2 * cgroup_freezer.c - control group freezer subsystem
4 * Copyright IBM Corporation, 2007
6 * Author : Cedric Le Goater <clg@fr.ibm.com>
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.
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.
17 #include <linux/export.h>
18 #include <linux/slab.h>
19 #include <linux/cgroup.h>
21 #include <linux/uaccess.h>
22 #include <linux/freezer.h>
23 #include <linux/seq_file.h>
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.
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 */
38 /* mask for all FREEZING flags */
39 CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
43 struct cgroup_subsys_state css;
48 static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
50 return css ? container_of(css, struct freezer, css) : NULL;
53 static inline struct freezer *cgroup_freezer(struct cgroup *cgroup)
55 return css_freezer(cgroup_css(cgroup, freezer_subsys_id));
58 static inline struct freezer *task_freezer(struct task_struct *task)
60 return css_freezer(task_css(task, freezer_subsys_id));
63 static struct freezer *parent_freezer(struct freezer *freezer)
65 return css_freezer(css_parent(&freezer->css));
68 bool cgroup_freezing(struct task_struct *task)
73 ret = task_freezer(task)->state & CGROUP_FREEZING;
80 * cgroups_write_string() limits the size of freezer state strings to
81 * CGROUP_LOCAL_BUFFER_SIZE
83 static const char *freezer_state_strs(unsigned int state)
85 if (state & CGROUP_FROZEN)
87 if (state & CGROUP_FREEZING)
92 struct cgroup_subsys freezer_subsys;
94 static struct cgroup_subsys_state *freezer_css_alloc(struct cgroup *cgroup)
96 struct freezer *freezer;
98 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
100 return ERR_PTR(-ENOMEM);
102 spin_lock_init(&freezer->lock);
103 return &freezer->css;
107 * freezer_css_online - commit creation of a freezer cgroup
108 * @cgroup: cgroup being created
110 * We're committing to creation of @cgroup. Mark it online and inherit
111 * parent's freezing state while holding both parent's and our
114 static int freezer_css_online(struct cgroup *cgroup)
116 struct freezer *freezer = cgroup_freezer(cgroup);
117 struct freezer *parent = parent_freezer(freezer);
120 * The following double locking and freezing state inheritance
121 * guarantee that @cgroup can never escape ancestors' freezing
122 * states. See cgroup_for_each_descendant_pre() for details.
125 spin_lock_irq(&parent->lock);
126 spin_lock_nested(&freezer->lock, SINGLE_DEPTH_NESTING);
128 freezer->state |= CGROUP_FREEZER_ONLINE;
130 if (parent && (parent->state & CGROUP_FREEZING)) {
131 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
132 atomic_inc(&system_freezing_cnt);
135 spin_unlock(&freezer->lock);
137 spin_unlock_irq(&parent->lock);
143 * freezer_css_offline - initiate destruction of @cgroup
144 * @cgroup: cgroup being destroyed
146 * @cgroup is going away. Mark it dead and decrement system_freezing_count
147 * if it was holding one.
149 static void freezer_css_offline(struct cgroup *cgroup)
151 struct freezer *freezer = cgroup_freezer(cgroup);
153 spin_lock_irq(&freezer->lock);
155 if (freezer->state & CGROUP_FREEZING)
156 atomic_dec(&system_freezing_cnt);
160 spin_unlock_irq(&freezer->lock);
163 static void freezer_css_free(struct cgroup *cgroup)
165 kfree(cgroup_freezer(cgroup));
169 * Tasks can be migrated into a different freezer anytime regardless of its
170 * current state. freezer_attach() is responsible for making new tasks
171 * conform to the current state.
173 * Freezer state changes and task migration are synchronized via
174 * @freezer->lock. freezer_attach() makes the new tasks conform to the
175 * current state and all following state changes can see the new tasks.
177 static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
179 struct freezer *freezer = cgroup_freezer(new_cgrp);
180 struct task_struct *task;
181 bool clear_frozen = false;
183 spin_lock_irq(&freezer->lock);
186 * Make the new tasks conform to the current state of @new_cgrp.
187 * For simplicity, when migrating any task to a FROZEN cgroup, we
188 * revert it to FREEZING and let update_if_frozen() determine the
189 * correct state later.
