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 *task_freezer(struct task_struct *task)
55 return css_freezer(task_css(task, freezer_subsys_id));
58 static struct freezer *parent_freezer(struct freezer *freezer)
60 return css_freezer(css_parent(&freezer->css));
63 bool cgroup_freezing(struct task_struct *task)
68 ret = task_freezer(task)->state & CGROUP_FREEZING;
75 * cgroups_write_string() limits the size of freezer state strings to
76 * CGROUP_LOCAL_BUFFER_SIZE
78 static const char *freezer_state_strs(unsigned int state)
80 if (state & CGROUP_FROZEN)
82 if (state & CGROUP_FREEZING)
87 struct cgroup_subsys freezer_subsys;
89 static struct cgroup_subsys_state *
90 freezer_css_alloc(struct cgroup_subsys_state *parent_css)
92 struct freezer *freezer;
94 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
96 return ERR_PTR(-ENOMEM);
98 spin_lock_init(&freezer->lock);
103 * freezer_css_online - commit creation of a freezer css
104 * @css: css being created
106 * We're committing to creation of @css. Mark it online and inherit
107 * parent's freezing state while holding both parent's and our
110 static int freezer_css_online(struct cgroup_subsys_state *css)
112 struct freezer *freezer = css_freezer(css);
113 struct freezer *parent = parent_freezer(freezer);
116 * The following double locking and freezing state inheritance
117 * guarantee that @cgroup can never escape ancestors' freezing
118 * states. See css_for_each_descendant_pre() for details.
121 spin_lock_irq(&parent->lock);
122 spin_lock_nested(&freezer->lock, SINGLE_DEPTH_NESTING);
124 freezer->state |= CGROUP_FREEZER_ONLINE;
126 if (parent && (parent->state & CGROUP_FREEZING)) {
127 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
128 atomic_inc(&system_freezing_cnt);
131 spin_unlock(&freezer->lock);
133 spin_unlock_irq(&parent->lock);
139 * freezer_css_offline - initiate destruction of a freezer css
140 * @css: css being destroyed
142 * @css is going away. Mark it dead and decrement system_freezing_count if
143 * it was holding one.
145 static void freezer_css_offline(struct cgroup_subsys_state *css)
147 struct freezer *freezer = css_freezer(css);
149 spin_lock_irq(&freezer->lock);
151 if (freezer->state & CGROUP_FREEZING)
152 atomic_dec(&system_freezing_cnt);
156 spin_unlock_irq(&freezer->lock);
159 static void freezer_css_free(struct cgroup_subsys_state *css)
161 kfree(css_freezer(css));
165 * Tasks can be migrated into a different freezer anytime regardless of its
166 * current state. freezer_attach() is responsible for making new tasks
167 * conform to the current state.
169 * Freezer state changes and task migration are synchronized via
170 * @freezer->lock. freezer_attach() makes the new tasks conform to the
171 * current state and all following state changes can see the new tasks.
173 static void freezer_attach(struct cgroup_subsys_state *new_css,
174 struct cgroup_taskset *tset)
176 struct freezer *freezer = css_freezer(new_css);
177 struct task_struct *task;
178 bool clear_frozen = false;
180 spin_lock_irq(&freezer->lock);
183 * Make the new tasks conform to the current state of @new_css.
184 * For simplicity, when migrating any task to a FROZEN cgroup, we
185 * revert it to FREEZING and let update_if_frozen() determine the
186 * correct state later.
188 * Tasks in @tset are on @new_css but may not conform to its
189 * current state before executing the following - !frozen tasks may
190 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
192 cgroup_taskset_for_each(task, new_css, tset) {
193 if (!(freezer->state & CGROUP_FREEZING)) {
197 freezer->state &= ~CGROUP_FROZEN;
202 spin_unlock_irq(&freezer->lock);
205 * Propagate FROZEN clearing upwards. We may race with
206 * update_if_frozen(), but as long as both work bottom-up, either
207 * update_if_frozen() sees child's FROZEN cleared or we clear the
208 * parent's FROZEN later. No parent w/ !FROZEN children can be
211 while (clear_frozen && (freezer = parent_freezer(freezer))) {
212 spin_lock_irq(&freezer->lock);
213 freezer->state &= ~CGROUP_FROZEN;
214 clear_frozen = freezer->state & CGROUP_FREEZING;
215 spin_unlock_irq(&freezer->lock);
219 static void freezer_fork(struct task_struct *task)
221 struct freezer *freezer;
224 freezer = task_freezer(task);
227 * The root cgroup is non-freezable, so we can skip the
230 if (!parent_freezer(freezer))
233 spin_lock_irq(&freezer->lock);
234 if (freezer->state & CGROUP_FREEZING)
236 spin_unlock_irq(&freezer->lock);
242 * update_if_frozen - update whether a cgroup finished freezing
243 * @css: css of interest
245 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
246 * calling this function. If the current state is FREEZING but not FROZEN,
247 * this function checks whether all tasks of this cgroup and the descendant
248 * cgroups finished freezing and, if so, sets FROZEN.
250 * The caller is responsible for grabbing RCU read lock and calling
251 * update_if_frozen() on all descendants prior to invoking this function.
253 * Task states and freezer state might disagree while tasks are being
254 * migrated into or out of @css, so we can't verify task states against
255 * @freezer state here. See freezer_attach() for details.
