path: root/kernel/cgroup_freezer.c (plain)
blob: 1b72d56edce5e2d9253c2c03f203e81aa76bd16c

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	};
482