtree_control);
2720         return 0;
2721 }
2722 
2723 /**
2724  * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
2725  * @cgrp: root of the subtree to update csses for
2726  *
2727  * @cgrp's control masks have changed and its subtree's css associations
2728  * need to be updated accordingly.  This function looks up all css_sets
2729  * which are attached to the subtree, creates the matching updated css_sets
2730  * and migrates the tasks to the new ones.
2731  */
2732 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
2733 {
2734         DEFINE_CGROUP_MGCTX(mgctx);
2735         struct cgroup_subsys_state *d_css;
2736         struct cgroup *dsct;
2737         struct css_set *src_cset;
2738         int ret;
2739 
2740         lockdep_assert_held(&cgroup_mutex);
2741 
2742         percpu_down_write(&cgroup_threadgroup_rwsem);
2743 
2744         /* look up all csses currently attached to @cgrp's subtree */
2745         spin_lock_irq(&css_set_lock);
2746         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2747                 struct cgrp_cset_link *link;
2748 
2749                 list_for_each_entry(link, &dsct->cset_links, cset_link)
2750                         cgroup_migrate_add_src(link->cset, dsct, &mgctx);
2751         }
2752         spin_unlock_irq(&css_set_lock);
2753 
2754         /* NULL dst indicates self on default hierarchy */
2755         ret = cgroup_migrate_prepare_dst(&mgctx);
2756         if (ret)
2757                 goto out_finish;
2758 
2759         spin_lock_irq(&css_set_lock);
2760         list_for_each_entry(src_cset, &mgctx.preloaded_src_csets, mg_preload_node) {
2761                 struct task_struct *task, *ntask;
2762 
2763                 /* all tasks in src_csets need to be migrated */
2764                 list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
2765                         cgroup_migrate_add_task(task, &mgctx);
2766         }
2767         spin_unlock_irq(&css_set_lock);
2768 
2769         ret = cgroup_migrate_execute(&mgctx);
2770 out_finish:
2771         cgroup_migrate_finish(&mgctx);
2772         percpu_up_write(&cgroup_threadgroup_rwsem);
2773         return ret;
2774 }
2775 
2776 /**
2777  * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
2778  * @cgrp: root of the target subtree
2779  *
2780  * Because css offlining is asynchronous, userland may try to re-enable a
2781  * controller while the previous css is still around.  This function grabs
2782  * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
2783  */
2784 void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
2785         __acquires(&cgroup_mutex)
2786 {
2787         struct cgroup *dsct;
2788         struct cgroup_subsys_state *d_css;
2789         struct cgroup_subsys *ss;
2790         int ssid;
2791 
2792 restart:
2793         mutex_lock(&cgroup_mutex);
2794 
2795         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
2796                 for_each_subsys(ss, ssid) {
2797                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
2798                         DEFINE_WAIT(wait);
2799 
2800                         if (!css || !percpu_ref_is_dying(&css->refcnt))
2801                                 continue;
2802 
2803                         cgroup_get_live(dsct);
2804                         prepare_to_wait(&dsct->offline_waitq, &wait,
2805                                         TASK_UNINTERRUPTIBLE);
2806 
2807                         mutex_unlock(&cgroup_mutex);
2808                         schedule();
2809                         finish_wait(&dsct->offline_waitq, &wait);
2810 
2811                         cgroup_put(dsct);
2812                         goto restart;
2813                 }
2814         }
2815 }
2816 
2817 /**
2818  * cgroup_save_control - save control masks of a subtree
2819  * @cgrp: root of the target subtree
2820  *
2821  * Save ->subtree_control and ->subtree_ss_mask to the respective old_
2822  * prefixed fields for @cgrp's subtree including @cgrp itself.
2823  */
2824 static void cgroup_save_control(struct cgroup *cgrp)
2825 {
2826         struct cgroup *dsct;
2827         struct cgroup_subsys_state *d_css;
2828 
2829         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2830                 dsct->old_subtree_control = dsct->subtree_control;
2831                 dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
2832         }
2833 }
2834 
2835 /**
2836  * cgroup_propagate_control - refresh control masks of a subtree
2837  * @cgrp: root of the target subtree
2838  *
2839  * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
2840  * ->subtree_control and propagate controller availability through the
2841  * subtree so that descendants don't have unavailable controllers enabled.
2842  */
2843 static void cgroup_propagate_control(struct cgroup *cgrp)
2844 {
2845         struct cgroup *dsct;
2846         struct cgroup_subsys_state *d_css;
2847 
2848         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2849                 dsct->subtree_control &= cgroup_control(dsct);
2850                 dsct->subtree_ss_mask =
2851                         cgroup_calc_subtree_ss_mask(dsct->subtree_control,
2852                                                     cgroup_ss_mask(dsct));
2853         }
2854 }
2855 
2856 /**
2857  * cgroup_restore_control - restore control masks of a subtree
2858  * @cgrp: root of the target subtree
2859  *
2860  * Restore ->subtree_control and ->subtree_ss_mask from the respective old_
2861  * prefixed fields for @cgrp's subtree including @cgrp itself.
2862  */
2863 static void cgroup_restore_control(struct cgroup *cgrp)
2864 {
2865         struct cgroup *dsct;
2866         struct cgroup_subsys_state *d_css;
2867 
2868         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
2869                 dsct->subtree_control = dsct->old_subtree_control;
2870                 dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
2871         }
2872 }
2873 
2874 static bool css_visible(struct cgroup_subsys_state *css)
2875 {
2876         struct cgroup_subsys *ss = css->ss;
2877         struct cgroup *cgrp = css->cgroup;
2878 
2879         if (cgroup_control(cgrp) & (1 << ss->id))
2880                 return true;
2881         if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
2882                 return false;
2883         return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
2884 }
2885 
2886 /**
2887  * cgroup_apply_control_enable - enable or show csses according to control
2888  * @cgrp: root of the target subtree
2889  *
2890  * Walk @cgrp's subtree and create new csses or make the existing ones
2891  * visible.  A css is created invisible if it's being implicitly enabled
2892  * through dependency.  An invisible css is made visible when the userland
2893  * explicitly enables it.
2894  *
2895  * Returns 0 on success, -errno on failure.  On failure, csses which have
2896  * been processed already aren't cleaned up.  The caller is responsible for
2897  * cleaning up with cgroup_apply_control_disable().
2898  */
2899 static int cgroup_apply_control_enable(struct cgroup *cgrp)
2900 {
2901         struct cgroup *dsct;
2902         struct cgroup_subsys_state *d_css;
2903         struct cgroup_subsys *ss;
2904         int ssid, ret;
2905 
2906         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2907                 for_each_subsys(ss, ssid) {
2908                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
2909 
2910                         WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
2911 
2912                         if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
2913                                 continue;
2914 
2915                         if (!css) {
2916                                 css = css_create(dsct, ss);
2917                                 if (IS_ERR(css))
2918                                         return PTR_ERR(css);
2919                         }
2920 
2921                         if (css_visible(css)) {
2922                                 ret = css_populate_dir(css);
2923                                 if (ret)
2924                                         return ret;
2925                         }
2926                 }
2927         }
2928 
2929         return 0;
2930 }
2931 
2932 /**
2933  * cgroup_apply_control_disable - kill or hide csses according to control
2934  * @cgrp: root of the target subtree
2935  *
2936  * Walk @cgrp's subtree and kill and hide csses so that they match
2937  * cgroup_ss_mask() and cgroup_visible_mask().
2938  *
2939  * A css is hidden when the userland requests it to be disabled while other
2940  * subsystems are still depending on it.  The css must not actively control
2941  * resources and be in the vanilla state if it's made visible again later.
2942  * Controllers which may be depended upon should provide ->css_reset() for
2943  * this purpose.
2944  */
2945 static void cgroup_apply_control_disable(struct cgroup *cgrp)
2946 {
2947         struct cgroup *dsct;
2948         struct cgroup_subsys_state *d_css;
2949         struct cgroup_subsys *ss;
2950         int ssid;
2951 
2952         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
2953                 for_each_subsys(ss, ssid) {
2954                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
2955 
2956                         WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
2957 
2958                         if (!css)
2959                                 continue;
2960 
2961                         if (css->parent &&
2962                             !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
2963                                 kill_css(css);
2964                         } else if (!css_visible(css)) {
2965                                 css_clear_dir(css);
2966                                 if (ss->css_reset)
2967                                         ss->css_reset(css);
2968                         }
2969                 }
2970         }
2971 }
2972 
2973 /**
2974  * cgroup_apply_control - apply control mask updates to the subtree
2975  * @cgrp: root of the target subtree
2976  *
2977  * subsystems can be enabled and disabled in a subtree using the following
2978  * steps.
2979  *
2980  * 1. Call cgroup_save_control() to stash the current state.
2981  * 2. Update ->subtree_control masks in the subtree as desired.
2982  * 3. Call cgroup_apply_control() to apply the changes.
2983  * 4. Optionally perform other related operations.
2984  * 5. Call cgroup_finalize_control() to finish up.
2985  *
2986  * This function implements step 3 and propagates the mask changes
2987  * throughout @cgrp's subtree, updates csses accordingly and perform
2988  * process migrations.
2989  */
2990 static int cgroup_apply_control(struct cgroup *cgrp)
2991 {
2992         int ret;
2993 
2994         cgroup_propagate_control(cgrp);
2995 
2996         ret = cgroup_apply_control_enable(cgrp);
2997         if (ret)
2998                 return ret;
2999 
3000         /*
3001          * At this point, cgroup_e_css() results reflect the new csses
3002          * making the following cgroup_update_dfl_csses() properly update
3003          * css associations of all tasks in the subtree.
3004          */
3005         ret = cgroup_update_dfl_csses(cgrp);
3006         if (ret)
3007                 return ret;
3008 
3009         return 0;
3010 }
3011 
3012 /**
3013  * cgroup_finalize_control - finalize control mask update
3014  * @cgrp: root of the target subtree
3015  * @ret: the result of the update
3016  *
3017  * Finalize control mask update.  See cgroup_apply_control() for more info.
3018  */
3019 static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3020 {
3021         if (ret) {
3022                 cgroup_restore_control(cgrp);
3023                 cgroup_propagate_control(cgrp);
3024         }
3025 
3026         cgroup_apply_control_disable(cgrp);
3027 }
3028 
3029 static int cgroup_vet_subtree_control_enable(struct cgroup *cgrp, u16 enable)
3030 {
3031         u16 domain_enable = enable & ~cgrp_dfl_threaded_ss_mask;
3032 
3033         /* if nothing is getting enabled, nothing to worry about */
3034         if (!enable)
3035                 return 0;
3036 
3037         /* can @cgrp host any resources? */
3038         if (!cgroup_is_valid_domain(cgrp->dom_cgrp))
3039                 return -EOPNOTSUPP;
3040 
3041         /* mixables don't care */
3042         if (cgroup_is_mixable(cgrp))
3043                 return 0;
3044 
3045         if (domain_enable) {
3046                 /* can't enable domain controllers inside a thread subtree */
3047                 if (cgroup_is_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3048                         return -EOPNOTSUPP;
3049         } else {
3050                 /*
3051                  * Threaded controllers can handle internal competitions
3052                  * and are always allowed inside a (prospective) thread
3053                  * subtree.
3054                  */
3055                 if (cgroup_can_be_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3056                         return 0;
3057         }
3058 
3059         /*
3060          * Controllers can't be enabled for a cgroup with tasks to avoid
3061          * child cgroups competing against tasks.
3062          */
3063         if (cgroup_has_tasks(cgrp))
3064                 return -EBUSY;
3065 
3066         return 0;
3067 }
3068 
3069 /* change the enabled child controllers for a cgroup in the default hierarchy */
3070 static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3071                                             char *buf, size_t nbytes,
3072                                             loff_t off)
3073 {
3074         u16 enable = 0, disable = 0;
3075         struct cgroup *cgrp, *child;
3076         struct cgroup_subsys *ss;
3077         char *tok;
3078         int ssid, ret;
3079 
3080         /*
3081          * Parse input - space separated list of subsystem names prefixed
3082          * with either + or -.
