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TOMOYO Linux Cross Reference
Linux/kernel/cgroup/cgroup-v1.c

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  1 #include "cgroup-internal.h"
  2 
  3 #include <linux/ctype.h>
  4 #include <linux/kmod.h>
  5 #include <linux/sort.h>
  6 #include <linux/delay.h>
  7 #include <linux/mm.h>
  8 #include <linux/sched/signal.h>
  9 #include <linux/sched/task.h>
 10 #include <linux/magic.h>
 11 #include <linux/slab.h>
 12 #include <linux/vmalloc.h>
 13 #include <linux/delayacct.h>
 14 #include <linux/pid_namespace.h>
 15 #include <linux/cgroupstats.h>
 16 
 17 #include <trace/events/cgroup.h>
 18 
 19 /*
 20  * pidlists linger the following amount before being destroyed.  The goal
 21  * is avoiding frequent destruction in the middle of consecutive read calls
 22  * Expiring in the middle is a performance problem not a correctness one.
 23  * 1 sec should be enough.
 24  */
 25 #define CGROUP_PIDLIST_DESTROY_DELAY    HZ
 26 
 27 /* Controllers blocked by the commandline in v1 */
 28 static u16 cgroup_no_v1_mask;
 29 
 30 /*
 31  * pidlist destructions need to be flushed on cgroup destruction.  Use a
 32  * separate workqueue as flush domain.
 33  */
 34 static struct workqueue_struct *cgroup_pidlist_destroy_wq;
 35 
 36 /*
 37  * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
 38  * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
 39  */
 40 static DEFINE_SPINLOCK(release_agent_path_lock);
 41 
 42 bool cgroup1_ssid_disabled(int ssid)
 43 {
 44         return cgroup_no_v1_mask & (1 << ssid);
 45 }
 46 
 47 /**
 48  * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
 49  * @from: attach to all cgroups of a given task
 50  * @tsk: the task to be attached
 51  */
 52 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 53 {
 54         struct cgroup_root *root;
 55         int retval = 0;
 56 
 57         mutex_lock(&cgroup_mutex);
 58         percpu_down_write(&cgroup_threadgroup_rwsem);
 59         for_each_root(root) {
 60                 struct cgroup *from_cgrp;
 61 
 62                 if (root == &cgrp_dfl_root)
 63                         continue;
 64 
 65                 spin_lock_irq(&css_set_lock);
 66                 from_cgrp = task_cgroup_from_root(from, root);
 67                 spin_unlock_irq(&css_set_lock);
 68 
 69                 retval = cgroup_attach_task(from_cgrp, tsk, false);
 70                 if (retval)
 71                         break;
 72         }
 73         percpu_up_write(&cgroup_threadgroup_rwsem);
 74         mutex_unlock(&cgroup_mutex);
 75 
 76         return retval;
 77 }
 78 EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
 79 
 80 /**
 81  * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
 82  * @to: cgroup to which the tasks will be moved
 83  * @from: cgroup in which the tasks currently reside
 84  *
 85  * Locking rules between cgroup_post_fork() and the migration path
 86  * guarantee that, if a task is forking while being migrated, the new child
 87  * is guaranteed to be either visible in the source cgroup after the
 88  * parent's migration is complete or put into the target cgroup.  No task
 89  * can slip out of migration through forking.
 90  */
 91 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
 92 {
 93         DEFINE_CGROUP_MGCTX(mgctx);
 94         struct cgrp_cset_link *link;
 95         struct css_task_iter it;
 96         struct task_struct *task;
 97         int ret;
 98 
 99         if (cgroup_on_dfl(to))
100                 return -EINVAL;
101 
102         ret = cgroup_migrate_vet_dst(to);
103         if (ret)
104                 return ret;
105 
106         mutex_lock(&cgroup_mutex);
107 
108         percpu_down_write(&cgroup_threadgroup_rwsem);
109 
110         /* all tasks in @from are being moved, all csets are source */
111         spin_lock_irq(&css_set_lock);
112         list_for_each_entry(link, &from->cset_links, cset_link)
113                 cgroup_migrate_add_src(link->cset, to, &mgctx);
114         spin_unlock_irq(&css_set_lock);
115 
116         ret = cgroup_migrate_prepare_dst(&mgctx);
117         if (ret)
118                 goto out_err;
119 
120         /*
121          * Migrate tasks one-by-one until @from is empty.  This fails iff
122          * ->can_attach() fails.
123          */
124         do {
125                 css_task_iter_start(&from->self, 0, &it);
126 
127                 do {
128                         task = css_task_iter_next(&it);
129                 } while (task && (task->flags & PF_EXITING));
130 
131                 if (task)
132                         get_task_struct(task);
133                 css_task_iter_end(&it);
134 
135                 if (task) {
136                         ret = cgroup_migrate(task, false, &mgctx);
137                         if (!ret)
138                                 trace_cgroup_transfer_tasks(to, task, false);
139                         put_task_struct(task);
140                 }
141         } while (task && !ret);
142 out_err:
143         cgroup_migrate_finish(&mgctx);
144         percpu_up_write(&cgroup_threadgroup_rwsem);
145         mutex_unlock(&cgroup_mutex);
146         return ret;
147 }
148 
149 /*
150  * Stuff for reading the 'tasks'/'procs' files.
151  *
152  * Reading this file can return large amounts of data if a cgroup has
153  * *lots* of attached tasks. So it may need several calls to read(),
154  * but we cannot guarantee that the information we produce is correct
155  * unless we produce it entirely atomically.
