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 struct cgroup *pcg = freezer->css.cgroup->parent;
68 return cgroup_freezer(pcg);
72 bool cgroup_freezing(struct task_struct *task)
77 ret = task_freezer(task)->state & CGROUP_FREEZING;
84 * cgroups_write_string() limits the size of freezer state strings to
85 * CGROUP_LOCAL_BUFFER_SIZE
87 static const char *freezer_state_strs(unsigned int state)
89 if (state & CGROUP_FROZEN)
91 if (state & CGROUP_FREEZING)
96 struct cgroup_subsys freezer_subsys;
98 static struct cgroup_subsys_state *freezer_css_alloc(struct cgroup *cgroup)
100 struct freezer *freezer;
102 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
104 return ERR_PTR(-ENOMEM);
106 spin_lock_init(&freezer->lock);
107 return &freezer->css;
111 * freezer_css_online - commit creation of a freezer cgroup
112 * @cgroup: cgroup being created
114 * We're committing to creation of @cgroup. Mark it online and inherit
115 * parent's freezing state while holding both parent's and our
118 static int freezer_css_online(struct cgroup *cgroup)
120 struct freezer *freezer = cgroup_freezer(cgroup);
121 struct freezer *parent = parent_freezer(freezer);
124 * The following double locking and freezing state inheritance
125 * guarantee that @cgroup can never escape ancestors' freezing
126 * states. See cgroup_for_each_descendant_pre() for details.
129 spin_lock_irq(&parent->lock);
130 spin_lock_nested(&freezer->lock, SINGLE_DEPTH_NESTING);
132 freezer->state |= CGROUP_FREEZER_ONLINE;
134 if (parent && (parent->state & CGROUP_FREEZING)) {
135 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
136 atomic_inc(&system_freezing_cnt);
139 spin_unlock(&freezer->lock);
141 spin_unlock_irq(&parent->lock);
147 * freezer_css_offline - initiate destruction of @cgroup
148 * @cgroup: cgroup being destroyed
150 * @cgroup is going away. Mark it dead and decrement system_freezing_count
151 * if it was holding one.
153 static void freezer_css_offline(struct cgroup *cgroup)
155 struct freezer *freezer = cgroup_freezer(cgroup);
157 spin_lock_irq(&freezer->lock);
159 if (freezer->state & CGROUP_FREEZING)
160 atomic_dec(&system_freezing_cnt);
164 spin_unlock_irq(&freezer->lock);
167 static void freezer_css_free(struct cgroup *cgroup)
169 kfree(cgroup_freezer(cgroup));
173 * Tasks can be migrated into a different freezer anytime regardless of its
174 * current state. freezer_attach() is responsible for making new tasks
175 * conform to the current state.
177 * Freezer state changes and task migration are synchronized via
178 * @freezer->lock. freezer_attach() makes the new tasks conform to the
179 * current state and all following state changes can see the new tasks.
181 static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
183 struct freezer *freezer = cgroup_freezer(new_cgrp);
184 struct task_struct *task;
185 bool clear_frozen = false;
187 spin_lock_irq(&freezer->lock);
190 * Make the new tasks conform to the current state of @new_cgrp.
191 * For simplicity, when migrating any task to a FROZEN cgroup, we
192 * revert it to FREEZING and let update_if_frozen() determine the
193 * correct state later.
