[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_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>
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
5a7aadfe	51	int cgroup_freezing_or_frozen(struct task_struct *task)
dc52ddc0 MH	52	{
	53	struct freezer *freezer;
	54	enum freezer_state state;
	55
	56	task_lock(task);
	57	freezer = task_freezer(task);
5a7aadfe MH	58	if (!freezer->css.cgroup->parent)
	59	state = CGROUP_THAWED; /* root cgroup can't be frozen */
	60	else
	61	state = freezer->state;
dc52ddc0 MH	62	task_unlock(task);
dc52ddc0 MH	63
5a7aadfe	64	return (state == CGROUP_FREEZING) \|\| (state == CGROUP_FROZEN);
dc52ddc0 MH	65	}
	66
	67	/*
	68	* cgroups_write_string() limits the size of freezer state strings to
	69	* CGROUP_LOCAL_BUFFER_SIZE
	70	*/
	71	static const char *freezer_state_strs[] = {
81dcf33c	72	"THAWED",
dc52ddc0 MH	73	"FREEZING",
	74	"FROZEN",
	75	};
	76
	77	/*
	78	* State diagram
	79	* Transitions are caused by userspace writes to the freezer.state file.
	80	* The values in parenthesis are state labels. The rest are edge labels.
	81	*
81dcf33c MH	82	* (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
	83	* ^ ^ \| \|
	84	* \| \_______THAWED_______/ \|
	85	* \__________________________THAWED____________/
dc52ddc0 MH	86	*/
	87
	88	struct cgroup_subsys freezer_subsys;
	89
	90	/* Locks taken and their ordering
	91	* ------------------------------
	92	* css_set_lock
	93	* cgroup_mutex (AKA cgroup_lock)
	94	* task->alloc_lock (AKA task_lock)
	95	* freezer->lock
	96	* task->sighand->siglock
	97	*
	98	* cgroup code forces css_set_lock to be taken before task->alloc_lock
	99	*
	100	* freezer_create(), freezer_destroy():
	101	* cgroup_mutex [ by cgroup core ]
	102	*
	103	* can_attach():
	104	* cgroup_mutex
	105	*
	106	* cgroup_frozen():
	107	* task->alloc_lock (to get task's cgroup)
	108	*
	109	* freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
	110	* task->alloc_lock (to get task's cgroup)
	111	* freezer->lock
	112	* sighand->siglock (if the cgroup is freezing)
	113	*
	114	* freezer_read():
	115	* cgroup_mutex
	116	* freezer->lock
	117	* read_lock css_set_lock (cgroup iterator start)
	118	*
	119	* freezer_write() (freeze):
	120	* cgroup_mutex
	121	* freezer->lock
	122	* read_lock css_set_lock (cgroup iterator start)
	123	* sighand->siglock
	124	*
	125	* freezer_write() (unfreeze):
	126	* cgroup_mutex
	127	* freezer->lock
	128	* read_lock css_set_lock (cgroup iterator start)
	129	* task->alloc_lock (to prevent races with freeze_task())
	130	* sighand->siglock
	131	*/
	132	static struct cgroup_subsys_state freezer_create(struct cgroup_subsys ss,
	133	struct cgroup *cgroup)
	134	{
	135	struct freezer *freezer;
	136
	137	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
	138	if (!freezer)
	139	return ERR_PTR(-ENOMEM);
	140
	141	spin_lock_init(&freezer->lock);
81dcf33c	142	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	143	return &freezer->css;
	144	}
	145
	146	static void freezer_destroy(struct cgroup_subsys *ss,
	147	struct cgroup *cgroup)
	148	{
	149	kfree(cgroup_freezer(cgroup));
	150	}
	151
957a4eea MH	152	/* Task is frozen or will freeze immediately when next it gets woken */
	153	static bool is_task_frozen_enough(struct task_struct *task)
	154	{
	155	return frozen(task) \|\|
	156	(task_is_stopped_or_traced(task) && freezing(task));
	157	}
dc52ddc0	158
957a4eea MH	159	/*
	160	* The call to cgroup_lock() in the freezer.state write method prevents
	161	* a write to that file racing against an attach, and hence the
	162	* can_attach() result will remain valid until the attach completes.
