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#include <linux/cpu.h>
26
27/*
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.
33 */
34enum 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 */
39
40 /* mask for all FREEZING flags */
41 CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
42};
43
44struct freezer {
45 struct cgroup_subsys_state css;
46 unsigned int state;
47};
48
49static DEFINE_MUTEX(freezer_mutex);
50
51static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
52{
53 return css ? container_of(css, struct freezer, css) : NULL;
54}
55
56static inline struct freezer *task_freezer(struct task_struct *task)
57{
58 return css_freezer(css: task_css(task, subsys_id: freezer_cgrp_id));
59}
60
61static struct freezer *parent_freezer(struct freezer *freezer)
62{
63 return css_freezer(css: freezer->css.parent);
64}
65
66bool cgroup_freezing(struct task_struct *task)
67{
68 bool ret;
69 unsigned int state;
70
71 rcu_read_lock();
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.
75 */
76 state = task_freezer(task)->state;
77 ret = (state & CGROUP_FREEZING) && !(state & CGROUP_FROZEN);
78 rcu_read_unlock();
79
80 return ret;
81}
82
83static const char *freezer_state_strs(unsigned int state)
84{
85 if (state & CGROUP_FROZEN)
86 return "FROZEN";
87 if (state & CGROUP_FREEZING)
88 return "FREEZING";
89 return "THAWED";
90};
91
92static struct cgroup_subsys_state *
93freezer_css_alloc(struct cgroup_subsys_state *parent_css)
94{
95 struct freezer *freezer;
96
97 freezer = kzalloc(size: sizeof(struct freezer), GFP_KERNEL);
98 if (!freezer)
99 return ERR_PTR(error: -ENOMEM);
100
101 return &freezer->css;
102}
103
104/**
105 * freezer_css_online - commit creation of a freezer css
106 * @css: css being created
107 *
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
110 * freezer->lock.
111 */
112static int freezer_css_online(struct cgroup_subsys_state *css)
113{
114 struct freezer *freezer = css_freezer(css);
115 struct freezer *parent = parent_freezer(freezer);
116
117 cpus_read_lock();
118 mutex_lock(&freezer_mutex);
119
120 freezer->state |= CGROUP_FREEZER_ONLINE;
121
122 if (parent && (parent->state & CGROUP_FREEZING)) {
123 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
124 static_branch_inc_cpuslocked(&freezer_active);
125 }
126
127 mutex_unlock(lock: &freezer_mutex);
128 cpus_read_unlock();
129 return 0;
130}
131
132/**
133 * freezer_css_offline - initiate destruction of a freezer css
134 * @css: css being destroyed
135 *
136 * @css is going away. Mark it dead and decrement system_freezing_count if
137 * it was holding one.
138 */
139static void freezer_css_offline(struct cgroup_subsys_state *css)
140{
141 struct freezer *freezer = css_freezer(css);
142
143 cpus_read_lock();
144 mutex_lock(&freezer_mutex);
145
146 if (freezer->state & CGROUP_FREEZING)
147 static_branch_dec_cpuslocked(&freezer_active);
148
149 freezer->state = 0;
150
151 mutex_unlock(lock: &freezer_mutex);
152 cpus_read_unlock();
153}
154
155static void freezer_css_free(struct cgroup_subsys_state *css)
156{
157 kfree(objp: css_freezer(css));
158}
159
160/*
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.
164 *
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.
168 */
169static void freezer_attach(struct cgroup_taskset *tset)
170{
171 struct task_struct *task;
172 struct cgroup_subsys_state *new_css;
173
174 mutex_lock(&freezer_mutex);
175
176 /*
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.
181 *
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.
185 */
186 cgroup_taskset_for_each(task, new_css, tset) {
187 struct freezer *freezer = css_freezer(css: new_css);
188
189 if (!(freezer->state & CGROUP_FREEZING)) {
190 __thaw_task(t: task);
191 } else {
192 freeze_task(p: task);
193
194 /* clear FROZEN and propagate upwards */
195 while (freezer && (freezer->state & CGROUP_FROZEN)) {
196 freezer->state &= ~CGROUP_FROZEN;
197 freezer = parent_freezer(freezer);
198 }
199 }
200 }
201
202 mutex_unlock(lock: &freezer_mutex);
203}
204
205/**
206 * freezer_fork - cgroup post fork callback
207 * @task: a task which has just been forked
208 *
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
213 * state.
