projects/linux·blob v3.18 · refs

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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 <[email protected]>
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_subsys_state *new_css,
159 struct cgroup_taskset *tset)
160{
161 struct freezer *freezer = css_freezer(new_css);
162 struct task_struct *task;
163 bool clear_frozen = false;
164
165 mutex_lock(&freezer_mutex);
166
167 /*
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.
172 *
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.
176 */
177 cgroup_taskset_for_each(task, tset) {
178 if (!(freezer->state & CGROUP_FREEZING)) {
179 __thaw_task(task);
180 } else {
181 freeze_task(task);
182 freezer->state &= ~CGROUP_FROZEN;
183 clear_frozen = true;
184 }
185 }
186
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;
191 }
192
193 mutex_unlock(&freezer_mutex);
194}
195
196/**
197 * freezer_fork - cgroup post fork callback
198 * @task: a task which has just been forked
199 *
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
204 * state.
205 */
206static void freezer_fork(struct task_struct *task)
207{
208 struct freezer *freezer;
209
210 /*
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
215 * right thing to do.
216 */
217 if (task_css_is_root(task, freezer_cgrp_id))
218 return;
219
220 mutex_lock(&freezer_mutex);
221 rcu_read_lock();
222
223 freezer = task_freezer(task);
224 if (freezer->state & CGROUP_FREEZING)
225 freeze_task(task);
226
227 rcu_read_unlock();
228 mutex_unlock(&freezer_mutex);
229}
230
231/**
232 * update_if_frozen - update whether a cgroup finished freezing
233 * @css: css of interest
234 *
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.
239 *
240 * The caller is responsible for grabbing RCU read lock and calling
241 * update_if_frozen() on all descendants prior to invoking this function.
242 *
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.
246 */
247static void update_if_frozen(struct cgroup_subsys_state *css)
248{
249 struct freezer *freezer = css_freezer(css);
250 struct cgroup_subsys_state *pos;
251 struct css_task_iter it;
252 struct task_struct *task;
253
254 lockdep_assert_held(&freezer_mutex);
255
256 if (!(freezer->state & CGROUP_FREEZING) ||
257 (freezer->state & CGROUP_FROZEN))
258 return;
259
260 /* are all (live) children frozen? */
261 rcu_read_lock();
262 css_for_each_child(pos, css) {
263 struct freezer *child = css_freezer(pos);
264
265 if ((child->state & CGROUP_FREEZER_ONLINE) &&
266 !(child->state & CGROUP_FROZEN)) {
267 rcu_read_unlock();
268 return;
269 }
270 }
271 rcu_read_unlock();
272
273 /* are all tasks frozen? */
274 css_task_iter_start(css, &it);
275
276 while ((task = css_task_iter_next(&it))) {
277 if (freezing(task)) {
278 /*
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.
283 */
284 if (!frozen(task) && !freezer_should_skip(task))
285 goto out_iter_end;
286 }
287 }
288
289 freezer->state |= CGROUP_FROZEN;
290out_iter_end:
291 css_task_iter_end(&it);
292}
293
294static int freezer_read(struct seq_file *m, void *v)
295{
296 struct cgroup_subsys_state *css = seq_css(m), *pos;
297
298 mutex_lock(&freezer_mutex);
299 rcu_read_lock();
300
301 /* update states bottom-up */
302 css_for_each_descendant_post(pos, css) {
303 if (!css_tryget_online(pos))
304 continue;
305 rcu_read_unlock();
306
307 update_if_frozen(pos);
308
309 rcu_read_lock();
310 css_put(pos);
311 }
312
313 rcu_read_unlock();
314 mutex_unlock(&freezer_mutex);
315
316 seq_puts(m, freezer_state_strs(css_freezer(css)->state));
317 seq_putc(m, '\n');
318 return 0;
319}
320
321static void freeze_cgroup(struct freezer *freezer)
322{
323 struct css_task_iter it;
324 struct task_struct *task;
325
326 css_task_iter_start(&freezer->css, &it);
327 while ((task = css_task_iter_next(&it)))
328 freeze_task(task);
329 css_task_iter_end(&it);
330}
331
332static void unfreeze_cgroup(struct freezer *freezer)
333{
334 struct css_task_iter it;
335 struct task_struct *task;
336
337 css_task_iter_start(&freezer->css, &it);
338 while ((task = css_task_iter_next(&it)))
339 __thaw_task(task);
340 css_task_iter_end(&it);
341}
342
343/**
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
348 *
349 * Set or clear @state on @cgroup according to @freeze, and perform
350 * freezing or thawing as necessary.