156  *
157  */
158 
159 /* which pidlist file are we talking about? */
160 enum cgroup_filetype {
161         CGROUP_FILE_PROCS,
162         CGROUP_FILE_TASKS,
163 };
164 
165 /*
166  * A pidlist is a list of pids that virtually represents the contents of one
167  * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
168  * a pair (one each for procs, tasks) for each pid namespace that's relevant
169  * to the cgroup.
170  */
171 struct cgroup_pidlist {
172         /*
173          * used to find which pidlist is wanted. doesn't change as long as
174          * this particular list stays in the list.
175         */
176         struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
177         /* array of xids */
178         pid_t *list;
179         /* how many elements the above list has */
180         int length;
181         /* each of these stored in a list by its cgroup */
182         struct list_head links;
183         /* pointer to the cgroup we belong to, for list removal purposes */
184         struct cgroup *owner;
185         /* for delayed destruction */
186         struct delayed_work destroy_dwork;
187 };
188 
189 /*
190  * The following two functions "fix" the issue where there are more pids
191  * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
192  * TODO: replace with a kernel-wide solution to this problem
193  */
194 #define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
195 static void *pidlist_allocate(int count)
196 {
197         if (PIDLIST_TOO_LARGE(count))
198                 return vmalloc(array_size(count, sizeof(pid_t)));
199         else
200                 return kmalloc_array(count, sizeof(pid_t), GFP_KERNEL);
201 }
202 
203 static void pidlist_free(void *p)
204 {
205         kvfree(p);
206 }
207 
208 /*
209  * Used to destroy all pidlists lingering waiting for destroy timer.  None
210  * should be left afterwards.
211  */
212 void cgroup1_pidlist_destroy_all(struct cgroup *cgrp)
213 {
214         struct cgroup_pidlist *l, *tmp_l;
215 
216         mutex_lock(&cgrp->pidlist_mutex);
217         list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
218                 mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
219         mutex_unlock(&cgrp->pidlist_mutex);
220 
221         flush_workqueue(cgroup_pidlist_destroy_wq);
222         BUG_ON(!list_empty(&cgrp->pidlists));
223 }
224 
225 static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
226 {
227         struct delayed_work *dwork = to_delayed_work(work);
228         struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
229                                                 destroy_dwork);
230         struct cgroup_pidlist *tofree = NULL;
231 
232         mutex_lock(&l->owner->pidlist_mutex);
233 
234         /*
235          * Destroy iff we didn't get queued again.  The state won't change
236          * as destroy_dwork can only be queued while locked.
237          */
238         if (!delayed_work_pending(dwork)) {
239                 list_del(&l->links);
240                 pidlist_free(l->list);
241                 put_pid_ns(l->key.ns);
242                 tofree = l;
243         }
244 
245         mutex_unlock(&l->owner->pidlist_mutex);
246         kfree(tofree);
247 }
248 
249 /*
250  * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
251  * Returns the number of unique elements.
252  */
253 static int pidlist_uniq(pid_t *list, int length)
254 {
255         int src, dest = 1;
256 
257         /*
258          * we presume the 0th element is unique, so i starts at 1. trivial
259          * edge cases first; no work needs to be done for either
260          */
261         if (length == 0 || length == 1)
262                 return length;
263         /* src and dest walk down the list; dest counts unique elements */
264         for (src = 1; src < length; src++) {
265                 /* find next unique element */
266                 while (list[src] == list[src-1]) {
267                         src++;
268                         if (src == length)
269                                 goto after;
270                 }
271                 /* dest always points to where the next unique element goes */
272                 list[dest] = list[src];
273                 dest++;
274         }
275 after:
276         return dest;
277 }
278 
279 /*
280  * The two pid files - task and cgroup.procs - guaranteed that the result
281  * is sorted, which forced this whole pidlist fiasco.  As pid order is
282  * different per namespace, each namespace needs differently sorted list,
283  * making it impossible to use, for example, single rbtree of member tasks
284  * sorted by task pointer.  As pidlists can be fairly large, allocating one
285  * per open file is dangerous, so cgroup had to implement shared pool of
286  * pidlists keyed by cgroup and namespace.
287  */
288 static int cmppid(const void *a, const void *b)
289 {
290         return *(pid_t *)a - *(pid_t *)b;
291 }
292 
293 static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
294                                                   enum cgroup_filetype type)
295 {
296         struct cgroup_pidlist *l;
297         /* don't need task_nsproxy() if we're looking at ourself */
298         struct pid_namespace *ns = task_active_pid_ns(current);
299 
300         lockdep_assert_held(&cgrp->pidlist_mutex);
301 
302         list_for_each_entry(l, &cgrp->pidlists, links)
303                 if (l->key.type == type && l->key.ns == ns)
304                         return l;
305         return NULL;
306 }
307 
308 /*
309  * find the appropriate pidlist for our purpose (given procs vs tasks)
310  * returns with the lock on that pidlist already held, and takes care
311  * of the use count, or returns NULL with no locks held if we're out of
312  * memory.