	163	*/
dc52ddc0 MH	164	static int freezer_can_attach(struct cgroup_subsys *ss,
dc52ddc0 MH	165	struct cgroup *new_cgroup,
be367d09	166	struct task_struct *task, bool threadgroup)
dc52ddc0 MH	167	{
dc52ddc0 MH	168	struct freezer *freezer;
957a4eea	169
80a6a2cf LZ	170	/*
	171	* Anything frozen can't move or be moved to/from.
	172	*
	173	* Since orig_freezer->state == FROZEN means that @task has been
	174	* frozen, so it's sufficient to check the latter condition.
	175	*/
957a4eea MH	176
	177	if (is_task_frozen_enough(task))
	178	return -EBUSY;
dc52ddc0	179
dc52ddc0	180	freezer = cgroup_freezer(new_cgroup);
81dcf33c	181	if (freezer->state == CGROUP_FROZEN)
957a4eea MH	182	return -EBUSY;
957a4eea MH	183
be367d09 BB	184	if (threadgroup) {
	185	struct task_struct *c;
	186
	187	rcu_read_lock();
	188	list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
	189	if (is_task_frozen_enough(c)) {
	190	rcu_read_unlock();
	191	return -EBUSY;
	192	}
	193	}
	194	rcu_read_unlock();
	195	}
	196
80a6a2cf	197	return 0;
dc52ddc0 MH	198	}
	199
	200	static void freezer_fork(struct cgroup_subsys ss, struct task_struct task)
	201	{
	202	struct freezer *freezer;
	203
68744676 LZ	204	/*
	205	* No lock is needed, since the task isn't on tasklist yet,
	206	* so it can't be moved to another cgroup, which means the
	207	* freezer won't be removed and will be valid during this
	208	* function call.
	209	*/
dc52ddc0	210	freezer = task_freezer(task);
dc52ddc0	211
3b1b3f6e LZ	212	/*
	213	* The root cgroup is non-freezable, so we can skip the
	214	* following check.
	215	*/
	216	if (!freezer->css.cgroup->parent)
	217	return;
	218
dc52ddc0	219	spin_lock_irq(&freezer->lock);
7ccb9743 LZ	220	BUG_ON(freezer->state == CGROUP_FROZEN);
7ccb9743 LZ	221
81dcf33c MH	222	/* Locking avoids race with FREEZING -> THAWED transitions. */
81dcf33c MH	223	if (freezer->state == CGROUP_FREEZING)
dc52ddc0 MH	224	freeze_task(task, true);
	225	spin_unlock_irq(&freezer->lock);
	226	}
	227
	228	/*
	229	* caller must hold freezer->lock
	230	*/
1aece348 MH	231	static void update_freezer_state(struct cgroup *cgroup,
1aece348 MH	232	struct freezer *freezer)
dc52ddc0 MH	233	{
	234	struct cgroup_iter it;
	235	struct task_struct *task;
	236	unsigned int nfrozen = 0, ntotal = 0;
	237
	238	cgroup_iter_start(cgroup, &it);
	239	while ((task = cgroup_iter_next(cgroup, &it))) {
	240	ntotal++;
957a4eea	241	if (is_task_frozen_enough(task))
dc52ddc0 MH	242	nfrozen++;
	243	}
	244
	245	/*
	246	* Transition to FROZEN when no new tasks can be added ensures
	247	* that we never exist in the FROZEN state while there are unfrozen
	248	* tasks.
	249	*/
	250	if (nfrozen == ntotal)
81dcf33c	251	freezer->state = CGROUP_FROZEN;
1aece348 MH	252	else if (nfrozen > 0)
	253	freezer->state = CGROUP_FREEZING;
	254	else
	255	freezer->state = CGROUP_THAWED;
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. */
1aece348	274	update_freezer_state(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;
957a4eea	296	if (is_task_frozen_enough(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
1aece348	330	update_freezer_state(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	};