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Linux/kernel/cgroup_freezer.c

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  1 /*
  2  * cgroup_freezer.c -  control group freezer subsystem
  3  *
  4  * Copyright IBM Corporation, 2007
  5  *
  6  * Author : Cedric Le Goater <clg@fr.ibm.com>
  7  *
  8  * This program is free software; you can redistribute it and/or modify it
  9  * under the terms of version 2.1 of the GNU Lesser General Public License
 10  * as published by the Free Software Foundation.
 11  *
 12  * This program is distributed in the hope that it would be useful, but
 13  * WITHOUT ANY WARRANTY; without even the implied warranty of
 14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 15  */
 16 
 17 #include <linux/export.h>
 18 #include <linux/slab.h>
 19 #include <linux/cgroup.h>
 20 #include <linux/fs.h>
 21 #include <linux/uaccess.h>
 22 #include <linux/freezer.h>
 23 #include <linux/seq_file.h>
 24 
 25 /*
 26  * A cgroup is freezing if any FREEZING flags are set.  FREEZING_SELF is
 27  * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
 28  * for "THAWED".  FREEZING_PARENT is set if the parent freezer is FREEZING
 29  * for whatever reason.  IOW, a cgroup has FREEZING_PARENT set if one of
 30  * its ancestors has FREEZING_SELF set.
 31  */
 32 enum freezer_state_flags {
 33         CGROUP_FREEZER_ONLINE   = (1 << 0), /* freezer is fully online */
 34         CGROUP_FREEZING_SELF    = (1 << 1), /* this freezer is freezing */
 35         CGROUP_FREEZING_PARENT  = (1 << 2), /* the parent freezer is freezing */
 36         CGROUP_FROZEN           = (1 << 3), /* this and its descendants frozen */
 37 
 38         /* mask for all FREEZING flags */
 39         CGROUP_FREEZING         = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
 40 };
 41 
 42 struct freezer {
 43         struct cgroup_subsys_state      css;
 44         unsigned int                    state;
 45         spinlock_t                      lock;
 46 };
 47 
 48 static inline struct freezer *cgroup_freezer(struct cgroup *cgroup)
 49 {
 50         return container_of(cgroup_subsys_state(cgroup, freezer_subsys_id),
 51                             struct freezer, css);
 52 }
 53 
 54 static inline struct freezer *task_freezer(struct task_struct *task)
 55 {
 56         return container_of(task_subsys_state(task, freezer_subsys_id),
 57                             struct freezer, css);
 58 }
 59 
 60 static struct freezer *parent_freezer(struct freezer *freezer)
 61 {
 62         struct cgroup *pcg = freezer->css.cgroup->parent;
 63 
 64         if (pcg)
 65                 return cgroup_freezer(pcg);
 66         return NULL;
 67 }
 68 
 69 bool cgroup_freezing(struct task_struct *task)
 70 {
 71         bool ret;
 72 
 73         rcu_read_lock();
 74         ret = task_freezer(task)->state & CGROUP_FREEZING;
 75         rcu_read_unlock();
 76 
 77         return ret;
 78 }
 79 
 80 /*
 81  * cgroups_write_string() limits the size of freezer state strings to
 82  * CGROUP_LOCAL_BUFFER_SIZE
 83  */
 84 static const char *freezer_state_strs(unsigned int state)
 85 {
 86         if (state & CGROUP_FROZEN)
 87                 return "FROZEN";
 88         if (state & CGROUP_FREEZING)
 89                 return "FREEZING";
 90         return "THAWED";
 91 };
 92 
 93 struct cgroup_subsys freezer_subsys;
 94 
 95 static struct cgroup_subsys_state *freezer_css_alloc(struct cgroup *cgroup)
 96 {
 97         struct freezer *freezer;
 98 
 99         freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
100         if (!freezer)
101                 return ERR_PTR(-ENOMEM);
102 
103         spin_lock_init(&freezer->lock);
104         return &freezer->css;
105 }
106 
107 /**
108  * freezer_css_online - commit creation of a freezer cgroup
109  * @cgroup: cgroup being created
110  *
111  * We're committing to creation of @cgroup.  Mark it online and inherit
112  * parent's freezing state while holding both parent's and our
113  * freezer->lock.
