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
25 /*
26 * A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is
27 * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
28 * for "THAWED". FREEZING_PARENT is set if the parent freezer is FREEZING
29 * for whatever reason. IOW, a cgroup has FREEZING_PARENT set if one of
30 * its ancestors has FREEZING_SELF set.
31 */
32 enum freezer_state_flags {
33 CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */
34 CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */
35 CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */
36 CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */
37
38 /* mask for all FREEZING flags */
39 CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
40 };
41
42 struct freezer {
43 struct cgroup_subsys_state css;
44 unsigned int state;
45 spinlock_t lock;
46 };
47
48 static inline struct freezer *cgroup_freezer(struct cgroup *cgroup)
49 {
50 return container_of(cgroup_subsys_state(cgroup, freezer_subsys_id),
51 struct freezer, css);
52 }
53
54 static inline struct freezer *task_freezer(struct task_struct *task)
55 {
56 return container_of(task_subsys_state(task, freezer_subsys_id),
57 struct freezer, css);
58 }
59
60 static struct freezer *parent_freezer(struct freezer *freezer)
61 {
62 struct cgroup *pcg = freezer->css.cgroup->parent;
63
64 if (pcg)
65 return cgroup_freezer(pcg);
66 return NULL;
67 }
68
69 bool cgroup_freezing(struct task_struct *task)
70 {
71 bool ret;
72
73 rcu_read_lock();
74 ret = task_freezer(task)->state & CGROUP_FREEZING;
75 rcu_read_unlock();
76
77 return ret;
78 }
79
80 /*
81 * cgroups_write_string() limits the size of freezer state strings to
82 * CGROUP_LOCAL_BUFFER_SIZE
83 */
84 static const char *freezer_state_strs(unsigned int state)
85 {
86 if (state & CGROUP_FROZEN)
87 return "FROZEN";
88 if (state & CGROUP_FREEZING)
89 return "FREEZING";
90 return "THAWED";
91 };
92
93 struct cgroup_subsys freezer_subsys;
94
95 static struct cgroup_subsys_state *freezer_css_alloc(struct cgroup *cgroup)
96 {
97 struct freezer *freezer;
98
99 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
100 if (!freezer)
101 return ERR_PTR(-ENOMEM);
102
103 spin_lock_init(&freezer->lock);
104 return &freezer->css;
105 }
106
107 /**
108 * freezer_css_online - commit creation of a freezer cgroup
109 * @cgroup: cgroup being created
110 *
111 * We're committing to creation of @cgroup. Mark it online and inherit
112 * parent's freezing state while holding both parent's and our
113 * freezer->lock.
114 */
115 static int freezer_css_online(struct cgroup *cgroup)
116 {
117 struct freezer *freezer = cgroup_freezer(cgroup);
118 struct freezer *parent = parent_freezer(freezer);
119
120 /*
121 * The following double locking and freezing state inheritance
122 * guarantee that @cgroup can never escape ancestors' freezing
123 * states. See cgroup_for_each_descendant_pre() for details.
124 */
125 if (parent)
126 spin_lock_irq(&parent->lock);
127 spin_lock_nested(&freezer->lock, SINGLE_DEPTH_NESTING);
128
129 freezer->state |= CGROUP_FREEZER_ONLINE;
130
131 if (parent && (parent->state & CGROUP_FREEZING)) {
132 freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
133 atomic_inc(&system_freezing_cnt);
134 }
135
136 spin_unlock(&freezer->lock);
137 if (parent)
138 spin_unlock_irq(&parent->lock);
139
140 return 0;
141 }
142
143 /**
144 * freezer_css_offline - initiate destruction of @cgroup
145 * @cgroup: cgroup being destroyed
146 *
147 * @cgroup is going away. Mark it dead and decrement system_freezing_count
148 * if it was holding one.
149 */
150 static void freezer_css_offline(struct cgroup *cgroup)
151 {
152 struct freezer *freezer = cgroup_freezer(cgroup);
153
154 spin_lock_irq(&freezer->lock);
155
156 if (freezer->state & CGROUP_FREEZING)
157 atomic_dec(&system_freezing_cnt);
158
159 freezer->state = 0;
160
161 spin_unlock_irq(&freezer->lock);
162 }
163
164 static void freezer_css_free(struct cgroup *cgroup)
165 {
166 kfree(cgroup_freezer(cgroup));
167 }
168
169 /*
170 * Tasks can be migrated into a different freezer anytime regardless of its
171 * current state. freezer_attach() is responsible for making new tasks
172 * conform to the current state.
173 *
174 * Freezer state changes and task migration are synchronized via
175 * @freezer->lock. freezer_attach() makes the new tasks conform to the
176 * current state and all following state changes can see the new tasks.
177 */
178 static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
179 {
180 struct freezer *freezer = cgroup_freezer(new_cgrp);
181 struct task_struct *task;
182 bool clear_frozen = false;
183
184 spin_lock_irq(&freezer->lock);
185
186 /*
187 * Make the new tasks conform to the current state of @new_cgrp.
