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Linux/kernel/cgroup_freezer.c

  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 #include <linux/mutex.h>
 25 
 26 /*
 27  * A cgroup is freezing if any FREEZING flags are set.  FREEZING_SELF is
 28  * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
 29  * for "THAWED".  FREEZING_PARENT is set if the parent freezer is FREEZING
 30  * for whatever reason.  IOW, a cgroup has FREEZING_PARENT set if one of
 31  * its ancestors has FREEZING_SELF set.
 32  */
 33 enum freezer_state_flags {
 34         CGROUP_FREEZER_ONLINE   = (1 << 0), /* freezer is fully online */
 35         CGROUP_FREEZING_SELF    = (1 << 1), /* this freezer is freezing */
 36         CGROUP_FREEZING_PARENT  = (1 << 2), /* the parent freezer is freezing */
 37         CGROUP_FROZEN           = (1 << 3), /* this and its descendants frozen */
 38 
 39         /* mask for all FREEZING flags */
 40         CGROUP_FREEZING         = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
 41 };
 42 
 43 struct freezer {
 44         struct cgroup_subsys_state      css;
 45         unsigned int                    state;
 46 };
 47 
 48 static DEFINE_MUTEX(freezer_mutex);
 49 
 50 static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
 51 {
 52         return css ? container_of(css, struct freezer, css) : NULL;
 53 }
 54 
 55 static inline struct freezer *task_freezer(struct task_struct *task)
 56 {
 57         return css_freezer(task_css(task, freezer_cgrp_id));
 58 }
 59 
 60 static struct freezer *parent_freezer(struct freezer *freezer)
 61 {
 62         return css_freezer(freezer->css.parent);
 63 }
 64 
 65 bool cgroup_freezing(struct task_struct *task)
 66 {
 67         bool ret;
 68 
 69         rcu_read_lock();
 70         ret = task_freezer(task)->state & CGROUP_FREEZING;
 71         rcu_read_unlock();
 72 
 73         return ret;
 74 }
 75 
 76 static const char *freezer_state_strs(unsigned int state)
 77 {
 78         if (state & CGROUP_FROZEN)
 79                 return "FROZEN";
 80         if (state & CGROUP_FREEZING)
 81                 return "FREEZING";
 82         return "THAWED";
 83 };
 84 
 85 static struct cgroup_subsys_state *
 86 freezer_css_alloc(struct cgroup_subsys_state *parent_css)
 87 {
 88         struct freezer *freezer;
 89 
 90         freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
 91         if (!freezer)
 92                 return ERR_PTR(-ENOMEM);
 93 
 94         return &freezer->css;
 95 }
 96 
 97 /**
 98  * freezer_css_online - commit creation of a freezer css
 99  * @css: css being created
100  *
101  * We're committing to creation of @css.  Mark it online and inherit
102  * parent's freezing state while holding both parent's and our
103  * freezer->lock.
104  */
105 static int freezer_css_online(struct cgroup_subsys_state *css)
106 {
107         struct freezer *freezer = css_freezer(css);
108         struct freezer *parent = parent_freezer(freezer);
109 
110         mutex_lock(&freezer_mutex);
111 
112         freezer->state |= CGROUP_FREEZER_ONLINE;
113 
114         if (parent && (parent->state & CGROUP_FREEZING)) {
115                 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
116                 atomic_inc(&system_freezing_cnt);
117         }
118 
119         mutex_unlock(&freezer_mutex);
120         return 0;
121 }
122 
123 /**
124  * freezer_css_offline - initiate destruction of a freezer css
125  * @css: css being destroyed
126  *
127  * @css is going away.  Mark it dead and decrement system_freezing_count if
128  * it was holding one.
