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>
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.
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 */
39 /* mask for all FREEZING flags */
40 CGROUP_FREEZING
= CGROUP_FREEZING_SELF
| CGROUP_FREEZING_PARENT
,
44 struct cgroup_subsys_state css
;
48 static DEFINE_MUTEX(freezer_mutex
);
50 static inline struct freezer
*css_freezer(struct cgroup_subsys_state
*css
)
52 return css
? container_of(css
, struct freezer
, css
) : NULL
;
55 static inline struct freezer
*task_freezer(struct task_struct
*task
)
57 return css_freezer(task_css(task
, freezer_cgrp_id
));
60 static struct freezer
*parent_freezer(struct freezer
*freezer
)
62 return css_freezer(freezer
->css
.parent
);
65 bool cgroup_freezing(struct task_struct
*task
)
70 ret
= task_freezer(task
)->state
& CGROUP_FREEZING
;
76 static const char *freezer_state_strs(unsigned int state
)
78 if (state
& CGROUP_FROZEN
)
80 if (state
& CGROUP_FREEZING
)
85 static struct cgroup_subsys_state
*
86 freezer_css_alloc(struct cgroup_subsys_state
*parent_css
)
88 struct freezer
*freezer
;
90 freezer
= kzalloc(sizeof(struct freezer
), GFP_KERNEL
);
92 return ERR_PTR(-ENOMEM
);
98 * freezer_css_online - commit creation of a freezer css
99 * @css: css being created
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
105 static int freezer_css_online(struct cgroup_subsys_state
*css
)
107 struct freezer
*freezer
= css_freezer(css
);
108 struct freezer
*parent
= parent_freezer(freezer
);
110 mutex_lock(&freezer_mutex
);
112 freezer
->state
|= CGROUP_FREEZER_ONLINE
;
114 if (parent
&& (parent
->state
& CGROUP_FREEZING
)) {
115 freezer
->state
|= CGROUP_FREEZING_PARENT
| CGROUP_FROZEN
;
116 atomic_inc(&system_freezing_cnt
);
119 mutex_unlock(&freezer_mutex
);
124 * freezer_css_offline - initiate destruction of a freezer css
125 * @css: css being destroyed
127 * @css is going away. Mark it dead and decrement system_freezing_count if
128 * it was holding one.
130 static void freezer_css_offline(struct cgroup_subsys_state
*css
)
132 struct freezer
*freezer
= css_freezer(css
);
134 mutex_lock(&freezer_mutex
);
136 if (freezer
->state
& CGROUP_FREEZING
)
137 atomic_dec(&system_freezing_cnt
);
141 mutex_unlock(&freezer_mutex
);
144 static void freezer_css_free(struct cgroup_subsys_state
*css
)
146 kfree(css_freezer(css
));
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.
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.
158 static void freezer_attach(struct cgroup_subsys_state
*new_css
,
159 struct cgroup_taskset
*tset
)
161 struct freezer
*freezer
= css_freezer(new_css
);
162 struct task_struct
*task
;
163 bool clear_frozen
= false;
165 mutex_lock(&freezer_mutex
);
168 * Make the new tasks conform to the current state of @new_css.
169 * For simplicity, when migrating any task to a FROZEN cgroup, we
170 * revert it to FREEZING and let update_if_frozen() determine the
171 * correct state later.
173 * Tasks in @tset are on @new_css but may not conform to its
174 * current state before executing the following - !frozen tasks may
175 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
177 cgroup_taskset_for_each(task
, tset
) {
178 if (!(freezer
->state
& CGROUP_FREEZING
)) {
182 freezer
->state
&= ~CGROUP_FROZEN
;
187 /* propagate FROZEN clearing upwards */
188 while (clear_frozen
&& (freezer
= parent_freezer(freezer
))) {
189 freezer
->state
&= ~CGROUP_FROZEN
;
190 clear_frozen
= freezer
->state
& CGROUP_FREEZING
;
193 mutex_unlock(&freezer_mutex
);
197 * freezer_fork - cgroup post fork callback
198 * @task: a task which has just been forked
200 * @task has just been created and should conform to the current state of
201 * the cgroup_freezer it belongs to. This function may race against
202 * freezer_attach(). Losing to freezer_attach() means that we don't have
203 * to do anything as freezer_attach() will put @task into the appropriate
206 static void freezer_fork(struct task_struct
*task
)
208 struct freezer
*freezer
;
211 * The root cgroup is non-freezable, so we can skip locking the
212 * freezer. This is safe regardless of race with task migration.