3083          */
3084         buf = strstrip(buf);
3085         while ((tok = strsep(&buf, " "))) {
3086                 if (tok[0] == '\0')
3087                         continue;
3088                 do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3089                         if (!cgroup_ssid_enabled(ssid) ||
3090                             strcmp(tok + 1, ss->name))
3091                                 continue;
3092 
3093                         if (*tok == '+') {
3094                                 enable |= 1 << ssid;
3095                                 disable &= ~(1 << ssid);
3096                         } else if (*tok == '-') {
3097                                 disable |= 1 << ssid;
3098                                 enable &= ~(1 << ssid);
3099                         } else {
3100                                 return -EINVAL;
3101                         }
3102                         break;
3103                 } while_each_subsys_mask();
3104                 if (ssid == CGROUP_SUBSYS_COUNT)
3105                         return -EINVAL;
3106         }
3107 
3108         cgrp = cgroup_kn_lock_live(of->kn, true);
3109         if (!cgrp)
3110                 return -ENODEV;
3111 
3112         for_each_subsys(ss, ssid) {
3113                 if (enable & (1 << ssid)) {
3114                         if (cgrp->subtree_control & (1 << ssid)) {
3115                                 enable &= ~(1 << ssid);
3116                                 continue;
3117                         }
3118 
3119                         if (!(cgroup_control(cgrp) & (1 << ssid))) {
3120                                 ret = -ENOENT;
3121                                 goto out_unlock;
3122                         }
3123                 } else if (disable & (1 << ssid)) {
3124                         if (!(cgrp->subtree_control & (1 << ssid))) {
3125                                 disable &= ~(1 << ssid);
3126                                 continue;
3127                         }
3128 
3129                         /* a child has it enabled? */
3130                         cgroup_for_each_live_child(child, cgrp) {
3131                                 if (child->subtree_control & (1 << ssid)) {
3132                                         ret = -EBUSY;
3133                                         goto out_unlock;
3134                                 }
3135                         }
3136                 }
3137         }
3138 
3139         if (!enable && !disable) {
3140                 ret = 0;
3141                 goto out_unlock;
3142         }
3143 
3144         ret = cgroup_vet_subtree_control_enable(cgrp, enable);
3145         if (ret)
3146                 goto out_unlock;
3147 
3148         /* save and update control masks and prepare csses */
3149         cgroup_save_control(cgrp);
3150 
3151         cgrp->subtree_control |= enable;
3152         cgrp->subtree_control &= ~disable;
3153 
3154         ret = cgroup_apply_control(cgrp);
3155         cgroup_finalize_control(cgrp, ret);
3156         if (ret)
3157                 goto out_unlock;
3158 
3159         kernfs_activate(cgrp->kn);
3160 out_unlock:
3161         cgroup_kn_unlock(of->kn);
3162         return ret ?: nbytes;
3163 }
3164 
3165 /**
3166  * cgroup_enable_threaded - make @cgrp threaded
3167  * @cgrp: the target cgroup
3168  *
3169  * Called when "threaded" is written to the cgroup.type interface file and
3170  * tries to make @cgrp threaded and join the parent's resource domain.
3171  * This function is never called on the root cgroup as cgroup.type doesn't
3172  * exist on it.
3173  */
3174 static int cgroup_enable_threaded(struct cgroup *cgrp)
3175 {
3176         struct cgroup *parent = cgroup_parent(cgrp);
3177         struct cgroup *dom_cgrp = parent->dom_cgrp;
3178         int ret;
3179 
3180         lockdep_assert_held(&cgroup_mutex);
3181 
3182         /* noop if already threaded */
3183         if (cgroup_is_threaded(cgrp))
3184                 return 0;
3185 
3186         /*
3187          * If @cgroup is populated or has domain controllers enabled, it
3188          * can't be switched.  While the below cgroup_can_be_thread_root()
3189          * test can catch the same conditions, that's only when @parent is
3190          * not mixable, so let's check it explicitly.
3191          */
3192         if (cgroup_is_populated(cgrp) ||
3193             cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
3194                 return -EOPNOTSUPP;
3195 
3196         /* we're joining the parent's domain, ensure its validity */
3197         if (!cgroup_is_valid_domain(dom_cgrp) ||
3198             !cgroup_can_be_thread_root(dom_cgrp))
3199                 return -EOPNOTSUPP;
3200 
3201         /*
3202          * The following shouldn't cause actual migrations and should
3203          * always succeed.
3204          */
3205         cgroup_save_control(cgrp);
3206 
3207         cgrp->dom_cgrp = dom_cgrp;
3208         ret = cgroup_apply_control(cgrp);
3209         if (!ret)
3210                 parent->nr_threaded_children++;
3211         else
3212                 cgrp->dom_cgrp = cgrp;
3213 
3214         cgroup_finalize_control(cgrp, ret);
3215         return ret;
3216 }
3217 
3218 static int cgroup_type_show(struct seq_file *seq, void *v)
3219 {
3220         struct cgroup *cgrp = seq_css(seq)->cgroup;
3221 
3222         if (cgroup_is_threaded(cgrp))
3223                 seq_puts(seq, "threaded\n");
3224         else if (!cgroup_is_valid_domain(cgrp))
3225                 seq_puts(seq, "domain invalid\n");
3226         else if (cgroup_is_thread_root(cgrp))
3227                 seq_puts(seq, "domain threaded\n");
3228         else
3229                 seq_puts(seq, "domain\n");
3230 
3231         return 0;
3232 }
3233 
3234 static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf,
3235                                  size_t nbytes, loff_t off)
3236 {
3237         struct cgroup *cgrp;
3238         int ret;
3239 
3240         /* only switching to threaded mode is supported */
3241         if (strcmp(strstrip(buf), "threaded"))
3242                 return -EINVAL;
3243 
3244         cgrp = cgroup_kn_lock_live(of->kn, false);
3245         if (!cgrp)
3246                 return -ENOENT;
3247 
3248         /* threaded can only be enabled */
3249         ret = cgroup_enable_threaded(cgrp);
3250 
3251         cgroup_kn_unlock(of->kn);
3252         return ret ?: nbytes;
3253 }
3254 
3255 static int cgroup_max_descendants_show(struct seq_file *seq, void *v)
3256 {
3257         struct cgroup *cgrp = seq_css(seq)->cgroup;
3258         int descendants = READ_ONCE(cgrp->max_descendants);
3259 
3260         if (descendants == INT_MAX)
3261                 seq_puts(seq, "max\n");
3262         else
3263                 seq_printf(seq, "%d\n", descendants);
3264 
3265         return 0;
3266 }
3267 
3268 static ssize_t cgroup_max_descendants_write(struct kernfs_open_file *of,
3269                                            char *buf, size_t nbytes, loff_t off)
3270 {
3271         struct cgroup *cgrp;
3272         int descendants;
3273         ssize_t ret;
3274 
3275         buf = strstrip(buf);
3276         if (!strcmp(buf, "max")) {
3277                 descendants = INT_MAX;
3278         } else {
3279                 ret = kstrtoint(buf, 0, &descendants);
3280                 if (ret)
3281                         return ret;
3282         }
3283 
3284         if (descendants < 0)
3285                 return -ERANGE;
3286 
3287         cgrp = cgroup_kn_lock_live(of->kn, false);
3288         if (!cgrp)
3289                 return -ENOENT;
3290 
3291         cgrp->max_descendants = descendants;
3292 
3293         cgroup_kn_unlock(of->kn);
3294 
3295         return nbytes;
3296 }
3297 
3298 static int cgroup_max_depth_show(struct seq_file *seq, void *v)
3299 {
3300         struct cgroup *cgrp = seq_css(seq)->cgroup;
3301         int depth = READ_ONCE(cgrp->max_depth);
3302 
3303         if (depth == INT_MAX)
3304                 seq_puts(seq, "max\n");
3305         else
3306                 seq_printf(seq, "%d\n", depth);
3307 
3308         return 0;
3309 }
3310 
3311 static ssize_t cgroup_max_depth_write(struct kernfs_open_file *of,
3312                                       char *buf, size_t nbytes, loff_t off)
3313 {
3314         struct cgroup *cgrp;
3315         ssize_t ret;
3316         int depth;
3317 
3318         buf = strstrip(buf);
3319         if (!strcmp(buf, "max")) {
3320                 depth = INT_MAX;
3321         } else {
3322                 ret = kstrtoint(buf, 0, &depth);
3323                 if (ret)
3324                         return ret;
3325         }
3326 
3327         if (depth < 0)
3328                 return -ERANGE;
3329 
3330         cgrp = cgroup_kn_lock_live(of->kn, false);
3331         if (!cgrp)
3332                 return -ENOENT;
3333 
3334         cgrp->max_depth = depth;
3335 
3336         cgroup_kn_unlock(of->kn);
3337 
3338         return nbytes;
3339 }
3340 
3341 static int cgroup_events_show(struct seq_file *seq, void *v)
3342 {
3343         seq_printf(seq, "populated %d\n",
3344                    cgroup_is_populated(seq_css(seq)->cgroup));
3345         return 0;
3346 }
3347 
3348 static int cgroup_stat_show(struct seq_file *seq, void *v)
3349 {
3350         struct cgroup *cgroup = seq_css(seq)->cgroup;
3351 
3352         seq_printf(seq, "nr_descendants %d\n",
3353                    cgroup->nr_descendants);
3354         seq_printf(seq, "nr_dying_descendants %d\n",
3355                    cgroup->nr_dying_descendants);
3356 
3357         return 0;
3358 }
3359 
3360 static int __maybe_unused cgroup_extra_stat_show(struct seq_file *seq,
3361                                                  struct cgroup *cgrp, int ssid)
3362 {
3363         struct cgroup_subsys *ss = cgroup_subsys[ssid];
3364         struct cgroup_subsys_state *css;
3365         int ret;
3366 
3367         if (!ss->css_extra_stat_show)
3368                 return 0;
3369 
3370         css = cgroup_tryget_css(cgrp, ss);
3371         if (!css)
3372                 return 0;
3373 
3374         ret = ss->css_extra_stat_show(seq, css);
3375         css_put(css);
3376         return ret;
3377 }
3378 
3379 static int cpu_stat_show(struct seq_file *seq, void *v)
3380 {
3381         struct cgroup __maybe_unused *cgrp = seq_css(seq)->cgroup;
3382         int ret = 0;
3383 
3384         cgroup_stat_show_cputime(seq);
3385 #ifdef CONFIG_CGROUP_SCHED
3386         ret = cgroup_extra_stat_show(seq, cgrp, cpu_cgrp_id);
3387 #endif
3388         return ret;
3389 }
3390 
3391 static int cgroup_file_open(struct kernfs_open_file *of)
3392 {
3393         struct cftype *cft = of->kn->priv;
3394 
3395         if (cft->open)
3396                 return cft->open(of);
3397         return 0;
3398 }
3399 
3400 static void cgroup_file_release(struct kernfs_open_file *of)
3401 {
3402         struct cftype *cft = of->kn->priv;
3403 
3404         if (cft->release)
3405                 cft->release(of);
3406 }
3407 
3408 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3409                                  size_t nbytes, loff_t off)
3410 {
3411         struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
3412         struct cgroup *cgrp = of->kn->parent->priv;
3413         struct cftype *cft = of->kn->priv;
3414         struct cgroup_subsys_state *css;
3415         int ret;
3416 
3417         /*
3418          * If namespaces are delegation boundaries, disallow writes to
3419          * files in an non-init namespace root from inside the namespace
3420          * except for the files explicitly marked delegatable -
3421          * cgroup.procs and cgroup.subtree_control.
3422          */
3423         if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) &&
3424             !(cft->flags & CFTYPE_NS_DELEGATABLE) &&
3425             ns != &init_cgroup_ns && ns->root_cset->dfl_cgrp == cgrp)
3426                 return -EPERM;
3427 
3428         if (cft->write)
3429                 return cft->write(of, buf, nbytes, off);
3430 
3431         /*
3432          * kernfs guarantees that a file isn't deleted with operations in
3433          * flight, which means that the matching css is and stays alive and
3434          * doesn't need to be pinned.  The RCU locking is not necessary
3435          * either.  It's just for the convenience of using cgroup_css().
3436          */
3437         rcu_read_lock();
3438         css = cgroup_css(cgrp, cft->ss);
3439         rcu_read_unlock();
3440 
3441         if (cft->write_u64) {
3442                 unsigned long long v;
3443                 ret = kstrtoull(buf, 0, &v);
3444                 if (!ret)
3445                         ret = cft->write_u64(css, cft, v);
3446         } else if (cft->write_s64) {
3447                 long long v;
3448                 ret = kstrtoll(buf, 0, &v);
3449                 if (!ret)
3450                         ret = cft->write_s64(css, cft, v);
3451         } else {
3452                 ret = -EINVAL;
3453         }
3454 
3455         return ret ?: nbytes;
3456 }
3457 
3458 static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3459 {
3460         return seq_cft(seq)->seq_start(seq, ppos);
3461 }
3462 
3463 static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3464 {
3465         return seq_cft(seq)->seq_next(seq, v, ppos);
3466 }
3467 
3468 static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3469 {
3470         if (seq_cft(seq)->seq_stop)
3471                 seq_cft(seq)->seq_stop(seq, v);
3472 }
3473 
3474 static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3475 {
3476         struct cftype *cft = seq_cft(m);
3477         struct cgroup_subsys_state *css = seq_css(m);
3478 
3479         if (cft->seq_show)
3480                 return cft->seq_show(m, arg);
3481 
3482         if (cft->read_u64)
3483                 seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3484         else if (cft->read_s64)
3485                 seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3486         else
3487                 return -EINVAL;
3488         return 0;
3489 }
3490 
3491 static struct kernfs_ops cgroup_kf_single_ops = {
3492         .atomic_write_len       = PAGE_SIZE,
3493         .open                   = cgroup_file_open,
3494         .release                = cgroup_file_release,
3495         .write                  = cgroup_file_write,
3496         .seq_show               = cgroup_seqfile_show,
3497 };
3498 
3499 static struct kernfs_ops cgroup_kf_ops = {
3500         .atomic_write_len       = PAGE_SIZE,
3501         .open                   = cgroup_file_open,
3502         .release                = cgroup_file_release,
3503         .write                  = cgroup_file_write,
3504         .seq_start              = cgroup_seqfile_start,
3505         .seq_next               = cgroup_seqfile_next,
3506         .seq_stop               = cgroup_seqfile_stop,
3507         .seq_show               = cgroup_seqfile_show,
3508 };
3509 
3510 /* set uid and gid of cgroup dirs and files to that of the creator */
3511 static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3512 {
3513         struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3514                                .ia_uid = current_fsuid(),
3515                                .ia_gid = current_fsgid(), };
3516 
3517         if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3518             gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3519                 return 0;
3520 
3521         return kernfs_setattr(kn, &iattr);
3522 }
3523 
3524 static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3525                            struct cftype *cft)
3526 {
3527         char name[CGROUP_FILE_NAME_MAX];
3528         struct kernfs_node *kn;
3529         struct lock_class_key *key = NULL;
3530         int ret;
3531 
3532 #ifdef CONFIG_DEBUG_LOCK_ALLOC
3533         key = &cft->lockdep_key;
3534 #endif
3535         kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3536                                   cgroup_file_mode(cft), 0, cft->kf_ops, cft,
3537                                   NULL, key);
3538         if (IS_ERR(kn))
3539                 return PTR_ERR(kn);
3540 
3541         ret = cgroup_kn_set_ugid(kn);
3542         if (ret) {
3543                 kernfs_remove(kn);
3544                 return ret;
3545         }
3546 
3547         if (cft->file_offset) {
3548                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
3549 
3550                 spin_lock_irq(&cgroup_file_kn_lock);
3551                 cfile->kn = kn;
3552                 spin_unlock_irq(&cgroup_file_kn_lock);
3553         }
3554 
3555         return 0;
3556 }
3557 
3558 /**
3559  * cgroup_addrm_files - add or remove files to a cgroup directory
3560  * @css: the target css
3561  * @cgrp: the target cgroup (usually css->cgroup)
3562  * @cfts: array of cftypes to be added
3563  * @is_add: whether to add or remove
3564  *
3565  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3566  * For removals, this function never fails.
