summaryrefslogtreecommitdiffstats
path: root/kernel/cgroup_freezer.c
blob: ee8bb671688ce89e852a5a0b4976bb42d0f364d1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
/*
 * cgroup_freezer.c -  control group freezer subsystem
 *
 * Copyright IBM Corporation, 2007
 *
 * Author : Cedric Le Goater <clg@fr.ibm.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of version 2.1 of the GNU Lesser General Public License
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 */

#include <linux/export.h>
#include <linux/slab.h>
#include <linux/cgroup.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/freezer.h>
#include <linux/seq_file.h>

/*
 * A cgroup is freezing if any FREEZING flags are set.  FREEZING_SELF is
 * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
 * for "THAWED".  FREEZING_PARENT is set if the parent freezer is FREEZING
 * for whatever reason.  IOW, a cgroup has FREEZING_PARENT set if one of
 * its ancestors has FREEZING_SELF set.
 */
enum freezer_state_flags {
	CGROUP_FREEZER_ONLINE	= (1 << 0), /* freezer is fully online */
	CGROUP_FREEZING_SELF	= (1 << 1), /* this freezer is freezing */
	CGROUP_FREEZING_PARENT	= (1 << 2), /* the parent freezer is freezing */
	CGROUP_FROZEN		= (1 << 3), /* this and its descendants frozen */

	/* mask for all FREEZING flags */
	CGROUP_FREEZING		= CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
};

struct freezer {
	struct cgroup_subsys_state	css;
	unsigned int			state;
	spinlock_t			lock;
};

static inline struct freezer *cgroup_freezer(struct cgroup *cgroup)
{
	return container_of(cgroup_subsys_state(cgroup, freezer_subsys_id),
			    struct freezer, css);
}

static inline struct freezer *task_freezer(struct task_struct *task)
{
	return container_of(task_subsys_state(task, freezer_subsys_id),
			    struct freezer, css);
}

static struct freezer *parent_freezer(struct freezer *freezer)
{
	struct cgroup *pcg = freezer->css.cgroup->parent;

	if (pcg)
		return cgroup_freezer(pcg);
	return NULL;
}

bool cgroup_freezing(struct task_struct *task)
{
	bool ret;

	rcu_read_lock();
	ret = task_freezer(task)->state & CGROUP_FREEZING;
	rcu_read_unlock();

	return ret;
}

/*
 * cgroups_write_string() limits the size of freezer state strings to
 * CGROUP_LOCAL_BUFFER_SIZE
 */
static const char *freezer_state_strs(unsigned int state)
{
	if (state & CGROUP_FROZEN)
		return "FROZEN";
	if (state & CGROUP_FREEZING)
		return "FREEZING";
	return "THAWED";
};

struct cgroup_subsys freezer_subsys;

static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
{
	struct freezer *freezer;

	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
	if (!freezer)
		return ERR_PTR(-ENOMEM);

	spin_lock_init(&freezer->lock);
	return &freezer->css;
}

/**
 * freezer_post_create - commit creation of a freezer cgroup
 * @cgroup: cgroup being created
 *
 * We're committing to creation of @cgroup.  Mark it online and inherit
 * parent's freezing state while holding both parent's and our
 * freezer->lock.
 */
static int freezer_post_create(struct cgroup *cgroup)
{
	struct freezer *freezer = cgroup_freezer(cgroup);
	struct freezer *parent = parent_freezer(freezer);

	/*
	 * The following double locking and freezing state inheritance
	 * guarantee that @cgroup can never escape ancestors' freezing
	 * states.  See cgroup_for_each_descendant_pre() for details.
	 */
	if (parent)
		spin_lock_irq(&parent->lock);
	spin_lock_nested(&freezer->lock, SINGLE_DEPTH_NESTING);

	freezer->state |= CGROUP_FREEZER_ONLINE;

	if (parent && (parent->state & CGROUP_FREEZING)) {
		freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
		atomic_inc(&system_freezing_cnt);
	}

	spin_unlock(&freezer->lock);
	if (parent)
		spin_unlock_irq(&parent->lock);

	return 0;
}

/**
 * freezer_pre_destroy - initiate destruction of @cgroup
 * @cgroup: cgroup being destroyed
 *
 * @cgroup is going away.  Mark it dead and decrement system_freezing_count
 * if it was holding one.
 */
static void freezer_pre_destroy(struct cgroup *cgroup)
{
	struct freezer *freezer = cgroup_freezer(cgroup);

	spin_lock_irq(&freezer->lock);

	if (freezer->state & CGROUP_FREEZING)
		atomic_dec(&system_freezing_cnt);

	freezer->state = 0;

	spin_unlock_irq(&freezer->lock);
}

static void freezer_destroy(struct cgroup *cgroup)
{
	kfree(cgroup_freezer(cgroup));
}