191 * Tasks in @tset are on @new_cgrp but may not conform to its
192 * current state before executing the following - !frozen tasks may
193 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
195 cgroup_taskset_for_each(task, new_cgrp, tset) {
196 if (!(freezer->state & CGROUP_FREEZING)) {
200 freezer->state &= ~CGROUP_FROZEN;
205 spin_unlock_irq(&freezer->lock);
208 * Propagate FROZEN clearing upwards. We may race with
209 * update_if_frozen(), but as long as both work bottom-up, either
210 * update_if_frozen() sees child's FROZEN cleared or we clear the
211 * parent's FROZEN later. No parent w/ !FROZEN children can be
214 while (clear_frozen && (freezer = parent_freezer(freezer))) {
215 spin_lock_irq(&freezer->lock);
216 freezer->state &= ~CGROUP_FROZEN;
217 clear_frozen = freezer->state & CGROUP_FREEZING;
218 spin_unlock_irq(&freezer->lock);
222 static void freezer_fork(struct task_struct *task)
224 struct freezer *freezer;
227 freezer = task_freezer(task);
230 * The root cgroup is non-freezable, so we can skip the
233 if (!parent_freezer(freezer))
236 spin_lock_irq(&freezer->lock);
237 if (freezer->state & CGROUP_FREEZING)
239 spin_unlock_irq(&freezer->lock);
245 * update_if_frozen - update whether a cgroup finished freezing
246 * @cgroup: cgroup of interest
248 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
249 * calling this function. If the current state is FREEZING but not FROZEN,
250 * this function checks whether all tasks of this cgroup and the descendant
251 * cgroups finished freezing and, if so, sets FROZEN.
253 * The caller is responsible for grabbing RCU read lock and calling
254 * update_if_frozen() on all descendants prior to invoking this function.
256 * Task states and freezer state might disagree while tasks are being
257 * migrated into or out of @cgroup, so we can't verify task states against
258 * @freezer state here. See freezer_attach() for details.
260 static void update_if_frozen(struct cgroup *cgroup)
262 struct freezer *freezer = cgroup_freezer(cgroup);
264 struct cgroup_iter it;
265 struct task_struct *task;
267 WARN_ON_ONCE(!rcu_read_lock_held());
269 spin_lock_irq(&freezer->lock);
271 if (!(freezer->state & CGROUP_FREEZING) ||
272 (freezer->state & CGROUP_FROZEN))
275 /* are all (live) children frozen? */
276 cgroup_for_each_child(pos, cgroup) {
277 struct freezer *child = cgroup_freezer(pos);
279 if ((child->state & CGROUP_FREEZER_ONLINE) &&
280 !(child->state & CGROUP_FROZEN))
284 /* are all tasks frozen? */
285 cgroup_iter_start(cgroup, &it);
287 while ((task = cgroup_iter_next(cgroup, &it))) {
288 if (freezing(task)) {
290 * freezer_should_skip() indicates that the task
291 * should be skipped when determining freezing
292 * completion. Consider it frozen in addition to
293 * the usual frozen condition.
295 if (!frozen(task) && !freezer_should_skip(task))
300 freezer->state |= CGROUP_FROZEN;
302 cgroup_iter_end(cgroup, &it);
304 spin_unlock_irq(&freezer->lock);
307 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
314 /* update states bottom-up */
315 cgroup_for_each_descendant_post(pos, cgroup)
316 update_if_frozen(pos);
317 update_if_frozen(cgroup);
321 seq_puts(m, freezer_state_strs(cgroup_freezer(cgroup)->state));
326 static void freeze_cgroup(struct freezer *freezer)
328 struct cgroup *cgroup = freezer->css.cgroup;
329 struct cgroup_iter it;
330 struct task_struct *task;
332 cgroup_iter_start(cgroup, &it);
333 while ((task = cgroup_iter_next(cgroup, &it)))
335 cgroup_iter_end(cgroup, &it);
338 static void unfreeze_cgroup(struct freezer *freezer)
340 struct cgroup *cgroup = freezer->css.cgroup;
341 struct cgroup_iter it;
342 struct task_struct *task;
344 cgroup_iter_start(cgroup, &it);
345 while ((task = cgroup_iter_next(cgroup, &it)))
347 cgroup_iter_end(cgroup, &it);
351 * freezer_apply_state - apply state change to a single cgroup_freezer
352 * @freezer: freezer to apply state change to
353 * @freeze: whether to freeze or unfreeze
354 * @state: CGROUP_FREEZING_* flag to set or clear
356 * Set or clear @state on @cgroup according to @freeze, and perform
357 * freezing or thawing as necessary.