313  */
314 static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
315                                                 enum cgroup_filetype type)
316 {
317         struct cgroup_pidlist *l;
318 
319         lockdep_assert_held(&cgrp->pidlist_mutex);
320 
321         l = cgroup_pidlist_find(cgrp, type);
322         if (l)
323                 return l;
324 
325         /* entry not found; create a new one */
326         l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
327         if (!l)
328                 return l;
329 
330         INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
331         l->key.type = type;
332         /* don't need task_nsproxy() if we're looking at ourself */
333         l->key.ns = get_pid_ns(task_active_pid_ns(current));
334         l->owner = cgrp;
335         list_add(&l->links, &cgrp->pidlists);
336         return l;
337 }
338 
339 /**
340  * cgroup_task_count - count the number of tasks in a cgroup.
341  * @cgrp: the cgroup in question
342  */
343 int cgroup_task_count(const struct cgroup *cgrp)
344 {
345         int count = 0;
346         struct cgrp_cset_link *link;
347 
348         spin_lock_irq(&css_set_lock);
349         list_for_each_entry(link, &cgrp->cset_links, cset_link)
350                 count += link->cset->nr_tasks;
351         spin_unlock_irq(&css_set_lock);
352         return count;
353 }
354 
355 /*
356  * Load a cgroup's pidarray with either procs' tgids or tasks' pids
357  */
358 static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
359                               struct cgroup_pidlist **lp)
360 {
361         pid_t *array;
362         int length;
363         int pid, n = 0; /* used for populating the array */
364         struct css_task_iter it;
365         struct task_struct *tsk;
366         struct cgroup_pidlist *l;
367 
368         lockdep_assert_held(&cgrp->pidlist_mutex);
369 
370         /*
371          * If cgroup gets more users after we read count, we won't have
372          * enough space - tough.  This race is indistinguishable to the
373          * caller from the case that the additional cgroup users didn't
374          * show up until sometime later on.
375          */
376         length = cgroup_task_count(cgrp);
377         array = pidlist_allocate(length);
378         if (!array)
379                 return -ENOMEM;
380         /* now, populate the array */
381         css_task_iter_start(&cgrp->self, 0, &it);
382         while ((tsk = css_task_iter_next(&it))) {
383                 if (unlikely(n == length))
384                         break;
385                 /* get tgid or pid for procs or tasks file respectively */
386                 if (type == CGROUP_FILE_PROCS)
387                         pid = task_tgid_vnr(tsk);
388                 else
389                         pid = task_pid_vnr(tsk);
390                 if (pid > 0) /* make sure to only use valid results */
391                         array[n++] = pid;
392         }
393         css_task_iter_end(&it);
394         length = n;
395         /* now sort & (if procs) strip out duplicates */
396         sort(array, length, sizeof(pid_t), cmppid, NULL);
397         if (type == CGROUP_FILE_PROCS)
398                 length = pidlist_uniq(array, length);
399 
400         l = cgroup_pidlist_find_create(cgrp, type);
401         if (!l) {
402                 pidlist_free(array);
403                 return -ENOMEM;
404         }
405 
406         /* store array, freeing old if necessary */
407         pidlist_free(l->list);
408         l->list = array;
409         l->length = length;
410         *lp = l;
411         return 0;
412 }
413 
414 /*
415  * seq_file methods for the tasks/procs files. The seq_file position is the
416  * next pid to display; the seq_file iterator is a pointer to the pid
417  * in the cgroup->l->list array.
418  */
419 
420 static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
421 {
422         /*
423          * Initially we receive a position value that corresponds to
424          * one more than the last pid shown (or 0 on the first call or
425          * after a seek to the start). Use a binary-search to find the
426          * next pid to display, if any
427          */
428         struct kernfs_open_file *of = s->private;
429         struct cgroup *cgrp = seq_css(s)->cgroup;
430         struct cgroup_pidlist *l;
431         enum cgroup_filetype type = seq_cft(s)->private;
432         int index = 0, pid = *pos;
433         int *iter, ret;
434 
435         mutex_lock(&cgrp->pidlist_mutex);
436 
437         /*
438          * !NULL @of->priv indicates that this isn't the first start()
439          * after open.  If the matching pidlist is around, we can use that.
440          * Look for it.  Note that @of->priv can't be used directly.  It
441          * could already have been destroyed.
442          */
443         if (of->priv)
444                 of->priv = cgroup_pidlist_find(cgrp, type);
445 
446         /*
447          * Either this is the first start() after open or the matching
448          * pidlist has been destroyed inbetween.  Create a new one.