3567  */
3568 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3569                               struct cgroup *cgrp, struct cftype cfts[],
3570                               bool is_add)
3571 {
3572         struct cftype *cft, *cft_end = NULL;
3573         int ret = 0;
3574 
3575         lockdep_assert_held(&cgroup_mutex);
3576 
3577 restart:
3578         for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3579                 /* does cft->flags tell us to skip this file on @cgrp? */
3580                 if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3581                         continue;
3582                 if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3583                         continue;
3584                 if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3585                         continue;
3586                 if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3587                         continue;
3588 
3589                 if (is_add) {
3590                         ret = cgroup_add_file(css, cgrp, cft);
3591                         if (ret) {
3592                                 pr_warn("%s: failed to add %s, err=%d\n",
3593                                         __func__, cft->name, ret);
3594                                 cft_end = cft;
3595                                 is_add = false;
3596                                 goto restart;
3597                         }
3598                 } else {
3599                         cgroup_rm_file(cgrp, cft);
3600                 }
3601         }
3602         return ret;
3603 }
3604 
3605 static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3606 {
3607         struct cgroup_subsys *ss = cfts[0].ss;
3608         struct cgroup *root = &ss->root->cgrp;
3609         struct cgroup_subsys_state *css;
3610         int ret = 0;
3611 
3612         lockdep_assert_held(&cgroup_mutex);
3613 
3614         /* add/rm files for all cgroups created before */
3615         css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3616                 struct cgroup *cgrp = css->cgroup;
3617 
3618                 if (!(css->flags & CSS_VISIBLE))
3619                         continue;
3620 
3621                 ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3622                 if (ret)
3623                         break;
3624         }
3625 
3626         if (is_add && !ret)
3627                 kernfs_activate(root->kn);
3628         return ret;
3629 }
3630 
3631 static void cgroup_exit_cftypes(struct cftype *cfts)
3632 {
3633         struct cftype *cft;
3634 
3635         for (cft = cfts; cft->name[0] != '\0'; cft++) {
3636                 /* free copy for custom atomic_write_len, see init_cftypes() */
3637                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3638                         kfree(cft->kf_ops);
3639                 cft->kf_ops = NULL;
3640                 cft->ss = NULL;
3641 
3642                 /* revert flags set by cgroup core while adding @cfts */
3643                 cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3644         }
3645 }
3646 
3647 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3648 {
3649         struct cftype *cft;
3650 
3651         for (cft = cfts; cft->name[0] != '\0'; cft++) {
3652                 struct kernfs_ops *kf_ops;
3653 
3654                 WARN_ON(cft->ss || cft->kf_ops);
3655 
3656                 if (cft->seq_start)
3657                         kf_ops = &cgroup_kf_ops;
3658                 else
3659                         kf_ops = &cgroup_kf_single_ops;
3660 
3661                 /*
3662                  * Ugh... if @cft wants a custom max_write_len, we need to
3663                  * make a copy of kf_ops to set its atomic_write_len.
3664                  */
3665                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3666                         kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3667                         if (!kf_ops) {
3668                                 cgroup_exit_cftypes(cfts);
3669                                 return -ENOMEM;
3670                         }
3671                         kf_ops->atomic_write_len = cft->max_write_len;
3672                 }
3673 
3674                 cft->kf_ops = kf_ops;
3675                 cft->ss = ss;
3676         }
3677 
3678         return 0;
3679 }
3680 
3681 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
3682 {
3683         lockdep_assert_held(&cgroup_mutex);
3684 
3685         if (!cfts || !cfts[0].ss)
3686                 return -ENOENT;
3687 
3688         list_del(&cfts->node);
3689         cgroup_apply_cftypes(cfts, false);
3690         cgroup_exit_cftypes(cfts);
3691         return 0;
3692 }
3693 
3694 /**
3695  * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
3696  * @cfts: zero-length name terminated array of cftypes
3697  *
3698  * Unregister @cfts.  Files described by @cfts are removed from all
3699  * existing cgroups and all future cgroups won't have them either.  This
3700  * function can be called anytime whether @cfts' subsys is attached or not.
3701  *
3702  * Returns 0 on successful unregistration, -ENOENT if @cfts is not
3703  * registered.
3704  */
3705 int cgroup_rm_cftypes(struct cftype *cfts)
3706 {
3707         int ret;
3708 
3709         mutex_lock(&cgroup_mutex);
3710         ret = cgroup_rm_cftypes_locked(cfts);
3711         mutex_unlock(&cgroup_mutex);
3712         return ret;
3713 }
3714 
3715 /**
3716  * cgroup_add_cftypes - add an array of cftypes to a subsystem
3717  * @ss: target cgroup subsystem
3718  * @cfts: zero-length name terminated array of cftypes
3719  *
3720  * Register @cfts to @ss.  Files described by @cfts are created for all
3721  * existing cgroups to which @ss is attached and all future cgroups will
3722  * have them too.  This function can be called anytime whether @ss is
3723  * attached or not.
3724  *
3725  * Returns 0 on successful registration, -errno on failure.  Note that this
3726  * function currently returns 0 as long as @cfts registration is successful
3727  * even if some file creation attempts on existing cgroups fail.
3728  */
3729 static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3730 {
3731         int ret;
3732 
3733         if (!cgroup_ssid_enabled(ss->id))
3734                 return 0;
3735 
3736         if (!cfts || cfts[0].name[0] == '\0')
3737                 return 0;
3738 
3739         ret = cgroup_init_cftypes(ss, cfts);
3740         if (ret)
3741                 return ret;
3742 
3743         mutex_lock(&cgroup_mutex);
3744 
3745         list_add_tail(&cfts->node, &ss->cfts);
3746         ret = cgroup_apply_cftypes(cfts, true);
3747         if (ret)
3748                 cgroup_rm_cftypes_locked(cfts);
3749 
3750         mutex_unlock(&cgroup_mutex);
3751         return ret;
3752 }
3753 
3754 /**
3755  * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
3756  * @ss: target cgroup subsystem
3757  * @cfts: zero-length name terminated array of cftypes
3758  *
3759  * Similar to cgroup_add_cftypes() but the added files are only used for
3760  * the default hierarchy.
3761  */
3762 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3763 {
3764         struct cftype *cft;
3765 
3766         for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3767                 cft->flags |= __CFTYPE_ONLY_ON_DFL;
3768         return cgroup_add_cftypes(ss, cfts);
3769 }
3770 
3771 /**
3772  * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
3773  * @ss: target cgroup subsystem
3774  * @cfts: zero-length name terminated array of cftypes
3775  *
3776  * Similar to cgroup_add_cftypes() but the added files are only used for
3777  * the legacy hierarchies.
3778  */
3779 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3780 {
3781         struct cftype *cft;
3782 
3783         for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3784                 cft->flags |= __CFTYPE_NOT_ON_DFL;
3785         return cgroup_add_cftypes(ss, cfts);
3786 }
3787 
3788 /**
3789  * cgroup_file_notify - generate a file modified event for a cgroup_file
3790  * @cfile: target cgroup_file
3791  *
3792  * @cfile must have been obtained by setting cftype->file_offset.
3793  */
3794 void cgroup_file_notify(struct cgroup_file *cfile)
3795 {
3796         unsigned long flags;
3797 
3798         spin_lock_irqsave(&cgroup_file_kn_lock, flags);
3799         if (cfile->kn)
3800                 kernfs_notify(cfile->kn);
3801         spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
3802 }
3803 
3804 /**
3805  * css_next_child - find the next child of a given css
3806  * @pos: the current position (%NULL to initiate traversal)
3807  * @parent: css whose children to walk
3808  *
3809  * This function returns the next child of @parent and should be called
3810  * under either cgroup_mutex or RCU read lock.  The only requirement is
3811  * that @parent and @pos are accessible.  The next sibling is guaranteed to
3812  * be returned regardless of their states.
3813  *
3814  * If a subsystem synchronizes ->css_online() and the start of iteration, a
3815  * css which finished ->css_online() is guaranteed to be visible in the
3816  * future iterations and will stay visible until the last reference is put.
3817  * A css which hasn't finished ->css_online() or already finished
3818  * ->css_offline() may show up during traversal.  It's each subsystem's
3819  * responsibility to synchronize against on/offlining.
3820  */
3821 struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
3822                                            struct cgroup_subsys_state *parent)
3823 {
3824         struct cgroup_subsys_state *next;
3825 
3826         cgroup_assert_mutex_or_rcu_locked();
3827 
3828         /*
3829          * @pos could already have been unlinked from the sibling list.
3830          * Once a cgroup is removed, its ->sibling.next is no longer
3831          * updated when its next sibling changes.  CSS_RELEASED is set when
3832          * @pos is taken off list, at which time its next pointer is valid,
3833          * and, as releases are serialized, the one pointed to by the next
3834          * pointer is guaranteed to not have started release yet.  This
3835          * implies that if we observe !CSS_RELEASED on @pos in this RCU
3836          * critical section, the one pointed to by its next pointer is
3837          * guaranteed to not have finished its RCU grace period even if we
3838          * have dropped rcu_read_lock() inbetween iterations.
3839          *
3840          * If @pos has CSS_RELEASED set, its next pointer can't be
3841          * dereferenced; however, as each css is given a monotonically
3842          * increasing unique serial number and always appended to the
3843          * sibling list, the next one can be found by walking the parent's
3844          * children until the first css with higher serial number than
3845          * @pos's.  While this path can be slower, it happens iff iteration
3846          * races against release and the race window is very small.
3847          */
3848         if (!pos) {
3849                 next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
3850         } else if (likely(!(pos->flags & CSS_RELEASED))) {
3851                 next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
3852         } else {
3853                 list_for_each_entry_rcu(next, &parent->children, sibling)
3854                         if (next->serial_nr > pos->serial_nr)
3855                                 break;
3856         }
3857 
3858         /*
3859          * @next, if not pointing to the head, can be dereferenced and is
3860          * the next sibling.
3861          */
3862         if (&next->sibling != &parent->children)
3863                 return next;
3864         return NULL;
3865 }
3866 
3867 /**
3868  * css_next_descendant_pre - find the next descendant for pre-order walk
3869  * @pos: the current position (%NULL to initiate traversal)
3870  * @root: css whose descendants to walk
3871  *
3872  * To be used by css_for_each_descendant_pre().  Find the next descendant
3873  * to visit for pre-order traversal of @root's descendants.  @root is
3874  * included in the iteration and the first node to be visited.
3875  *
3876  * While this function requires cgroup_mutex or RCU read locking, it
3877  * doesn't require the whole traversal to be contained in a single critical
3878  * section.  This function will return the correct next descendant as long
3879  * as both @pos and @root are accessible and @pos is a descendant of @root.
3880  *
3881  * If a subsystem synchronizes ->css_online() and the start of iteration, a
3882  * css which finished ->css_online() is guaranteed to be visible in the
3883  * future iterations and will stay visible until the last reference is put.
3884  * A css which hasn't finished ->css_online() or already finished
3885  * ->css_offline() may show up during traversal.  It's each subsystem's
3886  * responsibility to synchronize against on/offlining.
3887  */
3888 struct cgroup_subsys_state *
3889 css_next_descendant_pre(struct cgroup_subsys_state *pos,
3890                         struct cgroup_subsys_state *root)
3891 {
3892         struct cgroup_subsys_state *next;
3893 
3894         cgroup_assert_mutex_or_rcu_locked();
3895 
3896         /* if first iteration, visit @root */
3897         if (!pos)
3898                 return root;
3899 
3900         /* visit the first child if exists */
3901         next = css_next_child(NULL, pos);
3902         if (next)
3903                 return next;
3904 
3905         /* no child, visit my or the closest ancestor's next sibling */
3906         while (pos != root) {
3907                 next = css_next_child(pos, pos->parent);
3908                 if (next)
3909                         return next;
3910                 pos = pos->parent;
3911         }
3912 
3913         return NULL;
3914 }
3915 
3916 /**
3917  * css_rightmost_descendant - return the rightmost descendant of a css
3918  * @pos: css of interest
3919  *
3920  * Return the rightmost descendant of @pos.  If there's no descendant, @pos
3921  * is returned.  This can be used during pre-order traversal to skip
3922  * subtree of @pos.
3923  *
3924  * While this function requires cgroup_mutex or RCU read locking, it
3925  * doesn't require the whole traversal to be contained in a single critical
3926  * section.  This function will return the correct rightmost descendant as
3927  * long as @pos is accessible.