195 * Tasks in @tset are on @new_cgrp but may not conform to its
196 * current state before executing the following - !frozen tasks may
197 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
199 cgroup_taskset_for_each(task, new_cgrp, tset) {
200 if (!(freezer->state & CGROUP_FREEZING)) {
204 freezer->state &= ~CGROUP_FROZEN;
209 spin_unlock_irq(&freezer->lock);
212 * Propagate FROZEN clearing upwards. We may race with
213 * update_if_frozen(), but as long as both work bottom-up, either
214 * update_if_frozen() sees child's FROZEN cleared or we clear the
215 * parent's FROZEN later. No parent w/ !FROZEN children can be
218 while (clear_frozen && (freezer = parent_freezer(freezer))) {
219 spin_lock_irq(&freezer->lock);
220 freezer->state &= ~CGROUP_FROZEN;
221 clear_frozen = freezer->state & CGROUP_FREEZING;
222 spin_unlock_irq(&freezer->lock);
226 static void freezer_fork(struct task_struct *task)
228 struct freezer *freezer;
231 freezer = task_freezer(task);
234 * The root cgroup is non-freezable, so we can skip the
237 if (!freezer->css.cgroup->parent)
240 spin_lock_irq(&freezer->lock);
241 if (freezer->state & CGROUP_FREEZING)
243 spin_unlock_irq(&freezer->lock);
249 * update_if_frozen - update whether a cgroup finished freezing
250 * @cgroup: cgroup of interest
252 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
253 * calling this function. If the current state is FREEZING but not FROZEN,
254 * this function checks whether all tasks of this cgroup and the descendant
255 * cgroups finished freezing and, if so, sets FROZEN.
257 * The caller is responsible for grabbing RCU read lock and calling
258 * update_if_frozen() on all descendants prior to invoking this function.
260 * Task states and freezer state might disagree while tasks are being
261 * migrated into or out of @cgroup, so we can't verify task states against
262 * @freezer state here. See freezer_attach() for details.
264 static void update_if_frozen(struct cgroup *cgroup)
266 struct freezer *freezer = cgroup_freezer(cgroup);
268 struct cgroup_iter it;
269 struct task_struct *task;
271 WARN_ON_ONCE(!rcu_read_lock_held());
273 spin_lock_irq(&freezer->lock);
275 if (!(freezer->state & CGROUP_FREEZING) ||
276 (freezer->state & CGROUP_FROZEN))
279 /* are all (live) children frozen? */
280 cgroup_for_each_child(pos, cgroup) {
281 struct freezer *child = cgroup_freezer(pos);
283 if ((child->state & CGROUP_FREEZER_ONLINE) &&
284 !(child->state & CGROUP_FROZEN))
288 /* are all tasks frozen? */
289 cgroup_iter_start(cgroup, &it);
291 while ((task = cgroup_iter_next(cgroup, &it))) {
292 if (freezing(task)) {
294 * freezer_should_skip() indicates that the task
295 * should be skipped when determining freezing
296 * completion. Consider it frozen in addition to
297 * the usual frozen condition.
299 if (!frozen(task) && !freezer_should_skip(task))
304 freezer->state |= CGROUP_FROZEN;
306 cgroup_iter_end(cgroup, &it);
308 spin_unlock_irq(&freezer->lock);
311 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
318 /* update states bottom-up */
319 cgroup_for_each_descendant_post(pos, cgroup)
320 update_if_frozen(pos);
321 update_if_frozen(cgroup);
325 seq_puts(m, freezer_state_strs(cgroup_freezer(cgroup)->state));
330 static void freeze_cgroup(struct freezer *freezer)
332 struct cgroup *cgroup = freezer->css.cgroup;
333 struct cgroup_iter it;
334 struct task_struct *task;
336 cgroup_iter_start(cgroup, &it);
337 while ((task = cgroup_iter_next(cgroup, &it)))
339 cgroup_iter_end(cgroup, &it);
342 static void unfreeze_cgroup(struct freezer *freezer)
344 struct cgroup *cgroup = freezer->css.cgroup;
345 struct cgroup_iter it;
346 struct task_struct *task;
348 cgroup_iter_start(cgroup, &it);
349 while ((task = cgroup_iter_next(cgroup, &it)))
351 cgroup_iter_end(cgroup, &it);
355 * freezer_apply_state - apply state change to a single cgroup_freezer
356 * @freezer: freezer to apply state change to
357 * @freeze: whether to freeze or unfreeze
358 * @state: CGROUP_FREEZING_* flag to set or clear
360 * Set or clear @state on @cgroup according to @freeze, and perform
361 * freezing or thawing as necessary.
