[deliverable/linux.git] / kernel / cgroup_freezer.c

/*
 * 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/module.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>

enum freezer_state {
	CGROUP_THAWED = 0,
	CGROUP_FREEZING,
	CGROUP_FROZEN,
};

struct freezer {
	struct cgroup_subsys_state css;
	enum freezer_state state;
	spinlock_t lock; /* protects _writes_ to state */
};

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 inline int __cgroup_freezing_or_frozen(struct task_struct *task)
{
	enum freezer_state state = task_freezer(task)->state;
	return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN);
}

int cgroup_freezing_or_frozen(struct task_struct *task)
{
	int result;
	task_lock(task);
	result = __cgroup_freezing_or_frozen(task);
	task_unlock(task);
	return result;
}

/*
 * cgroups_write_string() limits the size of freezer state strings to
 * CGROUP_LOCAL_BUFFER_SIZE
 */
static const char *freezer_state_strs[] = {
	"THAWED",
	"FREEZING",
	"FROZEN",
};

/*
 * State diagram
 * Transitions are caused by userspace writes to the freezer.state file.
 * The values in parenthesis are state labels. The rest are edge labels.
 *
 * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
 *    ^ ^                    |                     |
 *    | \_______THAWED_______/                     |
 *    \__________________________THAWED____________/
 */

struct cgroup_subsys freezer_subsys;

/* Locks taken and their ordering
 * ------------------------------
 * cgroup_mutex (AKA cgroup_lock)
 * freezer->lock
 * css_set_lock
 * task->alloc_lock (AKA task_lock)
 * task->sighand->siglock
 *
 * cgroup code forces css_set_lock to be taken before task->alloc_lock
 *
 * freezer_create(), freezer_destroy():
 * cgroup_mutex [ by cgroup core ]
 *
 * freezer_can_attach():
 * cgroup_mutex (held by caller of can_attach)
 *
 * cgroup_freezing_or_frozen():
 * task->alloc_lock (to get task's cgroup)
 *
 * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
 * freezer->lock
 *  sighand->siglock (if the cgroup is freezing)
 *
 * freezer_read():
 * cgroup_mutex
 *  freezer->lock
 *   write_lock css_set_lock (cgroup iterator start)
 *    task->alloc_lock
 *   read_lock css_set_lock (cgroup iterator start)
 *
 * freezer_write() (freeze):
 * cgroup_mutex
 *  freezer->lock
 *   write_lock css_set_lock (cgroup iterator start)
 *    task->alloc_lock
 *   read_lock css_set_lock (cgroup iterator start)
 *    sighand->siglock (fake signal delivery inside freeze_task())
 *
 * freezer_write() (unfreeze):
 * cgroup_mutex
 *  freezer->lock
 *   write_lock css_set_lock (cgroup iterator start)
 *    task->alloc_lock
 *   read_lock css_set_lock (cgroup iterator start)
 *    task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
 *     sighand->siglock
 */
static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
						  struct cgroup *cgroup)
{
	struct freezer *freezer;

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

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

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

/*
 * The call to cgroup_lock() in the freezer.state write method prevents
 * a write to that file racing against an attach, and hence the
 * can_attach() result will remain valid until the attach completes.
 */
static int freezer_can_attach(struct cgroup_subsys *ss,
			      struct cgroup *new_cgroup,
			      struct task_struct *task, bool threadgroup)
{
	struct freezer *freezer;

	/*
	 * Anything frozen can't move or be moved to/from.
	 */

	freezer = cgroup_freezer(new_cgroup);
	if (freezer->state != CGROUP_THAWED)
		return -EBUSY;

	rcu_read_lock();
	if (__cgroup_freezing_or_frozen(task)) {
		rcu_read_unlock();
		return -EBUSY;
	}
	rcu_read_unlock();

	if (threadgroup) {
		struct task_struct *c;

		rcu_read_lock();
		list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
			if (__cgroup_freezing_or_frozen(c)) {
				rcu_read_unlock();
				return -EBUSY;
			}
		}
		rcu_read_unlock();
	}

	return 0;
}

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

	/*
	 * No lock is needed, since the task isn't on tasklist yet,
	 * so it can't be moved to another cgroup, which means the
	 * freezer won't be removed and will be valid during this
	 * function call.  Nevertheless, apply RCU read-side critical
	 * section to suppress RCU lockdep false positives.
	 */
	rcu_read_lock();
	freezer = task_freezer(task);
	rcu_read_unlock();

