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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 | */ | |
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 | 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 | bool 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 | ||
76 | static 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 | ||
85 | static struct cgroup_subsys_state * | |
86 | freezer_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 | */ | |
105 | static 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 | */ | |
130 | static 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 | ||
144 | static 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 | */ | |
158 | static 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 | */ | |
203 | static 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 | */ | |
244 | static 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; | |
287 | out_iter_end: | |
288 | css_task_iter_end(&it); | |
289 | } | |
290 | ||
291 | static 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 | ||
318 | static 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 | ||
329 | static 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 | */ | |
349 | static 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 | */ | |
385 | static 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 | ||
419 | static 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 | ||
437 | static 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 | ||
445 | static 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 | ||
453 | static 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 | ||
473 | struct 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 | }; |