[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
 * ------------------------------
 * 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));
}

/* 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.  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_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	* ------------------------------
dc52ddc0	92	* cgroup_mutex (AKA cgroup_lock)
dc52ddc0	93	* freezer->lock
8f77578c MH	94	* css_set_lock
8f77578c MH	95	* task->alloc_lock (AKA task_lock)
dc52ddc0 MH	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	*
8f77578c MH	103	* freezer_can_attach():
8f77578c MH	104	* cgroup_mutex (held by caller of can_attach)
dc52ddc0	105	*
8f77578c	106	* cgroup_freezing_or_frozen():
dc52ddc0 MH	107	* task->alloc_lock (to get task's cgroup)
	108	*
	109	* freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
dc52ddc0 MH	110	* freezer->lock
	111	* sighand->siglock (if the cgroup is freezing)
	112	*
	113	* freezer_read():
	114	* cgroup_mutex
	115	* freezer->lock
8f77578c MH	116	* write_lock css_set_lock (cgroup iterator start)
8f77578c MH	117	* task->alloc_lock
dc52ddc0 MH	118	* read_lock css_set_lock (cgroup iterator start)
	119	*
	120	* freezer_write() (freeze):
	121	* cgroup_mutex
	122	* freezer->lock
8f77578c MH	123	* write_lock css_set_lock (cgroup iterator start)
8f77578c MH	124	* task->alloc_lock
dc52ddc0	125	* read_lock css_set_lock (cgroup iterator start)
8f77578c	126	* sighand->siglock (fake signal delivery inside freeze_task())
dc52ddc0 MH	127	*
	128	* freezer_write() (unfreeze):
	129	* cgroup_mutex
	130	* freezer->lock
8f77578c MH	131	* write_lock css_set_lock (cgroup iterator start)
8f77578c MH	132	* task->alloc_lock
dc52ddc0	133	* read_lock css_set_lock (cgroup iterator start)
8f77578c	134	* task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
dc52ddc0 MH	135	* sighand->siglock
	136	*/
	137	static struct cgroup_subsys_state freezer_create(struct cgroup_subsys ss,
	138	struct cgroup *cgroup)
	139	{
	140	struct freezer *freezer;
	141
	142	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
	143	if (!freezer)
	144	return ERR_PTR(-ENOMEM);
	145
	146	spin_lock_init(&freezer->lock);
81dcf33c	147	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	148	return &freezer->css;
	149	}
	150
	151	static void freezer_destroy(struct cgroup_subsys *ss,
	152	struct cgroup *cgroup)
	153	{
	154	kfree(cgroup_freezer(cgroup));
	155	}
	156
957a4eea MH	157	/* Task is frozen or will freeze immediately when next it gets woken */
	158	static bool is_task_frozen_enough(struct task_struct *task)
	159	{
	160	return frozen(task) \|\|
	161	(task_is_stopped_or_traced(task) && freezing(task));
	162	}
dc52ddc0	163
957a4eea MH	164	/*
	165	* The call to cgroup_lock() in the freezer.state write method prevents
	166	* a write to that file racing against an attach, and hence the
	167	* can_attach() result will remain valid until the attach completes.
	168	*/
dc52ddc0 MH	169	static int freezer_can_attach(struct cgroup_subsys *ss,
dc52ddc0 MH	170	struct cgroup *new_cgroup,
be367d09	171	struct task_struct *task, bool threadgroup)
dc52ddc0 MH	172	{
dc52ddc0 MH	173	struct freezer *freezer;
957a4eea	174
80a6a2cf LZ	175	/*
	176	* Anything frozen can't move or be moved to/from.
	177	*
	178	* Since orig_freezer->state == FROZEN means that @task has been
	179	* frozen, so it's sufficient to check the latter condition.