3928  */
3929 struct cgroup_subsys_state *
3930 css_rightmost_descendant(struct cgroup_subsys_state *pos)
3931 {
3932         struct cgroup_subsys_state *last, *tmp;
3933 
3934         cgroup_assert_mutex_or_rcu_locked();
3935 
3936         do {
3937                 last = pos;
3938                 /* ->prev isn't RCU safe, walk ->next till the end */
3939                 pos = NULL;
3940                 css_for_each_child(tmp, last)
3941                         pos = tmp;
3942         } while (pos);
3943 
3944         return last;
3945 }
3946 
3947 static struct cgroup_subsys_state *
3948 css_leftmost_descendant(struct cgroup_subsys_state *pos)
3949 {
3950         struct cgroup_subsys_state *last;
3951 
3952         do {
3953                 last = pos;
3954                 pos = css_next_child(NULL, pos);
3955         } while (pos);
3956 
3957         return last;
3958 }
3959 
3960 /**
3961  * css_next_descendant_post - find the next descendant for post-order walk
3962  * @pos: the current position (%NULL to initiate traversal)
3963  * @root: css whose descendants to walk
3964  *
3965  * To be used by css_for_each_descendant_post().  Find the next descendant
3966  * to visit for post-order traversal of @root's descendants.  @root is
3967  * included in the iteration and the last node to be visited.
3968  *
3969  * While this function requires cgroup_mutex or RCU read locking, it
3970  * doesn't require the whole traversal to be contained in a single critical
3971  * section.  This function will return the correct next descendant as long
3972  * as both @pos and @cgroup are accessible and @pos is a descendant of
3973  * @cgroup.
3974  *
3975  * If a subsystem synchronizes ->css_online() and the start of iteration, a
3976  * css which finished ->css_online() is guaranteed to be visible in the
3977  * future iterations and will stay visible until the last reference is put.
3978  * A css which hasn't finished ->css_online() or already finished
3979  * ->css_offline() may show up during traversal.  It's each subsystem's
3980  * responsibility to synchronize against on/offlining.
3981  */
3982 struct cgroup_subsys_state *
3983 css_next_descendant_post(struct cgroup_subsys_state *pos,
3984                          struct cgroup_subsys_state *root)
3985 {
3986         struct cgroup_subsys_state *next;
3987 
3988         cgroup_assert_mutex_or_rcu_locked();
3989 
3990         /* if first iteration, visit leftmost descendant which may be @root */
3991         if (!pos)
3992                 return css_leftmost_descendant(root);
3993 
3994         /* if we visited @root, we're done */
3995         if (pos == root)
3996                 return NULL;
3997 
3998         /* if there's an unvisited sibling, visit its leftmost descendant */
3999         next = css_next_child(pos, pos->parent);
4000         if (next)
4001                 return css_leftmost_descendant(next);
4002 
4003         /* no sibling left, visit parent */
4004         return pos->parent;
4005 }
4006 
4007 /**
4008  * css_has_online_children - does a css have online children
4009  * @css: the target css
4010  *
4011  * Returns %true if @css has any online children; otherwise, %false.  This
4012  * function can be called from any context but the caller is responsible
4013  * for synchronizing against on/offlining as necessary.
4014  */
4015 bool css_has_online_children(struct cgroup_subsys_state *css)
4016 {
4017         struct cgroup_subsys_state *child;
4018         bool ret = false;
4019 
4020         rcu_read_lock();
4021         css_for_each_child(child, css) {
4022                 if (child->flags & CSS_ONLINE) {
4023                         ret = true;
4024                         break;
4025                 }
4026         }
4027         rcu_read_unlock();
4028         return ret;
4029 }
4030 
4031 static struct css_set *css_task_iter_next_css_set(struct css_task_iter *it)
4032 {
4033         struct list_head *l;
4034         struct cgrp_cset_link *link;
4035         struct css_set *cset;
4036 
4037         lockdep_assert_held(&css_set_lock);
4038 
4039         /* find the next threaded cset */
4040         if (it->tcset_pos) {
4041                 l = it->tcset_pos->next;
4042 
4043                 if (l != it->tcset_head) {
4044                         it->tcset_pos = l;
4045                         return container_of(l, struct css_set,
4046                                             threaded_csets_node);
4047                 }
4048 
4049                 it->tcset_pos = NULL;
4050         }
4051 
4052         /* find the next cset */
4053         l = it->cset_pos;
4054         l = l->next;
4055         if (l == it->cset_head) {
4056                 it->cset_pos = NULL;
4057                 return NULL;
4058         }
4059 
4060         if (it->ss) {
4061                 cset = container_of(l, struct css_set, e_cset_node[it->ss->id]);
4062         } else {
4063                 link = list_entry(l, struct cgrp_cset_link, cset_link);
4064                 cset = link->cset;
4065         }
4066 
4067         it->cset_pos = l;
4068 
4069         /* initialize threaded css_set walking */
4070         if (it->flags & CSS_TASK_ITER_THREADED) {
4071                 if (it->cur_dcset)
4072                         put_css_set_locked(it->cur_dcset);
4073                 it->cur_dcset = cset;
4074                 get_css_set(cset);
4075 
4076                 it->tcset_head = &cset->threaded_csets;
4077                 it->tcset_pos = &cset->threaded_csets;
4078         }
4079 
4080         return cset;
4081 }
4082 
4083 /**
4084  * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4085  * @it: the iterator to advance
4086  *
4087  * Advance @it to the next css_set to walk.
4088  */
4089 static void css_task_iter_advance_css_set(struct css_task_iter *it)
4090 {
4091         struct css_set *cset;
4092 
4093         lockdep_assert_held(&css_set_lock);
4094 
4095         /* Advance to the next non-empty css_set */
4096         do {
4097                 cset = css_task_iter_next_css_set(it);
4098                 if (!cset) {
4099                         it->task_pos = NULL;
4100                         return;
4101                 }
4102         } while (!css_set_populated(cset));
4103 
4104         if (!list_empty(&cset->tasks))
4105                 it->task_pos = cset->tasks.next;
4106         else
4107                 it->task_pos = cset->mg_tasks.next;
4108 
4109         it->tasks_head = &cset->tasks;
4110         it->mg_tasks_head = &cset->mg_tasks;
4111 
4112         /*
4113          * We don't keep css_sets locked across iteration steps and thus
4114          * need to take steps to ensure that iteration can be resumed after
4115          * the lock is re-acquired.  Iteration is performed at two levels -
4116          * css_sets and tasks in them.
4117          *
4118          * Once created, a css_set never leaves its cgroup lists, so a
4119          * pinned css_set is guaranteed to stay put and we can resume
4120          * iteration afterwards.
4121          *
4122          * Tasks may leave @cset across iteration steps.  This is resolved
4123          * by registering each iterator with the css_set currently being
4124          * walked and making css_set_move_task() advance iterators whose
4125          * next task is leaving.
4126          */
4127         if (it->cur_cset) {
4128                 list_del(&it->iters_node);
4129                 put_css_set_locked(it->cur_cset);
4130         }
4131         get_css_set(cset);
4132         it->cur_cset = cset;
4133         list_add(&it->iters_node, &cset->task_iters);
4134 }
4135 
4136 static void css_task_iter_advance(struct css_task_iter *it)
4137 {
4138         struct list_head *next;
4139 
4140         lockdep_assert_held(&css_set_lock);
4141 repeat:
4142         /*
4143          * Advance iterator to find next entry.  cset->tasks is consumed
4144          * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
4145          * next cset.
4146          */
4147         next = it->task_pos->next;
4148 
4149         if (next == it->tasks_head)
4150                 next = it->mg_tasks_head->next;
4151 
4152         if (next == it->mg_tasks_head)
4153                 css_task_iter_advance_css_set(it);
4154         else
4155                 it->task_pos = next;
4156 
4157         /* if PROCS, skip over tasks which aren't group leaders */
4158         if ((it->flags & CSS_TASK_ITER_PROCS) && it->task_pos &&
4159             !thread_group_leader(list_entry(it->task_pos, struct task_struct,
4160                                             cg_list)))
4161                 goto repeat;
4162 }
4163 
4164 /**
4165  * css_task_iter_start - initiate task iteration
4166  * @css: the css to walk tasks of
4167  * @flags: CSS_TASK_ITER_* flags
4168  * @it: the task iterator to use
4169  *
4170  * Initiate iteration through the tasks of @css.  The caller can call
4171  * css_task_iter_next() to walk through the tasks until the function
4172  * returns NULL.  On completion of iteration, css_task_iter_end() must be
4173  * called.
4174  */
4175 void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
4176                          struct css_task_iter *it)
4177 {
4178         /* no one should try to iterate before mounting cgroups */
4179         WARN_ON_ONCE(!use_task_css_set_links);
4180 
4181         memset(it, 0, sizeof(*it));
4182 
4183         spin_lock_irq(&css_set_lock);
4184 
4185         it->ss = css->ss;
4186         it->flags = flags;
4187 
4188         if (it->ss)
4189                 it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4190         else
4191                 it->cset_pos = &css->cgroup->cset_links;
4192 
4193         it->cset_head = it->cset_pos;
4194 
4195         css_task_iter_advance_css_set(it);
4196 
4197         spin_unlock_irq(&css_set_lock);
4198 }
4199 
4200 /**
4201  * css_task_iter_next - return the next task for the iterator
4202  * @it: the task iterator being iterated
4203  *
4204  * The "next" function for task iteration.  @it should have been
4205  * initialized via css_task_iter_start().  Returns NULL when the iteration
4206  * reaches the end.
4207  */
4208 struct task_struct *css_task_iter_next(struct css_task_iter *it)
4209 {
4210         if (it->cur_task) {
4211                 put_task_struct(it->cur_task);
4212                 it->cur_task = NULL;
4213         }
4214 
4215         spin_lock_irq(&css_set_lock);
4216 
4217         if (it->task_pos) {
4218                 it->cur_task = list_entry(it->task_pos, struct task_struct,
4219                                           cg_list);
4220                 get_task_struct(it->cur_task);
4221                 css_task_iter_advance(it);
4222         }
4223 
4224         spin_unlock_irq(&css_set_lock);
4225 
4226         return it->cur_task;
4227 }
4228 
4229 /**
4230  * css_task_iter_end - finish task iteration
4231  * @it: the task iterator to finish
4232  *
4233  * Finish task iteration started by css_task_iter_start().
4234  */
4235 void css_task_iter_end(struct css_task_iter *it)
4236 {
4237         if (it->cur_cset) {
4238                 spin_lock_irq(&css_set_lock);
4239                 list_del(&it->iters_node);
4240                 put_css_set_locked(it->cur_cset);
4241                 spin_unlock_irq(&css_set_lock);
4242         }
4243 
4244         if (it->cur_dcset)
4245                 put_css_set(it->cur_dcset);
4246 
4247         if (it->cur_task)
4248                 put_task_struct(it->cur_task);
4249 }
4250 
4251 static void cgroup_procs_release(struct kernfs_open_file *of)
4252 {
4253         if (of->priv) {
4254                 css_task_iter_end(of->priv);
4255                 kfree(of->priv);
4256         }
4257 }
4258 
4259 static void *cgroup_procs_next(struct seq_file *s, void *v, loff_t *pos)
4260 {
4261         struct kernfs_open_file *of = s->private;
4262         struct css_task_iter *it = of->priv;
4263 
4264         return css_task_iter_next(it);
4265 }
4266 
4267 static void *__cgroup_procs_start(struct seq_file *s, loff_t *pos,
4268                                   unsigned int iter_flags)
4269 {
4270         struct kernfs_open_file *of = s->private;
4271         struct cgroup *cgrp = seq_css(s)->cgroup;
4272         struct css_task_iter *it = of->priv;
4273 
4274         /*
4275          * When a seq_file is seeked, it's always traversed sequentially
4276          * from position 0, so we can simply keep iterating on !0 *pos.
4277          */
4278         if (!it) {
4279                 if (WARN_ON_ONCE((*pos)++))
4280                         return ERR_PTR(-EINVAL);
4281 
4282                 it = kzalloc(sizeof(*it), GFP_KERNEL);
4283                 if (!it)
4284                         return ERR_PTR(-ENOMEM);
4285                 of->priv = it;
4286                 css_task_iter_start(&cgrp->self, iter_flags, it);
4287         } else if (!(*pos)++) {
4288                 css_task_iter_end(it);
4289                 css_task_iter_start(&cgrp->self, iter_flags, it);
4290         }
4291 
4292         return cgroup_procs_next(s, NULL, NULL);
4293 }
4294 
4295 static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
4296 {
4297         struct cgroup *cgrp = seq_css(s)->cgroup;
4298 
4299         /*
4300          * All processes of a threaded subtree belong to the domain cgroup
4301          * of the subtree.  Only threads can be distributed across the
4302          * subtree.  Reject reads on cgroup.procs in the subtree proper.
4303          * They're always empty anyway.
