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1/*
2 * cgroup_freezer.c - control group freezer subsystem
3 *
4 * Copyright IBM Corporation, 2007
5 *
6 * Author : Cedric Le Goater <clg@fr.ibm.com>
7 *
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.
11 *
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.
15 */
16
17#include <linux/export.h>
18#include <linux/slab.h>
19#include <linux/cgroup.h>
20#include <linux/fs.h>
21#include <linux/uaccess.h>
22#include <linux/freezer.h>
23#include <linux/seq_file.h>
24#include <linux/mutex.h>
25
26/*
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.
32 */
33enum 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 */
38
39 /* mask for all FREEZING flags */
40 CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
41};
42
43struct freezer {
44 struct cgroup_subsys_state css;
45 unsigned int state;
46};
47
48static DEFINE_MUTEX(freezer_mutex);
49
50static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
51{
52 return css ? container_of(css, struct freezer, css) : NULL;
53}
54
55static inline struct freezer *task_freezer(struct task_struct *task)
56{
57 return css_freezer(task_css(task, freezer_cgrp_id));
58}
59
60static struct freezer *parent_freezer(struct freezer *freezer)
61{
62 return css_freezer(freezer->css.parent);
63}
64
65bool cgroup_freezing(struct task_struct *task)
66{
67 bool ret;
68
69 rcu_read_lock();
70 ret = task_freezer(task)->state & CGROUP_FREEZING;
71 rcu_read_unlock();
72
73 return ret;
74}
75
76static const char *freezer_state_strs(unsigned int state)
77{
78 if (state & CGROUP_FROZEN)
79 return "FROZEN";
80 if (state & CGROUP_FREEZING)
81 return "FREEZING";
82 return "THAWED";
83};
84
85static struct cgroup_subsys_state *
86freezer_css_alloc(struct cgroup_subsys_state *parent_css)
87{
88 struct freezer *freezer;
89
90 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
91 if (!freezer)
92 return ERR_PTR(-ENOMEM);
93
94 return &freezer->css;
95}
96
97/**
98 * freezer_css_online - commit creation of a freezer css
99 * @css: css being created
100 *
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
103 * freezer->lock.
104 */
105static int freezer_css_online(struct cgroup_subsys_state *css)
106{
107 struct freezer *freezer = css_freezer(css);
108 struct freezer *parent = parent_freezer(freezer);
109
110 mutex_lock(&freezer_mutex);
111
112 freezer->state |= CGROUP_FREEZER_ONLINE;
113
114 if (parent && (parent->state & CGROUP_FREEZING)) {
115 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
116 atomic_inc(&system_freezing_cnt);
117 }
118
119 mutex_unlock(&freezer_mutex);
120 return 0;
121}
122
123/**
124 * freezer_css_offline - initiate destruction of a freezer css
125 * @css: css being destroyed
126 *
127 * @css is going away. Mark it dead and decrement system_freezing_count if
128 * it was holding one.
129 */
130static void freezer_css_offline(struct cgroup_subsys_state *css)
131{
132 struct freezer *freezer = css_freezer(css);
133
134 mutex_lock(&freezer_mutex);
135
136 if (freezer->state & CGROUP_FREEZING)
137 atomic_dec(&system_freezing_cnt);
138
139 freezer->state = 0;
140
141 mutex_unlock(&freezer_mutex);
142}
143
144static void freezer_css_free(struct cgroup_subsys_state *css)
145{
146 kfree(css_freezer(css));
147}
148
149/*
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.
153 *
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.
157 */
158static void freezer_attach(struct cgroup_taskset *tset)
159{
160 struct task_struct *task;
161 struct cgroup_subsys_state *new_css;
162
163 mutex_lock(&freezer_mutex);
164
165 /*
166 * Make the new tasks conform to the current state of @new_css.
167 * For simplicity, when migrating any task to a FROZEN cgroup, we
168 * revert it to FREEZING and let update_if_frozen() determine the
169 * correct state later.