449          */
450         if (!of->priv) {
451                 ret = pidlist_array_load(cgrp, type,
452                                          (struct cgroup_pidlist **)&of->priv);
453                 if (ret)
454                         return ERR_PTR(ret);
455         }
456         l = of->priv;
457 
458         if (pid) {
459                 int end = l->length;
460 
461                 while (index < end) {
462                         int mid = (index + end) / 2;
463                         if (l->list[mid] == pid) {
464                                 index = mid;
465                                 break;
466                         } else if (l->list[mid] <= pid)
467                                 index = mid + 1;
468                         else
469                                 end = mid;
470                 }
471         }
472         /* If we're off the end of the array, we're done */
473         if (index >= l->length)
474                 return NULL;
475         /* Update the abstract position to be the actual pid that we found */
476         iter = l->list + index;
477         *pos = *iter;
478         return iter;
479 }
480 
481 static void cgroup_pidlist_stop(struct seq_file *s, void *v)
482 {
483         struct kernfs_open_file *of = s->private;
484         struct cgroup_pidlist *l = of->priv;
485 
486         if (l)
487                 mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
488                                  CGROUP_PIDLIST_DESTROY_DELAY);
489         mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
490 }
491 
492 static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
493 {
494         struct kernfs_open_file *of = s->private;
495         struct cgroup_pidlist *l = of->priv;
496         pid_t *p = v;
497         pid_t *end = l->list + l->length;
498         /*
499          * Advance to the next pid in the array. If this goes off the
500          * end, we're done
501          */
502         p++;
503         if (p >= end) {
504                 return NULL;
505         } else {
506                 *pos = *p;
507                 return p;
508         }
509 }
510 
511 static int cgroup_pidlist_show(struct seq_file *s, void *v)
512 {
513         seq_printf(s, "%d\n", *(int *)v);
514 
515         return 0;
516 }
517 
518 static ssize_t __cgroup1_procs_write(struct kernfs_open_file *of,
519                                      char *buf, size_t nbytes, loff_t off,
520                                      bool threadgroup)
521 {
522         struct cgroup *cgrp;
523         struct task_struct *task;
524         const struct cred *cred, *tcred;
525         ssize_t ret;
526 
527         cgrp = cgroup_kn_lock_live(of->kn, false);
528         if (!cgrp)
529                 return -ENODEV;
530 
531         task = cgroup_procs_write_start(buf, threadgroup);
532         ret = PTR_ERR_OR_ZERO(task);
533         if (ret)
534                 goto out_unlock;
535 
536         /*
537          * Even if we're attaching all tasks in the thread group, we only
538          * need to check permissions on one of them.
539          */
540         cred = current_cred();
541         tcred = get_task_cred(task);
542         if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
543             !uid_eq(cred->euid, tcred->uid) &&
544             !uid_eq(cred->euid, tcred->suid))
545                 ret = -EACCES;
546         put_cred(tcred);
547         if (ret)
548                 goto out_finish;
549 
550         ret = cgroup_attach_task(cgrp, task, threadgroup);
551 
552 out_finish:
553         cgroup_procs_write_finish(task);
554 out_unlock:
555         cgroup_kn_unlock(of->kn);
556 
557         return ret ?: nbytes;
558 }
559 
560 static ssize_t cgroup1_procs_write(struct kernfs_open_file *of,
561                                    char *buf, size_t nbytes, loff_t off)
562 {
563         return __cgroup1_procs_write(of, buf, nbytes, off, true);
564 }
565 
566 static ssize_t cgroup1_tasks_write(struct kernfs_open_file *of,
567                                    char *buf, size_t nbytes, loff_t off)
568 {
569         return __cgroup1_procs_write(of, buf, nbytes, off, false);
570 }
571 
572 static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
573                                           char *buf, size_t nbytes, loff_t off)
574 {
575         struct cgroup *cgrp;
576 
577         BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
578 
579         cgrp = cgroup_kn_lock_live(of->kn, false);
580         if (!cgrp)
581                 return -ENODEV;
582         spin_lock(&release_agent_path_lock);
583         strlcpy(cgrp->root->release_agent_path, strstrip(buf),
584                 sizeof(cgrp->root->release_agent_path));
585         spin_unlock(&release_agent_path_lock);
586         cgroup_kn_unlock(of->kn);
587         return nbytes;
588 }
589 
590 static int cgroup_release_agent_show(struct seq_file *seq, void *v)
591 {
592         struct cgroup *cgrp = seq_css(seq)->cgroup;
593 
594         spin_lock(&release_agent_path_lock);
595         seq_puts(seq, cgrp->root->release_agent_path);
596         spin_unlock(&release_agent_path_lock);
597         seq_putc(seq, '\n');
598         return 0;
599 }
600 
601 static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
602 {
603         seq_puts(seq, "\n");
604         return 0;
605 }
606 
607 static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
608                                          struct cftype *cft)
609 {
610         return notify_on_release(css->cgroup);
611 }
612 
613 static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
614                                           struct cftype *cft, u64 val)
615 {
616         if (val)
617                 set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
618         else
619                 clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
620         return 0;
621 }
622 
623 static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
624                                       struct cftype *cft)
625 {
626         return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
627 }
628 
629 static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
630                                        struct cftype *cft, u64 val)
631 {
632         if (val)
633                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
634         else
635                 clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
636         return 0;
637 }
638 
639 /* cgroup core interface files for the legacy hierarchies */
640 struct cftype cgroup1_base_files[] = {
641         {
642                 .name = "cgroup.procs",
643                 .seq_start = cgroup_pidlist_start,
644                 .seq_next = cgroup_pidlist_next,
645                 .seq_stop = cgroup_pidlist_stop,
646                 .seq_show = cgroup_pidlist_show,
647                 .private = CGROUP_FILE_PROCS,
648                 .write = cgroup1_procs_write,
649         },
650         {
651                 .name = "cgroup.clone_children",
652                 .read_u64 = cgroup_clone_children_read,
653                 .write_u64 = cgroup_clone_children_write,
654         },
655         {
656                 .name = "cgroup.sane_behavior",
657                 .flags = CFTYPE_ONLY_ON_ROOT,
658                 .seq_show = cgroup_sane_behavior_show,
659         },
660         {
661                 .name = "tasks",
662                 .seq_start = cgroup_pidlist_start,
663                 .seq_next = cgroup_pidlist_next,
664                 .seq_stop = cgroup_pidlist_stop,
665                 .seq_show = cgroup_pidlist_show,
666                 .private = CGROUP_FILE_TASKS,
667                 .write = cgroup1_tasks_write,
668         },
669         {
670                 .name = "notify_on_release",
671                 .read_u64 = cgroup_read_notify_on_release,
672                 .write_u64 = cgroup_write_notify_on_release,
673         },
674         {
675                 .name = "release_agent",
676                 .flags = CFTYPE_ONLY_ON_ROOT,
677                 .seq_show = cgroup_release_agent_show,
678                 .write = cgroup_release_agent_write,
679                 .max_write_len = PATH_MAX - 1,
680         },
681         { }     /* terminate */
682 };
683 
684 /* Display information about each subsystem and each hierarchy */
685 int proc_cgroupstats_show(struct seq_file *m, void *v)
686 {
687         struct cgroup_subsys *ss;
688         int i;
689 
690         seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
691         /*
692          * ideally we don't want subsystems moving around while we do this.