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

	spin_lock_irq(&freezer->lock);
	BUG_ON(freezer->state == CGROUP_FROZEN);

	/* Locking avoids race with FREEZING -> THAWED transitions. */
	if (freezer->state == CGROUP_FREEZING)
		freeze_task(task, true);
	spin_unlock_irq(&freezer->lock);
}

/*
 * caller must hold freezer->lock
 */
static void update_if_frozen(struct cgroup *cgroup,
				 struct freezer *freezer)
{
	struct cgroup_iter it;
	struct task_struct *task;
	unsigned int nfrozen = 0, ntotal = 0;
	enum freezer_state old_state = freezer->state;

	cgroup_iter_start(cgroup, &it);
	while ((task = cgroup_iter_next(cgroup, &it))) {
		ntotal++;
		if (frozen(task))
			nfrozen++;
	}

	if (old_state == CGROUP_THAWED) {
		BUG_ON(nfrozen > 0);
	} else if (old_state == CGROUP_FREEZING) {
		if (nfrozen == ntotal)
			freezer->state = CGROUP_FROZEN;
	} else { /* old_state == CGROUP_FROZEN */
		BUG_ON(nfrozen != ntotal);
	}

	cgroup_iter_end(cgroup, &it);
}

static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
			struct seq_file *m)
{
	struct freezer *freezer;
	enum freezer_state state;

	if (!cgroup_lock_live_group(cgroup))
		return -ENODEV;

	freezer = cgroup_freezer(cgroup);
	spin_lock_irq(&freezer->lock);
	state = freezer->state;
	if (state == CGROUP_FREEZING) {
		/* We change from FREEZING to FROZEN lazily if the cgroup was
		 * only partially frozen when we exitted write. */
		update_if_frozen(cgroup, freezer);
		state = freezer->state;
	}
	spin_unlock_irq(&freezer->lock);
	cgroup_unlock();

	seq_puts(m, freezer_state_strs[state]);
	seq_putc(m, '\n');
	return 0;
}

static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
{
	struct cgroup_iter it;
	struct task_struct *task;
	unsigned int num_cant_freeze_now = 0;

	freezer->state = CGROUP_FREEZING;
	cgroup_iter_start(cgroup, &it);
	while ((task = cgroup_iter_next(cgroup, &it))) {
		if (!freeze_task(task, true))
			continue;
		if (frozen(task))
			continue;
		if (!freezing(task) && !freezer_should_skip(task))
			num_cant_freeze_now++;
	}
	cgroup_iter_end(cgroup, &it);

	return num_cant_freeze_now ? -EBUSY : 0;
}

static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
{
	struct cgroup_iter it;
	struct task_struct *task;

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

	freezer->state = CGROUP_THAWED;
}

static int freezer_change_state(struct cgroup *cgroup,
				enum freezer_state goal_state)
{
	struct freezer *freezer;
	int retval = 0;

	freezer = cgroup_freezer(cgroup);

	spin_lock_irq(&freezer->lock);

	update_if_frozen(cgroup, freezer);
	if (goal_state == freezer->state)
		goto out;

	switch (goal_state) {
	case CGROUP_THAWED:
		unfreeze_cgroup(cgroup, freezer);
		break;
	case CGROUP_FROZEN:
		retval = try_to_freeze_cgroup(cgroup, freezer);
		break;
	default:
		BUG();
	}
out:
	spin_unlock_irq(&freezer->lock);

	return retval;
}

static int freezer_write(struct cgroup *cgroup,
			 struct cftype *cft,
			 const char *buffer)
{
	int retval;
	enum freezer_state goal_state;