214 */
215static void freezer_fork(struct task_struct *task)
216{
217 struct freezer *freezer;
218
219 /*
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
224 * right thing to do.
225 */
226 if (task_css_is_root(task, subsys_id: freezer_cgrp_id))
227 return;
228
229 mutex_lock(&freezer_mutex);
230 rcu_read_lock();
231
232 freezer = task_freezer(task);
233 if (freezer->state & CGROUP_FREEZING)
234 freeze_task(p: task);
235
236 rcu_read_unlock();
237 mutex_unlock(lock: &freezer_mutex);
238}
239
240/**
241 * update_if_frozen - update whether a cgroup finished freezing
242 * @css: css of interest
243 *
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.
248 *
249 * The caller is responsible for grabbing RCU read lock and calling
250 * update_if_frozen() on all descendants prior to invoking this function.
251 *
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.
255 */
256static void update_if_frozen(struct cgroup_subsys_state *css)
257{
258 struct freezer *freezer = css_freezer(css);
259 struct cgroup_subsys_state *pos;
260 struct css_task_iter it;
261 struct task_struct *task;
262
263 lockdep_assert_held(&freezer_mutex);
264
265 if (!(freezer->state & CGROUP_FREEZING) ||
266 (freezer->state & CGROUP_FROZEN))
267 return;
268
269 /* are all (live) children frozen? */
270 rcu_read_lock();
271 css_for_each_child(pos, css) {
272 struct freezer *child = css_freezer(css: pos);
273
274 if ((child->state & CGROUP_FREEZER_ONLINE) &&
275 !(child->state & CGROUP_FROZEN)) {
276 rcu_read_unlock();
277 return;
278 }
279 }
280 rcu_read_unlock();
281
282 /* are all tasks frozen? */
283 css_task_iter_start(css, flags: 0, it: &it);
284
285 while ((task = css_task_iter_next(it: &it))) {
286 if (freezing(p: task) && !frozen(p: task))
287 goto out_iter_end;
288 }
289
290 freezer->state |= CGROUP_FROZEN;
291out_iter_end:
292 css_task_iter_end(it: &it);
293}
294
295static int freezer_read(struct seq_file *m, void *v)
296{
297 struct cgroup_subsys_state *css = seq_css(seq: m), *pos;
298
299 mutex_lock(&freezer_mutex);
300 rcu_read_lock();
301
302 /* update states bottom-up */
303 css_for_each_descendant_post(pos, css) {
304 if (!css_tryget_online(css: pos))
305 continue;
306 rcu_read_unlock();
307
308 update_if_frozen(css: pos);
309
310 rcu_read_lock();
311 css_put(css: pos);
312 }
313
314 rcu_read_unlock();
315 mutex_unlock(lock: &freezer_mutex);
316
317 seq_puts(m, s: freezer_state_strs(state: css_freezer(css)->state));
318 seq_putc(m, c: '\n');
319 return 0;
320}
321
322static void freeze_cgroup(struct freezer *freezer)
323{
324 struct css_task_iter it;
325 struct task_struct *task;
326
327 css_task_iter_start(css: &freezer->css, flags: 0, it: &it);
328 while ((task = css_task_iter_next(it: &it)))
329 freeze_task(p: task);
330 css_task_iter_end(it: &it);
331}
332
333static void unfreeze_cgroup(struct freezer *freezer)
334{
335 struct css_task_iter it;
336 struct task_struct *task;
337
338 css_task_iter_start(css: &freezer->css, flags: 0, it: &it);
339 while ((task = css_task_iter_next(it: &it)))
340 __thaw_task(t: task);
341 css_task_iter_end(it: &it);
342}
343
344/**
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
349 *
350 * Set or clear @state on @cgroup according to @freeze, and perform
351 * freezing or thawing as necessary.