4304          */
4305         if (cgroup_is_threaded(cgrp))
4306                 return ERR_PTR(-EOPNOTSUPP);
4307 
4308         return __cgroup_procs_start(s, pos, CSS_TASK_ITER_PROCS |
4309                                             CSS_TASK_ITER_THREADED);
4310 }
4311 
4312 static int cgroup_procs_show(struct seq_file *s, void *v)
4313 {
4314         seq_printf(s, "%d\n", task_pid_vnr(v));
4315         return 0;
4316 }
4317 
4318 static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
4319                                          struct cgroup *dst_cgrp,
4320                                          struct super_block *sb)
4321 {
4322         struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
4323         struct cgroup *com_cgrp = src_cgrp;
4324         struct inode *inode;
4325         int ret;
4326 
4327         lockdep_assert_held(&cgroup_mutex);
4328 
4329         /* find the common ancestor */
4330         while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
4331                 com_cgrp = cgroup_parent(com_cgrp);
4332 
4333         /* %current should be authorized to migrate to the common ancestor */
4334         inode = kernfs_get_inode(sb, com_cgrp->procs_file.kn);
4335         if (!inode)
4336                 return -ENOMEM;
4337 
4338         ret = inode_permission(inode, MAY_WRITE);
4339         iput(inode);
4340         if (ret)
4341                 return ret;
4342 
4343         /*
4344          * If namespaces are delegation boundaries, %current must be able
4345          * to see both source and destination cgroups from its namespace.
4346          */
4347         if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
4348             (!cgroup_is_descendant(src_cgrp, ns->root_cset->dfl_cgrp) ||
4349              !cgroup_is_descendant(dst_cgrp, ns->root_cset->dfl_cgrp)))
4350                 return -ENOENT;
4351 
4352         return 0;
4353 }
4354 
4355 static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
4356                                   char *buf, size_t nbytes, loff_t off)
4357 {
4358         struct cgroup *src_cgrp, *dst_cgrp;
4359         struct task_struct *task;
4360         ssize_t ret;
4361 
4362         dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4363         if (!dst_cgrp)
4364                 return -ENODEV;
4365 
4366         task = cgroup_procs_write_start(buf, true);
4367         ret = PTR_ERR_OR_ZERO(task);
4368         if (ret)
4369                 goto out_unlock;
4370 
4371         /* find the source cgroup */
4372         spin_lock_irq(&css_set_lock);
4373         src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4374         spin_unlock_irq(&css_set_lock);
4375 
4376         ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
4377                                             of->file->f_path.dentry->d_sb);
4378         if (ret)
4379                 goto out_finish;
4380 
4381         ret = cgroup_attach_task(dst_cgrp, task, true);
4382 
4383 out_finish:
4384         cgroup_procs_write_finish(task);
4385 out_unlock:
4386         cgroup_kn_unlock(of->kn);
4387 
4388         return ret ?: nbytes;
4389 }
4390 
4391 static void *cgroup_threads_start(struct seq_file *s, loff_t *pos)
4392 {
4393         return __cgroup_procs_start(s, pos, 0);
4394 }
4395 
4396 static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
4397                                     char *buf, size_t nbytes, loff_t off)
4398 {
4399         struct cgroup *src_cgrp, *dst_cgrp;
4400         struct task_struct *task;
4401         ssize_t ret;
4402 
4403         buf = strstrip(buf);
4404 
4405         dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4406         if (!dst_cgrp)
4407                 return -ENODEV;
4408 
4409         task = cgroup_procs_write_start(buf, false);
4410         ret = PTR_ERR_OR_ZERO(task);
4411         if (ret)
4412                 goto out_unlock;
4413 
4414         /* find the source cgroup */
4415         spin_lock_irq(&css_set_lock);
4416         src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4417         spin_unlock_irq(&css_set_lock);
4418 
4419         /* thread migrations follow the cgroup.procs delegation rule */
4420         ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
4421                                             of->file->f_path.dentry->d_sb);
4422         if (ret)
4423                 goto out_finish;
4424 
4425         /* and must be contained in the same domain */
4426         ret = -EOPNOTSUPP;
4427         if (src_cgrp->dom_cgrp != dst_cgrp->dom_cgrp)
4428                 goto out_finish;
4429 
4430         ret = cgroup_attach_task(dst_cgrp, task, false);
4431 
4432 out_finish:
4433         cgroup_procs_write_finish(task);
4434 out_unlock:
4435         cgroup_kn_unlock(of->kn);
4436 
4437         return ret ?: nbytes;
4438 }
4439 
4440 /* cgroup core interface files for the default hierarchy */
4441 static struct cftype cgroup_base_files[] = {
4442         {
4443                 .name = "cgroup.type",
4444                 .flags = CFTYPE_NOT_ON_ROOT,
4445                 .seq_show = cgroup_type_show,
4446                 .write = cgroup_type_write,
4447         },
4448         {
4449                 .name = "cgroup.procs",
4450                 .flags = CFTYPE_NS_DELEGATABLE,
4451                 .file_offset = offsetof(struct cgroup, procs_file),
4452                 .release = cgroup_procs_release,
4453                 .seq_start = cgroup_procs_start,
4454                 .seq_next = cgroup_procs_next,
4455                 .seq_show = cgroup_procs_show,
4456                 .write = cgroup_procs_write,
4457         },
4458         {
4459                 .name = "cgroup.threads",
4460                 .flags = CFTYPE_NS_DELEGATABLE,
4461                 .release = cgroup_procs_release,
4462                 .seq_start = cgroup_threads_start,
4463                 .seq_next = cgroup_procs_next,
4464                 .seq_show = cgroup_procs_show,
4465                 .write = cgroup_threads_write,
4466         },
4467         {
4468                 .name = "cgroup.controllers",
4469                 .seq_show = cgroup_controllers_show,
4470         },
4471         {
4472                 .name = "cgroup.subtree_control",
4473                 .flags = CFTYPE_NS_DELEGATABLE,
4474                 .seq_show = cgroup_subtree_control_show,
4475                 .write = cgroup_subtree_control_write,
4476         },
4477         {
4478                 .name = "cgroup.events",
4479                 .flags = CFTYPE_NOT_ON_ROOT,
4480                 .file_offset = offsetof(struct cgroup, events_file),
4481                 .seq_show = cgroup_events_show,
4482         },
4483         {
4484                 .name = "cgroup.max.descendants",
4485                 .seq_show = cgroup_max_descendants_show,
4486                 .write = cgroup_max_descendants_write,
4487         },
4488         {
4489                 .name = "cgroup.max.depth",
4490                 .seq_show = cgroup_max_depth_show,
4491                 .write = cgroup_max_depth_write,
4492         },
4493         {
4494                 .name = "cgroup.stat",
4495                 .seq_show = cgroup_stat_show,
4496         },
4497         {
4498                 .name = "cpu.stat",
4499                 .flags = CFTYPE_NOT_ON_ROOT,
4500                 .seq_show = cpu_stat_show,
4501         },
4502         { }     /* terminate */
4503 };
4504 
4505 /*
4506  * css destruction is four-stage process.
4507  *
4508  * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4509  *    Implemented in kill_css().
4510  *
4511  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4512  *    and thus css_tryget_online() is guaranteed to fail, the css can be
4513  *    offlined by invoking offline_css().  After offlining, the base ref is
4514  *    put.  Implemented in css_killed_work_fn().
4515  *
4516  * 3. When the percpu_ref reaches zero, the only possible remaining
4517  *    accessors are inside RCU read sections.  css_release() schedules the
4518  *    RCU callback.
4519  *
4520  * 4. After the grace period, the css can be freed.  Implemented in
4521  *    css_free_work_fn().
4522  *
4523  * It is actually hairier because both step 2 and 4 require process context
4524  * and thus involve punting to css->destroy_work adding two additional
4525  * steps to the already complex sequence.
4526  */
4527 static void css_free_rwork_fn(struct work_struct *work)
4528 {
4529         struct cgroup_subsys_state *css = container_of(to_rcu_work(work),
4530                                 struct cgroup_subsys_state, destroy_rwork);
4531         struct cgroup_subsys *ss = css->ss;
4532         struct cgroup *cgrp = css->cgroup;
4533 
4534         percpu_ref_exit(&css->refcnt);
4535 
4536         if (ss) {
4537                 /* css free path */
4538                 struct cgroup_subsys_state *parent = css->parent;
4539                 int id = css->id;
4540 
4541                 ss->css_free(css);
4542                 cgroup_idr_remove(&ss->css_idr, id);
4543                 cgroup_put(cgrp);
4544 
4545                 if (parent)
4546                         css_put(parent);
4547         } else {
4548                 /* cgroup free path */
4549                 atomic_dec(&cgrp->root->nr_cgrps);
4550                 cgroup1_pidlist_destroy_all(cgrp);
4551                 cancel_work_sync(&cgrp->release_agent_work);
4552 
4553                 if (cgroup_parent(cgrp)) {
4554                         /*
4555                          * We get a ref to the parent, and put the ref when
4556                          * this cgroup is being freed, so it's guaranteed
4557                          * that the parent won't be destroyed before its
4558                          * children.
4559                          */
4560                         cgroup_put(cgroup_parent(cgrp));
4561                         kernfs_put(cgrp->kn);
4562                         if (cgroup_on_dfl(cgrp))
4563                                 cgroup_stat_exit(cgrp);
4564                         kfree(cgrp);
4565                 } else {
4566                         /*
4567                          * This is root cgroup's refcnt reaching zero,
4568                          * which indicates that the root should be
4569                          * released.
4570                          */
4571                         cgroup_destroy_root(cgrp->root);
4572                 }
4573         }
4574 }
4575 
4576 static void css_release_work_fn(struct work_struct *work)
4577 {
4578         struct cgroup_subsys_state *css =
4579                 container_of(work, struct cgroup_subsys_state, destroy_work);
4580         struct cgroup_subsys *ss = css->ss;
4581         struct cgroup *cgrp = css->cgroup;
4582 
4583         mutex_lock(&cgroup_mutex);
4584 
4585         css->flags |= CSS_RELEASED;
4586         list_del_rcu(&css->sibling);
4587 
4588         if (ss) {
4589                 /* css release path */
4590                 cgroup_idr_replace(&ss->css_idr, NULL, css->id);
4591                 if (ss->css_released)
4592                         ss->css_released(css);
4593         } else {
4594                 struct cgroup *tcgrp;
4595 
4596                 /* cgroup release path */
4597                 trace_cgroup_release(cgrp);
4598 
4599                 if (cgroup_on_dfl(cgrp))
4600                         cgroup_stat_flush(cgrp);
4601 
4602                 for (tcgrp = cgroup_parent(cgrp); tcgrp;
4603                      tcgrp = cgroup_parent(tcgrp))
4604                         tcgrp->nr_dying_descendants--;
4605 
4606                 cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
4607                 cgrp->id = -1;
4608 
4609                 /*
4610                  * There are two control paths which try to determine
4611                  * cgroup from dentry without going through kernfs -
4612                  * cgroupstats_build() and css_tryget_online_from_dir().
4613                  * Those are supported by RCU protecting clearing of
4614                  * cgrp->kn->priv backpointer.
4615                  */
4616                 if (cgrp->kn)
4617                         RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
4618                                          NULL);
4619 
4620                 cgroup_bpf_put(cgrp);
4621         }
4622 
4623         mutex_unlock(&cgroup_mutex);
4624 
4625         INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
4626         queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
4627 }
4628 
4629 static void css_release(struct percpu_ref *ref)
4630 {
4631         struct cgroup_subsys_state *css =
4632                 container_of(ref, struct cgroup_subsys_state, refcnt);
4633 
4634         INIT_WORK(&css->destroy_work, css_release_work_fn);
4635         queue_work(cgroup_destroy_wq, &css->destroy_work);
4636 }
4637 
4638 static void init_and_link_css(struct cgroup_subsys_state *css,
4639                               struct cgroup_subsys *ss, struct cgroup *cgrp)
4640 {
4641         lockdep_assert_held(&cgroup_mutex);
4642 
4643         cgroup_get_live(cgrp);
4644 
4645         memset(css, 0, sizeof(*css));
4646         css->cgroup = cgrp;
4647         css->ss = ss;
4648         css->id = -1;
4649         INIT_LIST_HEAD(&css->sibling);
4650         INIT_LIST_HEAD(&css->children);
4651         css->serial_nr = css_serial_nr_next++;
4652         atomic_set(&css->online_cnt, 0);
4653 
4654         if (cgroup_parent(cgrp)) {
4655                 css->parent = cgroup_css(cgroup_parent(cgrp), ss);
4656                 css_get(css->parent);
4657         }
4658 
4659         BUG_ON(cgroup_css(cgrp, ss));
4660 }
4661 
4662 /* invoke ->css_online() on a new CSS and mark it online if successful */
4663 static int online_css(struct cgroup_subsys_state *css)
4664 {
4665         struct cgroup_subsys *ss = css->ss;
4666         int ret = 0;
4667 
4668         lockdep_assert_held(&cgroup_mutex);
4669 
4670         if (ss->css_online)
4671                 ret = ss->css_online(css);
4672         if (!ret) {
4673                 css->flags |= CSS_ONLINE;
4674                 rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
4675 
4676                 atomic_inc(&css->online_cnt);
4677                 if (css->parent)
4678                         atomic_inc(&css->parent->online_cnt);
4679         }
4680         return ret;
4681 }
4682 
4683 /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
4684 static void offline_css(struct cgroup_subsys_state *css)
4685 {
4686         struct cgroup_subsys *ss = css->ss;
4687 
4688         lockdep_assert_held(&cgroup_mutex);
4689 
4690         if (!(css->flags & CSS_ONLINE))
4691                 return;
4692 
4693         if (ss->css_offline)
4694                 ss->css_offline(css);
4695 
4696         css->flags &= ~CSS_ONLINE;
4697         RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
4698 
4699         wake_up_all(&css->cgroup->offline_waitq);
4700 }
4701 
4702 /**
4703  * css_create - create a cgroup_subsys_state
4704  * @cgrp: the cgroup new css will be associated with
4705  * @ss: the subsys of new css
4706  *
4707  * Create a new css associated with @cgrp - @ss pair.  On success, the new
4708  * css is online and installed in @cgrp.  This function doesn't create the
4709  * interface files.  Returns 0 on success, -errno on failure.