	if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
		goal_state = CGROUP_THAWED;
	else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
		goal_state = CGROUP_FROZEN;
	else
		return -EINVAL;

	if (!cgroup_lock_live_group(cgroup))
		return -ENODEV;
	retval = freezer_change_state(cgroup, goal_state);
	cgroup_unlock();
	return retval;
}

static struct cftype files[] = {
	{
		.name = "state",
		.read_seq_string = freezer_read,
		.write_string = freezer_write,
	},
};

static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
{
	if (!cgroup->parent)
		return 0;
	return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
}

struct cgroup_subsys freezer_subsys = {
	.name		= "freezer",
	.create		= freezer_create,
	.destroy	= freezer_destroy,
	.populate	= freezer_populate,
	.subsys_id	= freezer_subsys_id,
	.can_attach	= freezer_can_attach,
	.attach		= NULL,
	.fork		= freezer_fork,
	.exit		= NULL,
};
Commit	Line	Data
dc52ddc0 MH	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/module.h>
5a0e3ad6	18	#include <linux/slab.h>
dc52ddc0 MH	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	enum freezer_state {
81dcf33c MH	26	CGROUP_THAWED = 0,
	27	CGROUP_FREEZING,
	28	CGROUP_FROZEN,
dc52ddc0 MH	29	};
	30
	31	struct freezer {
	32	struct cgroup_subsys_state css;
	33	enum freezer_state state;
	34	spinlock_t lock; /* protects _writes_ to state */
	35	};
	36
	37	static inline struct freezer *cgroup_freezer(
	38	struct cgroup *cgroup)
	39	{
	40	return container_of(
	41	cgroup_subsys_state(cgroup, freezer_subsys_id),
	42	struct freezer, css);
	43	}
	44
	45	static inline struct freezer task_freezer(struct task_struct task)
	46	{
	47	return container_of(task_subsys_state(task, freezer_subsys_id),
	48	struct freezer, css);
	49	}
	50
d5de4ddb	51	static inline int __cgroup_freezing_or_frozen(struct task_struct *task)
dc52ddc0	52	{
d5de4ddb TB	53	enum freezer_state state = task_freezer(task)->state;
	54	return (state == CGROUP_FREEZING) \|\| (state == CGROUP_FROZEN);
	55	}
dc52ddc0	56
d5de4ddb TB	57	int cgroup_freezing_or_frozen(struct task_struct *task)
	58	{
	59	int result;
dc52ddc0	60	task_lock(task);
d5de4ddb	61	result = __cgroup_freezing_or_frozen(task);
dc52ddc0	62	task_unlock(task);
d5de4ddb	63	return result;
dc52ddc0 MH	64	}
	65
	66	/*
	67	* cgroups_write_string() limits the size of freezer state strings to
	68	* CGROUP_LOCAL_BUFFER_SIZE
	69	*/
	70	static const char *freezer_state_strs[] = {
81dcf33c	71	"THAWED",
dc52ddc0 MH	72	"FREEZING",
	73	"FROZEN",
	74	};
	75
	76	/*
	77	* State diagram
	78	* Transitions are caused by userspace writes to the freezer.state file.
	79	* The values in parenthesis are state labels. The rest are edge labels.
	80	*
81dcf33c MH	81	* (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
	82	* ^ ^ \| \|
	83	* \| \_______THAWED_______/ \|
	84	* \__________________________THAWED____________/
dc52ddc0 MH	85	*/
	86
	87	struct cgroup_subsys freezer_subsys;
	88
	89	/* Locks taken and their ordering
	90	* ------------------------------
dc52ddc0	91	* cgroup_mutex (AKA cgroup_lock)
dc52ddc0	92	* freezer->lock
8f77578c MH	93	* css_set_lock