188 * For simplicity, when migrating any task to a FROZEN cgroup, we
189 * revert it to FREEZING and let update_if_frozen() determine the
190 * correct state later.
191 *
192 * Tasks in @tset are on @new_cgrp but may not conform to its
193 * current state before executing the following - !frozen tasks may
194 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
195 */
196 cgroup_taskset_for_each(task, new_cgrp, tset) {
197 if (!(freezer->state & CGROUP_FREEZING)) {
198 __thaw_task(task);
199 } else {
200 freeze_task(task);
201 freezer->state &= ~CGROUP_FROZEN;
202 clear_frozen = true;
203 }
204 }
205
206 spin_unlock_irq(&freezer->lock);
207
208 /*
209 * Propagate FROZEN clearing upwards. We may race with
210 * update_if_frozen(), but as long as both work bottom-up, either
211 * update_if_frozen() sees child's FROZEN cleared or we clear the
212 * parent's FROZEN later. No parent w/ !FROZEN children can be
213 * left FROZEN.
214 */
215 while (clear_frozen && (freezer = parent_freezer(freezer))) {
216 spin_lock_irq(&freezer->lock);
217 freezer->state &= ~CGROUP_FROZEN;
218 clear_frozen = freezer->state & CGROUP_FREEZING;
219 spin_unlock_irq(&freezer->lock);
220 }
221 }
222
223 static void freezer_fork(struct task_struct *task)
224 {
225 struct freezer *freezer;
226
227 rcu_read_lock();
228 freezer = task_freezer(task);
229
230 /*
231 * The root cgroup is non-freezable, so we can skip the
232 * following check.
233 */
234 if (!freezer->css.cgroup->parent)
235 goto out;
236
237 spin_lock_irq(&freezer->lock);
238 if (freezer->state & CGROUP_FREEZING)
239 freeze_task(task);
240 spin_unlock_irq(&freezer->lock);
241 out:
242 rcu_read_unlock();
243 }
244
245 /**
246 * update_if_frozen - update whether a cgroup finished freezing
247 * @cgroup: cgroup of interest
248 *
249 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
250 * calling this function. If the current state is FREEZING but not FROZEN,
251 * this function checks whether all tasks of this cgroup and the descendant
252 * cgroups finished freezing and, if so, sets FROZEN.
253 *
254 * The caller is responsible for grabbing RCU read lock and calling
255 * update_if_frozen() on all descendants prior to invoking this function.
256 *
257 * Task states and freezer state might disagree while tasks are being
258 * migrated into or out of @cgroup, so we can't verify task states against
259 * @freezer state here. See freezer_attach() for details.
260 */
261 static void update_if_frozen(struct cgroup *cgroup)
262 {
263 struct freezer *freezer = cgroup_freezer(cgroup);
264 struct cgroup *pos;
265 struct cgroup_iter it;
266 struct task_struct *task;
267
268 WARN_ON_ONCE(!rcu_read_lock_held());
269
270 spin_lock_irq(&freezer->lock);
271
272 if (!(freezer->state & CGROUP_FREEZING) ||
273 (freezer->state & CGROUP_FROZEN))
274 goto out_unlock;
275
276 /* are all (live) children frozen? */
277 cgroup_for_each_child(pos, cgroup) {
278 struct freezer *child = cgroup_freezer(pos);
279
280 if ((child->state & CGROUP_FREEZER_ONLINE) &&
281 !(child->state & CGROUP_FROZEN))
282 goto out_unlock;
283 }
284
285 /* are all tasks frozen? */
286 cgroup_iter_start(cgroup, &it);
287
288 while ((task = cgroup_iter_next(cgroup, &it))) {
289 if (freezing(task)) {
290 /*
291 * freezer_should_skip() indicates that the task
292 * should be skipped when determining freezing
293 * completion. Consider it frozen in addition to
294 * the usual frozen condition.
295 */
296 if (!frozen(task) && !freezer_should_skip(task))
297 goto out_iter_end;
298 }
299 }
300
301 freezer->state |= CGROUP_FROZEN;
302 out_iter_end:
303 cgroup_iter_end(cgroup, &it);
304 out_unlock:
305 spin_unlock_irq(&freezer->lock);
306 }
307
308 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
309 struct seq_file *m)
310 {
311 struct cgroup *pos;
312
313 rcu_read_lock();
314
315 /* update states bottom-up */
316 cgroup_for_each_descendant_post(pos, cgroup)
317 update_if_frozen(pos);
318 update_if_frozen(cgroup);
319
320 rcu_read_unlock();
321
322 seq_puts(m, freezer_state_strs(cgroup_freezer(cgroup)->state));
323 seq_putc(m, '\n');
324 return 0;
325 }
326
327 static void freeze_cgroup(struct freezer *freezer)
328 {
329 struct cgroup *cgroup = freezer->css.cgroup;
330 struct cgroup_iter it;
331 struct task_struct *task;
332
333 cgroup_iter_start(cgroup, &it);
334 while ((task = cgroup_iter_next(cgroup, &it)))
335 freeze_task(task);
336 cgroup_iter_end(cgroup, &it);
337 }
338
339 static void unfreeze_cgroup(struct freezer *freezer)
340 {
341 struct cgroup *cgroup = freezer->css.cgroup;
342 struct cgroup_iter it;
343 struct task_struct *task;
344
345 cgroup_iter_start(cgroup, &it);
346 while ((task = cgroup_iter_next(cgroup, &it)))
347 __thaw_task(task);
348 cgroup_iter_end(cgroup, &it);
349 }
350
351 /**
352 * freezer_apply_state - apply state change to a single cgroup_freezer
353 * @freezer: freezer to apply state change to
354 * @freeze: whether to freeze or unfreeze
355 * @state: CGROUP_FREEZING_* flag to set or clear
356 *
357 * Set or clear @state on @cgroup according to @freeze, and perform
358 * freezing or thawing as necessary.