4710  */
4711 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
4712                                               struct cgroup_subsys *ss)
4713 {
4714         struct cgroup *parent = cgroup_parent(cgrp);
4715         struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
4716         struct cgroup_subsys_state *css;
4717         int err;
4718 
4719         lockdep_assert_held(&cgroup_mutex);
4720 
4721         css = ss->css_alloc(parent_css);
4722         if (!css)
4723                 css = ERR_PTR(-ENOMEM);
4724         if (IS_ERR(css))
4725                 return css;
4726 
4727         init_and_link_css(css, ss, cgrp);
4728 
4729         err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
4730         if (err)
4731                 goto err_free_css;
4732 
4733         err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
4734         if (err < 0)
4735                 goto err_free_css;
4736         css->id = err;
4737 
4738         /* @css is ready to be brought online now, make it visible */
4739         list_add_tail_rcu(&css->sibling, &parent_css->children);
4740         cgroup_idr_replace(&ss->css_idr, css, css->id);
4741 
4742         err = online_css(css);
4743         if (err)
4744                 goto err_list_del;
4745 
4746         if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
4747             cgroup_parent(parent)) {
4748                 pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
4749                         current->comm, current->pid, ss->name);
4750                 if (!strcmp(ss->name, "memory"))
4751                         pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
4752                 ss->warned_broken_hierarchy = true;
4753         }
4754 
4755         return css;
4756 
4757 err_list_del:
4758         list_del_rcu(&css->sibling);
4759 err_free_css:
4760         INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
4761         queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
4762         return ERR_PTR(err);
4763 }
4764 
4765 /*
4766  * The returned cgroup is fully initialized including its control mask, but
4767  * it isn't associated with its kernfs_node and doesn't have the control
4768  * mask applied.
4769  */
4770 static struct cgroup *cgroup_create(struct cgroup *parent)
4771 {
4772         struct cgroup_root *root = parent->root;
4773         struct cgroup *cgrp, *tcgrp;
4774         int level = parent->level + 1;
4775         int ret;
4776 
4777         /* allocate the cgroup and its ID, 0 is reserved for the root */
4778         cgrp = kzalloc(sizeof(*cgrp) +
4779                        sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
4780         if (!cgrp)
4781                 return ERR_PTR(-ENOMEM);
4782 
4783         ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
4784         if (ret)
4785                 goto out_free_cgrp;
4786 
4787         if (cgroup_on_dfl(parent)) {
4788                 ret = cgroup_stat_init(cgrp);
4789                 if (ret)
4790                         goto out_cancel_ref;
4791         }
4792 
4793         /*
4794          * Temporarily set the pointer to NULL, so idr_find() won't return
4795          * a half-baked cgroup.
4796          */
4797         cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
4798         if (cgrp->id < 0) {
4799                 ret = -ENOMEM;
4800                 goto out_stat_exit;
4801         }
4802 
4803         init_cgroup_housekeeping(cgrp);
4804 
4805         cgrp->self.parent = &parent->self;
4806         cgrp->root = root;
4807         cgrp->level = level;
4808         ret = cgroup_bpf_inherit(cgrp);
4809         if (ret)
4810                 goto out_idr_free;
4811 
4812         for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
4813                 cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
4814 
4815                 if (tcgrp != cgrp)
4816                         tcgrp->nr_descendants++;
4817         }
4818 
4819         if (notify_on_release(parent))
4820                 set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
4821 
4822         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
4823                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
4824 
4825         cgrp->self.serial_nr = css_serial_nr_next++;
4826 
4827         /* allocation complete, commit to creation */
4828         list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
4829         atomic_inc(&root->nr_cgrps);
4830         cgroup_get_live(parent);
4831 
4832         /*
4833          * @cgrp is now fully operational.  If something fails after this
4834          * point, it'll be released via the normal destruction path.
4835          */
4836         cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
4837 
4838         /*
4839          * On the default hierarchy, a child doesn't automatically inherit
4840          * subtree_control from the parent.  Each is configured manually.
4841          */
4842         if (!cgroup_on_dfl(cgrp))
4843                 cgrp->subtree_control = cgroup_control(cgrp);
4844 
4845         cgroup_propagate_control(cgrp);
4846 
4847         return cgrp;
4848 
4849 out_idr_free:
4850         cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
4851 out_stat_exit:
4852         if (cgroup_on_dfl(parent))
4853                 cgroup_stat_exit(cgrp);
4854 out_cancel_ref:
4855         percpu_ref_exit(&cgrp->self.refcnt);
4856 out_free_cgrp:
4857         kfree(cgrp);
4858         return ERR_PTR(ret);
4859 }
4860 
4861 static bool cgroup_check_hierarchy_limits(struct cgroup *parent)
4862 {
4863         struct cgroup *cgroup;
4864         int ret = false;
4865         int level = 1;
4866 
4867         lockdep_assert_held(&cgroup_mutex);
4868 
4869         for (cgroup = parent; cgroup; cgroup = cgroup_parent(cgroup)) {
4870                 if (cgroup->nr_descendants >= cgroup->max_descendants)
4871                         goto fail;
4872 
4873                 if (level > cgroup->max_depth)
4874                         goto fail;
4875 
4876                 level++;
4877         }
4878 
4879         ret = true;
4880 fail:
4881         return ret;
4882 }
4883 
4884 int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
4885 {
4886         struct cgroup *parent, *cgrp;
4887         struct kernfs_node *kn;
4888         int ret;
4889 
4890         /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
4891         if (strchr(name, '\n'))
4892                 return -EINVAL;
4893 
4894         parent = cgroup_kn_lock_live(parent_kn, false);
4895         if (!parent)
4896                 return -ENODEV;
4897 
4898         if (!cgroup_check_hierarchy_limits(parent)) {
4899                 ret = -EAGAIN;
4900                 goto out_unlock;
4901         }
4902 
4903         cgrp = cgroup_create(parent);
4904         if (IS_ERR(cgrp)) {
4905                 ret = PTR_ERR(cgrp);
4906                 goto out_unlock;
4907         }
4908 
4909         /* create the directory */
4910         kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
4911         if (IS_ERR(kn)) {
4912                 ret = PTR_ERR(kn);
4913                 goto out_destroy;
4914         }
4915         cgrp->kn = kn;
4916 
4917         /*
4918          * This extra ref will be put in cgroup_free_fn() and guarantees
4919          * that @cgrp->kn is always accessible.
4920          */
4921         kernfs_get(kn);
4922 
4923         ret = cgroup_kn_set_ugid(kn);
4924         if (ret)
4925                 goto out_destroy;
4926 
4927         ret = css_populate_dir(&cgrp->self);
4928         if (ret)
4929                 goto out_destroy;
4930 
4931         ret = cgroup_apply_control_enable(cgrp);
4932         if (ret)
4933                 goto out_destroy;
4934 
4935         trace_cgroup_mkdir(cgrp);
4936 
4937         /* let's create and online css's */
4938         kernfs_activate(kn);
4939 
4940         ret = 0;
4941         goto out_unlock;
4942 
4943 out_destroy:
4944         cgroup_destroy_locked(cgrp);
4945 out_unlock:
4946         cgroup_kn_unlock(parent_kn);
4947         return ret;
4948 }
4949 
4950 /*
4951  * This is called when the refcnt of a css is confirmed to be killed.
4952  * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
4953  * initate destruction and put the css ref from kill_css().
4954  */
4955 static void css_killed_work_fn(struct work_struct *work)
4956 {
4957         struct cgroup_subsys_state *css =
4958                 container_of(work, struct cgroup_subsys_state, destroy_work);
4959 
4960         mutex_lock(&cgroup_mutex);
4961 
4962         do {
4963                 offline_css(css);
4964                 css_put(css);
4965                 /* @css can't go away while we're holding cgroup_mutex */
4966                 css = css->parent;
4967         } while (css && atomic_dec_and_test(&css->online_cnt));
4968 
4969         mutex_unlock(&cgroup_mutex);
4970 }
4971 
4972 /* css kill confirmation processing requires process context, bounce */
4973 static void css_killed_ref_fn(struct percpu_ref *ref)
4974 {
4975         struct cgroup_subsys_state *css =
4976                 container_of(ref, struct cgroup_subsys_state, refcnt);
4977 
4978         if (atomic_dec_and_test(&css->online_cnt)) {
4979                 INIT_WORK(&css->destroy_work, css_killed_work_fn);
4980                 queue_work(cgroup_destroy_wq, &css->destroy_work);
4981         }
4982 }
4983 
4984 /**
4985  * kill_css - destroy a css
4986  * @css: css to destroy
4987  *
4988  * This function initiates destruction of @css by removing cgroup interface
4989  * files and putting its base reference.  ->css_offline() will be invoked
4990  * asynchronously once css_tryget_online() is guaranteed to fail and when
4991  * the reference count reaches zero, @css will be released.
4992  */
4993 static void kill_css(struct cgroup_subsys_state *css)
4994 {
4995         lockdep_assert_held(&cgroup_mutex);
4996 
4997         if (css->flags & CSS_DYING)
4998                 return;
4999 
5000         css->flags |= CSS_DYING;
5001 
5002         /*
5003          * This must happen before css is disassociated with its cgroup.
5004          * See seq_css() for details.
5005          */
5006         css_clear_dir(css);
5007 
5008         /*
5009          * Killing would put the base ref, but we need to keep it alive
5010          * until after ->css_offline().
5011          */
5012         css_get(css);
5013 
5014         /*
5015          * cgroup core guarantees that, by the time ->css_offline() is
5016          * invoked, no new css reference will be given out via
5017          * css_tryget_online().  We can't simply call percpu_ref_kill() and
5018          * proceed to offlining css's because percpu_ref_kill() doesn't
5019          * guarantee that the ref is seen as killed on all CPUs on return.
5020          *
5021          * Use percpu_ref_kill_and_confirm() to get notifications as each
5022          * css is confirmed to be seen as killed on all CPUs.
5023          */
5024         percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5025 }
5026 
5027 /**
5028  * cgroup_destroy_locked - the first stage of cgroup destruction
5029  * @cgrp: cgroup to be destroyed
5030  *
5031  * css's make use of percpu refcnts whose killing latency shouldn't be
5032  * exposed to userland and are RCU protected.  Also, cgroup core needs to
5033  * guarantee that css_tryget_online() won't succeed by the time
5034  * ->css_offline() is invoked.  To satisfy all the requirements,
5035  * destruction is implemented in the following two steps.
5036  *
5037  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5038  *     userland visible parts and start killing the percpu refcnts of
5039  *     css's.  Set up so that the next stage will be kicked off once all
5040  *     the percpu refcnts are confirmed to be killed.
5041  *
5042  * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5043  *     rest of destruction.  Once all cgroup references are gone, the
5044  *     cgroup is RCU-freed.
5045  *
5046  * This function implements s1.  After this step, @cgrp is gone as far as
5047  * the userland is concerned and a new cgroup with the same name may be
5048  * created.  As cgroup doesn't care about the names internally, this
5049  * doesn't cause any problem.
5050  */
5051 static int cgroup_destroy_locked(struct cgroup *cgrp)
5052         __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5053 {
5054         struct cgroup *tcgrp, *parent = cgroup_parent(cgrp);
5055         struct cgroup_subsys_state *css;
5056         struct cgrp_cset_link *link;
5057         int ssid;
5058 
5059         lockdep_assert_held(&cgroup_mutex);
5060 
5061         /*
5062          * Only migration can raise populated from zero and we're already
5063          * holding cgroup_mutex.
5064          */
5065         if (cgroup_is_populated(cgrp))
5066                 return -EBUSY;
5067 
5068         /*
5069          * Make sure there's no live children.  We can't test emptiness of
5070          * ->self.children as dead children linger on it while being
5071          * drained; otherwise, "rmdir parent/child parent" may fail.
5072          */
5073         if (css_has_online_children(&cgrp->self))
5074                 return -EBUSY;
5075 
5076         /*
5077          * Mark @cgrp and the associated csets dead.  The former prevents
5078          * further task migration and child creation by disabling
5079          * cgroup_lock_live_group().  The latter makes the csets ignored by
5080          * the migration path.
5081          */
5082         cgrp->self.flags &= ~CSS_ONLINE;
5083 
5084         spin_lock_irq(&css_set_lock);
5085         list_for_each_entry(link, &cgrp->cset_links, cset_link)
5086                 link->cset->dead = true;
5087         spin_unlock_irq(&css_set_lock);
5088 
5089         /* initiate massacre of all css's */
5090         for_each_css(css, ssid, cgrp)
5091                 kill_css(css);
5092 
5093         /*
5094          * Remove @cgrp directory along with the base files.  @cgrp has an
5095          * extra ref on its kn.