	180	*/
957a4eea MH	181
	182	if (is_task_frozen_enough(task))
	183	return -EBUSY;
dc52ddc0	184
dc52ddc0	185	freezer = cgroup_freezer(new_cgroup);
81dcf33c	186	if (freezer->state == CGROUP_FROZEN)
957a4eea MH	187	return -EBUSY;
957a4eea MH	188
be367d09 BB	189	if (threadgroup) {
	190	struct task_struct *c;
	191
	192	rcu_read_lock();
	193	list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
	194	if (is_task_frozen_enough(c)) {
	195	rcu_read_unlock();
	196	return -EBUSY;
	197	}
	198	}
	199	rcu_read_unlock();
	200	}
	201
80a6a2cf	202	return 0;
dc52ddc0 MH	203	}
	204
	205	static void freezer_fork(struct cgroup_subsys ss, struct task_struct task)
	206	{
	207	struct freezer *freezer;
	208
68744676 LZ	209	/*
	210	* No lock is needed, since the task isn't on tasklist yet,
	211	* so it can't be moved to another cgroup, which means the
	212	* freezer won't be removed and will be valid during this
8b46f880 PM	213	* function call. Nevertheless, apply RCU read-side critical
8b46f880 PM	214	* section to suppress RCU lockdep false positives.
68744676	215	*/
8b46f880	216	rcu_read_lock();
dc52ddc0	217	freezer = task_freezer(task);
8b46f880	218	rcu_read_unlock();
dc52ddc0	219
3b1b3f6e LZ	220	/*
	221	* The root cgroup is non-freezable, so we can skip the
	222	* following check.
	223	*/
	224	if (!freezer->css.cgroup->parent)
	225	return;
	226
dc52ddc0	227	spin_lock_irq(&freezer->lock);
7ccb9743 LZ	228	BUG_ON(freezer->state == CGROUP_FROZEN);
7ccb9743 LZ	229
81dcf33c MH	230	/* Locking avoids race with FREEZING -> THAWED transitions. */
81dcf33c MH	231	if (freezer->state == CGROUP_FREEZING)
dc52ddc0 MH	232	freeze_task(task, true);
	233	spin_unlock_irq(&freezer->lock);
	234	}
	235
	236	/*
	237	* caller must hold freezer->lock
	238	*/
1aece348 MH	239	static void update_freezer_state(struct cgroup *cgroup,
1aece348 MH	240	struct freezer *freezer)
dc52ddc0 MH	241	{
	242	struct cgroup_iter it;
	243	struct task_struct *task;
	244	unsigned int nfrozen = 0, ntotal = 0;
	245
	246	cgroup_iter_start(cgroup, &it);
	247	while ((task = cgroup_iter_next(cgroup, &it))) {
	248	ntotal++;
957a4eea	249	if (is_task_frozen_enough(task))
dc52ddc0 MH	250	nfrozen++;
	251	}
	252
	253	/*
	254	* Transition to FROZEN when no new tasks can be added ensures
	255	* that we never exist in the FROZEN state while there are unfrozen
	256	* tasks.
	257	*/
	258	if (nfrozen == ntotal)
81dcf33c	259	freezer->state = CGROUP_FROZEN;
1aece348 MH	260	else if (nfrozen > 0)
	261	freezer->state = CGROUP_FREEZING;
	262	else
	263	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	264	cgroup_iter_end(cgroup, &it);
	265	}
	266
	267	static int freezer_read(struct cgroup cgroup, struct cftype cft,
	268	struct seq_file *m)
	269	{
	270	struct freezer *freezer;
	271	enum freezer_state state;
	272
	273	if (!cgroup_lock_live_group(cgroup))
	274	return -ENODEV;
	275
	276	freezer = cgroup_freezer(cgroup);
	277	spin_lock_irq(&freezer->lock);
	278	state = freezer->state;
81dcf33c	279	if (state == CGROUP_FREEZING) {
dc52ddc0 MH	280	/* We change from FREEZING to FROZEN lazily if the cgroup was
dc52ddc0 MH	281	* only partially frozen when we exitted write. */
1aece348	282	update_freezer_state(cgroup, freezer);
dc52ddc0 MH	283	state = freezer->state;
	284	}
	285	spin_unlock_irq(&freezer->lock);
	286	cgroup_unlock();
	287