8f77578c MH	94	* task->alloc_lock (AKA task_lock)
dc52ddc0 MH	95	* task->sighand->siglock
	96	*
	97	* cgroup code forces css_set_lock to be taken before task->alloc_lock
	98	*
	99	* freezer_create(), freezer_destroy():
	100	* cgroup_mutex [ by cgroup core ]
	101	*
8f77578c MH	102	* freezer_can_attach():
8f77578c MH	103	* cgroup_mutex (held by caller of can_attach)
dc52ddc0	104	*
8f77578c	105	* cgroup_freezing_or_frozen():
dc52ddc0 MH	106	* task->alloc_lock (to get task's cgroup)
	107	*
	108	* freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
dc52ddc0 MH	109	* freezer->lock
	110	* sighand->siglock (if the cgroup is freezing)
	111	*
	112	* freezer_read():
	113	* cgroup_mutex
	114	* freezer->lock
8f77578c MH	115	* write_lock css_set_lock (cgroup iterator start)
8f77578c MH	116	* task->alloc_lock
dc52ddc0 MH	117	* read_lock css_set_lock (cgroup iterator start)
	118	*
	119	* freezer_write() (freeze):
	120	* cgroup_mutex
	121	* freezer->lock
8f77578c MH	122	* write_lock css_set_lock (cgroup iterator start)
8f77578c MH	123	* task->alloc_lock
dc52ddc0	124	* read_lock css_set_lock (cgroup iterator start)
8f77578c	125	* sighand->siglock (fake signal delivery inside freeze_task())
dc52ddc0 MH	126	*
	127	* freezer_write() (unfreeze):
	128	* cgroup_mutex
	129	* freezer->lock
8f77578c MH	130	* write_lock css_set_lock (cgroup iterator start)
8f77578c MH	131	* task->alloc_lock
dc52ddc0	132	* read_lock css_set_lock (cgroup iterator start)
8f77578c	133	* task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
dc52ddc0 MH	134	* sighand->siglock
	135	*/
	136	static struct cgroup_subsys_state freezer_create(struct cgroup_subsys ss,
	137	struct cgroup *cgroup)
	138	{
	139	struct freezer *freezer;
	140
	141	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
	142	if (!freezer)
	143	return ERR_PTR(-ENOMEM);
	144
	145	spin_lock_init(&freezer->lock);
81dcf33c	146	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	147	return &freezer->css;
	148	}
	149
	150	static void freezer_destroy(struct cgroup_subsys *ss,
	151	struct cgroup *cgroup)
	152	{
	153	kfree(cgroup_freezer(cgroup));
	154	}
	155
957a4eea MH	156	/*
	157	* The call to cgroup_lock() in the freezer.state write method prevents
	158	* a write to that file racing against an attach, and hence the
	159	* can_attach() result will remain valid until the attach completes.
	160	*/
dc52ddc0 MH	161	static int freezer_can_attach(struct cgroup_subsys *ss,
dc52ddc0 MH	162	struct cgroup *new_cgroup,
be367d09	163	struct task_struct *task, bool threadgroup)
dc52ddc0 MH	164	{
dc52ddc0 MH	165	struct freezer *freezer;
957a4eea	166
80a6a2cf LZ	167	/*
80a6a2cf LZ	168	* Anything frozen can't move or be moved to/from.
80a6a2cf	169	*/
957a4eea	170
0bdba580 TB	171	freezer = cgroup_freezer(new_cgroup);
0bdba580 TB	172	if (freezer->state != CGROUP_THAWED)
957a4eea	173	return -EBUSY;
dc52ddc0	174
0bdba580 TB	175	rcu_read_lock();
	176	if (__cgroup_freezing_or_frozen(task)) {
	177	rcu_read_unlock();
957a4eea	178	return -EBUSY;
0bdba580 TB	179	}
0bdba580 TB	180	rcu_read_unlock();
957a4eea	181
be367d09 BB	182	if (threadgroup) {
	183	struct task_struct *c;
	184
	185	rcu_read_lock();
