[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/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_freezing_or_frozen(struct task_struct *task)
{
	struct freezer *freezer;
	enum freezer_state state;

	task_lock(task);
	freezer = task_freezer(task);
	if (!freezer->css.cgroup->parent)
		state = CGROUP_THAWED; /* root cgroup can't be frozen */
	else
		state = freezer->state;
	task_unlock(task);

	return (state == CGROUP_FREEZING) || (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>
	18	#include <linux/cgroup.h>
	19	#include <linux/fs.h>
	20	#include <linux/uaccess.h>
	21	#include <linux/freezer.h>
	22	#include <linux/seq_file.h>
	23
	24	enum freezer_state {
81dcf33c MH	25	CGROUP_THAWED = 0,
	26	CGROUP_FREEZING,
	27	CGROUP_FROZEN,
dc52ddc0 MH	28	};
	29
	30	struct freezer {
	31	struct cgroup_subsys_state css;
	32	enum freezer_state state;
	33	spinlock_t lock; /* protects _writes_ to state */
	34	};
	35
	36	static inline struct freezer *cgroup_freezer(
	37	struct cgroup *cgroup)
	38	{
	39	return container_of(
	40	cgroup_subsys_state(cgroup, freezer_subsys_id),
	41	struct freezer, css);
	42	}
	43
	44	static inline struct freezer task_freezer(struct task_struct task)
	45	{
	46	return container_of(task_subsys_state(task, freezer_subsys_id),
	47	struct freezer, css);
	48	}
	49
5a7aadfe	50	int cgroup_freezing_or_frozen(struct task_struct *task)
dc52ddc0 MH	51	{
	52	struct freezer *freezer;
	53	enum freezer_state state;
	54
	55	task_lock(task);
	56	freezer = task_freezer(task);
5a7aadfe MH	57	if (!freezer->css.cgroup->parent)
	58	state = CGROUP_THAWED; /* root cgroup can't be frozen */
	59	else
	60	state = freezer->state;
dc52ddc0 MH	61	task_unlock(task);
dc52ddc0 MH	62
5a7aadfe	63	return (state == CGROUP_FREEZING) \|\| (state == CGROUP_FROZEN);
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	* ------------------------------
	91	* css_set_lock
	92	* cgroup_mutex (AKA cgroup_lock)
	93	* task->alloc_lock (AKA task_lock)
	94	* freezer->lock
	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	*
	102	* can_attach():
	103	* cgroup_mutex
	104	*
	105	* cgroup_frozen():
	106	* task->alloc_lock (to get task's cgroup)
	107	*
	108	* freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
	109	* task->alloc_lock (to get task's cgroup)
	110	* freezer->lock
	111	* sighand->siglock (if the cgroup is freezing)
	112	*
	113	* freezer_read():
	114	* cgroup_mutex
	115	* freezer->lock
	116	* read_lock css_set_lock (cgroup iterator start)
	117	*
	118	* freezer_write() (freeze):
	119	* cgroup_mutex
	120	* freezer->lock
	121	* read_lock css_set_lock (cgroup iterator start)
	122	* sighand->siglock
	123	*
	124	* freezer_write() (unfreeze):
	125	* cgroup_mutex
	126	* freezer->lock
	127	* read_lock css_set_lock (cgroup iterator start)
	128	* task->alloc_lock (to prevent races with freeze_task())
	129	* sighand->siglock
	130	*/
	131	static struct cgroup_subsys_state freezer_create(struct cgroup_subsys ss,
	132	struct cgroup *cgroup)
	133	{
	134	struct freezer *freezer;
	135
	136	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
	137	if (!freezer)
	138	return ERR_PTR(-ENOMEM);
	139
	140	spin_lock_init(&freezer->lock);
81dcf33c	141	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	142	return &freezer->css;
	143	}
	144
	145	static void freezer_destroy(struct cgroup_subsys *ss,
	146	struct cgroup *cgroup)
	147	{
	148	kfree(cgroup_freezer(cgroup));
	149	}
	150
957a4eea MH	151	/* Task is frozen or will freeze immediately when next it gets woken */
	152	static bool is_task_frozen_enough(struct task_struct *task)
	153	{
	154	return frozen(task) \|\|
	155	(task_is_stopped_or_traced(task) && freezing(task));
	156	}
dc52ddc0	157
957a4eea MH	158	/*
	159	* The call to cgroup_lock() in the freezer.state write method prevents
	160	* a write to that file racing against an attach, and hence the
	161	* can_attach() result will remain valid until the attach completes.