129  */
130 static void freezer_css_offline(struct cgroup_subsys_state *css)
131 {
132         struct freezer *freezer = css_freezer(css);
133 
134         mutex_lock(&freezer_mutex);
135 
136         if (freezer->state & CGROUP_FREEZING)
137                 atomic_dec(&system_freezing_cnt);
138 
139         freezer->state = 0;
140 
141         mutex_unlock(&freezer_mutex);
142 }
143 
144 static void freezer_css_free(struct cgroup_subsys_state *css)
145 {
146         kfree(css_freezer(css));
147 }
148 
149 /*
150  * Tasks can be migrated into a different freezer anytime regardless of its
151  * current state.  freezer_attach() is responsible for making new tasks
152  * conform to the current state.
153  *
154  * Freezer state changes and task migration are synchronized via
155  * @freezer->lock.  freezer_attach() makes the new tasks conform to the
156  * current state and all following state changes can see the new tasks.
157  */
158 static void freezer_attach(struct cgroup_taskset *tset)
159 {
160         struct task_struct *task;
161         struct cgroup_subsys_state *new_css;
162 
163         mutex_lock(&freezer_mutex);
164 
165         /*
166          * Make the new tasks conform to the current state of @new_css.
167          * For simplicity, when migrating any task to a FROZEN cgroup, we
168          * revert it to FREEZING and let update_if_frozen() determine the
169          * correct state later.
170          *
171          * Tasks in @tset are on @new_css but may not conform to its
172          * current state before executing the following - !frozen tasks may
173          * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
174          */
175         cgroup_taskset_for_each(task, new_css, tset) {
176                 struct freezer *freezer = css_freezer(new_css);
177 
178                 if (!(freezer->state & CGROUP_FREEZING)) {
179                         __thaw_task(task);
180                 } else {
181                         freeze_task(task);
182                         /* clear FROZEN and propagate upwards */
183                         while (freezer && (freezer->state & CGROUP_FROZEN)) {
184                                 freezer->state &= ~CGROUP_FROZEN;
185                                 freezer = parent_freezer(freezer);
186                         }
187                 }
188         }
189 
190         mutex_unlock(&freezer_mutex);
191 }
192 
193 /**
194  * freezer_fork - cgroup post fork callback
195  * @task: a task which has just been forked
196  *
197  * @task has just been created and should conform to the current state of
198  * the cgroup_freezer it belongs to.  This function may race against
199  * freezer_attach().  Losing to freezer_attach() means that we don't have
200  * to do anything as freezer_attach() will put @task into the appropriate
201  * state.
202  */
203 static void freezer_fork(struct task_struct *task)
204 {
205         struct freezer *freezer;
206 
207         /*
208          * The root cgroup is non-freezable, so we can skip locking the
209          * freezer.  This is safe regardless of race with task migration.
210          * If we didn't race or won, skipping is obviously the right thing
211          * to do.  If we lost and root is the new cgroup, noop is still the
212          * right thing to do.
213          */
214         if (task_css_is_root(task, freezer_cgrp_id))
215                 return;
216 
217         mutex_lock(&freezer_mutex);
218         rcu_read_lock();
219 
220         freezer = task_freezer(task);
221         if (freezer->state & CGROUP_FREEZING)
222                 freeze_task(task);
223 
224         rcu_read_unlock();
225         mutex_unlock(&freezer_mutex);
226 }
227 
228 /**
229  * update_if_frozen - update whether a cgroup finished freezing
230  * @css: css of interest
231  *
232  * Once FREEZING is initiated, transition to FROZEN is lazily updated by
233  * calling this function.  If the current state is FREEZING but not FROZEN,
234  * this function checks whether all tasks of this cgroup and the descendant
235  * cgroups finished freezing and, if so, sets FROZEN.
236  *
237  * The caller is responsible for grabbing RCU read lock and calling
238  * update_if_frozen() on all descendants prior to invoking this function.
239  *
240  * Task states and freezer state might disagree while tasks are being
241  * migrated into or out of @css, so we can't verify task states against
242  * @freezer state here.  See freezer_attach() for details.