693          * cgroup_mutex is also necessary to guarantee an atomic snapshot of
694          * subsys/hierarchy state.
695          */
696         mutex_lock(&cgroup_mutex);
697 
698         for_each_subsys(ss, i)
699                 seq_printf(m, "%s\t%d\t%d\t%d\n",
700                            ss->legacy_name, ss->root->hierarchy_id,
701                            atomic_read(&ss->root->nr_cgrps),
702                            cgroup_ssid_enabled(i));
703 
704         mutex_unlock(&cgroup_mutex);
705         return 0;
706 }
707 
708 /**
709  * cgroupstats_build - build and fill cgroupstats
710  * @stats: cgroupstats to fill information into
711  * @dentry: A dentry entry belonging to the cgroup for which stats have
712  * been requested.
713  *
714  * Build and fill cgroupstats so that taskstats can export it to user
715  * space.
716  */
717 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
718 {
719         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
720         struct cgroup *cgrp;
721         struct css_task_iter it;
722         struct task_struct *tsk;
723 
724         /* it should be kernfs_node belonging to cgroupfs and is a directory */
725         if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
726             kernfs_type(kn) != KERNFS_DIR)
727                 return -EINVAL;
728 
729         mutex_lock(&cgroup_mutex);
730 
731         /*
732          * We aren't being called from kernfs and there's no guarantee on
733          * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
734          * @kn->priv is RCU safe.  Let's do the RCU dancing.
735          */
736         rcu_read_lock();
737         cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
738         if (!cgrp || cgroup_is_dead(cgrp)) {
739                 rcu_read_unlock();
740                 mutex_unlock(&cgroup_mutex);
741                 return -ENOENT;
742         }
743         rcu_read_unlock();
744 
745         css_task_iter_start(&cgrp->self, 0, &it);
746         while ((tsk = css_task_iter_next(&it))) {
747                 switch (tsk->state) {
748                 case TASK_RUNNING:
749                         stats->nr_running++;
750                         break;
751                 case TASK_INTERRUPTIBLE:
752                         stats->nr_sleeping++;
753                         break;
754                 case TASK_UNINTERRUPTIBLE:
755                         stats->nr_uninterruptible++;
756                         break;
757                 case TASK_STOPPED:
758                         stats->nr_stopped++;
759                         break;
760                 default:
761                         if (delayacct_is_task_waiting_on_io(tsk))
762                                 stats->nr_io_wait++;
763                         break;
764                 }
765         }
766         css_task_iter_end(&it);
767 
768         mutex_unlock(&cgroup_mutex);
769         return 0;
770 }
771 
772 void cgroup1_check_for_release(struct cgroup *cgrp)
773 {
774         if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) &&
775             !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
776                 schedule_work(&cgrp->release_agent_work);
777 }
778 
779 /*
780  * Notify userspace when a cgroup is released, by running the
781  * configured release agent with the name of the cgroup (path
782  * relative to the root of cgroup file system) as the argument.
783  *
784  * Most likely, this user command will try to rmdir this cgroup.
785  *
786  * This races with the possibility that some other task will be
787  * attached to this cgroup before it is removed, or that some other
788  * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
789  * The presumed 'rmdir' will fail quietly if this cgroup is no longer
790  * unused, and this cgroup will be reprieved from its death sentence,
791  * to continue to serve a useful existence.  Next time it's released,
792  * we will get notified again, if it still has 'notify_on_release' set.
793  *
794  * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
795  * means only wait until the task is successfully execve()'d.  The
796  * separate release agent task is forked by call_usermodehelper(),
797  * then control in this thread returns here, without waiting for the
798  * release agent task.  We don't bother to wait because the caller of
799  * this routine has no use for the exit status of the release agent
800  * task, so no sense holding our caller up for that.
801  */
802 void cgroup1_release_agent(struct work_struct *work)
803 {
804         struct cgroup *cgrp =
805                 container_of(work, struct cgroup, release_agent_work);
806         char *pathbuf = NULL, *agentbuf = NULL;
807         char *argv[3], *envp[3];
808         int ret;
809 
810         mutex_lock(&cgroup_mutex);
811 
812         pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
813         agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
814         if (!pathbuf || !agentbuf)
815                 goto out;
816 
817         spin_lock_irq(&css_set_lock);
818         ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
819         spin_unlock_irq(&css_set_lock);
820         if (ret < 0 || ret >= PATH_MAX)
821                 goto out;
822 
823         argv[0] = agentbuf;
824         argv[1] = pathbuf;
825         argv[2] = NULL;
826 
827         /* minimal command environment */
828         envp[0] = "HOME=/";
829         envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
830         envp[2] = NULL;
831 
832         mutex_unlock(&cgroup_mutex);
833         call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
834         goto out_free;
835 out:
836         mutex_unlock(&cgroup_mutex);
837 out_free:
838         kfree(agentbuf);
839         kfree(pathbuf);
840 }
841 
842 /*
843  * cgroup_rename - Only allow simple rename of directories in place.