359 */
360 static void freezer_apply_state(struct freezer *freezer, bool freeze,
361 unsigned int state)
362 {
363 /* also synchronizes against task migration, see freezer_attach() */
364 lockdep_assert_held(&freezer->lock);
365
366 if (!(freezer->state & CGROUP_FREEZER_ONLINE))
367 return;
368
369 if (freeze) {
370 if (!(freezer->state & CGROUP_FREEZING))
371 atomic_inc(&system_freezing_cnt);
372 freezer->state |= state;
373 freeze_cgroup(freezer);
374 } else {
375 bool was_freezing = freezer->state & CGROUP_FREEZING;
376
377 freezer->state &= ~state;
378
379 if (!(freezer->state & CGROUP_FREEZING)) {
380 if (was_freezing)
381 atomic_dec(&system_freezing_cnt);
382 freezer->state &= ~CGROUP_FROZEN;
383 unfreeze_cgroup(freezer);
384 }
385 }
386 }
387
388 /**
389 * freezer_change_state - change the freezing state of a cgroup_freezer
390 * @freezer: freezer of interest
391 * @freeze: whether to freeze or thaw
392 *
393 * Freeze or thaw @freezer according to @freeze. The operations are
394 * recursive - all descendants of @freezer will be affected.
395 */
396 static void freezer_change_state(struct freezer *freezer, bool freeze)
397 {
398 struct cgroup *pos;
399
400 /* update @freezer */
401 spin_lock_irq(&freezer->lock);
402 freezer_apply_state(freezer, freeze, CGROUP_FREEZING_SELF);
403 spin_unlock_irq(&freezer->lock);
404
405 /*
406 * Update all its descendants in pre-order traversal. Each
407 * descendant will try to inherit its parent's FREEZING state as
408 * CGROUP_FREEZING_PARENT.
409 */
410 rcu_read_lock();
411 cgroup_for_each_descendant_pre(pos, freezer->css.cgroup) {
412 struct freezer *pos_f = cgroup_freezer(pos);
413 struct freezer *parent = parent_freezer(pos_f);
414
415 /*
416 * Our update to @parent->state is already visible which is
417 * all we need. No need to lock @parent. For more info on
418 * synchronization, see freezer_post_create().
419 */
420 spin_lock_irq(&pos_f->lock);
421 freezer_apply_state(pos_f, parent->state & CGROUP_FREEZING,
422 CGROUP_FREEZING_PARENT);
423 spin_unlock_irq(&pos_f->lock);
424 }
425 rcu_read_unlock();
426 }
427
428 static int freezer_write(struct cgroup *cgroup, struct cftype *cft,
429 const char *buffer)
430 {
431 bool freeze;
432
433 if (strcmp(buffer, freezer_state_strs(0)) == 0)
434 freeze = false;
435 else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
436 freeze = true;
437 else
438 return -EINVAL;
439
440 freezer_change_state(cgroup_freezer(cgroup), freeze);
441 return 0;
442 }
443
444 static u64 freezer_self_freezing_read(struct cgroup *cgroup, struct cftype *cft)
445 {
446 struct freezer *freezer = cgroup_freezer(cgroup);
447
448 return (bool)(freezer->state & CGROUP_FREEZING_SELF);
449 }
450
451 static u64 freezer_parent_freezing_read(struct cgroup *cgroup, struct cftype *cft)
452 {
453 struct freezer *freezer = cgroup_freezer(cgroup);
454
455 return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
456 }
457
458 static struct cftype files[] = {
459 {
460 .name = "state",
461 .flags = CFTYPE_NOT_ON_ROOT,
462 .read_seq_string = freezer_read,
463 .write_string = freezer_write,
464 },
465 {
466 .name = "self_freezing",
467 .flags = CFTYPE_NOT_ON_ROOT,
468 .read_u64 = freezer_self_freezing_read,
469 },
470 {
471 .name = "parent_freezing",
472 .flags = CFTYPE_NOT_ON_ROOT,
473 .read_u64 = freezer_parent_freezing_read,
474 },
475 { } /* terminate */
476 };
477
478 struct cgroup_subsys freezer_subsys = {
479 .name = "freezer",
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 .subsys_id = freezer_subsys_id,
485 .attach = freezer_attach,
486 .fork = freezer_fork,
487 .base_cftypes = files,
488 };
489
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