114  */
115 static int freezer_css_online(struct cgroup *cgroup)
116 {
117         struct freezer *freezer = cgroup_freezer(cgroup);
118         struct freezer *parent = parent_freezer(freezer);
119 
120         /*
121          * The following double locking and freezing state inheritance
122          * guarantee that @cgroup can never escape ancestors' freezing
123          * states.  See cgroup_for_each_descendant_pre() for details.
124          */
125         if (parent)
126                 spin_lock_irq(&parent->lock);
127         spin_lock_nested(&freezer->lock, SINGLE_DEPTH_NESTING);
128 
129         freezer->state |= CGROUP_FREEZER_ONLINE;
130 
131         if (parent && (parent->state & CGROUP_FREEZING)) {
132                 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
133                 atomic_inc(&system_freezing_cnt);
134         }
135 
136         spin_unlock(&freezer->lock);
137         if (parent)
138                 spin_unlock_irq(&parent->lock);
139 
140         return 0;
141 }
142 
143 /**
144  * freezer_css_offline - initiate destruction of @cgroup
145  * @cgroup: cgroup being destroyed
146  *
147  * @cgroup is going away.  Mark it dead and decrement system_freezing_count
148  * if it was holding one.
149  */
150 static void freezer_css_offline(struct cgroup *cgroup)
151 {
152         struct freezer *freezer = cgroup_freezer(cgroup);
153 
154         spin_lock_irq(&freezer->lock);
155 
156         if (freezer->state & CGROUP_FREEZING)
157                 atomic_dec(&system_freezing_cnt);
158 
159         freezer->state = 0;
160 
161         spin_unlock_irq(&freezer->lock);
162 }
163 
164 static void freezer_css_free(struct cgroup *cgroup)
165 {
166         kfree(cgroup_freezer(cgroup));
167 }
168 
169 /*
170  * Tasks can be migrated into a different freezer anytime regardless of its
171  * current state.  freezer_attach() is responsible for making new tasks
172  * conform to the current state.
173  *
174  * Freezer state changes and task migration are synchronized via
175  * @freezer->lock.  freezer_attach() makes the new tasks conform to the
176  * current state and all following state changes can see the new tasks.
177  */
178 static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
179 {
180         struct freezer *freezer = cgroup_freezer(new_cgrp);
181         struct task_struct *task;
182         bool clear_frozen = false;
183 
184         spin_lock_irq(&freezer->lock);
185 
186         /*
187          * Make the new tasks conform to the current state of @new_cgrp.
188          * For simplicity, when migrating any task to a FROZEN cgroup, we
189          * revert it to FREEZING and let update_if_frozen() determine the
190          * correct state later.
191          *
192          * Tasks in @tset are on @new_cgrp but may not conform to its
193          * current state before executing the following - !frozen tasks may
194          * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
195          */
196         cgroup_taskset_for_each(task, new_cgrp, tset) {
197                 if (!(freezer->state & CGROUP_FREEZING)) {
198                         __thaw_task(task);
199                 } else {
200                         freeze_task(task);
201                         freezer->state &= ~CGROUP_FROZEN;
202                         clear_frozen = true;
203                 }
204         }
205 
206         spin_unlock_irq(&freezer->lock);
207 
208         /*
209          * Propagate FROZEN clearing upwards.  We may race with
210          * update_if_frozen(), but as long as both work bottom-up, either
211          * update_if_frozen() sees child's FROZEN cleared or we clear the
212          * parent's FROZEN later.  No parent w/ !FROZEN children can be
213          * left FROZEN.
214          */
215         while (clear_frozen && (freezer = parent_freezer(freezer))) {
216                 spin_lock_irq(&freezer->lock);
217                 freezer->state &= ~CGROUP_FROZEN;
218                 clear_frozen = freezer->state & CGROUP_FREEZING;
219                 spin_unlock_irq(&freezer->lock);
220         }
221 }
222 
223 static void freezer_fork(struct task_struct *task)
224 {
225         struct freezer *freezer;
226 
227         rcu_read_lock();
228         freezer = task_freezer(task);
229 
230         /*
231          * The root cgroup is non-freezable, so we can skip the
232          * following check.
233          */
234         if (!freezer->css.cgroup->parent)
235                 goto out;
236 
237         spin_lock_irq(&freezer->lock);
238         if (freezer->state & CGROUP_FREEZING)
239                 freeze_task(task);
240         spin_unlock_irq(&freezer->lock);
241 out:
242         rcu_read_unlock();
243 }
244 
245 /**
246  * update_if_frozen - update whether a cgroup finished freezing
247  * @cgroup: cgroup of interest
248  *
249  * Once FREEZING is initiated, transition to FROZEN is lazily updated by
250  * calling this function.  If the current state is FREEZING but not FROZEN,
251  * this function checks whether all tasks of this cgroup and the descendant
252  * cgroups finished freezing and, if so, sets FROZEN.