	186	list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
0bdba580	187	if (__cgroup_freezing_or_frozen(c)) {
be367d09 BB	188	rcu_read_unlock();
	189	return -EBUSY;
	190	}
	191	}
	192	rcu_read_unlock();
	193	}
	194
80a6a2cf	195	return 0;
dc52ddc0 MH	196	}
	197
	198	static void freezer_fork(struct cgroup_subsys ss, struct task_struct task)
	199	{
	200	struct freezer *freezer;
	201
68744676 LZ	202	/*
	203	* No lock is needed, since the task isn't on tasklist yet,
	204	* so it can't be moved to another cgroup, which means the
	205	* freezer won't be removed and will be valid during this
8b46f880 PM	206	* function call. Nevertheless, apply RCU read-side critical
8b46f880 PM	207	* section to suppress RCU lockdep false positives.
68744676	208	*/
8b46f880	209	rcu_read_lock();
dc52ddc0	210	freezer = task_freezer(task);
8b46f880	211	rcu_read_unlock();
dc52ddc0	212
3b1b3f6e LZ	213	/*
	214	* The root cgroup is non-freezable, so we can skip the
	215	* following check.
	216	*/
	217	if (!freezer->css.cgroup->parent)
	218	return;
	219
dc52ddc0	220	spin_lock_irq(&freezer->lock);
7ccb9743 LZ	221	BUG_ON(freezer->state == CGROUP_FROZEN);
7ccb9743 LZ	222
81dcf33c MH	223	/* Locking avoids race with FREEZING -> THAWED transitions. */
81dcf33c MH	224	if (freezer->state == CGROUP_FREEZING)
dc52ddc0 MH	225	freeze_task(task, true);
	226	spin_unlock_irq(&freezer->lock);
	227	}
	228
	229	/*
	230	* caller must hold freezer->lock
	231	*/
2d3cbf8b	232	static void update_if_frozen(struct cgroup *cgroup,
1aece348	233	struct freezer *freezer)
dc52ddc0 MH	234	{
	235	struct cgroup_iter it;
	236	struct task_struct *task;
	237	unsigned int nfrozen = 0, ntotal = 0;
2d3cbf8b	238	enum freezer_state old_state = freezer->state;
dc52ddc0 MH	239
	240	cgroup_iter_start(cgroup, &it);
	241	while ((task = cgroup_iter_next(cgroup, &it))) {
	242	ntotal++;
2d3cbf8b	243	if (frozen(task))
dc52ddc0 MH	244	nfrozen++;
	245	}
	246
2d3cbf8b TB	247	if (old_state == CGROUP_THAWED) {
	248	BUG_ON(nfrozen > 0);
	249	} else if (old_state == CGROUP_FREEZING) {
	250	if (nfrozen == ntotal)
	251	freezer->state = CGROUP_FROZEN;
	252	} else { /* old_state == CGROUP_FROZEN */
	253	BUG_ON(nfrozen != ntotal);
	254	}
	255
dc52ddc0 MH	256	cgroup_iter_end(cgroup, &it);
	257	}
	258
	259	static int freezer_read(struct cgroup cgroup, struct cftype cft,
	260	struct seq_file *m)
	261	{
	262	struct freezer *freezer;
	263	enum freezer_state state;
	264
	265	if (!cgroup_lock_live_group(cgroup))
	266	return -ENODEV;
	267
	268	freezer = cgroup_freezer(cgroup);
	269	spin_lock_irq(&freezer->lock);
	270	state = freezer->state;
81dcf33c	271	if (state == CGROUP_FREEZING) {
dc52ddc0 MH	272	/* We change from FREEZING to FROZEN lazily if the cgroup was
dc52ddc0 MH	273	* only partially frozen when we exitted write. */
2d3cbf8b	274	update_if_frozen(cgroup, freezer);
dc52ddc0 MH	275	state = freezer->state;
	276	}
	277	spin_unlock_irq(&freezer->lock);
	278	cgroup_unlock();
	279
	280	seq_puts(m, freezer_state_strs[state]);
	281	seq_putc(m, '\n');
	282	return 0;
	283	}
	284
	285	static int try_to_freeze_cgroup(struct cgroup cgroup, struct freezer freezer)
	286	{