	162	*/
dc52ddc0 MH	163	static int freezer_can_attach(struct cgroup_subsys *ss,
dc52ddc0 MH	164	struct cgroup *new_cgroup,
be367d09	165	struct task_struct *task, bool threadgroup)
dc52ddc0 MH	166	{
dc52ddc0 MH	167	struct freezer *freezer;
957a4eea	168
80a6a2cf LZ	169	/*
	170	* Anything frozen can't move or be moved to/from.
	171	*
	172	* Since orig_freezer->state == FROZEN means that @task has been
	173	* frozen, so it's sufficient to check the latter condition.
	174	*/
957a4eea MH	175
	176	if (is_task_frozen_enough(task))
	177	return -EBUSY;
dc52ddc0	178
dc52ddc0	179	freezer = cgroup_freezer(new_cgroup);
81dcf33c	180	if (freezer->state == CGROUP_FROZEN)
957a4eea MH	181	return -EBUSY;
957a4eea MH	182
be367d09 BB	183	if (threadgroup) {
	184	struct task_struct *c;
	185
	186	rcu_read_lock();
	187	list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
	188	if (is_task_frozen_enough(c)) {
	189	rcu_read_unlock();
	190	return -EBUSY;
	191	}
	192	}
	193	rcu_read_unlock();
	194	}
	195
80a6a2cf	196	return 0;
dc52ddc0 MH	197	}
	198
	199	static void freezer_fork(struct cgroup_subsys ss, struct task_struct task)
	200	{
	201	struct freezer *freezer;
	202
68744676 LZ	203	/*
	204	* No lock is needed, since the task isn't on tasklist yet,
	205	* so it can't be moved to another cgroup, which means the
	206	* freezer won't be removed and will be valid during this
	207	* function call.
	208	*/
dc52ddc0	209	freezer = task_freezer(task);
dc52ddc0	210
3b1b3f6e LZ	211	/*
	212	* The root cgroup is non-freezable, so we can skip the
	213	* following check.
	214	*/
	215	if (!freezer->css.cgroup->parent)
	216	return;
	217
dc52ddc0	218	spin_lock_irq(&freezer->lock);
7ccb9743 LZ	219	BUG_ON(freezer->state == CGROUP_FROZEN);
7ccb9743 LZ	220
81dcf33c MH	221	/* Locking avoids race with FREEZING -> THAWED transitions. */
81dcf33c MH	222	if (freezer->state == CGROUP_FREEZING)
dc52ddc0 MH	223	freeze_task(task, true);
	224	spin_unlock_irq(&freezer->lock);
	225	}
	226
	227	/*
	228	* caller must hold freezer->lock
	229	*/
1aece348 MH	230	static void update_freezer_state(struct cgroup *cgroup,
1aece348 MH	231	struct freezer *freezer)
dc52ddc0 MH	232	{
	233	struct cgroup_iter it;
	234	struct task_struct *task;
	235	unsigned int nfrozen = 0, ntotal = 0;
	236
	237	cgroup_iter_start(cgroup, &it);
	238	while ((task = cgroup_iter_next(cgroup, &it))) {
	239	ntotal++;
957a4eea	240	if (is_task_frozen_enough(task))
dc52ddc0 MH	241	nfrozen++;
	242	}
	243
	244	/*
	245	* Transition to FROZEN when no new tasks can be added ensures
	246	* that we never exist in the FROZEN state while there are unfrozen
	247	* tasks.