359 static void freezer_apply_state(struct freezer *freezer, bool freeze,
362 /* also synchronizes against task migration, see freezer_attach() */
363 lockdep_assert_held(&freezer->lock);
365 if (!(freezer->state & CGROUP_FREEZER_ONLINE))
369 if (!(freezer->state & CGROUP_FREEZING))
370 atomic_inc(&system_freezing_cnt);
371 freezer->state |= state;
372 freeze_cgroup(freezer);
374 bool was_freezing = freezer->state & CGROUP_FREEZING;
376 freezer->state &= ~state;
378 if (!(freezer->state & CGROUP_FREEZING)) {
380 atomic_dec(&system_freezing_cnt);
381 freezer->state &= ~CGROUP_FROZEN;
382 unfreeze_cgroup(freezer);
388 * freezer_change_state - change the freezing state of a cgroup_freezer
389 * @freezer: freezer of interest
390 * @freeze: whether to freeze or thaw
392 * Freeze or thaw @freezer according to @freeze. The operations are
393 * recursive - all descendants of @freezer will be affected.
395 static void freezer_change_state(struct freezer *freezer, bool freeze)
399 /* update @freezer */
400 spin_lock_irq(&freezer->lock);
401 freezer_apply_state(freezer, freeze, CGROUP_FREEZING_SELF);
402 spin_unlock_irq(&freezer->lock);
405 * Update all its descendants in pre-order traversal. Each
406 * descendant will try to inherit its parent's FREEZING state as
407 * CGROUP_FREEZING_PARENT.
410 cgroup_for_each_descendant_pre(pos, freezer->css.cgroup) {
411 struct freezer *pos_f = cgroup_freezer(pos);
412 struct freezer *parent = parent_freezer(pos_f);
415 * Our update to @parent->state is already visible which is
416 * all we need. No need to lock @parent. For more info on
417 * synchronization, see freezer_post_create().
419 spin_lock_irq(&pos_f->lock);
420 freezer_apply_state(pos_f, parent->state & CGROUP_FREEZING,
421 CGROUP_FREEZING_PARENT);
422 spin_unlock_irq(&pos_f->lock);
427 static int freezer_write(struct cgroup *cgroup, struct cftype *cft,
432 if (strcmp(buffer, freezer_state_strs(0)) == 0)
434 else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
439 freezer_change_state(cgroup_freezer(cgroup), freeze);
443 static u64 freezer_self_freezing_read(struct cgroup *cgroup, struct cftype *cft)
445 struct freezer *freezer = cgroup_freezer(cgroup);
447 return (bool)(freezer->state & CGROUP_FREEZING_SELF);
450 static u64 freezer_parent_freezing_read(struct cgroup *cgroup, struct cftype *cft)
452 struct freezer *freezer = cgroup_freezer(cgroup);
454 return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
457 static struct cftype files[] = {
460 .flags = CFTYPE_NOT_ON_ROOT,
461 .read_seq_string = freezer_read,
462 .write_string = freezer_write,
465 .name = "self_freezing",
466 .flags = CFTYPE_NOT_ON_ROOT,
467 .read_u64 = freezer_self_freezing_read,
470 .name = "parent_freezing",
471 .flags = CFTYPE_NOT_ON_ROOT,
472 .read_u64 = freezer_parent_freezing_read,
477 struct cgroup_subsys freezer_subsys = {
479 .css_alloc = freezer_css_alloc,
480 .css_online = freezer_css_online,
481 .css_offline = freezer_css_offline,
482 .css_free = freezer_css_free,
483 .subsys_id = freezer_subsys_id,
484 .attach = freezer_attach,
485 .fork = freezer_fork,
486 .base_cftypes = files,