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#include <linux/cpu.h>
26
27/*
28 * A cgroup is freezing if any FREEZING flags are set.  FREEZING_SELF is
29 * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
30 * for "THAWED".  FREEZING_PARENT is set if the parent freezer is FREEZING
31 * for whatever reason.  IOW, a cgroup has FREEZING_PARENT set if one of
32 * its ancestors has FREEZING_SELF set.
33 */
34enum freezer_state_flags {
35	CGROUP_FREEZER_ONLINE	= (1 << 0), /* freezer is fully online */
36	CGROUP_FREEZING_SELF	= (1 << 1), /* this freezer is freezing */
37	CGROUP_FREEZING_PARENT	= (1 << 2), /* the parent freezer is freezing */
38	CGROUP_FROZEN		= (1 << 3), /* this and its descendants frozen */
39
40	/* mask for all FREEZING flags */
41	CGROUP_FREEZING		= CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
42};
43
44struct freezer {
45	struct cgroup_subsys_state	css;
46	unsigned int			state;
47};
48
49static DEFINE_MUTEX(freezer_mutex);
50
51static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
52{
53	return css ? container_of(css, struct freezer, css) : NULL;
54}
55
56static inline struct freezer *task_freezer(struct task_struct *task)
57{
58	return css_freezer(task_css(task, freezer_cgrp_id));
59}
60
61static struct freezer *parent_freezer(struct freezer *freezer)
62{
63	return css_freezer(freezer->css.parent);
64}
65
66bool cgroup_freezing(struct task_struct *task)
67{
68	bool ret;
69	unsigned int state;
70
71	rcu_read_lock();
72	/* Check if the cgroup is still FREEZING, but not FROZEN. The extra
73	 * !FROZEN check is required, because the FREEZING bit is not cleared
74	 * when the state FROZEN is reached.
75	 */
76	state = task_freezer(task)->state;
77	ret = (state & CGROUP_FREEZING) && !(state & CGROUP_FROZEN);
78	rcu_read_unlock();
79
80	return ret;
81}
82
83static const char *freezer_state_strs(unsigned int state)
84{
85	if (state & CGROUP_FROZEN)
86		return "FROZEN";
87	if (state & CGROUP_FREEZING)
88		return "FREEZING";
89	return "THAWED";
90};
91
92static struct cgroup_subsys_state *
93freezer_css_alloc(struct cgroup_subsys_state *parent_css)
94{
95	struct freezer *freezer;
96
97	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
98	if (!freezer)
99		return ERR_PTR(-ENOMEM);
100
101	return &freezer->css;
102}
103
104/**
105 * freezer_css_online - commit creation of a freezer css
106 * @css: css being created
107 *
108 * We're committing to creation of @css.  Mark it online and inherit
109 * parent's freezing state while holding cpus read lock and freezer_mutex.
110 */
111static int freezer_css_online(struct cgroup_subsys_state *css)
112{
113	struct freezer *freezer = css_freezer(css);
114	struct freezer *parent = parent_freezer(freezer);
115
116	cpus_read_lock();
117	mutex_lock(&freezer_mutex);
118
119	freezer->state |= CGROUP_FREEZER_ONLINE;
120
121	if (parent && (parent->state & CGROUP_FREEZING)) {
122		freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
123		static_branch_inc_cpuslocked(&freezer_active);
124	}
125
126	mutex_unlock(&freezer_mutex);
127	cpus_read_unlock();
128	return 0;
129}
130
131/**
132 * freezer_css_offline - initiate destruction of a freezer css
133 * @css: css being destroyed
134 *
135 * @css is going away.  Mark it dead and decrement freezer_active if
136 * it was holding one.
137 */
138static void freezer_css_offline(struct cgroup_subsys_state *css)
139{
140	struct freezer *freezer = css_freezer(css);
141
142	cpus_read_lock();
143	mutex_lock(&freezer_mutex);
144
145	if (freezer->state & CGROUP_FREEZING)
146		static_branch_dec_cpuslocked(&freezer_active);
147
148	freezer->state = 0;
149
150	mutex_unlock(&freezer_mutex);
151	cpus_read_unlock();
152}
153
154static void freezer_css_free(struct cgroup_subsys_state *css)
155{
156	kfree(css_freezer(css));
157}
158
159/*
160 * Tasks can be migrated into a different freezer anytime regardless of its
161 * current state.  freezer_attach() is responsible for making new tasks
162 * conform to the current state.
163 *
164 * Freezer state changes and task migration are synchronized via
165 * @freezer->lock.  freezer_attach() makes the new tasks conform to the
166 * current state and all following state changes can see the new tasks.