170 *
171 * Tasks in @tset are on @new_css but may not conform to its
172 * current state before executing the following - !frozen tasks may
173 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
174 */
175 cgroup_taskset_for_each(task, new_css, tset) {
176 struct freezer *freezer = css_freezer(new_css);
177
178 if (!(freezer->state & CGROUP_FREEZING)) {
179 __thaw_task(task);
180 } else {
181 freeze_task(task);
182 /* clear FROZEN and propagate upwards */
183 while (freezer && (freezer->state & CGROUP_FROZEN)) {
184 freezer->state &= ~CGROUP_FROZEN;
185 freezer = parent_freezer(freezer);
186 }
187 }
188 }
189
190 mutex_unlock(&freezer_mutex);
191}
192
193/**
194 * freezer_fork - cgroup post fork callback
195 * @task: a task which has just been forked
196 *
197 * @task has just been created and should conform to the current state of
198 * the cgroup_freezer it belongs to. This function may race against
199 * freezer_attach(). Losing to freezer_attach() means that we don't have
200 * to do anything as freezer_attach() will put @task into the appropriate
201 * state.
202 */
203static void freezer_fork(struct task_struct *task)
204{
205 struct freezer *freezer;
206
207 /*
208 * The root cgroup is non-freezable, so we can skip locking the
209 * freezer. This is safe regardless of race with task migration.
210 * If we didn't race or won, skipping is obviously the right thing
211 * to do. If we lost and root is the new cgroup, noop is still the
212 * right thing to do.
213 */
214 if (task_css_is_root(task, freezer_cgrp_id))
215 return;
216
217 mutex_lock(&freezer_mutex);
218 rcu_read_lock();
219
220 freezer = task_freezer(task);
221 if (freezer->state & CGROUP_FREEZING)
222 freeze_task(task);
223
224 rcu_read_unlock();
225 mutex_unlock(&freezer_mutex);
226}
227
228/**
229 * update_if_frozen - update whether a cgroup finished freezing
230 * @css: css of interest
231 *
232 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
233 * calling this function. If the current state is FREEZING but not FROZEN,
234 * this function checks whether all tasks of this cgroup and the descendant
235 * cgroups finished freezing and, if so, sets FROZEN.
236 *
237 * The caller is responsible for grabbing RCU read lock and calling
238 * update_if_frozen() on all descendants prior to invoking this function.
239 *
240 * Task states and freezer state might disagree while tasks are being
241 * migrated into or out of @css, so we can't verify task states against
242 * @freezer state here. See freezer_attach() for details.
243 */
244static void update_if_frozen(struct cgroup_subsys_state *css)
245{
246 struct freezer *freezer = css_freezer(css);
247 struct cgroup_subsys_state *pos;
248 struct css_task_iter it;
249 struct task_struct *task;
250
251 lockdep_assert_held(&freezer_mutex);
252
253 if (!(freezer->state & CGROUP_FREEZING) ||
254 (freezer->state & CGROUP_FROZEN))
255 return;
256
257 /* are all (live) children frozen? */
258 rcu_read_lock();
259 css_for_each_child(pos, css) {
260 struct freezer *child = css_freezer(pos);
261
262 if ((child->state & CGROUP_FREEZER_ONLINE) &&
263 !(child->state & CGROUP_FROZEN)) {
264 rcu_read_unlock();
265 return;
266 }
267 }
268 rcu_read_unlock();
269
270 /* are all tasks frozen? */
271 css_task_iter_start(css, &it);
272
273 while ((task = css_task_iter_next(&it))) {
274 if (freezing(task)) {
275 /*
276 * freezer_should_skip() indicates that the task
277 * should be skipped when determining freezing
278 * completion. Consider it frozen in addition to
279 * the usual frozen condition.
