[net-next-2.6.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);
}

int cgroup_frozen(struct task_struct *task)
{
	struct freezer *freezer;
	enum freezer_state state;

	task_lock(task);
	freezer = task_freezer(task);
	state = freezer->state;
	task_unlock(task);

	return state == CGROUP_FROZEN;
}

/*
 * 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
 * ------------------------------
 * css_set_lock
 * cgroup_mutex (AKA cgroup_lock)
 * task->alloc_lock (AKA task_lock)
 * freezer->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 ]
 *
 * can_attach():
 * cgroup_mutex
 *
 * cgroup_frozen():
 * task->alloc_lock (to get task's cgroup)
 *
 * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
 * task->alloc_lock (to get task's cgroup)
 * freezer->lock
 *  sighand->siglock (if the cgroup is freezing)
 *
 * freezer_read():
 * cgroup_mutex
 *  freezer->lock
 *   read_lock css_set_lock (cgroup iterator start)
 *
 * freezer_write() (freeze):
 * cgroup_mutex
 *  freezer->lock
 *   read_lock css_set_lock (cgroup iterator start)
 *    sighand->siglock
 *
 * freezer_write() (unfreeze):
 * cgroup_mutex
 *  freezer->lock
 *   read_lock css_set_lock (cgroup iterator start)
 *    task->alloc_lock (to prevent races with freeze_task())
 *     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));
}

/* Task is frozen or will freeze immediately when next it gets woken */
static bool is_task_frozen_enough(struct task_struct *task)
{
	return frozen(task) ||
		(task_is_stopped_or_traced(task) && freezing(task));
}

/*
 * 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.
	 *
	 * Since orig_freezer->state == FROZEN means that @task has been
	 * frozen, so it's sufficient to check the latter condition.
	 */

	if (is_task_frozen_enough(task))
		return -EBUSY;

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

	if (threadgroup) {
		struct task_struct *c;

		rcu_read_lock();
		list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
			if (is_task_frozen_enough(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.
	 */
	freezer = task_freezer(task);

	/*
	 * 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_freezer_state(struct cgroup *cgroup,
				 struct freezer *freezer)
{
	struct cgroup_iter it;
	struct task_struct *task;
	unsigned int nfrozen = 0, ntotal = 0;

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

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