167 */
168static void freezer_attach(struct cgroup_taskset *tset)
169{
170	struct task_struct *task;
171	struct cgroup_subsys_state *new_css;
172
173	mutex_lock(&freezer_mutex);
174
175	/*
176	 * Make the new tasks conform to the current state of @new_css.
177	 * For simplicity, when migrating any task to a FROZEN cgroup, we
178	 * revert it to FREEZING and let update_if_frozen() determine the
179	 * correct state later.
180	 *
181	 * Tasks in @tset are on @new_css but may not conform to its
182	 * current state before executing the following - !frozen tasks may
183	 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
184	 */
185	cgroup_taskset_for_each(task, new_css, tset) {
186		struct freezer *freezer = css_freezer(new_css);
187
188		if (!(freezer->state & CGROUP_FREEZING)) {
189			__thaw_task(task);
190		} else {
191			freeze_task(task);
192
193			/* clear FROZEN and propagate upwards */
194			while (freezer && (freezer->state & CGROUP_FROZEN)) {
195				freezer->state &= ~CGROUP_FROZEN;
196				freezer = parent_freezer(freezer);
197			}
198		}
199	}
200
201	mutex_unlock(&freezer_mutex);
202}
203
204/**
205 * freezer_fork - cgroup post fork callback
206 * @task: a task which has just been forked
207 *
208 * @task has just been created and should conform to the current state of
209 * the cgroup_freezer it belongs to.  This function may race against
210 * freezer_attach().  Losing to freezer_attach() means that we don't have
211 * to do anything as freezer_attach() will put @task into the appropriate
212 * state.
213 */
214static void freezer_fork(struct task_struct *task)
215{
216	struct freezer *freezer;
217
218	/*
219	 * The root cgroup is non-freezable, so we can skip locking the
220	 * freezer.  This is safe regardless of race with task migration.
221	 * If we didn't race or won, skipping is obviously the right thing
222	 * to do.  If we lost and root is the new cgroup, noop is still the
223	 * right thing to do.
224	 */
225	if (task_css_is_root(task, freezer_cgrp_id))
226		return;
227
228	mutex_lock(&freezer_mutex);
229	rcu_read_lock();
230
231	freezer = task_freezer(task);
232	if (freezer->state & CGROUP_FREEZING)
233		freeze_task(task);
234
235	rcu_read_unlock();
236	mutex_unlock(&freezer_mutex);
237}
238
239/**
240 * update_if_frozen - update whether a cgroup finished freezing
241 * @css: css of interest
242 *
243 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
244 * calling this function.  If the current state is FREEZING but not FROZEN,
245 * this function checks whether all tasks of this cgroup and the descendant
246 * cgroups finished freezing and, if so, sets FROZEN.
247 *
248 * The caller is responsible for grabbing RCU read lock and calling
249 * update_if_frozen() on all descendants prior to invoking this function.
250 *
251 * Task states and freezer state might disagree while tasks are being
252 * migrated into or out of @css, so we can't verify task states against
253 * @freezer state here.  See freezer_attach() for details.
254 */
255static void update_if_frozen(struct cgroup_subsys_state *css)
256{
257	struct freezer *freezer = css_freezer(css);
258	struct cgroup_subsys_state *pos;
259	struct css_task_iter it;
260	struct task_struct *task;
261
262	lockdep_assert_held(&freezer_mutex);
263
264	if (!(freezer->state & CGROUP_FREEZING) ||
265	    (freezer->state & CGROUP_FROZEN))
266		return;
267
268	/* are all (live) children frozen? */
269	rcu_read_lock();
270	css_for_each_child(pos, css) {
271		struct freezer *child = css_freezer(pos);
272
273		if ((child->state & CGROUP_FREEZER_ONLINE) &&
274		    !(child->state & CGROUP_FROZEN)) {
275			rcu_read_unlock();
276			return;
277		}
278	}
279	rcu_read_unlock();
280
281	/* are all tasks frozen? */
282	css_task_iter_start(css, 0, &it);
283
284	while ((task = css_task_iter_next(&it))) {
285		if (freezing(task) && !frozen(task))
286			goto out_iter_end;
287	}
288
289	freezer->state |= CGROUP_FROZEN;
290out_iter_end:
291	css_task_iter_end(&it);
292}
293
294static int freezer_read(struct seq_file *m, void *v)
295{
296	struct cgroup_subsys_state *css = seq_css(m), *pos;