280 */
281 if (!frozen(task) && !freezer_should_skip(task))
282 goto out_iter_end;
283 }
284 }
285
286 freezer->state |= CGROUP_FROZEN;
287out_iter_end:
288 css_task_iter_end(&it);
289}
290
291static int freezer_read(struct seq_file *m, void *v)
292{
293 struct cgroup_subsys_state *css = seq_css(m), *pos;
294
295 mutex_lock(&freezer_mutex);
296 rcu_read_lock();
297
298 /* update states bottom-up */
299 css_for_each_descendant_post(pos, css) {
300 if (!css_tryget_online(pos))
301 continue;
302 rcu_read_unlock();
303
304 update_if_frozen(pos);
305
306 rcu_read_lock();
307 css_put(pos);
308 }
309
310 rcu_read_unlock();
311 mutex_unlock(&freezer_mutex);
312
313 seq_puts(m, freezer_state_strs(css_freezer(css)->state));
314 seq_putc(m, '\n');
315 return 0;
316}
317
318static void freeze_cgroup(struct freezer *freezer)
319{
320 struct css_task_iter it;
321 struct task_struct *task;
322
323 css_task_iter_start(&freezer->css, &it);
324 while ((task = css_task_iter_next(&it)))
325 freeze_task(task);
326 css_task_iter_end(&it);
327}
328
329static void unfreeze_cgroup(struct freezer *freezer)
330{
331 struct css_task_iter it;
332 struct task_struct *task;
333
334 css_task_iter_start(&freezer->css, &it);
335 while ((task = css_task_iter_next(&it)))
336 __thaw_task(task);
337 css_task_iter_end(&it);
338}
339
340/**
341 * freezer_apply_state - apply state change to a single cgroup_freezer
342 * @freezer: freezer to apply state change to
343 * @freeze: whether to freeze or unfreeze
344 * @state: CGROUP_FREEZING_* flag to set or clear
345 *
346 * Set or clear @state on @cgroup according to @freeze, and perform
347 * freezing or thawing as necessary.
348 */
349static void freezer_apply_state(struct freezer *freezer, bool freeze,
350 unsigned int state)
351{
352 /* also synchronizes against task migration, see freezer_attach() */
353 lockdep_assert_held(&freezer_mutex);
354
355 if (!(freezer->state & CGROUP_FREEZER_ONLINE))
356 return;
357
358 if (freeze) {
359 if (!(freezer->state & CGROUP_FREEZING))
360 atomic_inc(&system_freezing_cnt);
361 freezer->state |= state;
362 freeze_cgroup(freezer);
363 } else {
364 bool was_freezing = freezer->state & CGROUP_FREEZING;
365
366 freezer->state &= ~state;
367
368 if (!(freezer->state & CGROUP_FREEZING)) {
369 if (was_freezing)
370 atomic_dec(&system_freezing_cnt);
371 freezer->state &= ~CGROUP_FROZEN;
372 unfreeze_cgroup(freezer);
373 }
374 }
375}
376
377/**
378 * freezer_change_state - change the freezing state of a cgroup_freezer
379 * @freezer: freezer of interest
380 * @freeze: whether to freeze or thaw
381 *
382 * Freeze or thaw @freezer according to @freeze. The operations are
383 * recursive - all descendants of @freezer will be affected.
384 */
385static void freezer_change_state(struct freezer *freezer, bool freeze)
386{
387 struct cgroup_subsys_state *pos;
388
389 /*
390 * Update all its descendants in pre-order traversal. Each
391 * descendant will try to inherit its parent's FREEZING state as
392 * CGROUP_FREEZING_PARENT.
393 */
394 mutex_lock(&freezer_mutex);
395 rcu_read_lock();
396 css_for_each_descendant_pre(pos, &freezer->css) {
397 struct freezer *pos_f = css_freezer(pos);
398 struct freezer *parent = parent_freezer(pos_f);
399
400 if (!css_tryget_online(pos))
401 continue;
402 rcu_read_unlock();
403
404 if (pos_f == freezer)
405 freezer_apply_state(pos_f, freeze,
406 CGROUP_FREEZING_SELF);
407 else
408 freezer_apply_state(pos_f,
409 parent->state & CGROUP_FREEZING,
410 CGROUP_FREEZING_PARENT);
411
412 rcu_read_lock();