213 * If we didn't race or won, skipping is obviously the right thing
214 * to do. If we lost and root is the new cgroup, noop is still the
217 if (task_css_is_root(task
, freezer_cgrp_id
))
220 mutex_lock(&freezer_mutex
);
223 freezer
= task_freezer(task
);
224 if (freezer
->state
& CGROUP_FREEZING
)
228 mutex_unlock(&freezer_mutex
);
232 * update_if_frozen - update whether a cgroup finished freezing
233 * @css: css of interest
235 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
236 * calling this function. If the current state is FREEZING but not FROZEN,
237 * this function checks whether all tasks of this cgroup and the descendant
238 * cgroups finished freezing and, if so, sets FROZEN.
240 * The caller is responsible for grabbing RCU read lock and calling
241 * update_if_frozen() on all descendants prior to invoking this function.
243 * Task states and freezer state might disagree while tasks are being
244 * migrated into or out of @css, so we can't verify task states against
245 * @freezer state here. See freezer_attach() for details.
247 static void update_if_frozen(struct cgroup_subsys_state
*css
)
249 struct freezer
*freezer
= css_freezer(css
);
250 struct cgroup_subsys_state
*pos
;
251 struct css_task_iter it
;
252 struct task_struct
*task
;
254 lockdep_assert_held(&freezer_mutex
);
256 if (!(freezer
->state
& CGROUP_FREEZING
) ||
257 (freezer
->state
& CGROUP_FROZEN
))
260 /* are all (live) children frozen? */
262 css_for_each_child(pos
, css
) {
263 struct freezer
*child
= css_freezer(pos
);
265 if ((child
->state
& CGROUP_FREEZER_ONLINE
) &&
266 !(child
->state
& CGROUP_FROZEN
)) {
273 /* are all tasks frozen? */
274 css_task_iter_start(css
, &it
);
276 while ((task
= css_task_iter_next(&it
))) {
277 if (freezing(task
)) {
279 * freezer_should_skip() indicates that the task
280 * should be skipped when determining freezing
281 * completion. Consider it frozen in addition to
282 * the usual frozen condition.
284 if (!frozen(task
) && !freezer_should_skip(task
))
289 freezer
->state
|= CGROUP_FROZEN
;
291 css_task_iter_end(&it
);
294 static int freezer_read(struct seq_file
*m
, void *v
)
296 struct cgroup_subsys_state
*css
= seq_css(m
), *pos
;
298 mutex_lock(&freezer_mutex
);
301 /* update states bottom-up */
302 css_for_each_descendant_post(pos
, css
) {
303 if (!css_tryget_online(pos
))
307 update_if_frozen(pos
);
314 mutex_unlock(&freezer_mutex
);
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_mutex
);
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.
397 mutex_lock(&freezer_mutex
);
399 css_for_each_descendant_pre(pos
, &freezer
->css
) {
400 struct freezer
*pos_f
= css_freezer(pos
);
401 struct freezer
*parent
= parent_freezer(pos_f
);
403 if (!css_tryget_online(pos
))
407 if (pos_f
== freezer
)
408 freezer_apply_state(pos_f
, freeze
,
409 CGROUP_FREEZING_SELF
);
411 freezer_apply_state(pos_f
,
412 parent
->state
& CGROUP_FREEZING
,
413 CGROUP_FREEZING_PARENT
);
419 mutex_unlock(&freezer_mutex
);
422 static ssize_t
freezer_write(struct kernfs_open_file
*of
,
423 char *buf
, size_t nbytes
, loff_t off
)
429 if (strcmp(buf
, freezer_state_strs(0)) == 0)
431 else if (strcmp(buf
, freezer_state_strs(CGROUP_FROZEN
)) == 0)
436 freezer_change_state(css_freezer(of_css(of
)), 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
= 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_cgrp_subsys
= {
477 .css_alloc
= freezer_css_alloc
,
478 .css_online
= freezer_css_online
,
479 .css_offline
= freezer_css_offline
,
480 .css_free
= freezer_css_free
,
481 .attach
= freezer_attach
,
482 .fork
= freezer_fork
,
483 .legacy_cftypes
= files
,