253  *
254  * The caller is responsible for grabbing RCU read lock and calling
255  * update_if_frozen() on all descendants prior to invoking this function.
256  *
257  * Task states and freezer state might disagree while tasks are being
258  * migrated into or out of @cgroup, so we can't verify task states against
259  * @freezer state here.  See freezer_attach() for details.
260  */
261 static void update_if_frozen(struct cgroup *cgroup)
262 {
263         struct freezer *freezer = cgroup_freezer(cgroup);
264         struct cgroup *pos;
265         struct cgroup_iter it;
266         struct task_struct *task;
267 
268         WARN_ON_ONCE(!rcu_read_lock_held());
269 
270         spin_lock_irq(&freezer->lock);
271 
272         if (!(freezer->state & CGROUP_FREEZING) ||
273             (freezer->state & CGROUP_FROZEN))
274                 goto out_unlock;
275 
276         /* are all (live) children frozen? */
277         cgroup_for_each_child(pos, cgroup) {
278                 struct freezer *child = cgroup_freezer(pos);
279 
280                 if ((child->state & CGROUP_FREEZER_ONLINE) &&
281                     !(child->state & CGROUP_FROZEN))
282                         goto out_unlock;
283         }
284 
285         /* are all tasks frozen? */
286         cgroup_iter_start(cgroup, &it);
287 
288         while ((task = cgroup_iter_next(cgroup, &it))) {
289                 if (freezing(task)) {
290                         /*
291                          * freezer_should_skip() indicates that the task
292                          * should be skipped when determining freezing
293                          * completion.  Consider it frozen in addition to
294                          * the usual frozen condition.
295                          */
296                         if (!frozen(task) && !freezer_should_skip(task))
297                                 goto out_iter_end;
298                 }
299         }
300 
301         freezer->state |= CGROUP_FROZEN;
302 out_iter_end:
303         cgroup_iter_end(cgroup, &it);
304 out_unlock:
305         spin_unlock_irq(&freezer->lock);
306 }
307 
308 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
309                         struct seq_file *m)
310 {
311         struct cgroup *pos;
312 
313         rcu_read_lock();
314 
315         /* update states bottom-up */
316         cgroup_for_each_descendant_post(pos, cgroup)
317                 update_if_frozen(pos);
318         update_if_frozen(cgroup);
319 
320         rcu_read_unlock();
321 
322         seq_puts(m, freezer_state_strs(cgroup_freezer(cgroup)->state));
323         seq_putc(m, '\n');
324         return 0;
325 }
326 
327 static void freeze_cgroup(struct freezer *freezer)
328 {
329         struct cgroup *cgroup = freezer->css.cgroup;
330         struct cgroup_iter it;
331         struct task_struct *task;
332 
333         cgroup_iter_start(cgroup, &it);
334         while ((task = cgroup_iter_next(cgroup, &it)))
335                 freeze_task(task);
336         cgroup_iter_end(cgroup, &it);
337 }
338 
339 static void unfreeze_cgroup(struct freezer *freezer)
340 {
341         struct cgroup *cgroup = freezer->css.cgroup;
342         struct cgroup_iter it;
343         struct task_struct *task;
344 
345         cgroup_iter_start(cgroup, &it);
346         while ((task = cgroup_iter_next(cgroup, &it)))
347                 __thaw_task(task);
348         cgroup_iter_end(cgroup, &it);
349 }
350 
351 /**
352  * freezer_apply_state - apply state change to a single cgroup_freezer
353  * @freezer: freezer to apply state change to
354  * @freeze: whether to freeze or unfreeze
355  * @state: CGROUP_FREEZING_* flag to set or clear
356  *
357  * Set or clear @state on @cgroup according to @freeze, and perform
358  * freezing or thawing as necessary.