844  */
845 static int cgroup1_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
846                           const char *new_name_str)
847 {
848         struct cgroup *cgrp = kn->priv;
849         int ret;
850 
851         if (kernfs_type(kn) != KERNFS_DIR)
852                 return -ENOTDIR;
853         if (kn->parent != new_parent)
854                 return -EIO;
855 
856         /*
857          * We're gonna grab cgroup_mutex which nests outside kernfs
858          * active_ref.  kernfs_rename() doesn't require active_ref
859          * protection.  Break them before grabbing cgroup_mutex.
860          */
861         kernfs_break_active_protection(new_parent);
862         kernfs_break_active_protection(kn);
863 
864         mutex_lock(&cgroup_mutex);
865 
866         ret = kernfs_rename(kn, new_parent, new_name_str);
867         if (!ret)
868                 trace_cgroup_rename(cgrp);
869 
870         mutex_unlock(&cgroup_mutex);
871 
872         kernfs_unbreak_active_protection(kn);
873         kernfs_unbreak_active_protection(new_parent);
874         return ret;
875 }
876 
877 static int cgroup1_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
878 {
879         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
880         struct cgroup_subsys *ss;
881         int ssid;
882 
883         for_each_subsys(ss, ssid)
884                 if (root->subsys_mask & (1 << ssid))
885                         seq_show_option(seq, ss->legacy_name, NULL);
886         if (root->flags & CGRP_ROOT_NOPREFIX)
887                 seq_puts(seq, ",noprefix");
888         if (root->flags & CGRP_ROOT_XATTR)
889                 seq_puts(seq, ",xattr");
890         if (root->flags & CGRP_ROOT_CPUSET_V2_MODE)
891                 seq_puts(seq, ",cpuset_v2_mode");
892 
893         spin_lock(&release_agent_path_lock);
894         if (strlen(root->release_agent_path))
895                 seq_show_option(seq, "release_agent",
896                                 root->release_agent_path);
897         spin_unlock(&release_agent_path_lock);
898 
899         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
900                 seq_puts(seq, ",clone_children");
901         if (strlen(root->name))
902                 seq_show_option(seq, "name", root->name);
903         return 0;
904 }
905 
906 static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
907 {
908         char *token, *o = data;
909         bool all_ss = false, one_ss = false;
910         u16 mask = U16_MAX;
911         struct cgroup_subsys *ss;
912         int nr_opts = 0;
913         int i;
914 
915 #ifdef CONFIG_CPUSETS
916         mask = ~((u16)1 << cpuset_cgrp_id);
917 #endif
918 
919         memset(opts, 0, sizeof(*opts));
920 
921         while ((token = strsep(&o, ",")) != NULL) {
922                 nr_opts++;
923 
924                 if (!*token)
925                         return -EINVAL;
926                 if (!strcmp(token, "none")) {
927                         /* Explicitly have no subsystems */
928                         opts->none = true;
929                         continue;
930                 }
931                 if (!strcmp(token, "all")) {
932                         /* Mutually exclusive option 'all' + subsystem name */
933                         if (one_ss)
934                                 return -EINVAL;
935                         all_ss = true;
936                         continue;
937                 }
938                 if (!strcmp(token, "noprefix")) {
939                         opts->flags |= CGRP_ROOT_NOPREFIX;
940                         continue;
941                 }
942                 if (!strcmp(token, "clone_children")) {
943                         opts->cpuset_clone_children = true;
944                         continue;
945                 }
946                 if (!strcmp(token, "cpuset_v2_mode")) {
947                         opts->flags |= CGRP_ROOT_CPUSET_V2_MODE;
948                         continue;
949                 }
950                 if (!strcmp(token, "xattr")) {
951                         opts->flags |= CGRP_ROOT_XATTR;
952                         continue;
953                 }
954                 if (!strncmp(token, "release_agent=", 14)) {
955                         /* Specifying two release agents is forbidden */
956                         if (opts->release_agent)
957                                 return -EINVAL;
958                         opts->release_agent =
959                                 kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
960                         if (!opts->release_agent)
961                                 return -ENOMEM;
962                         continue;
963                 }
964                 if (!strncmp(token, "name=", 5)) {
965                         const char *name = token + 5;
966                         /* Can't specify an empty name */
967                         if (!strlen(name))
968                                 return -EINVAL;
969                         /* Must match [\w.-]+ */
970                         for (i = 0; i < strlen(name); i++) {
971                                 char c = name[i];
972                                 if (isalnum(c))
973                                         continue;
974                                 if ((c == '.') || (c == '-') || (c == '_'))
975                                         continue;
976                                 return -EINVAL;
977                         }
978                         /* Specifying two names is forbidden */
979                         if (opts->name)
980                                 return -EINVAL;
981                         opts->name = kstrndup(name,
982                                               MAX_CGROUP_ROOT_NAMELEN - 1,
983                                               GFP_KERNEL);
984                         if (!opts->name)
985                                 return -ENOMEM;
986 
987                         continue;
988                 }
989 
990                 for_each_subsys(ss, i) {
991                         if (strcmp(token, ss->legacy_name))
992                                 continue;
993                         if (!cgroup_ssid_enabled(i))
994                                 continue;
995                         if (cgroup1_ssid_disabled(i))
996                                 continue;
997 
998                         /* Mutually exclusive option 'all' + subsystem name */
999                         if (all_ss)
1000                                 return -EINVAL;
1001                         opts->subsys_mask |= (1 << i);
1002                         one_ss = true;
1003 
1004                         break;
1005                 }
1006                 if (i == CGROUP_SUBSYS_COUNT)
1007                         return -ENOENT;
1008         }
1009 
1010         /*
1011          * If the 'all' option was specified select all the subsystems,
1012          * otherwise if 'none', 'name=' and a subsystem name options were
1013          * not specified, let's default to 'all'
1014          */
1015         if (all_ss || (!one_ss && !opts->none && !opts->name))
1016                 for_each_subsys(ss, i)
1017                         if (cgroup_ssid_enabled(i) && !cgroup1_ssid_disabled(i))
1018                                 opts->subsys_mask |= (1 << i);
1019 
1020         /*
1021          * We either have to specify by name or by subsystems. (So all
1022          * empty hierarchies must have a name).