352 */
353static void freezer_apply_state(struct freezer *freezer, bool freeze,
354 unsigned int state)
355{
356 /* also synchronizes against task migration, see freezer_attach() */
357 lockdep_assert_held(&freezer_mutex);
358
359 if (!(freezer->state & CGROUP_FREEZER_ONLINE))
360 return;
361
362 if (freeze) {
363 if (!(freezer->state & CGROUP_FREEZING))
364 static_branch_inc_cpuslocked(&freezer_active);
365 freezer->state |= state;
366 freeze_cgroup(freezer);
367 } else {
368 bool was_freezing = freezer->state & CGROUP_FREEZING;
369
370 freezer->state &= ~state;
371
372 if (!(freezer->state & CGROUP_FREEZING)) {
373 freezer->state &= ~CGROUP_FROZEN;
374 if (was_freezing)
375 static_branch_dec_cpuslocked(&freezer_active);
376 unfreeze_cgroup(freezer);
377 }
378 }
379}
380
381/**
382 * freezer_change_state - change the freezing state of a cgroup_freezer
383 * @freezer: freezer of interest
384 * @freeze: whether to freeze or thaw
385 *
386 * Freeze or thaw @freezer according to @freeze. The operations are
387 * recursive - all descendants of @freezer will be affected.
388 */
389static void freezer_change_state(struct freezer *freezer, bool freeze)
390{
391 struct cgroup_subsys_state *pos;
392
393 cpus_read_lock();
394 /*
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.
398 */
399 mutex_lock(&freezer_mutex);
400 rcu_read_lock();
401 css_for_each_descendant_pre(pos, &freezer->css) {
402 struct freezer *pos_f = css_freezer(css: pos);
403 struct freezer *parent = parent_freezer(freezer: pos_f);
404
405 if (!css_tryget_online(css: pos))
406 continue;
407 rcu_read_unlock();
408
409 if (pos_f == freezer)
410 freezer_apply_state(freezer: pos_f, freeze,
411 state: CGROUP_FREEZING_SELF);
412 else
413 freezer_apply_state(freezer: pos_f,
414 freeze: parent->state & CGROUP_FREEZING,
415 state: CGROUP_FREEZING_PARENT);
416
417 rcu_read_lock();
418 css_put(css: pos);
419 }
420 rcu_read_unlock();
421 mutex_unlock(lock: &freezer_mutex);
422 cpus_read_unlock();
423}
424
425static ssize_t freezer_write(struct kernfs_open_file *of,
426 char *buf, size_t nbytes, loff_t off)
427{
428 bool freeze;
429
430 buf = strstrip(str: buf);
431
432 if (strcmp(buf, freezer_state_strs(state: 0)) == 0)
433 freeze = false;
434 else if (strcmp(buf, freezer_state_strs(state: CGROUP_FROZEN)) == 0)
435 freeze = true;
436 else
437 return -EINVAL;
438
439 freezer_change_state(freezer: css_freezer(css: of_css(of)), freeze);
440 return nbytes;
441}
442
443static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
444 struct cftype *cft)
445{
446 struct freezer *freezer = css_freezer(css);
447
448 return (bool)(freezer->state & CGROUP_FREEZING_SELF);
449}
450
451static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
452 struct cftype *cft)
453{
454 struct freezer *freezer = css_freezer(css);
455
456 return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
457}
458
459static struct cftype files[] = {
460 {
461 .name = "state",
462 .flags = CFTYPE_NOT_ON_ROOT,
463 .seq_show = freezer_read,
464 .write = freezer_write,
465 },
466 {
467 .name = "self_freezing",
468 .flags = CFTYPE_NOT_ON_ROOT,
469 .read_u64 = freezer_self_freezing_read,
470 },
471 {
472 .name = "parent_freezing",
473 .flags = CFTYPE_NOT_ON_ROOT,
474 .read_u64 = freezer_parent_freezing_read,
475 },
476 { } /* terminate */
477};
478
479struct 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,
487};
488

source code of linux/kernel/cgroup/legacy_freezer.c