243  */
244 static void update_if_frozen(struct cgroup_subsys_state *css)
245 {
246         struct freezer *freezer = css_freezer(css);
247         struct cgroup_subsys_state *pos;
248         struct css_task_iter it;
249         struct task_struct *task;
250 
251         lockdep_assert_held(&freezer_mutex);
252 
253         if (!(freezer->state & CGROUP_FREEZING) ||
254             (freezer->state & CGROUP_FROZEN))
255                 return;
256 
257         /* are all (live) children frozen? */
258         rcu_read_lock();
259         css_for_each_child(pos, css) {
260                 struct freezer *child = css_freezer(pos);
261 
262                 if ((child->state & CGROUP_FREEZER_ONLINE) &&
263                     !(child->state & CGROUP_FROZEN)) {
264                         rcu_read_unlock();
265                         return;
266                 }
267         }
268         rcu_read_unlock();
269 
270         /* are all tasks frozen? */
271         css_task_iter_start(css, &it);
272 
273         while ((task = css_task_iter_next(&it))) {
274                 if (freezing(task)) {
275                         /*
276                          * freezer_should_skip() indicates that the task
277                          * should be skipped when determining freezing
278                          * completion.  Consider it frozen in addition to
279                          * the usual frozen condition.
280                          */
281                         if (!frozen(task) && !freezer_should_skip(task))
282                                 goto out_iter_end;
283                 }
284         }
285 
286         freezer->state |= CGROUP_FROZEN;
287 out_iter_end:
288         css_task_iter_end(&it);
289 }
290 
291 static int freezer_read(struct seq_file *m, void *v)
292 {
293         struct cgroup_subsys_state *css = seq_css(m), *pos;
294 
295         mutex_lock(&freezer_mutex);
296         rcu_read_lock();
297 
298         /* update states bottom-up */
299         css_for_each_descendant_post(pos, css) {
300                 if (!css_tryget_online(pos))
301                         continue;
302                 rcu_read_unlock();
303 
304                 update_if_frozen(pos);
305 
306                 rcu_read_lock();
307                 css_put(pos);
308         }
309 
310         rcu_read_unlock();
311         mutex_unlock(&freezer_mutex);
312 
313         seq_puts(m, freezer_state_strs(css_freezer(css)->state));
314         seq_putc(m, '\n');
315         return 0;
316 }
317 
318 static void freeze_cgroup(struct freezer *freezer)
319 {
320         struct css_task_iter it;
321         struct task_struct *task;
322 
323         css_task_iter_start(&freezer->css, &it);
324         while ((task = css_task_iter_next(&it)))
325                 freeze_task(task);
326         css_task_iter_end(&it);
327 }
328 
329 static void unfreeze_cgroup(struct freezer *freezer)
330 {
331         struct css_task_iter it;
332         struct task_struct *task;
333 
334         css_task_iter_start(&freezer->css, &it);
335         while ((task = css_task_iter_next(&it)))
336                 __thaw_task(task);
337         css_task_iter_end(&it);
338 }
339 
340 /**
341  * freezer_apply_state - apply state change to a single cgroup_freezer
342  * @freezer: freezer to apply state change to
343  * @freeze: whether to freeze or unfreeze
344  * @state: CGROUP_FREEZING_* flag to set or clear
345  *
346  * Set or clear @state on @cgroup according to @freeze, and perform
347  * freezing or thawing as necessary.