/*
 * Tasks can be migrated into a different freezer anytime regardless of its
 * current state.  freezer_attach() is responsible for making new tasks
 * conform to the current state.
 *
 * Freezer state changes and task migration are synchronized via
 * @freezer->lock.  freezer_attach() makes the new tasks conform to the
 * current state and all following state changes can see the new tasks.
 */
static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
{
	struct freezer *freezer = cgroup_freezer(new_cgrp);
	struct task_struct *task;
	bool clear_frozen = false;

	spin_lock_irq(&freezer->lock);

	/*
	 * Make the new tasks conform to the current state of @new_cgrp.
	 * For simplicity, when migrating any task to a FROZEN cgroup, we
	 * revert it to FREEZING and let update_if_frozen() determine the
	 * correct state later.
	 *
	 * Tasks in @tset are on @new_cgrp but may not conform to its
	 * current state before executing the following - !frozen tasks may
	 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
	 */
	cgroup_taskset_for_each(task, new_cgrp, tset) {
		if (!(freezer->state & CGROUP_FREEZING)) {
			__thaw_task(task);
		} else {
			freeze_task(task);
			freezer->state &= ~CGROUP_FROZEN;
			clear_frozen = true;
		}
	}

	spin_unlock_irq(&freezer->lock);

	/*
	 * Propagate FROZEN clearing upwards.  We may race with
	 * update_if_frozen(), but as long as both work bottom-up, either
	 * update_if_frozen() sees child's FROZEN cleared or we clear the
	 * parent's FROZEN later.  No parent w/ !FROZEN children can be
	 * left FROZEN.
	 */
	while (clear_frozen && (freezer = parent_freezer(freezer))) {
		spin_lock_irq(&freezer->lock);
		freezer->state &= ~CGROUP_FROZEN;
		clear_frozen = freezer->state & CGROUP_FREEZING;
		spin_unlock_irq(&freezer->lock);
	}
}

static void freezer_fork(struct task_struct *task)
{
	struct freezer *freezer;

	rcu_read_lock();
	freezer = task_freezer(task);

	/*
	 * The root cgroup is non-freezable, so we can skip the
	 * following check.
	 */
	if (!freezer->css.cgroup->parent)
		goto out;

	spin_lock_irq(&freezer->lock);
	if (freezer->state & CGROUP_FREEZING)
		freeze_task(task);
	spin_unlock_irq(&freezer->lock);
out:
	rcu_read_unlock();
}

/**
 * update_if_frozen - update whether a cgroup finished freezing
 * @cgroup: cgroup of interest
 *
 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
 * calling this function.  If the current state is FREEZING but not FROZEN,
 * this function checks whether all tasks of this cgroup and the descendant
 * cgroups finished freezing and, if so, sets FROZEN.
 *
 * The caller is responsible for grabbing RCU read lock and calling
 * update_if_frozen() on all descendants prior to invoking this function.
 *
 * Task states and freezer state might disagree while tasks are being
 * migrated into or out of @cgroup, so we can't verify task states against
 * @freezer state here.  See freezer_attach() for details.
 */
static void update_if_frozen(struct cgroup *cgroup)
{
	struct freezer *freezer = cgroup_freezer(cgroup);
	struct cgroup *pos;
	struct cgroup_iter it;
	struct task_struct *task;

	WARN_ON_ONCE(!rcu_read_lock_held());

	spin_lock_irq(&freezer->lock);

	if (!(freezer->state & CGROUP_FREEZING) ||
	    (freezer->state & CGROUP_FROZEN))
		goto out_unlock;

	/* are all (live) children frozen? */
	cgroup_for_each_child(pos, cgroup) {
		struct freezer *child = cgroup_freezer(pos);

		if ((child->state & CGROUP_FREEZER_ONLINE) &&
		    !(child->state & CGROUP_FROZEN))
			goto out_unlock;
	}

	/* are all tasks frozen? */
	cgroup_iter_start(cgroup, &it);

	while ((task = cgroup_iter_next(cgroup, &it))) {
		if (freezing(task)) {
			/*
			 * freezer_should_skip() indicates that the task
			 * should be skipped when determining freezing
			 * completion.  Consider it frozen in addition to
			 * the usual frozen condition.
			 */
			if (!frozen(task) && !freezer_should_skip(task))
				goto out_iter_end;
		}
	}

	freezer->state |= CGROUP_FROZEN;
out_iter_end:
	cgroup_iter_end(cgroup, &it);
out_unlock:
	spin_unlock_irq(&freezer->lock);
}

static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
			struct seq_file *m)
{
	struct cgroup *pos;

	rcu_read_lock();

	/* update states bottom-up */
	cgroup_for_each_descendant_post(pos, cgroup)
		update_if_frozen(pos);
	update_if_frozen(cgroup);

	rcu_read_unlock();

	seq_puts(m, freezer_state_strs(cgroup_freezer(cgroup)->state));
	seq_putc(m, '\n');
	return 0;
}

static void freeze_cgroup(struct freezer *freezer)
{
	struct cgroup *cgroup = freezer->css.cgroup;
	struct cgroup_iter it;
	struct task_struct *task;

	cgroup_iter_start(cgroup, &it);
	while ((task = cgroup_iter_next(cgroup, &it)))
		freeze_task(task);
	cgroup_iter_end(cgroup, &it);
}

static void unfreeze_cgroup(struct freezer *freezer)
{
	struct cgroup *cgroup = freezer->css.cgroup;
	struct cgroup_iter it;
	struct task_struct *task;

	cgroup_iter_start(cgroup, &it);
	while ((task = cgroup_iter_next(cgroup, &it)))
		__thaw_task(task);
	cgroup_iter_end(cgroup, &it);
}