297
298	mutex_lock(&freezer_mutex);
299	rcu_read_lock();
300
301	/* update states bottom-up */
302	css_for_each_descendant_post(pos, css) {
303		if (!css_tryget_online(pos))
304			continue;
305		rcu_read_unlock();
306
307		update_if_frozen(pos);
308
309		rcu_read_lock();
310		css_put(pos);
311	}
312
313	rcu_read_unlock();
314	mutex_unlock(&freezer_mutex);
315
316	seq_puts(m, freezer_state_strs(css_freezer(css)->state));
317	seq_putc(m, '\n');
318	return 0;
319}
320
321static void freeze_cgroup(struct freezer *freezer)
322{
323	struct css_task_iter it;
324	struct task_struct *task;
325
326	css_task_iter_start(&freezer->css, 0, &it);
327	while ((task = css_task_iter_next(&it)))
328		freeze_task(task);
329	css_task_iter_end(&it);
330}
331
332static void unfreeze_cgroup(struct freezer *freezer)
333{
334	struct css_task_iter it;
335	struct task_struct *task;
336
337	css_task_iter_start(&freezer->css, 0, &it);
338	while ((task = css_task_iter_next(&it)))
339		__thaw_task(task);
340	css_task_iter_end(&it);
341}
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 */
352static 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	if (!(freezer->state & CGROUP_FREEZER_ONLINE))
359		return;
360
361	if (freeze) {
362		if (!(freezer->state & CGROUP_FREEZING))
363			static_branch_inc_cpuslocked(&freezer_active);
364		freezer->state |= state;
365		freeze_cgroup(freezer);
366	} else {
367		bool was_freezing = freezer->state & CGROUP_FREEZING;
368
369		freezer->state &= ~state;
370
371		if (!(freezer->state & CGROUP_FREEZING)) {
372			freezer->state &= ~CGROUP_FROZEN;
373			if (was_freezing)
374				static_branch_dec_cpuslocked(&freezer_active);
375			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 */
388static void freezer_change_state(struct freezer *freezer, bool freeze)
389{
390	struct cgroup_subsys_state *pos;
391
392	cpus_read_lock();
393	/*
394	 * Update all its descendants in pre-order traversal.  Each
395	 * descendant will try to inherit its parent's FREEZING state as
396	 * CGROUP_FREEZING_PARENT.
397	 */
398	mutex_lock(&freezer_mutex);
399	rcu_read_lock();
400	css_for_each_descendant_pre(pos, &freezer->css) {
401		struct freezer *pos_f = css_freezer(pos);
402		struct freezer *parent = parent_freezer(pos_f);
403
404		if (!css_tryget_online(pos))
405			continue;
406		rcu_read_unlock();
407
408		if (pos_f == freezer)
409			freezer_apply_state(pos_f, freeze,
410					    CGROUP_FREEZING_SELF);
411		else
412			freezer_apply_state(pos_f,
413					    parent->state & CGROUP_FREEZING,
414					    CGROUP_FREEZING_PARENT);
415
416		rcu_read_lock();
417		css_put(pos);
418	}
419	rcu_read_unlock();
420	mutex_unlock(&freezer_mutex);
421	cpus_read_unlock();
422}
423
424static ssize_t freezer_write(struct kernfs_open_file *of,
425			     char *buf, size_t nbytes, loff_t off)
426{
427	bool freeze;
428
429	buf = strstrip(buf);
430
431	if (strcmp(buf, freezer_state_strs(0)) == 0)
432		freeze = false;
433	else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
434		freeze = true;
435	else
436		return -EINVAL;
437
438	freezer_change_state(css_freezer(of_css(of)), freeze);
439	return nbytes;
440}
441
442static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
443				      struct cftype *cft)
444{
445	struct freezer *freezer = css_freezer(css);
446
447	return (bool)(freezer->state & CGROUP_FREEZING_SELF);
448}
449
450static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
451					struct cftype *cft)
452{
453	struct freezer *freezer = css_freezer(css);
454
455	return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
456}
457
458static struct cftype files[] = {
459	{
460		.name = "state",
461		.flags = CFTYPE_NOT_ON_ROOT,
462		.seq_show = freezer_read,
463		.write = 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
478struct cgroup_subsys freezer_cgrp_subsys = {
479	.css_alloc	= freezer_css_alloc,
480	.css_online	= freezer_css_online,
481	.css_offline	= freezer_css_offline,
482	.css_free	= freezer_css_free,
483	.attach		= freezer_attach,
484	.fork		= freezer_fork,
485	.legacy_cftypes	= files,
486};
487