Line data Source code
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 : */
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 */
38 :
39 : /* mask for all FREEZING flags */
40 : CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
41 : };
42 :
43 : struct freezer {
44 : struct cgroup_subsys_state css;
45 : unsigned int state;
46 : };
47 :
48 : static DEFINE_MUTEX(freezer_mutex);
49 :
50 : static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
51 : {
52 2 : return css ? container_of(css, struct freezer, css) : NULL;
53 : }
54 :
55 : static inline struct freezer *task_freezer(struct task_struct *task)
56 : {
57 : return css_freezer(task_css(task, freezer_cgrp_id));
58 : }
59 :
60 : static struct freezer *parent_freezer(struct freezer *freezer)
61 : {
62 : return css_freezer(freezer->css.parent);
63 : }
64 :
65 0 : bool cgroup_freezing(struct task_struct *task)
66 : {
67 : bool ret;
68 :
69 : rcu_read_lock();
70 0 : ret = task_freezer(task)->state & CGROUP_FREEZING;
71 : rcu_read_unlock();
72 :
73 0 : return ret;
74 : }
75 :
76 : static const char *freezer_state_strs(unsigned int state)
77 : {
78 0 : if (state & CGROUP_FROZEN)
79 : return "FROZEN";
80 0 : if (state & CGROUP_FREEZING)
81 : return "FREEZING";
82 : return "THAWED";
83 : };
84 :
85 : static struct cgroup_subsys_state *
86 1 : freezer_css_alloc(struct cgroup_subsys_state *parent_css)
87 : {
88 : struct freezer *freezer;
89 :
90 : freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
91 1 : if (!freezer)
92 : return ERR_PTR(-ENOMEM);
93 :
94 1 : 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 : */
105 1 : static int freezer_css_online(struct cgroup_subsys_state *css)
106 : {
107 1 : struct freezer *freezer = css_freezer(css);
108 : struct freezer *parent = parent_freezer(freezer);
109 :
110 1 : mutex_lock(&freezer_mutex);
111 :
112 1 : freezer->state |= CGROUP_FREEZER_ONLINE;
113 :
114 1 : if (parent && (parent->state & CGROUP_FREEZING)) {
115 0 : freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
116 : atomic_inc(&system_freezing_cnt);
117 : }
118 :
119 1 : mutex_unlock(&freezer_mutex);
120 1 : 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 : */
130 0 : static void freezer_css_offline(struct cgroup_subsys_state *css)
131 : {
132 : struct freezer *freezer = css_freezer(css);
133 :
134 0 : mutex_lock(&freezer_mutex);
135 :
136 0 : if (freezer->state & CGROUP_FREEZING)
137 : atomic_dec(&system_freezing_cnt);
138 :
139 0 : freezer->state = 0;
140 :
141 0 : mutex_unlock(&freezer_mutex);
142 0 : }
143 :
144 0 : static void freezer_css_free(struct cgroup_subsys_state *css)
145 : {
146 0 : kfree(css_freezer(css));
147 0 : }
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 : */
158 0 : static void freezer_attach(struct cgroup_subsys_state *new_css,
159 : struct cgroup_taskset *tset)
160 : {
161 0 : struct freezer *freezer = css_freezer(new_css);
162 : struct task_struct *task;
163 : bool clear_frozen = false;
164 :
165 0 : 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 0 : cgroup_taskset_for_each(task, tset) {
178 0 : if (!(freezer->state & CGROUP_FREEZING)) {
179 0 : __thaw_task(task);
180 : } else {
181 0 : freeze_task(task);
182 0 : freezer->state &= ~CGROUP_FROZEN;
183 : clear_frozen = true;
184 : }
185 : }
186 :
187 : /* propagate FROZEN clearing upwards */
188 0 : while (clear_frozen && (freezer = parent_freezer(freezer))) {
189 0 : freezer->state &= ~CGROUP_FROZEN;
190 0 : clear_frozen = freezer->state & CGROUP_FREEZING;
191 : }
192 :
193 0 : mutex_unlock(&freezer_mutex);
194 0 : }
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 : */
206 2992 : static 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 2992 : if (task_css_is_root(task, freezer_cgrp_id))
218 2992 : return;
219 :
220 0 : mutex_lock(&freezer_mutex);
221 : rcu_read_lock();
222 :
223 : freezer = task_freezer(task);
224 0 : if (freezer->state & CGROUP_FREEZING)
225 0 : freeze_task(task);
226 :
227 : rcu_read_unlock();
228 0 : 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 : */
247 0 : static 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 0 : if (!(freezer->state & CGROUP_FREEZING) ||
257 0 : (freezer->state & CGROUP_FROZEN))
258 0 : return;
259 :
260 : /* are all (live) children frozen? */
261 : rcu_read_lock();
