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>
24 #include <linux/mutex.h>
25 #include <linux/cpu.h>
28 * A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is
29 * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
30 * for "THAWED". FREEZING_PARENT is set if the parent freezer is FREEZING
31 * for whatever reason. IOW, a cgroup has FREEZING_PARENT set if one of
32 * its ancestors has FREEZING_SELF set.
34 enum freezer_state_flags {
35 CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */
36 CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */
37 CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */
38 CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */
40 /* mask for all FREEZING flags */
41 CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
45 struct cgroup_subsys_state css;
49 static DEFINE_MUTEX(freezer_mutex);
51 static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
53 return css ? container_of(css, struct freezer, css) : NULL;
56 static inline struct freezer *task_freezer(struct task_struct *task)
58 return css_freezer(task_css(task, freezer_cgrp_id));
61 static struct freezer *parent_freezer(struct freezer *freezer)
63 return css_freezer(freezer->css.parent);
66 bool cgroup_freezing(struct task_struct *task)
72 /* Check if the cgroup is still FREEZING, but not FROZEN. The extra
73 * !FROZEN check is required, because the FREEZING bit is not cleared
74 * when the state FROZEN is reached.
76 state = task_freezer(task)->state;
77 ret = (state & CGROUP_FREEZING) && !(state & CGROUP_FROZEN);
83 static const char *freezer_state_strs(unsigned int state)
85 if (state & CGROUP_FROZEN)
87 if (state & CGROUP_FREEZING)
92 static struct cgroup_subsys_state *
93 freezer_css_alloc(struct cgroup_subsys_state *parent_css)
95 struct freezer *freezer;
97 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
99 return ERR_PTR(-ENOMEM);
101 return &freezer->css;
105 * freezer_css_online - commit creation of a freezer css
106 * @css: css being created
108 * We're committing to creation of @css. Mark it online and inherit
109 * parent's freezing state while holding both parent's and our
112 static int freezer_css_online(struct cgroup_subsys_state *css)
114 struct freezer *freezer = css_freezer(css);
115 struct freezer *parent = parent_freezer(freezer);
118 mutex_lock(&freezer_mutex);
120 freezer->state |= CGROUP_FREEZER_ONLINE;
122 if (parent && (parent->state & CGROUP_FREEZING)) {
123 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
124 static_branch_inc_cpuslocked(&freezer_active);
127 mutex_unlock(&freezer_mutex);
133 * freezer_css_offline - initiate destruction of a freezer css
134 * @css: css being destroyed
136 * @css is going away. Mark it dead and decrement system_freezing_count if
137 * it was holding one.
139 static void freezer_css_offline(struct cgroup_subsys_state *css)
141 struct freezer *freezer = css_freezer(css);
144 mutex_lock(&freezer_mutex);
146 if (freezer->state & CGROUP_FREEZING)
147 static_branch_dec_cpuslocked(&freezer_active);
151 mutex_unlock(&freezer_mutex);
155 static void freezer_css_free(struct cgroup_subsys_state *css)
157 kfree(css_freezer(css));
161 * Tasks can be migrated into a different freezer anytime regardless of its
162 * current state. freezer_attach() is responsible for making new tasks
163 * conform to the current state.
165 * Freezer state changes and task migration are synchronized via
166 * @freezer->lock. freezer_attach() makes the new tasks conform to the
167 * current state and all following state changes can see the new tasks.
169 static void freezer_attach(struct cgroup_taskset *tset)
171 struct task_struct *task;
172 struct cgroup_subsys_state *new_css;
174 mutex_lock(&freezer_mutex);
177 * Make the new tasks conform to the current state of @new_css.
178 * For simplicity, when migrating any task to a FROZEN cgroup, we
179 * revert it to FREEZING and let update_if_frozen() determine the
180 * correct state later.
182 * Tasks in @tset are on @new_css but may not conform to its
183 * current state before executing the following - !frozen tasks may
184 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
186 cgroup_taskset_for_each(task, new_css, tset) {
187 struct freezer *freezer = css_freezer(new_css);
189 if (!(freezer->state & CGROUP_FREEZING)) {
194 /* clear FROZEN and propagate upwards */
195 while (freezer && (freezer->state & CGROUP_FROZEN)) {
196 freezer->state &= ~CGROUP_FROZEN;
197 freezer = parent_freezer(freezer);
202 mutex_unlock(&freezer_mutex);
206 * freezer_fork - cgroup post fork callback
207 * @task: a task which has just been forked
209 * @task has just been created and should conform to the current state of
210 * the cgroup_freezer it belongs to. This function may race against
211 * freezer_attach(). Losing to freezer_attach() means that we don't have
212 * to do anything as freezer_attach() will put @task into the appropriate
215 static void freezer_fork(struct task_struct *task)
217 struct freezer *freezer;
220 * The root cgroup is non-freezable, so we can skip locking the
221 * freezer. This is safe regardless of race with task migration.
222 * If we didn't race or won, skipping is obviously the right thing
223 * to do. If we lost and root is the new cgroup, noop is still the
226 if (task_css_is_root(task, freezer_cgrp_id))
229 mutex_lock(&freezer_mutex);
232 freezer = task_freezer(task);
233 if (freezer->state & CGROUP_FREEZING)
237 mutex_unlock(&freezer_mutex);
241 * update_if_frozen - update whether a cgroup finished freezing
242 * @css: css of interest
244 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
245 * calling this function. If the current state is FREEZING but not FROZEN,
246 * this function checks whether all tasks of this cgroup and the descendant
247 * cgroups finished freezing and, if so, sets FROZEN.
249 * The caller is responsible for grabbing RCU read lock and calling
250 * update_if_frozen() on all descendants prior to invoking this function.