1023          */
1024         if (!opts->subsys_mask && !opts->name)
1025                 return -EINVAL;
1026 
1027         /*
1028          * Option noprefix was introduced just for backward compatibility
1029          * with the old cpuset, so we allow noprefix only if mounting just
1030          * the cpuset subsystem.
1031          */
1032         if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1033                 return -EINVAL;
1034 
1035         /* Can't specify "none" and some subsystems */
1036         if (opts->subsys_mask && opts->none)
1037                 return -EINVAL;
1038 
1039         return 0;
1040 }
1041 
1042 static int cgroup1_remount(struct kernfs_root *kf_root, int *flags, char *data)
1043 {
1044         int ret = 0;
1045         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1046         struct cgroup_sb_opts opts;
1047         u16 added_mask, removed_mask;
1048 
1049         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1050 
1051         /* See what subsystems are wanted */
1052         ret = parse_cgroupfs_options(data, &opts);
1053         if (ret)
1054                 goto out_unlock;
1055 
1056         if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
1057                 pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
1058                         task_tgid_nr(current), current->comm);
1059 
1060         added_mask = opts.subsys_mask & ~root->subsys_mask;
1061         removed_mask = root->subsys_mask & ~opts.subsys_mask;
1062 
1063         /* Don't allow flags or name to change at remount */
1064         if ((opts.flags ^ root->flags) ||
1065             (opts.name && strcmp(opts.name, root->name))) {
1066                 pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
1067                        opts.flags, opts.name ?: "", root->flags, root->name);
1068                 ret = -EINVAL;
1069                 goto out_unlock;
1070         }
1071 
1072         /* remounting is not allowed for populated hierarchies */
1073         if (!list_empty(&root->cgrp.self.children)) {
1074                 ret = -EBUSY;
1075                 goto out_unlock;
1076         }
1077 
1078         ret = rebind_subsystems(root, added_mask);
1079         if (ret)
1080                 goto out_unlock;
1081 
1082         WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
1083 
1084         if (opts.release_agent) {
1085                 spin_lock(&release_agent_path_lock);
1086                 strcpy(root->release_agent_path, opts.release_agent);
1087                 spin_unlock(&release_agent_path_lock);
1088         }
1089 
1090         trace_cgroup_remount(root);
1091 
1092  out_unlock:
1093         kfree(opts.release_agent);
1094         kfree(opts.name);
1095         mutex_unlock(&cgroup_mutex);
1096         return ret;
1097 }
1098 
1099 struct kernfs_syscall_ops cgroup1_kf_syscall_ops = {
1100         .rename                 = cgroup1_rename,
1101         .show_options           = cgroup1_show_options,
1102         .remount_fs             = cgroup1_remount,
1103         .mkdir                  = cgroup_mkdir,
1104         .rmdir                  = cgroup_rmdir,
1105         .show_path              = cgroup_show_path,
1106 };
1107 
1108 struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
1109                              void *data, unsigned long magic,
1110                              struct cgroup_namespace *ns)
1111 {
1112         struct super_block *pinned_sb = NULL;
1113         struct cgroup_sb_opts opts;
1114         struct cgroup_root *root;
1115         struct cgroup_subsys *ss;
1116         struct dentry *dentry;
1117         int i, ret;
1118         bool new_root = false;
1119 
1120         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1121 
1122         /* First find the desired set of subsystems */
1123         ret = parse_cgroupfs_options(data, &opts);
1124         if (ret)
1125                 goto out_unlock;
1126 
1127         /*
1128          * Destruction of cgroup root is asynchronous, so subsystems may
1129          * still be dying after the previous unmount.  Let's drain the
1130          * dying subsystems.  We just need to ensure that the ones
1131          * unmounted previously finish dying and don't care about new ones
1132          * starting.  Testing ref liveliness is good enough.
1133          */
1134         for_each_subsys(ss, i) {
1135                 if (!(opts.subsys_mask & (1 << i)) ||
1136                     ss->root == &cgrp_dfl_root)
1137                         continue;
1138 
1139                 if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
1140                         mutex_unlock(&cgroup_mutex);
1141                         msleep(10);
1142                         ret = restart_syscall();
1143                         goto out_free;
1144                 }
1145                 cgroup_put(&ss->root->cgrp);
1146         }
1147 
1148         for_each_root(root) {
1149                 bool name_match = false;
1150 
1151                 if (root == &cgrp_dfl_root)
1152                         continue;
1153 
1154                 /*
1155                  * If we asked for a name then it must match.  Also, if
1156                  * name matches but sybsys_mask doesn't, we should fail.