351 */
352static void freezer_apply_state(struct freezer *freezer, bool freeze,
353 unsigned int state)
354{
355 /* also synchronizes against task migration, see freezer_attach() */
356 lockdep_assert_held(&freezer_mutex);
357
358 if (!(freezer->state & CGROUP_FREEZER_ONLINE))
359 return;
360
361 if (freeze) {
362 if (!(freezer->state & CGROUP_FREEZING))
363 atomic_inc(&system_freezing_cnt);
364 freezer->state |= state;
365 freeze_cgroup(freezer);
366 } else {
367 bool was_freezing = freezer->state & CGROUP_FREEZING;
368
369 freezer->state &= ~state;
370
371 if (!(freezer->state & CGROUP_FREEZING)) {
372 if (was_freezing)
373 atomic_dec(&system_freezing_cnt);
374 freezer->state &= ~CGROUP_FROZEN;
375 unfreeze_cgroup(freezer);
376 }
377 }
378}
379
380/**
381 * freezer_change_state - change the freezing state of a cgroup_freezer
382 * @freezer: freezer of interest
383 * @freeze: whether to freeze or thaw
384 *
385 * Freeze or thaw @freezer according to @freeze. The operations are
386 * recursive - all descendants of @freezer will be affected.
387 */
388static void freezer_change_state(struct freezer *freezer, bool freeze)
389{
390 struct cgroup_subsys_state *pos;
391
392 /*
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.
396 */
397 mutex_lock(&freezer_mutex);
398 rcu_read_lock();
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);
402
403 if (!css_tryget_online(pos))
404 continue;
405 rcu_read_unlock();
406
407 if (pos_f == freezer)
408 freezer_apply_state(pos_f, freeze,
409 CGROUP_FREEZING_SELF);
410 else
411 freezer_apply_state(pos_f,
412 parent->state & CGROUP_FREEZING,
413 CGROUP_FREEZING_PARENT);
414
415 rcu_read_lock();
416 css_put(pos);
417 }
418 rcu_read_unlock();
419 mutex_unlock(&freezer_mutex);
420}
421
422static ssize_t freezer_write(struct kernfs_open_file *of,
423 char *buf, size_t nbytes, loff_t off)
424{
425 bool freeze;
426
427 buf = strstrip(buf);
428
429 if (strcmp(buf, freezer_state_strs(0)) == 0)
430 freeze = false;
431 else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
432 freeze = true;
433 else
434 return -EINVAL;
435
436 freezer_change_state(css_freezer(of_css(of)), freeze);
437 return nbytes;
438}
439
440static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
441 struct cftype *cft)
442{
443 struct freezer *freezer = css_freezer(css);
444
445 return (bool)(freezer->state & CGROUP_FREEZING_SELF);
446}
447
448static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
449 struct cftype *cft)
450{
451 struct freezer *freezer = css_freezer(css);
452
453 return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
454}
455
456static struct cftype files[] = {
457 {
458 .name = "state",
459 .flags = CFTYPE_NOT_ON_ROOT,
460 .seq_show = freezer_read,
461 .write = freezer_write,
462 },
463 {
464 .name = "self_freezing",
465 .flags = CFTYPE_NOT_ON_ROOT,
466 .read_u64 = freezer_self_freezing_read,
467 },
468 {
469 .name = "parent_freezing",
470 .flags = CFTYPE_NOT_ON_ROOT,
471 .read_u64 = freezer_parent_freezing_read,
472 },
473 { } /* terminate */
474};
475
476struct 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,
484};