	248	*/
	249	if (nfrozen == ntotal)
81dcf33c	250	freezer->state = CGROUP_FROZEN;
1aece348 MH	251	else if (nfrozen > 0)
	252	freezer->state = CGROUP_FREEZING;
	253	else
	254	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	255	cgroup_iter_end(cgroup, &it);
	256	}
	257
	258	static int freezer_read(struct cgroup cgroup, struct cftype cft,
	259	struct seq_file *m)
	260	{
	261	struct freezer *freezer;
	262	enum freezer_state state;
	263
	264	if (!cgroup_lock_live_group(cgroup))
	265	return -ENODEV;
	266
	267	freezer = cgroup_freezer(cgroup);
	268	spin_lock_irq(&freezer->lock);
	269	state = freezer->state;
81dcf33c	270	if (state == CGROUP_FREEZING) {
dc52ddc0 MH	271	/* We change from FREEZING to FROZEN lazily if the cgroup was
dc52ddc0 MH	272	* only partially frozen when we exitted write. */
1aece348	273	update_freezer_state(cgroup, freezer);
dc52ddc0 MH	274	state = freezer->state;
	275	}
	276	spin_unlock_irq(&freezer->lock);
	277	cgroup_unlock();
	278
	279	seq_puts(m, freezer_state_strs[state]);
	280	seq_putc(m, '\n');
	281	return 0;
	282	}
	283
	284	static int try_to_freeze_cgroup(struct cgroup cgroup, struct freezer freezer)
	285	{
	286	struct cgroup_iter it;
	287	struct task_struct *task;
	288	unsigned int num_cant_freeze_now = 0;
	289
81dcf33c	290	freezer->state = CGROUP_FREEZING;
dc52ddc0 MH	291	cgroup_iter_start(cgroup, &it);
	292	while ((task = cgroup_iter_next(cgroup, &it))) {
	293	if (!freeze_task(task, true))
	294	continue;
957a4eea	295	if (is_task_frozen_enough(task))
dc52ddc0 MH	296	continue;
	297	if (!freezing(task) && !freezer_should_skip(task))
	298	num_cant_freeze_now++;
	299	}
	300	cgroup_iter_end(cgroup, &it);
	301
	302	return num_cant_freeze_now ? -EBUSY : 0;
	303	}
	304
00c2e63c	305	static void unfreeze_cgroup(struct cgroup cgroup, struct freezer freezer)
dc52ddc0 MH	306	{
	307	struct cgroup_iter it;
	308	struct task_struct *task;
	309
	310	cgroup_iter_start(cgroup, &it);
	311	while ((task = cgroup_iter_next(cgroup, &it))) {
00c2e63c	312	thaw_process(task);
dc52ddc0 MH	313	}
dc52ddc0 MH	314	cgroup_iter_end(cgroup, &it);
dc52ddc0	315
00c2e63c	316	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	317	}
	318
	319	static int freezer_change_state(struct cgroup *cgroup,
	320	enum freezer_state goal_state)
	321	{
	322	struct freezer *freezer;
	323	int retval = 0;
	324
	325	freezer = cgroup_freezer(cgroup);
51308ee5	326
dc52ddc0	327	spin_lock_irq(&freezer->lock);
51308ee5	328
1aece348	329	update_freezer_state(cgroup, freezer);
dc52ddc0 MH	330	if (goal_state == freezer->state)
dc52ddc0 MH	331	goto out;
51308ee5 LZ	332
51308ee5 LZ	333	switch (goal_state) {
81dcf33c	334	case CGROUP_THAWED:
51308ee5	335	unfreeze_cgroup(cgroup, freezer);
dc52ddc0	336	break;
81dcf33c	337	case CGROUP_FROZEN:
51308ee5	338	retval = try_to_freeze_cgroup(cgroup, freezer);
dc52ddc0 MH	339	break;
dc52ddc0 MH	340	default:
51308ee5	341	BUG();
dc52ddc0 MH	342	}
	343	out:
	344	spin_unlock_irq(&freezer->lock);
	345
	346	return retval;
	347	}
	348
	349	static int freezer_write(struct cgroup *cgroup,
	350	struct cftype *cft,
	351	const char *buffer)
	352	{
	353	int retval;
	354	enum freezer_state goal_state;
	355
81dcf33c MH	356	if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
	357	goal_state = CGROUP_THAWED;
	358	else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
	359	goal_state = CGROUP_FROZEN;
dc52ddc0	360	else
3b1b3f6e	361	return -EINVAL;
dc52ddc0 MH	362
	363	if (!cgroup_lock_live_group(cgroup))
	364	return -ENODEV;
	365	retval = freezer_change_state(cgroup, goal_state);
	366	cgroup_unlock();
	367	return retval;
	368	}
	369
	370	static struct cftype files[] = {
	371	{
	372	.name = "state",
	373	.read_seq_string = freezer_read,
	374	.write_string = freezer_write,
	375	},
	376	};
	377
	378	static int freezer_populate(struct cgroup_subsys ss, struct cgroup cgroup)
	379	{
3b1b3f6e LZ	380	if (!cgroup->parent)
3b1b3f6e LZ	381	return 0;
dc52ddc0 MH	382	return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
	383	}
	384
	385	struct cgroup_subsys freezer_subsys = {
	386	.name = "freezer",
	387	.create = freezer_create,
	388	.destroy = freezer_destroy,
	389	.populate = freezer_populate,
	390	.subsys_id = freezer_subsys_id,
	391	.can_attach = freezer_can_attach,
	392	.attach = NULL,
	393	.fork = freezer_fork,
	394	.exit = NULL,
	395	};