257 static void update_if_frozen(struct cgroup_subsys_state *css)
259 struct freezer *freezer = css_freezer(css);
260 struct cgroup_subsys_state *pos;
261 struct css_task_iter it;
262 struct task_struct *task;
264 WARN_ON_ONCE(!rcu_read_lock_held());
266 spin_lock_irq(&freezer->lock);
268 if (!(freezer->state & CGROUP_FREEZING) ||
269 (freezer->state & CGROUP_FROZEN))
272 /* are all (live) children frozen? */
273 css_for_each_child(pos, css) {
274 struct freezer *child = css_freezer(pos);
276 if ((child->state & CGROUP_FREEZER_ONLINE) &&
277 !(child->state & CGROUP_FROZEN))
281 /* are all tasks frozen? */
282 css_task_iter_start(css, &it);
284 while ((task = css_task_iter_next(&it))) {
285 if (freezing(task)) {
287 * freezer_should_skip() indicates that the task
288 * should be skipped when determining freezing
289 * completion. Consider it frozen in addition to
290 * the usual frozen condition.
292 if (!frozen(task) && !freezer_should_skip(task))
297 freezer->state |= CGROUP_FROZEN;
299 css_task_iter_end(&it);
301 spin_unlock_irq(&freezer->lock);
304 static int freezer_read(struct seq_file *m, void *v)
306 struct cgroup_subsys_state *css = seq_css(m), *pos;
310 /* update states bottom-up */
311 css_for_each_descendant_post(pos, css)
312 update_if_frozen(pos);
316 seq_puts(m, freezer_state_strs(css_freezer(css)->state));
321 static void freeze_cgroup(struct freezer *freezer)
323 struct css_task_iter it;
324 struct task_struct *task;
326 css_task_iter_start(&freezer->css, &it);
327 while ((task = css_task_iter_next(&it)))
329 css_task_iter_end(&it);
332 static void unfreeze_cgroup(struct freezer *freezer)
334 struct css_task_iter it;
335 struct task_struct *task;
337 css_task_iter_start(&freezer->css, &it);
338 while ((task = css_task_iter_next(&it)))
340 css_task_iter_end(&it);
344 * freezer_apply_state - apply state change to a single cgroup_freezer
345 * @freezer: freezer to apply state change to
346 * @freeze: whether to freeze or unfreeze
347 * @state: CGROUP_FREEZING_* flag to set or clear
349 * Set or clear @state on @cgroup according to @freeze, and perform
350 * freezing or thawing as necessary.
352 static void freezer_apply_state(struct freezer *freezer, bool freeze,
355 /* also synchronizes against task migration, see freezer_attach() */
356 lockdep_assert_held(&freezer->lock);
358 if (!(freezer->state & CGROUP_FREEZER_ONLINE))
362 if (!(freezer->state & CGROUP_FREEZING))
363 atomic_inc(&system_freezing_cnt);
364 freezer->state |= state;
365 freeze_cgroup(freezer);
367 bool was_freezing = freezer->state & CGROUP_FREEZING;
369 freezer->state &= ~state;
371 if (!(freezer->state & CGROUP_FREEZING)) {
373 atomic_dec(&system_freezing_cnt);
374 freezer->state &= ~CGROUP_FROZEN;
375 unfreeze_cgroup(freezer);
381 * freezer_change_state - change the freezing state of a cgroup_freezer
382 * @freezer: freezer of interest
383 * @freeze: whether to freeze or thaw
385 * Freeze or thaw @freezer according to @freeze. The operations are
386 * recursive - all descendants of @freezer will be affected.
388 static void freezer_change_state(struct freezer *freezer, bool freeze)
390 struct cgroup_subsys_state *pos;
393 * Update all its descendants in pre-order traversal. Each
394 * descendant will try to inherit its parent's FREEZING state as
395 * CGROUP_FREEZING_PARENT.
398 css_for_each_descendant_pre(pos, &freezer->css) {
399 struct freezer *pos_f = css_freezer(pos);
400 struct freezer *parent = parent_freezer(pos_f);
402 spin_lock_irq(&pos_f->lock);
404 if (pos_f == freezer) {
405 freezer_apply_state(pos_f, freeze,
406 CGROUP_FREEZING_SELF);
409 * Our update to @parent->state is already visible
410 * which is all we need. No need to lock @parent.
411 * For more info on synchronization, see
412 * freezer_post_create().
414 freezer_apply_state(pos_f,
415 parent->state & CGROUP_FREEZING,
416 CGROUP_FREEZING_PARENT);
419 spin_unlock_irq(&pos_f->lock);
424 static int freezer_write(struct cgroup_subsys_state *css, struct cftype *cft,
429 if (strcmp(buffer, freezer_state_strs(0)) == 0)
431 else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
436 freezer_change_state(css_freezer(css), freeze);
440 static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
443 struct freezer *freezer = css_freezer(css);
445 return (bool)(freezer->state & CGROUP_FREEZING_SELF);
448 static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
451 struct freezer *freezer = css_freezer(css);
453 return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
456 static struct cftype files[] = {
459 .flags = CFTYPE_NOT_ON_ROOT,
460 .seq_show = freezer_read,
461 .write_string = freezer_write,
464 .name = "self_freezing",
465 .flags = CFTYPE_NOT_ON_ROOT,
466 .read_u64 = freezer_self_freezing_read,
469 .name = "parent_freezing",
470 .flags = CFTYPE_NOT_ON_ROOT,
471 .read_u64 = freezer_parent_freezing_read,
476 struct cgroup_subsys freezer_subsys = {
478 .css_alloc = freezer_css_alloc,
479 .css_online = freezer_css_online,
480 .css_offline = freezer_css_offline,
481 .css_free = freezer_css_free,
482 .subsys_id = freezer_subsys_id,
483 .attach = freezer_attach,
484 .fork = freezer_fork,
485 .base_cftypes = files,