413 css_put(pos);
414 }
415 rcu_read_unlock();
416 mutex_unlock(&freezer_mutex);
417}
418
419static ssize_t freezer_write(struct kernfs_open_file *of,
420 char *buf, size_t nbytes, loff_t off)
421{
422 bool freeze;
423
424 buf = strstrip(buf);
425
426 if (strcmp(buf, freezer_state_strs(0)) == 0)
427 freeze = false;
428 else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
429 freeze = true;
430 else
431 return -EINVAL;
432
433 freezer_change_state(css_freezer(of_css(of)), freeze);
434 return nbytes;
435}
436
437static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
438 struct cftype *cft)
439{
440 struct freezer *freezer = css_freezer(css);
441
442 return (bool)(freezer->state & CGROUP_FREEZING_SELF);
443}
444
445static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
446 struct cftype *cft)
447{
448 struct freezer *freezer = css_freezer(css);
449
450 return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
451}
452
453static struct cftype files[] = {
454 {
455 .name = "state",
456 .flags = CFTYPE_NOT_ON_ROOT,
457 .seq_show = freezer_read,
458 .write = freezer_write,
459 },
460 {
461 .name = "self_freezing",
462 .flags = CFTYPE_NOT_ON_ROOT,
463 .read_u64 = freezer_self_freezing_read,
464 },
465 {
466 .name = "parent_freezing",
467 .flags = CFTYPE_NOT_ON_ROOT,
468 .read_u64 = freezer_parent_freezing_read,
469 },
470 { } /* terminate */
471};
472
473struct cgroup_subsys freezer_cgrp_subsys = {
474 .css_alloc = freezer_css_alloc,
475 .css_online = freezer_css_online,
476 .css_offline = freezer_css_offline,
477 .css_free = freezer_css_free,
478 .attach = freezer_attach,
479 .fork = freezer_fork,
480 .legacy_cftypes = files,
481};
1/*
2 * cgroup_freezer.c - control group freezer subsystem
3 *
4 * Copyright IBM Corporation, 2007
5 *
6 * Author : Cedric Le Goater <clg@fr.ibm.com>
7 *
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.
11 *
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.
15 */
16
17#include <linux/module.h>
18#include <linux/slab.h>
19#include <linux/cgroup.h>
20#include <linux/fs.h>
21#include <linux/uaccess.h>
22#include <linux/freezer.h>
23#include <linux/seq_file.h>
24
25enum freezer_state {
26 CGROUP_THAWED = 0,
27 CGROUP_FREEZING,
28 CGROUP_FROZEN,
29};
30
31struct freezer {
32 struct cgroup_subsys_state css;
33 enum freezer_state state;
34 spinlock_t lock; /* protects _writes_ to state */
35};
36
37static inline struct freezer *cgroup_freezer(
38 struct cgroup *cgroup)
39{
40 return container_of(
41 cgroup_subsys_state(cgroup, freezer_subsys_id),
42 struct freezer, css);
43}
44
45static inline struct freezer *task_freezer(struct task_struct *task)
46{
47 return container_of(task_subsys_state(task, freezer_subsys_id),
48 struct freezer, css);
49}
50
51static inline int __cgroup_freezing_or_frozen(struct task_struct *task)
52{
53 enum freezer_state state = task_freezer(task)->state;
54 return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN);
55}
56
57int cgroup_freezing_or_frozen(struct task_struct *task)
58{
59 int result;
60 task_lock(task);
61 result = __cgroup_freezing_or_frozen(task);
62 task_unlock(task);
63 return result;
64}
65
66/*
67 * cgroups_write_string() limits the size of freezer state strings to
68 * CGROUP_LOCAL_BUFFER_SIZE
69 */
70static const char *freezer_state_strs[] = {
71 "THAWED",
72 "FREEZING",
73 "FROZEN",
74};
75
76/*
77 * State diagram
78 * Transitions are caused by userspace writes to the freezer.state file.
79 * The values in parenthesis are state labels. The rest are edge labels.