5096          */
5097         kernfs_remove(cgrp->kn);
5098 
5099         if (parent && cgroup_is_threaded(cgrp))
5100                 parent->nr_threaded_children--;
5101 
5102         for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5103                 tcgrp->nr_descendants--;
5104                 tcgrp->nr_dying_descendants++;
5105         }
5106 
5107         cgroup1_check_for_release(parent);
5108 
5109         /* put the base reference */
5110         percpu_ref_kill(&cgrp->self.refcnt);
5111 
5112         return 0;
5113 };
5114 
5115 int cgroup_rmdir(struct kernfs_node *kn)
5116 {
5117         struct cgroup *cgrp;
5118         int ret = 0;
5119 
5120         cgrp = cgroup_kn_lock_live(kn, false);
5121         if (!cgrp)
5122                 return 0;
5123 
5124         ret = cgroup_destroy_locked(cgrp);
5125 
5126         if (!ret)
5127                 trace_cgroup_rmdir(cgrp);
5128 
5129         cgroup_kn_unlock(kn);
5130         return ret;
5131 }
5132 
5133 static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5134         .show_options           = cgroup_show_options,
5135         .remount_fs             = cgroup_remount,
5136         .mkdir                  = cgroup_mkdir,
5137         .rmdir                  = cgroup_rmdir,
5138         .show_path              = cgroup_show_path,
5139 };
5140 
5141 static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5142 {
5143         struct cgroup_subsys_state *css;
5144 
5145         pr_debug("Initializing cgroup subsys %s\n", ss->name);
5146 
5147         mutex_lock(&cgroup_mutex);
5148 
5149         idr_init(&ss->css_idr);
5150         INIT_LIST_HEAD(&ss->cfts);
5151 
5152         /* Create the root cgroup state for this subsystem */
5153         ss->root = &cgrp_dfl_root;
5154         css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5155         /* We don't handle early failures gracefully */
5156         BUG_ON(IS_ERR(css));
5157         init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5158 
5159         /*
5160          * Root csses are never destroyed and we can't initialize
5161          * percpu_ref during early init.  Disable refcnting.
5162          */
5163         css->flags |= CSS_NO_REF;
5164 
5165         if (early) {
5166                 /* allocation can't be done safely during early init */
5167                 css->id = 1;
5168         } else {
5169                 css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5170                 BUG_ON(css->id < 0);
5171         }
5172 
5173         /* Update the init_css_set to contain a subsys
5174          * pointer to this state - since the subsystem is
5175          * newly registered, all tasks and hence the
5176          * init_css_set is in the subsystem's root cgroup. */
5177         init_css_set.subsys[ss->id] = css;
5178 
5179         have_fork_callback |= (bool)ss->fork << ss->id;
5180         have_exit_callback |= (bool)ss->exit << ss->id;
5181         have_free_callback |= (bool)ss->free << ss->id;
5182         have_canfork_callback |= (bool)ss->can_fork << ss->id;
5183 
5184         /* At system boot, before all subsystems have been
5185          * registered, no tasks have been forked, so we don't
5186          * need to invoke fork callbacks here. */
5187         BUG_ON(!list_empty(&init_task.tasks));
5188 
5189         BUG_ON(online_css(css));
5190 
5191         mutex_unlock(&cgroup_mutex);
5192 }
5193 
5194 /**
5195  * cgroup_init_early - cgroup initialization at system boot
5196  *
5197  * Initialize cgroups at system boot, and initialize any
5198  * subsystems that request early init.
5199  */
5200 int __init cgroup_init_early(void)
5201 {
5202         static struct cgroup_sb_opts __initdata opts;
5203         struct cgroup_subsys *ss;
5204         int i;
5205 
5206         init_cgroup_root(&cgrp_dfl_root, &opts);
5207         cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5208 
5209         RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5210 
5211         for_each_subsys(ss, i) {
5212                 WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5213                      "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5214                      i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5215                      ss->id, ss->name);
5216                 WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5217                      "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5218 
5219                 ss->id = i;
5220                 ss->name = cgroup_subsys_name[i];
5221                 if (!ss->legacy_name)
5222                         ss->legacy_name = cgroup_subsys_name[i];
5223 
5224                 if (ss->early_init)
5225                         cgroup_init_subsys(ss, true);
5226         }
5227         return 0;
5228 }
5229 
5230 static u16 cgroup_disable_mask __initdata;
5231 
5232 /**
5233  * cgroup_init - cgroup initialization
5234  *
5235  * Register cgroup filesystem and /proc file, and initialize
5236  * any subsystems that didn't request early init.
5237  */
5238 int __init cgroup_init(void)
5239 {
5240         struct cgroup_subsys *ss;
5241         int ssid;
5242 
5243         BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5244         BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
5245         BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
5246         BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));
5247 
5248         cgroup_stat_boot();
5249 
5250         /*
5251          * The latency of the synchronize_sched() is too high for cgroups,
5252          * avoid it at the cost of forcing all readers into the slow path.
5253          */
5254         rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5255 
5256         get_user_ns(init_cgroup_ns.user_ns);
5257 
5258         mutex_lock(&cgroup_mutex);
5259 
5260         /*
5261          * Add init_css_set to the hash table so that dfl_root can link to
5262          * it during init.
5263          */
5264         hash_add(css_set_table, &init_css_set.hlist,
5265                  css_set_hash(init_css_set.subsys));
5266 
5267         BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0, 0));
5268 
5269         mutex_unlock(&cgroup_mutex);
5270 
5271         for_each_subsys(ss, ssid) {
5272                 if (ss->early_init) {
5273                         struct cgroup_subsys_state *css =
5274                                 init_css_set.subsys[ss->id];
5275 
5276                         css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5277                                                    GFP_KERNEL);
5278                         BUG_ON(css->id < 0);
5279                 } else {
5280                         cgroup_init_subsys(ss, false);
5281                 }
5282 
5283                 list_add_tail(&init_css_set.e_cset_node[ssid],
5284                               &cgrp_dfl_root.cgrp.e_csets[ssid]);
5285 
5286                 /*
5287                  * Setting dfl_root subsys_mask needs to consider the
5288                  * disabled flag and cftype registration needs kmalloc,
5289                  * both of which aren't available during early_init.
5290                  */
5291                 if (cgroup_disable_mask & (1 << ssid)) {
5292                         static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5293                         printk(KERN_INFO "Disabling %s control group subsystem\n",
5294                                ss->name);
5295                         continue;
5296                 }
5297 
5298                 if (cgroup1_ssid_disabled(ssid))
5299                         printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5300                                ss->name);
5301 
5302                 cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5303 
5304                 /* implicit controllers must be threaded too */
5305                 WARN_ON(ss->implicit_on_dfl && !ss->threaded);
5306 
5307                 if (ss->implicit_on_dfl)
5308                         cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5309                 else if (!ss->dfl_cftypes)
5310                         cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5311 
5312                 if (ss->threaded)
5313                         cgrp_dfl_threaded_ss_mask |= 1 << ss->id;
5314 
5315                 if (ss->dfl_cftypes == ss->legacy_cftypes) {
5316                         WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5317                 } else {
5318                         WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5319                         WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5320                 }
5321 
5322                 if (ss->bind)
5323                         ss->bind(init_css_set.subsys[ssid]);
5324 
5325                 mutex_lock(&cgroup_mutex);
5326                 css_populate_dir(init_css_set.subsys[ssid]);
5327                 mutex_unlock(&cgroup_mutex);
5328         }
5329 
5330         /* init_css_set.subsys[] has been updated, re-hash */
5331         hash_del(&init_css_set.hlist);
5332         hash_add(css_set_table, &init_css_set.hlist,
5333                  css_set_hash(init_css_set.subsys));
5334 
5335         WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5336         WARN_ON(register_filesystem(&cgroup_fs_type));
5337         WARN_ON(register_filesystem(&cgroup2_fs_type));
5338         WARN_ON(!proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations));
5339 
5340         return 0;
5341 }
5342 
5343 static int __init cgroup_wq_init(void)
5344 {
5345         /*
5346          * There isn't much point in executing destruction path in
5347          * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5348          * Use 1 for @max_active.
5349          *
5350          * We would prefer to do this in cgroup_init() above, but that
5351          * is called before init_workqueues(): so leave this until after.
5352          */
5353         cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5354         BUG_ON(!cgroup_destroy_wq);
5355         return 0;
5356 }
5357 core_initcall(cgroup_wq_init);
5358 
5359 void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
5360                                         char *buf, size_t buflen)
5361 {
5362         struct kernfs_node *kn;
5363 
5364         kn = kernfs_get_node_by_id(cgrp_dfl_root.kf_root, id);
5365         if (!kn)
5366                 return;
5367         kernfs_path(kn, buf, buflen);
5368         kernfs_put(kn);
5369 }
5370 
5371 /*
5372  * proc_cgroup_show()
5373  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5374  *  - Used for /proc/<pid>/cgroup.
5375  */
5376 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5377                      struct pid *pid, struct task_struct *tsk)
5378 {
5379         char *buf;
5380         int retval;
5381         struct cgroup_root *root;
5382 
5383         retval = -ENOMEM;
5384         buf = kmalloc(PATH_MAX, GFP_KERNEL);
5385         if (!buf)
5386                 goto out;
5387 
5388         mutex_lock(&cgroup_mutex);
5389         spin_lock_irq(&css_set_lock);
5390 
5391         for_each_root(root) {
5392                 struct cgroup_subsys *ss;
5393                 struct cgroup *cgrp;
5394                 int ssid, count = 0;
5395 
5396                 if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5397                         continue;
5398 
5399                 seq_printf(m, "%d:", root->hierarchy_id);
5400                 if (root != &cgrp_dfl_root)
5401                         for_each_subsys(ss, ssid)
5402                                 if (root->subsys_mask & (1 << ssid))
5403                                         seq_printf(m, "%s%s", count++ ? "," : "",
5404                                                    ss->legacy_name);
5405                 if (strlen(root->name))
5406                         seq_printf(m, "%sname=%s", count ? "," : "",
5407                                    root->name);
5408                 seq_putc(m, ':');
5409 
5410                 cgrp = task_cgroup_from_root(tsk, root);
5411 
5412                 /*
5413                  * On traditional hierarchies, all zombie tasks show up as
5414                  * belonging to the root cgroup.  On the default hierarchy,
5415                  * while a zombie doesn't show up in "cgroup.procs" and
5416                  * thus can't be migrated, its /proc/PID/cgroup keeps
5417                  * reporting the cgroup it belonged to before exiting.  If
5418                  * the cgroup is removed before the zombie is reaped,
5419                  * " (deleted)" is appended to the cgroup path.
5420                  */
5421                 if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5422                         retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5423                                                 current->nsproxy->cgroup_ns);
5424                         if (retval >= PATH_MAX)
5425                                 retval = -ENAMETOOLONG;
5426                         if (retval < 0)
5427                                 goto out_unlock;
5428 
5429                         seq_puts(m, buf);
5430                 } else {
5431                         seq_puts(m, "/");
5432                 }
5433 
5434                 if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5435                         seq_puts(m, " (deleted)\n");
5436                 else
5437                         seq_putc(m, '\n');
5438         }
5439 
5440         retval = 0;
5441 out_unlock:
5442         spin_unlock_irq(&css_set_lock);
5443         mutex_unlock(&cgroup_mutex);
5444         kfree(buf);
5445 out:
5446         return retval;
5447 }
5448 
5449 /**
5450  * cgroup_fork - initialize cgroup related fields during copy_process()
5451  * @child: pointer to task_struct of forking parent process.
5452  *
5453  * A task is associated with the init_css_set until cgroup_post_fork()
5454  * attaches it to the parent's css_set.  Empty cg_list indicates that
5455  * @child isn't holding reference to its css_set.
5456  */
5457 void cgroup_fork(struct task_struct *child)
5458 {
5459         RCU_INIT_POINTER(child->cgroups, &init_css_set);
5460         INIT_LIST_HEAD(&child->cg_list);
5461 }
5462 
5463 /**
5464  * cgroup_can_fork - called on a new task before the process is exposed
5465  * @child: the task in question.
5466  *
5467  * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5468  * returns an error, the fork aborts with that error code. This allows for
5469  * a cgroup subsystem to conditionally allow or deny new forks.
5470  */
5471 int cgroup_can_fork(struct task_struct *child)
5472 {
5473         struct cgroup_subsys *ss;
5474         int i, j, ret;
5475 
5476         do_each_subsys_mask(ss, i, have_canfork_callback) {
5477                 ret = ss->can_fork(child);
5478                 if (ret)
5479                         goto out_revert;
5480         } while_each_subsys_mask();
5481 
5482         return 0;
5483 
5484 out_revert:
5485         for_each_subsys(ss, j) {
5486                 if (j >= i)
5487                         break;
5488                 if (ss->cancel_fork)
5489                         ss->cancel_fork(child);
5490         }
5491 
5492         return ret;
5493 }
5494 
5495 /**
5496  * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5497  * @child: the task in question
5498  *
5499  * This calls the cancel_fork() callbacks if a fork failed *after*
5500  * cgroup_can_fork() succeded.
5501  */
5502 void cgroup_cancel_fork(struct task_struct *child)
5503 {
5504         struct cgroup_subsys *ss;
5505         int i;
5506 
5507         for_each_subsys(ss, i)
5508                 if (ss->cancel_fork)
5509                         ss->cancel_fork(child);
5510 }
5511 
5512 /**
5513  * cgroup_post_fork - called on a new task after adding it to the task list
5514  * @child: the task in question
5515  *
5516  * Adds the task to the list running through its css_set if necessary and
5517  * call the subsystem fork() callbacks.  Has to be after the task is
5518  * visible on the task list in case we race with the first call to
5519  * cgroup_task_iter_start() - to guarantee that the new task ends up on its
5520  * list.
5521  */
5522 void cgroup_post_fork(struct task_struct *child)
5523 {
5524         struct cgroup_subsys *ss;
5525         int i;
5526 
5527         /*
5528          * This may race against cgroup_enable_task_cg_lists().  As that
5529          * function sets use_task_css_set_links before grabbing
5530          * tasklist_lock and we just went through tasklist_lock to add
5531          * @child, it's guaranteed that either we see the set
5532          * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
5533          * @child during its iteration.