/**
 * freezer_apply_state - apply state change to a single cgroup_freezer
 * @freezer: freezer to apply state change to
 * @freeze: whether to freeze or unfreeze
 * @state: CGROUP_FREEZING_* flag to set or clear
 *
 * Set or clear @state on @cgroup according to @freeze, and perform
 * freezing or thawing as necessary.
 */
static void freezer_apply_state(struct freezer *freezer, bool freeze,
				unsigned int state)
{
	/* also synchronizes against task migration, see freezer_attach() */
	lockdep_assert_held(&freezer->lock);

	if (!(freezer->state & CGROUP_FREEZER_ONLINE))
		return;

	if (freeze) {
		if (!(freezer->state & CGROUP_FREEZING))
			atomic_inc(&system_freezing_cnt);
		freezer->state |= state;
		freeze_cgroup(freezer);
	} else {
		bool was_freezing = freezer->state & CGROUP_FREEZING;

		freezer->state &= ~state;

		if (!(freezer->state & CGROUP_FREEZING)) {
			if (was_freezing)
				atomic_dec(&system_freezing_cnt);
			freezer->state &= ~CGROUP_FROZEN;
			unfreeze_cgroup(freezer);
		}
	}
}

/**
 * freezer_change_state - change the freezing state of a cgroup_freezer
 * @freezer: freezer of interest
 * @freeze: whether to freeze or thaw
 *
 * Freeze or thaw @freezer according to @freeze.  The operations are
 * recursive - all descendants of @freezer will be affected.
 */
static void freezer_change_state(struct freezer *freezer, bool freeze)
{
	struct cgroup *pos;

	/* update @freezer */
	spin_lock_irq(&freezer->lock);
	freezer_apply_state(freezer, freeze, CGROUP_FREEZING_SELF);
	spin_unlock_irq(&freezer->lock);

	/*
	 * Update all its descendants in pre-order traversal.  Each
	 * descendant will try to inherit its parent's FREEZING state as
	 * CGROUP_FREEZING_PARENT.
	 */
	rcu_read_lock();
	cgroup_for_each_descendant_pre(pos, freezer->css.cgroup) {
		struct freezer *pos_f = cgroup_freezer(pos);
		struct freezer *parent = parent_freezer(pos_f);

		/*
		 * Our update to @parent->state is already visible which is
		 * all we need.  No need to lock @parent.  For more info on
		 * synchronization, see freezer_post_create().
		 */
		spin_lock_irq(&pos_f->lock);
		freezer_apply_state(pos_f, parent->state & CGROUP_FREEZING,
				    CGROUP_FREEZING_PARENT);
		spin_unlock_irq(&pos_f->lock);
	}
	rcu_read_unlock();
}

static int freezer_write(struct cgroup *cgroup, struct cftype *cft,
			 const char *buffer)
{
	bool freeze;

	if (strcmp(buffer, freezer_state_strs(0)) == 0)
		freeze = false;
	else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
		freeze = true;
	else
		return -EINVAL;

	freezer_change_state(cgroup_freezer(cgroup), freeze);
	return 0;
}

static u64 freezer_self_freezing_read(struct cgroup *cgroup, struct cftype *cft)
{
	struct freezer *freezer = cgroup_freezer(cgroup);

	return (bool)(freezer->state & CGROUP_FREEZING_SELF);
}

static u64 freezer_parent_freezing_read(struct cgroup *cgroup, struct cftype *cft)
{
	struct freezer *freezer = cgroup_freezer(cgroup);

	return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
}

static struct cftype files[] = {
	{
		.name = "state",
		.flags = CFTYPE_NOT_ON_ROOT,
		.read_seq_string = freezer_read,
		.write_string = freezer_write,
	},
	{
		.name = "self_freezing",
		.flags = CFTYPE_NOT_ON_ROOT,
		.read_u64 = freezer_self_freezing_read,
	},
	{
		.name = "parent_freezing",
		.flags = CFTYPE_NOT_ON_ROOT,
		.read_u64 = freezer_parent_freezing_read,
	},
	{ }	/* terminate */
};

struct cgroup_subsys freezer_subsys = {
	.name		= "freezer",
	.create		= freezer_create,
	.post_create	= freezer_post_create,
	.pre_destroy	= freezer_pre_destroy,
	.destroy	= freezer_destroy,
	.subsys_id	= freezer_subsys_id,
	.attach		= freezer_attach,
	.fork		= freezer_fork,
	.base_cftypes	= files,
};
OpenPOWER on IntegriCloud