	287	struct cgroup_iter it;
	288	struct task_struct *task;
	289	unsigned int num_cant_freeze_now = 0;
	290
81dcf33c	291	freezer->state = CGROUP_FREEZING;
dc52ddc0 MH	292	cgroup_iter_start(cgroup, &it);
	293	while ((task = cgroup_iter_next(cgroup, &it))) {
	294	if (!freeze_task(task, true))
	295	continue;
2d3cbf8b	296	if (frozen(task))
dc52ddc0 MH	297	continue;
	298	if (!freezing(task) && !freezer_should_skip(task))
	299	num_cant_freeze_now++;
	300	}
	301	cgroup_iter_end(cgroup, &it);
	302
	303	return num_cant_freeze_now ? -EBUSY : 0;
	304	}
	305
00c2e63c	306	static void unfreeze_cgroup(struct cgroup cgroup, struct freezer freezer)
dc52ddc0 MH	307	{
	308	struct cgroup_iter it;
	309	struct task_struct *task;
	310
	311	cgroup_iter_start(cgroup, &it);
	312	while ((task = cgroup_iter_next(cgroup, &it))) {
00c2e63c	313	thaw_process(task);
dc52ddc0 MH	314	}
dc52ddc0 MH	315	cgroup_iter_end(cgroup, &it);
dc52ddc0	316
00c2e63c	317	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	318	}
	319
	320	static int freezer_change_state(struct cgroup *cgroup,
	321	enum freezer_state goal_state)
	322	{
	323	struct freezer *freezer;
	324	int retval = 0;
	325
	326	freezer = cgroup_freezer(cgroup);
51308ee5	327
dc52ddc0	328	spin_lock_irq(&freezer->lock);
51308ee5	329
2d3cbf8b	330	update_if_frozen(cgroup, freezer);
dc52ddc0 MH	331	if (goal_state == freezer->state)
dc52ddc0 MH	332	goto out;
51308ee5 LZ	333
51308ee5 LZ	334	switch (goal_state) {
81dcf33c	335	case CGROUP_THAWED:
51308ee5	336	unfreeze_cgroup(cgroup, freezer);
dc52ddc0	337	break;
81dcf33c	338	case CGROUP_FROZEN:
51308ee5	339	retval = try_to_freeze_cgroup(cgroup, freezer);
dc52ddc0 MH	340	break;
dc52ddc0 MH	341	default:
51308ee5	342	BUG();
dc52ddc0 MH	343	}
	344	out:
	345	spin_unlock_irq(&freezer->lock);
	346
	347	return retval;
	348	}
	349
	350	static int freezer_write(struct cgroup *cgroup,
	351	struct cftype *cft,
	352	const char *buffer)
	353	{
	354	int retval;
	355	enum freezer_state goal_state;
	356
81dcf33c MH	357	if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
	358	goal_state = CGROUP_THAWED;
	359	else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
	360	goal_state = CGROUP_FROZEN;
dc52ddc0	361	else
3b1b3f6e	362	return -EINVAL;
dc52ddc0 MH	363
	364	if (!cgroup_lock_live_group(cgroup))
	365	return -ENODEV;
	366	retval = freezer_change_state(cgroup, goal_state);
	367	cgroup_unlock();
	368	return retval;
	369	}
	370
	371	static struct cftype files[] = {
	372	{
	373	.name = "state",
	374	.read_seq_string = freezer_read,
	375	.write_string = freezer_write,
	376	},
	377	};
	378
	379	static int freezer_populate(struct cgroup_subsys ss, struct cgroup cgroup)
	380	{
3b1b3f6e LZ	381	if (!cgroup->parent)
3b1b3f6e LZ	382	return 0;
dc52ddc0 MH	383	return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
	384	}
	385
	386	struct cgroup_subsys freezer_subsys = {
	387	.name = "freezer",
	388	.create = freezer_create,
	389	.destroy = freezer_destroy,
	390	.populate = freezer_populate,
	391	.subsys_id = freezer_subsys_id,
	392	.can_attach = freezer_can_attach,
	393	.attach = NULL,
	394	.fork = freezer_fork,
	395	.exit = NULL,
	396	};