80 *
81 * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
82 * ^ ^ | |
83 * | \_______THAWED_______/ |
84 * \__________________________THAWED____________/
85 */
86
87struct cgroup_subsys freezer_subsys;
88
89/* Locks taken and their ordering
90 * ------------------------------
91 * cgroup_mutex (AKA cgroup_lock)
92 * freezer->lock
93 * css_set_lock
94 * task->alloc_lock (AKA task_lock)
95 * task->sighand->siglock
96 *
97 * cgroup code forces css_set_lock to be taken before task->alloc_lock
98 *
99 * freezer_create(), freezer_destroy():
100 * cgroup_mutex [ by cgroup core ]
101 *
102 * freezer_can_attach():
103 * cgroup_mutex (held by caller of can_attach)
104 *
105 * cgroup_freezing_or_frozen():
106 * task->alloc_lock (to get task's cgroup)
107 *
108 * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
109 * freezer->lock
110 * sighand->siglock (if the cgroup is freezing)
111 *
112 * freezer_read():
113 * cgroup_mutex
114 * freezer->lock
115 * write_lock css_set_lock (cgroup iterator start)
116 * task->alloc_lock
117 * read_lock css_set_lock (cgroup iterator start)
118 *
119 * freezer_write() (freeze):
120 * cgroup_mutex
121 * freezer->lock
122 * write_lock css_set_lock (cgroup iterator start)
123 * task->alloc_lock
124 * read_lock css_set_lock (cgroup iterator start)
125 * sighand->siglock (fake signal delivery inside freeze_task())
126 *
127 * freezer_write() (unfreeze):
128 * cgroup_mutex
129 * freezer->lock
130 * write_lock css_set_lock (cgroup iterator start)
131 * task->alloc_lock
132 * read_lock css_set_lock (cgroup iterator start)
133 * task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
134 * sighand->siglock
135 */
136static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
137 struct cgroup *cgroup)
138{
139 struct freezer *freezer;
140
141 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
142 if (!freezer)
143 return ERR_PTR(-ENOMEM);
144
145 spin_lock_init(&freezer->lock);
146 freezer->state = CGROUP_THAWED;
147 return &freezer->css;
148}
149
150static void freezer_destroy(struct cgroup_subsys *ss,
151 struct cgroup *cgroup)
152{
153 kfree(cgroup_freezer(cgroup));
154}
155
156/*
157 * The call to cgroup_lock() in the freezer.state write method prevents
158 * a write to that file racing against an attach, and hence the
159 * can_attach() result will remain valid until the attach completes.
160 */
161static int freezer_can_attach(struct cgroup_subsys *ss,
162 struct cgroup *new_cgroup,
163 struct task_struct *task)
164{
165 struct freezer *freezer;
166
167 /*
168 * Anything frozen can't move or be moved to/from.
169 */
170
171 freezer = cgroup_freezer(new_cgroup);
172 if (freezer->state != CGROUP_THAWED)
173 return -EBUSY;
174
175 return 0;
176}
177
178static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
179{
180 rcu_read_lock();
181 if (__cgroup_freezing_or_frozen(tsk)) {
182 rcu_read_unlock();
183 return -EBUSY;
184 }
185 rcu_read_unlock();
186 return 0;
187}
188
189static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
190{
191 struct freezer *freezer;
192
193 /*
194 * No lock is needed, since the task isn't on tasklist yet,
195 * so it can't be moved to another cgroup, which means the
196 * freezer won't be removed and will be valid during this
197 * function call. Nevertheless, apply RCU read-side critical
198 * section to suppress RCU lockdep false positives.
199 */
200 rcu_read_lock();
201 freezer = task_freezer(task);
202 rcu_read_unlock();
203
204 /*
205 * The root cgroup is non-freezable, so we can skip the
206 * following check.