363 static void freezer_apply_state(struct freezer *freezer, bool freeze,
366 /* also synchronizes against task migration, see freezer_attach() */
367 lockdep_assert_held(&freezer->lock);
369 if (!(freezer->state & CGROUP_FREEZER_ONLINE))
373 if (!(freezer->state & CGROUP_FREEZING))
374 atomic_inc(&system_freezing_cnt);
375 freezer->state |= state;
376 freeze_cgroup(freezer);
378 bool was_freezing = freezer->state & CGROUP_FREEZING;
380 freezer->state &= ~state;
382 if (!(freezer->state & CGROUP_FREEZING)) {
384 atomic_dec(&system_freezing_cnt);
385 freezer->state &= ~CGROUP_FROZEN;
386 unfreeze_cgroup(freezer);
392 * freezer_change_state - change the freezing state of a cgroup_freezer
393 * @freezer: freezer of interest
394 * @freeze: whether to freeze or thaw
396 * Freeze or thaw @freezer according to @freeze. The operations are
397 * recursive - all descendants of @freezer will be affected.
399 static void freezer_change_state(struct freezer *freezer, bool freeze)
403 /* update @freezer */
404 spin_lock_irq(&freezer->lock);
405 freezer_apply_state(freezer, freeze, CGROUP_FREEZING_SELF);
406 spin_unlock_irq(&freezer->lock);
409 * Update all its descendants in pre-order traversal. Each
410 * descendant will try to inherit its parent's FREEZING state as
411 * CGROUP_FREEZING_PARENT.
414 cgroup_for_each_descendant_pre(pos, freezer->css.cgroup) {
415 struct freezer *pos_f = cgroup_freezer(pos);
416 struct freezer *parent = parent_freezer(pos_f);
419 * Our update to @parent->state is already visible which is
420 * all we need. No need to lock @parent. For more info on
421 * synchronization, see freezer_post_create().
423 spin_lock_irq(&pos_f->lock);
424 freezer_apply_state(pos_f, parent->state & CGROUP_FREEZING,
425 CGROUP_FREEZING_PARENT);
426 spin_unlock_irq(&pos_f->lock);
431 static int freezer_write(struct cgroup *cgroup, struct cftype *cft,
436 if (strcmp(buffer, freezer_state_strs(0)) == 0)
438 else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
443 freezer_change_state(cgroup_freezer(cgroup), freeze);
447 static u64 freezer_self_freezing_read(struct cgroup *cgroup, struct cftype *cft)
449 struct freezer *freezer = cgroup_freezer(cgroup);
451 return (bool)(freezer->state & CGROUP_FREEZING_SELF);
454 static u64 freezer_parent_freezing_read(struct cgroup *cgroup, struct cftype *cft)
456 struct freezer *freezer = cgroup_freezer(cgroup);
458 return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
461 static struct cftype files[] = {
464 .flags = CFTYPE_NOT_ON_ROOT,
465 .read_seq_string = freezer_read,
466 .write_string = freezer_write,
469 .name = "self_freezing",
470 .flags = CFTYPE_NOT_ON_ROOT,
471 .read_u64 = freezer_self_freezing_read,
474 .name = "parent_freezing",
475 .flags = CFTYPE_NOT_ON_ROOT,
476 .read_u64 = freezer_parent_freezing_read,
481 struct cgroup_subsys freezer_subsys = {
483 .css_alloc = freezer_css_alloc,
484 .css_online = freezer_css_online,
485 .css_offline = freezer_css_offline,
486 .css_free = freezer_css_free,
487 .subsys_id = freezer_subsys_id,
488 .attach = freezer_attach,
489 .fork = freezer_fork,
490 .base_cftypes = files,