1157                  * Remember whether name matched.
1158                  */
1159                 if (opts.name) {
1160                         if (strcmp(opts.name, root->name))
1161                                 continue;
1162                         name_match = true;
1163                 }
1164 
1165                 /*
1166                  * If we asked for subsystems (or explicitly for no
1167                  * subsystems) then they must match.
1168                  */
1169                 if ((opts.subsys_mask || opts.none) &&
1170                     (opts.subsys_mask != root->subsys_mask)) {
1171                         if (!name_match)
1172                                 continue;
1173                         ret = -EBUSY;
1174                         goto out_unlock;
1175                 }
1176 
1177                 if (root->flags ^ opts.flags)
1178                         pr_warn("new mount options do not match the existing superblock, will be ignored\n");
1179 
1180                 /*
1181                  * We want to reuse @root whose lifetime is governed by its
1182                  * ->cgrp.  Let's check whether @root is alive and keep it
1183                  * that way.  As cgroup_kill_sb() can happen anytime, we
1184                  * want to block it by pinning the sb so that @root doesn't
1185                  * get killed before mount is complete.
1186                  *
1187                  * With the sb pinned, tryget_live can reliably indicate
1188                  * whether @root can be reused.  If it's being killed,
1189                  * drain it.  We can use wait_queue for the wait but this
1190                  * path is super cold.  Let's just sleep a bit and retry.
1191                  */
1192                 pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
1193                 if (IS_ERR(pinned_sb) ||
1194                     !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
1195                         mutex_unlock(&cgroup_mutex);
1196                         if (!IS_ERR_OR_NULL(pinned_sb))
1197                                 deactivate_super(pinned_sb);
1198                         msleep(10);
1199                         ret = restart_syscall();
1200                         goto out_free;
1201                 }
1202 
1203                 ret = 0;
1204                 goto out_unlock;
1205         }
1206 
1207         /*
1208          * No such thing, create a new one.  name= matching without subsys
1209          * specification is allowed for already existing hierarchies but we
1210          * can't create new one without subsys specification.
1211          */
1212         if (!opts.subsys_mask && !opts.none) {
1213                 ret = -EINVAL;
1214                 goto out_unlock;
1215         }
1216 
1217         /* Hierarchies may only be created in the initial cgroup namespace. */
1218         if (ns != &init_cgroup_ns) {
1219                 ret = -EPERM;
1220                 goto out_unlock;
1221         }
1222 
1223         root = kzalloc(sizeof(*root), GFP_KERNEL);
1224         if (!root) {
1225                 ret = -ENOMEM;
1226                 goto out_unlock;
1227         }
1228         new_root = true;
1229 
1230         init_cgroup_root(root, &opts);
1231 
1232         ret = cgroup_setup_root(root, opts.subsys_mask, PERCPU_REF_INIT_DEAD);
1233         if (ret)
1234                 cgroup_free_root(root);
1235 
1236 out_unlock:
1237         mutex_unlock(&cgroup_mutex);
1238 out_free:
1239         kfree(opts.release_agent);
1240         kfree(opts.name);
1241 
1242         if (ret)
1243                 return ERR_PTR(ret);
1244 
1245         dentry = cgroup_do_mount(&cgroup_fs_type, flags, root,
1246                                  CGROUP_SUPER_MAGIC, ns);
1247 
1248         /*
1249          * There's a race window after we release cgroup_mutex and before
1250          * allocating a superblock. Make sure a concurrent process won't
1251          * be able to re-use the root during this window by delaying the
1252          * initialization of root refcnt.
1253          */
1254         if (new_root) {
1255                 mutex_lock(&cgroup_mutex);
1256                 percpu_ref_reinit(&root->cgrp.self.refcnt);
1257                 mutex_unlock(&cgroup_mutex);
1258         }
1259 
1260         /*
1261          * If @pinned_sb, we're reusing an existing root and holding an
1262          * extra ref on its sb.  Mount is complete.  Put the extra ref.
1263          */
1264         if (pinned_sb)
1265                 deactivate_super(pinned_sb);
1266 
1267         return dentry;
1268 }
1269 
1270 static int __init cgroup1_wq_init(void)
1271 {
1272         /*
1273          * Used to destroy pidlists and separate to serve as flush domain.
1274          * Cap @max_active to 1 too.
1275          */
1276         cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
1277                                                     0, 1);
1278         BUG_ON(!cgroup_pidlist_destroy_wq);
1279         return 0;
1280 }
1281 core_initcall(cgroup1_wq_init);
1282 
1283 static int __init cgroup_no_v1(char *str)
1284 {
1285         struct cgroup_subsys *ss;
1286         char *token;
1287         int i;
1288 
1289         while ((token = strsep(&str, ",")) != NULL) {
1290                 if (!*token)
1291                         continue;
1292 
1293                 if (!strcmp(token, "all")) {
1294                         cgroup_no_v1_mask = U16_MAX;
1295                         break;
1296                 }
1297 
1298                 for_each_subsys(ss, i) {
1299                         if (strcmp(token, ss->name) &&
1300                             strcmp(token, ss->legacy_name))
1301                                 continue;
1302 
1303                         cgroup_no_v1_mask |= 1 << i;
1304                 }
1305         }
1306         return 1;
1307 }
1308 __setup("cgroup_no_v1=", cgroup_no_v1);
1309 

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