262 0 : css_for_each_child(pos, css) {
263 : struct freezer *child = css_freezer(pos);
264 :
265 0 : 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 0 : css_task_iter_start(css, &it);
275 :
276 0 : while ((task = css_task_iter_next(&it))) {
277 0 : 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 0 : if (!frozen(task) && !freezer_should_skip(task))
285 : goto out_iter_end;
286 : }
287 : }
288 :
289 0 : freezer->state |= CGROUP_FROZEN;
290 : out_iter_end:
291 0 : css_task_iter_end(&it);
292 : }
293 :
294 0 : static int freezer_read(struct seq_file *m, void *v)
295 : {
296 : struct cgroup_subsys_state *css = seq_css(m), *pos;
297 :
298 0 : mutex_lock(&freezer_mutex);
299 : rcu_read_lock();
300 :
301 : /* update states bottom-up */
302 0 : css_for_each_descendant_post(pos, css) {
303 0 : if (!css_tryget_online(pos))
304 0 : continue;
305 : rcu_read_unlock();
306 :
307 0 : update_if_frozen(pos);
308 :
309 : rcu_read_lock();
310 : css_put(pos);
311 : }
312 :
313 : rcu_read_unlock();
314 0 : mutex_unlock(&freezer_mutex);
315 :
316 0 : seq_puts(m, freezer_state_strs(css_freezer(css)->state));
317 0 : seq_putc(m, '\n');
318 0 : return 0;
319 : }
320 :
321 0 : static void freeze_cgroup(struct freezer *freezer)
322 : {
323 : struct css_task_iter it;
324 : struct task_struct *task;
325 :
326 0 : css_task_iter_start(&freezer->css, &it);
327 0 : while ((task = css_task_iter_next(&it)))
328 0 : freeze_task(task);
329 0 : css_task_iter_end(&it);
330 0 : }
331 :
332 0 : static void unfreeze_cgroup(struct freezer *freezer)
333 : {
334 : struct css_task_iter it;
335 : struct task_struct *task;
336 :
337 0 : css_task_iter_start(&freezer->css, &it);
338 0 : while ((task = css_task_iter_next(&it)))
339 0 : __thaw_task(task);
340 0 : css_task_iter_end(&it);
341 0 : }
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 : */
352 0 : static 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 0 : if (!(freezer->state & CGROUP_FREEZER_ONLINE))
359 0 : return;
360 :
361 0 : if (freeze) {
362 0 : if (!(freezer->state & CGROUP_FREEZING))
363 : atomic_inc(&system_freezing_cnt);
364 0 : freezer->state |= state;
365 0 : freeze_cgroup(freezer);
366 : } else {
367 0 : bool was_freezing = freezer->state & CGROUP_FREEZING;
368 :
369 0 : freezer->state &= ~state;
370 :
371 0 : if (!(freezer->state & CGROUP_FREEZING)) {
372 0 : if (was_freezing)
373 : atomic_dec(&system_freezing_cnt);
374 0 : freezer->state &= ~CGROUP_FROZEN;
375 0 : 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 : */
388 0 : static 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 0 : mutex_lock(&freezer_mutex);
398 : rcu_read_lock();
399 0 : css_for_each_descendant_pre(pos, &freezer->css) {
400 0 : struct freezer *pos_f = css_freezer(pos);
401 : struct freezer *parent = parent_freezer(pos_f);
402 :
403 0 : if (!css_tryget_online(pos))
404 0 : continue;
405 : rcu_read_unlock();
406 :
407 0 : if (pos_f == freezer)
408 0 : freezer_apply_state(pos_f, freeze,
409 : CGROUP_FREEZING_SELF);
410 : else
411 0 : freezer_apply_state(pos_f,
412 0 : parent->state & CGROUP_FREEZING,
413 : CGROUP_FREEZING_PARENT);
414 :
415 : rcu_read_lock();
416 : css_put(pos);
417 : }
418 : rcu_read_unlock();
419 0 : mutex_unlock(&freezer_mutex);
420 0 : }
421 :
422 0 : static 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 0 : if (strcmp(buf, freezer_state_strs(0)) == 0)
430 : freeze = false;
431 0 : else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
432 : freeze = true;
433 : else
434 : return -EINVAL;
435 :
436 0 : freezer_change_state(css_freezer(of_css(of)), freeze);
437 0 : return nbytes;
438 : }
439 :
440 0 : static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
441 : struct cftype *cft)
442 : {
443 : struct freezer *freezer = css_freezer(css);
444 :
445 0 : return (bool)(freezer->state & CGROUP_FREEZING_SELF);
446 : }
447 :
448 0 : static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
449 : struct cftype *cft)
450 : {
451 : struct freezer *freezer = css_freezer(css);
452 :
453 0 : return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
454 : }
455 :
456 : static 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 :
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,
484 : };
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