359  */
360 static void freezer_apply_state(struct freezer *freezer, bool freeze,
361                                 unsigned int state)
362 {
363         /* also synchronizes against task migration, see freezer_attach() */
364         lockdep_assert_held(&freezer->lock);
365 
366         if (!(freezer->state & CGROUP_FREEZER_ONLINE))
367                 return;
368 
369         if (freeze) {
370                 if (!(freezer->state & CGROUP_FREEZING))
371                         atomic_inc(&system_freezing_cnt);
372                 freezer->state |= state;
373                 freeze_cgroup(freezer);
374         } else {
375                 bool was_freezing = freezer->state & CGROUP_FREEZING;
376 
377                 freezer->state &= ~state;
378 
379                 if (!(freezer->state & CGROUP_FREEZING)) {
380                         if (was_freezing)
381                                 atomic_dec(&system_freezing_cnt);
382                         freezer->state &= ~CGROUP_FROZEN;
383                         unfreeze_cgroup(freezer);
384                 }
385         }
386 }
387 
388 /**
389  * freezer_change_state - change the freezing state of a cgroup_freezer
390  * @freezer: freezer of interest
391  * @freeze: whether to freeze or thaw
392  *
393  * Freeze or thaw @freezer according to @freeze.  The operations are
394  * recursive - all descendants of @freezer will be affected.
395  */
396 static void freezer_change_state(struct freezer *freezer, bool freeze)
397 {
398         struct cgroup *pos;
399 
400         /* update @freezer */
401         spin_lock_irq(&freezer->lock);
402         freezer_apply_state(freezer, freeze, CGROUP_FREEZING_SELF);
403         spin_unlock_irq(&freezer->lock);
404 
405         /*
406          * Update all its descendants in pre-order traversal.  Each
407          * descendant will try to inherit its parent's FREEZING state as
408          * CGROUP_FREEZING_PARENT.
409          */
410         rcu_read_lock();
411         cgroup_for_each_descendant_pre(pos, freezer->css.cgroup) {
412                 struct freezer *pos_f = cgroup_freezer(pos);
413                 struct freezer *parent = parent_freezer(pos_f);
414 
415                 /*
416                  * Our update to @parent->state is already visible which is
417                  * all we need.  No need to lock @parent.  For more info on
418                  * synchronization, see freezer_post_create().
419                  */
420                 spin_lock_irq(&pos_f->lock);
421                 freezer_apply_state(pos_f, parent->state & CGROUP_FREEZING,
422                                     CGROUP_FREEZING_PARENT);
423                 spin_unlock_irq(&pos_f->lock);
424         }
425         rcu_read_unlock();
426 }
427 
428 static int freezer_write(struct cgroup *cgroup, struct cftype *cft,
429                          const char *buffer)
430 {
431         bool freeze;
432 
433         if (strcmp(buffer, freezer_state_strs(0)) == 0)
434                 freeze = false;
435         else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
436                 freeze = true;
437         else
438                 return -EINVAL;
439 
440         freezer_change_state(cgroup_freezer(cgroup), freeze);
441         return 0;
442 }
443 
444 static u64 freezer_self_freezing_read(struct cgroup *cgroup, struct cftype *cft)
445 {
446         struct freezer *freezer = cgroup_freezer(cgroup);
447 
448         return (bool)(freezer->state & CGROUP_FREEZING_SELF);
449 }
450 
451 static u64 freezer_parent_freezing_read(struct cgroup *cgroup, struct cftype *cft)
452 {
453         struct freezer *freezer = cgroup_freezer(cgroup);
454 
455         return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
456 }
457 
458 static struct cftype files[] = {
459         {
460                 .name = "state",
461                 .flags = CFTYPE_NOT_ON_ROOT,
462                 .read_seq_string = freezer_read,
463                 .write_string = freezer_write,
464         },
465         {
466                 .name = "self_freezing",
467                 .flags = CFTYPE_NOT_ON_ROOT,
468                 .read_u64 = freezer_self_freezing_read,
469         },
470         {
471                 .name = "parent_freezing",
472                 .flags = CFTYPE_NOT_ON_ROOT,
473                 .read_u64 = freezer_parent_freezing_read,
474         },
475         { }     /* terminate */
476 };
477 
478 struct cgroup_subsys freezer_subsys = {
479         .name           = "freezer",
480         .css_alloc      = freezer_css_alloc,
481         .css_online     = freezer_css_online,
482         .css_offline    = freezer_css_offline,
483         .css_free       = freezer_css_free,
484         .subsys_id      = freezer_subsys_id,
485         .attach         = freezer_attach,
486         .fork           = freezer_fork,
487         .base_cftypes   = files,
488 };
489 

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