	288	seq_puts(m, freezer_state_strs[state]);
	289	seq_putc(m, '\n');
	290	return 0;
	291	}
	292
	293	static int try_to_freeze_cgroup(struct cgroup cgroup, struct freezer freezer)
	294	{
	295	struct cgroup_iter it;
	296	struct task_struct *task;
	297	unsigned int num_cant_freeze_now = 0;
	298
81dcf33c	299	freezer->state = CGROUP_FREEZING;
dc52ddc0 MH	300	cgroup_iter_start(cgroup, &it);
	301	while ((task = cgroup_iter_next(cgroup, &it))) {
	302	if (!freeze_task(task, true))
	303	continue;
957a4eea	304	if (is_task_frozen_enough(task))
dc52ddc0 MH	305	continue;
	306	if (!freezing(task) && !freezer_should_skip(task))
	307	num_cant_freeze_now++;
	308	}
	309	cgroup_iter_end(cgroup, &it);
	310
	311	return num_cant_freeze_now ? -EBUSY : 0;
	312	}
	313
00c2e63c	314	static void unfreeze_cgroup(struct cgroup cgroup, struct freezer freezer)
dc52ddc0 MH	315	{
	316	struct cgroup_iter it;
	317	struct task_struct *task;
	318
	319	cgroup_iter_start(cgroup, &it);
	320	while ((task = cgroup_iter_next(cgroup, &it))) {
00c2e63c	321	thaw_process(task);
dc52ddc0 MH	322	}
dc52ddc0 MH	323	cgroup_iter_end(cgroup, &it);
dc52ddc0	324
00c2e63c	325	freezer->state = CGROUP_THAWED;
dc52ddc0 MH	326	}
	327
	328	static int freezer_change_state(struct cgroup *cgroup,
	329	enum freezer_state goal_state)
	330	{
	331	struct freezer *freezer;
	332	int retval = 0;
	333
	334	freezer = cgroup_freezer(cgroup);
51308ee5	335
dc52ddc0	336	spin_lock_irq(&freezer->lock);
51308ee5	337
1aece348	338	update_freezer_state(cgroup, freezer);
dc52ddc0 MH	339	if (goal_state == freezer->state)
dc52ddc0 MH	340	goto out;
51308ee5 LZ	341
51308ee5 LZ	342	switch (goal_state) {
81dcf33c	343	case CGROUP_THAWED:
51308ee5	344	unfreeze_cgroup(cgroup, freezer);
dc52ddc0	345	break;
81dcf33c	346	case CGROUP_FROZEN:
51308ee5	347	retval = try_to_freeze_cgroup(cgroup, freezer);
dc52ddc0 MH	348	break;
dc52ddc0 MH	349	default:
51308ee5	350	BUG();
dc52ddc0 MH	351	}
	352	out:
	353	spin_unlock_irq(&freezer->lock);
	354
	355	return retval;
	356	}
	357
	358	static int freezer_write(struct cgroup *cgroup,
	359	struct cftype *cft,
	360	const char *buffer)
	361	{
	362	int retval;
	363	enum freezer_state goal_state;
	364
81dcf33c MH	365	if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
	366	goal_state = CGROUP_THAWED;
	367	else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
	368	goal_state = CGROUP_FROZEN;
dc52ddc0	369	else
3b1b3f6e	370	return -EINVAL;
dc52ddc0 MH	371
	372	if (!cgroup_lock_live_group(cgroup))
	373	return -ENODEV;
	374	retval = freezer_change_state(cgroup, goal_state);
	375	cgroup_unlock();
	376	return retval;
	377	}
	378
	379	static struct cftype files[] = {
	380	{
	381	.name = "state",
	382	.read_seq_string = freezer_read,
	383	.write_string = freezer_write,
	384	},
	385	};
	386
	387	static int freezer_populate(struct cgroup_subsys ss, struct cgroup cgroup)
	388	{
3b1b3f6e LZ	389	if (!cgroup->parent)
3b1b3f6e LZ	390	return 0;
dc52ddc0 MH	391	return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
	392	}
	393
	394	struct cgroup_subsys freezer_subsys = {
	395	.name = "freezer",
	396	.create = freezer_create,
	397	.destroy = freezer_destroy,
	398	.populate = freezer_populate,
	399	.subsys_id = freezer_subsys_id,
	400	.can_attach = freezer_can_attach,
	401	.attach = NULL,
	402	.fork = freezer_fork,
	403	.exit = NULL,
	404	};