348  */
349 static void freezer_apply_state(struct freezer *freezer, bool freeze,
350                                 unsigned int state)
351 {
352         /* also synchronizes against task migration, see freezer_attach() */
353         lockdep_assert_held(&freezer_mutex);
354 
355         if (!(freezer->state & CGROUP_FREEZER_ONLINE))
356                 return;
357 
358         if (freeze) {
359                 if (!(freezer->state & CGROUP_FREEZING))
360                         atomic_inc(&system_freezing_cnt);
361                 freezer->state |= state;
362                 freeze_cgroup(freezer);
363         } else {
364                 bool was_freezing = freezer->state & CGROUP_FREEZING;
365 
366                 freezer->state &= ~state;
367 
368                 if (!(freezer->state & CGROUP_FREEZING)) {
369                         if (was_freezing)
370                                 atomic_dec(&system_freezing_cnt);
371                         freezer->state &= ~CGROUP_FROZEN;
372                         unfreeze_cgroup(freezer);
373                 }
374         }
375 }
376 
377 /**
378  * freezer_change_state - change the freezing state of a cgroup_freezer
379  * @freezer: freezer of interest
380  * @freeze: whether to freeze or thaw
381  *
382  * Freeze or thaw @freezer according to @freeze.  The operations are
383  * recursive - all descendants of @freezer will be affected.
384  */
385 static void freezer_change_state(struct freezer *freezer, bool freeze)
386 {
387         struct cgroup_subsys_state *pos;
388 
389         /*
390          * Update all its descendants in pre-order traversal.  Each
391          * descendant will try to inherit its parent's FREEZING state as
392          * CGROUP_FREEZING_PARENT.
393          */
394         mutex_lock(&freezer_mutex);
395         rcu_read_lock();
396         css_for_each_descendant_pre(pos, &freezer->css) {
397                 struct freezer *pos_f = css_freezer(pos);
398                 struct freezer *parent = parent_freezer(pos_f);
399 
400                 if (!css_tryget_online(pos))
401                         continue;
402                 rcu_read_unlock();
403 
404                 if (pos_f == freezer)
405                         freezer_apply_state(pos_f, freeze,
406                                             CGROUP_FREEZING_SELF);
407                 else
408                         freezer_apply_state(pos_f,
409                                             parent->state & CGROUP_FREEZING,
410                                             CGROUP_FREEZING_PARENT);
411 
412                 rcu_read_lock();
413                 css_put(pos);
414         }
415         rcu_read_unlock();
416         mutex_unlock(&freezer_mutex);
417 }
418 
419 static ssize_t freezer_write(struct kernfs_open_file *of,
420                              char *buf, size_t nbytes, loff_t off)
421 {
422         bool freeze;
423 
424         buf = strstrip(buf);
425 
426         if (strcmp(buf, freezer_state_strs(0)) == 0)
427                 freeze = false;
428         else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
429                 freeze = true;
430         else
431                 return -EINVAL;
432 
433         freezer_change_state(css_freezer(of_css(of)), freeze);
434         return nbytes;
435 }
436 
437 static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
438                                       struct cftype *cft)
439 {
440         struct freezer *freezer = css_freezer(css);
441 
442         return (bool)(freezer->state & CGROUP_FREEZING_SELF);
443 }
444 
445 static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
446                                         struct cftype *cft)
447 {
448         struct freezer *freezer = css_freezer(css);
449 
450         return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
451 }
452 
453 static struct cftype files[] = {
454         {
455                 .name = "state",
456                 .flags = CFTYPE_NOT_ON_ROOT,
457                 .seq_show = freezer_read,
458                 .write = freezer_write,
459         },
460         {
461                 .name = "self_freezing",
462                 .flags = CFTYPE_NOT_ON_ROOT,
463                 .read_u64 = freezer_self_freezing_read,
464         },
465         {
466                 .name = "parent_freezing",
467                 .flags = CFTYPE_NOT_ON_ROOT,
468                 .read_u64 = freezer_parent_freezing_read,
469         },
470         { }     /* terminate */
471 };
472 
473 struct cgroup_subsys freezer_cgrp_subsys = {
474         .css_alloc      = freezer_css_alloc,
475         .css_online     = freezer_css_online,
476         .css_offline    = freezer_css_offline,
477         .css_free       = freezer_css_free,
478         .attach         = freezer_attach,
479         .fork           = freezer_fork,
480         .legacy_cftypes = files,
481 };
482 

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