5534          *
5535          * If we won the race, @child is associated with %current's
5536          * css_set.  Grabbing css_set_lock guarantees both that the
5537          * association is stable, and, on completion of the parent's
5538          * migration, @child is visible in the source of migration or
5539          * already in the destination cgroup.  This guarantee is necessary
5540          * when implementing operations which need to migrate all tasks of
5541          * a cgroup to another.
5542          *
5543          * Note that if we lose to cgroup_enable_task_cg_lists(), @child
5544          * will remain in init_css_set.  This is safe because all tasks are
5545          * in the init_css_set before cg_links is enabled and there's no
5546          * operation which transfers all tasks out of init_css_set.
5547          */
5548         if (use_task_css_set_links) {
5549                 struct css_set *cset;
5550 
5551                 spin_lock_irq(&css_set_lock);
5552                 cset = task_css_set(current);
5553                 if (list_empty(&child->cg_list)) {
5554                         get_css_set(cset);
5555                         cset->nr_tasks++;
5556                         css_set_move_task(child, NULL, cset, false);
5557                 }
5558                 spin_unlock_irq(&css_set_lock);
5559         }
5560 
5561         /*
5562          * Call ss->fork().  This must happen after @child is linked on
5563          * css_set; otherwise, @child might change state between ->fork()
5564          * and addition to css_set.
5565          */
5566         do_each_subsys_mask(ss, i, have_fork_callback) {
5567                 ss->fork(child);
5568         } while_each_subsys_mask();
5569 }
5570 
5571 /**
5572  * cgroup_exit - detach cgroup from exiting task
5573  * @tsk: pointer to task_struct of exiting process
5574  *
5575  * Description: Detach cgroup from @tsk and release it.
5576  *
5577  * Note that cgroups marked notify_on_release force every task in
5578  * them to take the global cgroup_mutex mutex when exiting.
5579  * This could impact scaling on very large systems.  Be reluctant to
5580  * use notify_on_release cgroups where very high task exit scaling
5581  * is required on large systems.
5582  *
5583  * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
5584  * call cgroup_exit() while the task is still competent to handle
5585  * notify_on_release(), then leave the task attached to the root cgroup in
5586  * each hierarchy for the remainder of its exit.  No need to bother with
5587  * init_css_set refcnting.  init_css_set never goes away and we can't race
5588  * with migration path - PF_EXITING is visible to migration path.
5589  */
5590 void cgroup_exit(struct task_struct *tsk)
5591 {
5592         struct cgroup_subsys *ss;
5593         struct css_set *cset;
5594         int i;
5595 
5596         /*
5597          * Unlink from @tsk from its css_set.  As migration path can't race
5598          * with us, we can check css_set and cg_list without synchronization.
5599          */
5600         cset = task_css_set(tsk);
5601 
5602         if (!list_empty(&tsk->cg_list)) {
5603                 spin_lock_irq(&css_set_lock);
5604                 css_set_move_task(tsk, cset, NULL, false);
5605                 cset->nr_tasks--;
5606                 spin_unlock_irq(&css_set_lock);
5607         } else {
5608                 get_css_set(cset);
5609         }
5610 
5611         /* see cgroup_post_fork() for details */
5612         do_each_subsys_mask(ss, i, have_exit_callback) {
5613                 ss->exit(tsk);
5614         } while_each_subsys_mask();
5615 }
5616 
5617 void cgroup_free(struct task_struct *task)
5618 {
5619         struct css_set *cset = task_css_set(task);
5620         struct cgroup_subsys *ss;
5621         int ssid;
5622 
5623         do_each_subsys_mask(ss, ssid, have_free_callback) {
5624                 ss->free(task);
5625         } while_each_subsys_mask();
5626 
5627         put_css_set(cset);
5628 }
5629 
5630 static int __init cgroup_disable(char *str)
5631 {
5632         struct cgroup_subsys *ss;
5633         char *token;
5634         int i;
5635 
5636         while ((token = strsep(&str, ",")) != NULL) {
5637                 if (!*token)
5638                         continue;
5639 
5640                 for_each_subsys(ss, i) {
5641                         if (strcmp(token, ss->name) &&
5642                             strcmp(token, ss->legacy_name))
5643                                 continue;
5644                         cgroup_disable_mask |= 1 << i;
5645                 }
5646         }
5647         return 1;
5648 }
5649 __setup("cgroup_disable=", cgroup_disable);
5650 
5651 /**
5652  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
5653  * @dentry: directory dentry of interest
5654  * @ss: subsystem of interest
5655  *
5656  * If @dentry is a directory for a cgroup which has @ss enabled on it, try
5657  * to get the corresponding css and return it.  If such css doesn't exist
5658  * or can't be pinned, an ERR_PTR value is returned.
5659  */
5660 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
5661                                                        struct cgroup_subsys *ss)
5662 {
5663         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
5664         struct file_system_type *s_type = dentry->d_sb->s_type;
5665         struct cgroup_subsys_state *css = NULL;
5666         struct cgroup *cgrp;
5667 
5668         /* is @dentry a cgroup dir? */
5669         if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
5670             !kn || kernfs_type(kn) != KERNFS_DIR)
5671                 return ERR_PTR(-EBADF);
5672 
5673         rcu_read_lock();
5674 
5675         /*
5676          * This path doesn't originate from kernfs and @kn could already
5677          * have been or be removed at any point.  @kn->priv is RCU
5678          * protected for this access.  See css_release_work_fn() for details.
5679          */
5680         cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
5681         if (cgrp)
5682                 css = cgroup_css(cgrp, ss);
5683 
5684         if (!css || !css_tryget_online(css))
5685                 css = ERR_PTR(-ENOENT);
5686 
5687         rcu_read_unlock();
5688         return css;
5689 }
5690 
5691 /**
5692  * css_from_id - lookup css by id
5693  * @id: the cgroup id
5694  * @ss: cgroup subsys to be looked into
5695  *
5696  * Returns the css if there's valid one with @id, otherwise returns NULL.
5697  * Should be called under rcu_read_lock().
5698  */
5699 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
5700 {
5701         WARN_ON_ONCE(!rcu_read_lock_held());
5702         return idr_find(&ss->css_idr, id);
5703 }
5704 
5705 /**
5706  * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
5707  * @path: path on the default hierarchy
5708  *
5709  * Find the cgroup at @path on the default hierarchy, increment its
5710  * reference count and return it.  Returns pointer to the found cgroup on
5711  * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
5712  * if @path points to a non-directory.
5713  */
5714 struct cgroup *cgroup_get_from_path(const char *path)
5715 {
5716         struct kernfs_node *kn;
5717         struct cgroup *cgrp;
5718 
5719         mutex_lock(&cgroup_mutex);
5720 
5721         kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
5722         if (kn) {
5723                 if (kernfs_type(kn) == KERNFS_DIR) {
5724                         cgrp = kn->priv;
5725                         cgroup_get_live(cgrp);
5726                 } else {
5727                         cgrp = ERR_PTR(-ENOTDIR);
5728                 }
5729                 kernfs_put(kn);
5730         } else {
5731                 cgrp = ERR_PTR(-ENOENT);
5732         }
5733 
5734         mutex_unlock(&cgroup_mutex);
5735         return cgrp;
5736 }
5737 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
5738 
5739 /**
5740  * cgroup_get_from_fd - get a cgroup pointer from a fd
5741  * @fd: fd obtained by open(cgroup2_dir)
5742  *
5743  * Find the cgroup from a fd which should be obtained
5744  * by opening a cgroup directory.  Returns a pointer to the
5745  * cgroup on success. ERR_PTR is returned if the cgroup
5746  * cannot be found.
5747  */
5748 struct cgroup *cgroup_get_from_fd(int fd)
5749 {
5750         struct cgroup_subsys_state *css;
5751         struct cgroup *cgrp;
5752         struct file *f;
5753 
5754         f = fget_raw(fd);
5755         if (!f)
5756                 return ERR_PTR(-EBADF);
5757 
5758         css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
5759         fput(f);
5760         if (IS_ERR(css))
5761                 return ERR_CAST(css);
5762 
5763         cgrp = css->cgroup;
5764         if (!cgroup_on_dfl(cgrp)) {
5765                 cgroup_put(cgrp);
5766                 return ERR_PTR(-EBADF);
5767         }
5768 
5769         return cgrp;
5770 }
5771 EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
5772 
5773 /*
5774  * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
5775  * definition in cgroup-defs.h.
5776  */
5777 #ifdef CONFIG_SOCK_CGROUP_DATA
5778 
5779 #if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
5780 
5781 DEFINE_SPINLOCK(cgroup_sk_update_lock);
5782 static bool cgroup_sk_alloc_disabled __read_mostly;
5783 
5784 void cgroup_sk_alloc_disable(void)
5785 {
5786         if (cgroup_sk_alloc_disabled)
5787                 return;
5788         pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
5789         cgroup_sk_alloc_disabled = true;
5790 }
5791 
5792 #else
5793 
5794 #define cgroup_sk_alloc_disabled        false
5795 
5796 #endif
5797 
5798 void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
5799 {
5800         if (cgroup_sk_alloc_disabled)
5801                 return;
5802 
5803         /* Socket clone path */
5804         if (skcd->val) {
5805                 /*
5806                  * We might be cloning a socket which is left in an empty
5807                  * cgroup and the cgroup might have already been rmdir'd.
5808                  * Don't use cgroup_get_live().
5809                  */
5810                 cgroup_get(sock_cgroup_ptr(skcd));
5811                 return;
5812         }
5813 
5814         rcu_read_lock();
5815 
5816         while (true) {
5817                 struct css_set *cset;
5818 
5819                 cset = task_css_set(current);
5820                 if (likely(cgroup_tryget(cset->dfl_cgrp))) {
5821                         skcd->val = (unsigned long)cset->dfl_cgrp;
5822                         break;
5823                 }
5824                 cpu_relax();
5825         }
5826 
5827         rcu_read_unlock();
5828 }
5829 
5830 void cgroup_sk_free(struct sock_cgroup_data *skcd)
5831 {
5832         cgroup_put(sock_cgroup_ptr(skcd));
5833 }
5834 
5835 #endif  /* CONFIG_SOCK_CGROUP_DATA */
5836 
5837 #ifdef CONFIG_CGROUP_BPF
5838 int cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
5839                       enum bpf_attach_type type, u32 flags)
5840 {
5841         int ret;
5842 
5843         mutex_lock(&cgroup_mutex);
5844         ret = __cgroup_bpf_attach(cgrp, prog, type, flags);
5845         mutex_unlock(&cgroup_mutex);
5846         return ret;
5847 }
5848 int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
5849                       enum bpf_attach_type type, u32 flags)
5850 {
5851         int ret;
5852 
5853         mutex_lock(&cgroup_mutex);
5854         ret = __cgroup_bpf_detach(cgrp, prog, type, flags);
5855         mutex_unlock(&cgroup_mutex);
5856         return ret;
5857 }
5858 int cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
5859                      union bpf_attr __user *uattr)
5860 {
5861         int ret;
5862 
5863         mutex_lock(&cgroup_mutex);
5864         ret = __cgroup_bpf_query(cgrp, attr, uattr);
5865         mutex_unlock(&cgroup_mutex);
5866         return ret;
5867 }
5868 #endif /* CONFIG_CGROUP_BPF */
5869 
5870 #ifdef CONFIG_SYSFS
5871 static ssize_t show_delegatable_files(struct cftype *files, char *buf,
5872                                       ssize_t size, const char *prefix)
5873 {
5874         struct cftype *cft;
5875         ssize_t ret = 0;
5876 
5877         for (cft = files; cft && cft->name[0] != '\0'; cft++) {
5878                 if (!(cft->flags & CFTYPE_NS_DELEGATABLE))
5879                         continue;
5880 
5881                 if (prefix)
5882                         ret += snprintf(buf + ret, size - ret, "%s.", prefix);
5883 
5884                 ret += snprintf(buf + ret, size - ret, "%s\n", cft->name);
5885 
5886                 if (unlikely(ret >= size)) {
5887                         WARN_ON(1);
5888                         break;
5889                 }
5890         }
5891 
5892         return ret;
5893 }
5894 
5895 static ssize_t delegate_show(struct kobject *kobj, struct kobj_attribute *attr,
5896                               char *buf)
5897 {
5898         struct cgroup_subsys *ss;
5899         int ssid;
5900         ssize_t ret = 0;
5901 
5902         ret = show_delegatable_files(cgroup_base_files, buf, PAGE_SIZE - ret,
5903                                      NULL);
5904 
5905         for_each_subsys(ss, ssid)
5906                 ret += show_delegatable_files(ss->dfl_cftypes, buf + ret,
5907                                               PAGE_SIZE - ret,
5908                                               cgroup_subsys_name[ssid]);
5909 
5910         return ret;
5911 }
5912 static struct kobj_attribute cgroup_delegate_attr = __ATTR_RO(delegate);
5913 
5914 static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr,
5915                              char *buf)
5916 {
5917         return snprintf(buf, PAGE_SIZE, "nsdelegate\n");
5918 }
5919 static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features);
5920 
5921 static struct attribute *cgroup_sysfs_attrs[] = {
5922         &cgroup_delegate_attr.attr,
5923         &cgroup_features_attr.attr,
5924         NULL,
5925 };
5926 
5927 static const struct attribute_group cgroup_sysfs_attr_group = {
5928         .attrs = cgroup_sysfs_attrs,
5929         .name = "cgroup",
5930 };
5931 
5932 static int __init cgroup_sysfs_init(void)
5933 {
5934         return sysfs_create_group(kernel_kobj, &cgroup_sysfs_attr_group);
5935 }
5936 subsys_initcall(cgroup_sysfs_init);
5937 #endif /* CONFIG_SYSFS */
5938 

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