207 */
208 if (!freezer->css.cgroup->parent)
209 return;
210
211 spin_lock_irq(&freezer->lock);
212 BUG_ON(freezer->state == CGROUP_FROZEN);
213
214 /* Locking avoids race with FREEZING -> THAWED transitions. */
215 if (freezer->state == CGROUP_FREEZING)
216 freeze_task(task, true);
217 spin_unlock_irq(&freezer->lock);
218}
219
220/*
221 * caller must hold freezer->lock
222 */
223static void update_if_frozen(struct cgroup *cgroup,
224 struct freezer *freezer)
225{
226 struct cgroup_iter it;
227 struct task_struct *task;
228 unsigned int nfrozen = 0, ntotal = 0;
229 enum freezer_state old_state = freezer->state;
230
231 cgroup_iter_start(cgroup, &it);
232 while ((task = cgroup_iter_next(cgroup, &it))) {
233 ntotal++;
234 if (frozen(task))
235 nfrozen++;
236 }
237
238 if (old_state == CGROUP_THAWED) {
239 BUG_ON(nfrozen > 0);
240 } else if (old_state == CGROUP_FREEZING) {
241 if (nfrozen == ntotal)
242 freezer->state = CGROUP_FROZEN;
243 } else { /* old_state == CGROUP_FROZEN */
244 BUG_ON(nfrozen != ntotal);
245 }
246
247 cgroup_iter_end(cgroup, &it);
248}
249
250static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
251 struct seq_file *m)
252{
253 struct freezer *freezer;
254 enum freezer_state state;
255
256 if (!cgroup_lock_live_group(cgroup))
257 return -ENODEV;
258
259 freezer = cgroup_freezer(cgroup);
260 spin_lock_irq(&freezer->lock);
261 state = freezer->state;
262 if (state == CGROUP_FREEZING) {
263 /* We change from FREEZING to FROZEN lazily if the cgroup was
264 * only partially frozen when we exitted write. */
265 update_if_frozen(cgroup, freezer);
266 state = freezer->state;
267 }
268 spin_unlock_irq(&freezer->lock);
269 cgroup_unlock();
270
271 seq_puts(m, freezer_state_strs[state]);
272 seq_putc(m, '\n');
273 return 0;
274}
275
276static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
277{
278 struct cgroup_iter it;
279 struct task_struct *task;
280 unsigned int num_cant_freeze_now = 0;
281
282 freezer->state = CGROUP_FREEZING;
283 cgroup_iter_start(cgroup, &it);
284 while ((task = cgroup_iter_next(cgroup, &it))) {
285 if (!freeze_task(task, true))
286 continue;
287 if (frozen(task))
288 continue;
289 if (!freezing(task) && !freezer_should_skip(task))
290 num_cant_freeze_now++;
291 }
292 cgroup_iter_end(cgroup, &it);
293
294 return num_cant_freeze_now ? -EBUSY : 0;
295}
296
297static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
298{
299 struct cgroup_iter it;
300 struct task_struct *task;
301
302 cgroup_iter_start(cgroup, &it);
303 while ((task = cgroup_iter_next(cgroup, &it))) {
304 thaw_process(task);
305 }
306 cgroup_iter_end(cgroup, &it);
307
308 freezer->state = CGROUP_THAWED;
309}
310
311static int freezer_change_state(struct cgroup *cgroup,
312 enum freezer_state goal_state)
313{
314 struct freezer *freezer;
315 int retval = 0;
316
317 freezer = cgroup_freezer(cgroup);
318
319 spin_lock_irq(&freezer->lock);
320
321 update_if_frozen(cgroup, freezer);
322 if (goal_state == freezer->state)
323 goto out;
324
325 switch (goal_state) {
326 case CGROUP_THAWED:
327 unfreeze_cgroup(cgroup, freezer);
328 break;
329 case CGROUP_FROZEN:
330 retval = try_to_freeze_cgroup(cgroup, freezer);
331 break;
332 default:
333 BUG();
334 }
335out:
336 spin_unlock_irq(&freezer->lock);
337
338 return retval;
339}
340
341static int freezer_write(struct cgroup *cgroup,
342 struct cftype *cft,
343 const char *buffer)
344{
345 int retval;
346 enum freezer_state goal_state;
347
348 if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
349 goal_state = CGROUP_THAWED;
350 else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
351 goal_state = CGROUP_FROZEN;
352 else
353 return -EINVAL;
354
355 if (!cgroup_lock_live_group(cgroup))
356 return -ENODEV;
357 retval = freezer_change_state(cgroup, goal_state);
358 cgroup_unlock();
359 return retval;
360}
361
362static struct cftype files[] = {
363 {
364 .name = "state",
365 .read_seq_string = freezer_read,
366 .write_string = freezer_write,
367 },
368};
369
370static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
371{
372 if (!cgroup->parent)
373 return 0;
374 return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
375}
376
377struct cgroup_subsys freezer_subsys = {
378 .name = "freezer",
379 .create = freezer_create,
380 .destroy = freezer_destroy,
381 .populate = freezer_populate,
382 .subsys_id = freezer_subsys_id,
383 .can_attach = freezer_can_attach,
384 .can_attach_task = freezer_can_attach_task,
385 .pre_attach = NULL,
386 .attach_task = NULL,
387 .attach = NULL,
388 .fork = freezer_fork,
389 .exit = NULL,
390};