252 * Task states and freezer state might disagree while tasks are being
253 * migrated into or out of @css, so we can't verify task states against
254 * @freezer state here. See freezer_attach() for details.
256 static void update_if_frozen(struct cgroup_subsys_state *css)
258 struct freezer *freezer = css_freezer(css);
259 struct cgroup_subsys_state *pos;
260 struct css_task_iter it;
261 struct task_struct *task;
263 lockdep_assert_held(&freezer_mutex);
265 if (!(freezer->state & CGROUP_FREEZING) ||
266 (freezer->state & CGROUP_FROZEN))
269 /* are all (live) children frozen? */
271 css_for_each_child(pos, css) {
272 struct freezer *child = css_freezer(pos);
274 if ((child->state & CGROUP_FREEZER_ONLINE) &&
275 !(child->state & CGROUP_FROZEN)) {
282 /* are all tasks frozen? */
283 css_task_iter_start(css, 0, &it);
285 while ((task = css_task_iter_next(&it))) {
286 if (freezing(task) && !frozen(task))
290 freezer->state |= CGROUP_FROZEN;
292 css_task_iter_end(&it);
295 static int freezer_read(struct seq_file *m, void *v)
297 struct cgroup_subsys_state *css = seq_css(m), *pos;
299 mutex_lock(&freezer_mutex);
302 /* update states bottom-up */
303 css_for_each_descendant_post(pos, css) {
304 if (!css_tryget_online(pos))
308 update_if_frozen(pos);
315 mutex_unlock(&freezer_mutex);
317 seq_puts(m, freezer_state_strs(css_freezer(css)->state));
322 static void freeze_cgroup(struct freezer *freezer)
324 struct css_task_iter it;
325 struct task_struct *task;
327 css_task_iter_start(&freezer->css, 0, &it);
328 while ((task = css_task_iter_next(&it)))
330 css_task_iter_end(&it);
333 static void unfreeze_cgroup(struct freezer *freezer)
335 struct css_task_iter it;
336 struct task_struct *task;
338 css_task_iter_start(&freezer->css, 0, &it);
339 while ((task = css_task_iter_next(&it)))
341 css_task_iter_end(&it);
345 * freezer_apply_state - apply state change to a single cgroup_freezer
346 * @freezer: freezer to apply state change to
347 * @freeze: whether to freeze or unfreeze
348 * @state: CGROUP_FREEZING_* flag to set or clear
350 * Set or clear @state on @cgroup according to @freeze, and perform
351 * freezing or thawing as necessary.
353 static void freezer_apply_state(struct freezer *freezer, bool freeze,
356 /* also synchronizes against task migration, see freezer_attach() */
357 lockdep_assert_held(&freezer_mutex);
359 if (!(freezer->state & CGROUP_FREEZER_ONLINE))
363 if (!(freezer->state & CGROUP_FREEZING))
364 static_branch_inc_cpuslocked(&freezer_active);
365 freezer->state |= state;
366 freeze_cgroup(freezer);
368 bool was_freezing = freezer->state & CGROUP_FREEZING;
370 freezer->state &= ~state;
372 if (!(freezer->state & CGROUP_FREEZING)) {
373 freezer->state &= ~CGROUP_FROZEN;
375 static_branch_dec_cpuslocked(&freezer_active);
376 unfreeze_cgroup(freezer);
382 * freezer_change_state - change the freezing state of a cgroup_freezer
383 * @freezer: freezer of interest
384 * @freeze: whether to freeze or thaw
386 * Freeze or thaw @freezer according to @freeze. The operations are
387 * recursive - all descendants of @freezer will be affected.
389 static void freezer_change_state(struct freezer *freezer, bool freeze)
391 struct cgroup_subsys_state *pos;
395 * Update all its descendants in pre-order traversal. Each
396 * descendant will try to inherit its parent's FREEZING state as
397 * CGROUP_FREEZING_PARENT.
399 mutex_lock(&freezer_mutex);
401 css_for_each_descendant_pre(pos, &freezer->css) {
402 struct freezer *pos_f = css_freezer(pos);
403 struct freezer *parent = parent_freezer(pos_f);
405 if (!css_tryget_online(pos))
409 if (pos_f == freezer)
410 freezer_apply_state(pos_f, freeze,
411 CGROUP_FREEZING_SELF);
413 freezer_apply_state(pos_f,
414 parent->state & CGROUP_FREEZING,
415 CGROUP_FREEZING_PARENT);
421 mutex_unlock(&freezer_mutex);
425 static ssize_t freezer_write(struct kernfs_open_file *of,
426 char *buf, size_t nbytes, loff_t off)
432 if (strcmp(buf, freezer_state_strs(0)) == 0)
434 else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
439 freezer_change_state(css_freezer(of_css(of)), freeze);
443 static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
446 struct freezer *freezer = css_freezer(css);
448 return (bool)(freezer->state & CGROUP_FREEZING_SELF);
451 static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
454 struct freezer *freezer = css_freezer(css);
456 return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
459 static struct cftype files[] = {
462 .flags = CFTYPE_NOT_ON_ROOT,
463 .seq_show = freezer_read,
464 .write = freezer_write,
467 .name = "self_freezing",
468 .flags = CFTYPE_NOT_ON_ROOT,
469 .read_u64 = freezer_self_freezing_read,
472 .name = "parent_freezing",
473 .flags = CFTYPE_NOT_ON_ROOT,
474 .read_u64 = freezer_parent_freezing_read,
479 struct cgroup_subsys freezer_cgrp_subsys = {
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 .attach = freezer_attach,
485 .fork = freezer_fork,
486 .legacy_cftypes = files,