[linux-2.6-block.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/export.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>
#include <linux/mutex.h>

/*
 * A cgroup is freezing if any FREEZING flags are set.  FREEZING_SELF is
 * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
 * for "THAWED".  FREEZING_PARENT is set if the parent freezer is FREEZING
 * for whatever reason.  IOW, a cgroup has FREEZING_PARENT set if one of
 * its ancestors has FREEZING_SELF set.
 */
enum freezer_state_flags {
	CGROUP_FREEZER_ONLINE	= (1 << 0), /* freezer is fully online */
	CGROUP_FREEZING_SELF	= (1 << 1), /* this freezer is freezing */
	CGROUP_FREEZING_PARENT	= (1 << 2), /* the parent freezer is freezing */
	CGROUP_FROZEN		= (1 << 3), /* this and its descendants frozen */

	/* mask for all FREEZING flags */
	CGROUP_FREEZING		= CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
};

struct freezer {
	struct cgroup_subsys_state	css;
	unsigned int			state;
};

static DEFINE_MUTEX(freezer_mutex);

static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
{
	return css ? container_of(css, struct freezer, css) : NULL;
}

static inline struct freezer *task_freezer(struct task_struct *task)
{
	return css_freezer(task_css(task, freezer_cgrp_id));
}

static struct freezer *parent_freezer(struct freezer *freezer)
{
	return css_freezer(freezer->css.parent);
}

bool cgroup_freezing(struct task_struct *task)
{
	bool ret;

	rcu_read_lock();
	ret = task_freezer(task)->state & CGROUP_FREEZING;
	rcu_read_unlock();

	return ret;
}

static const char *freezer_state_strs(unsigned int state)
{
	if (state & CGROUP_FROZEN)
		return "FROZEN";
	if (state & CGROUP_FREEZING)
		return "FREEZING";
	return "THAWED";
};

static struct cgroup_subsys_state *
freezer_css_alloc(struct cgroup_subsys_state *parent_css)
{
	struct freezer *freezer;

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

	return &freezer->css;
}

/**
 * freezer_css_online - commit creation of a freezer css
 * @css: css being created
 *
 * We're committing to creation of @css.  Mark it online and inherit
 * parent's freezing state while holding both parent's and our
 * freezer->lock.
 */
static int freezer_css_online(struct cgroup_subsys_state *css)
{
	struct freezer *freezer = css_freezer(css);
	struct freezer *parent = parent_freezer(freezer);

	mutex_lock(&freezer_mutex);

	freezer->state |= CGROUP_FREEZER_ONLINE;

	if (parent && (parent->state & CGROUP_FREEZING)) {
		freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
		atomic_inc(&system_freezing_cnt);
	}

	mutex_unlock(&freezer_mutex);
	return 0;
}

/**
 * freezer_css_offline - initiate destruction of a freezer css
 * @css: css being destroyed
 *
 * @css is going away.  Mark it dead and decrement system_freezing_count if
 * it was holding one.
 */
static void freezer_css_offline(struct cgroup_subsys_state *css)
{
	struct freezer *freezer = css_freezer(css);

	mutex_lock(&freezer_mutex);

	if (freezer->state & CGROUP_FREEZING)
		atomic_dec(&system_freezing_cnt);

	freezer->state = 0;

	mutex_unlock(&freezer_mutex);
}

static void freezer_css_free(struct cgroup_subsys_state *css)
{
	kfree(css_freezer(css));
}

/*
 * Tasks can be migrated into a different freezer anytime regardless of its
 * current state.  freezer_attach() is responsible for making new tasks
 * conform to the current state.
 *
 * Freezer state changes and task migration are synchronized via
 * @freezer->lock.  freezer_attach() makes the new tasks conform to the
 * current state and all following state changes can see the new tasks.
 */
static void freezer_attach(struct cgroup_subsys_state *new_css,
			   struct cgroup_taskset *tset)
{
	struct freezer *freezer = css_freezer(new_css);
	struct task_struct *task;
	bool clear_frozen = false;

	mutex_lock(&freezer_mutex);

	/*
	 * Make the new tasks conform to the current state of @new_css.
	 * For simplicity, when migrating any task to a FROZEN cgroup, we
	 * revert it to FREEZING and let update_if_frozen() determine the
	 * correct state later.
	 *
	 * Tasks in @tset are on @new_css but may not conform to its
	 * current state before executing the following - !frozen tasks may
	 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
	 */
	cgroup_taskset_for_each(task, tset) {
		if (!(freezer->state & CGROUP_FREEZING)) {
			__thaw_task(task);
		} else {
			freeze_task(task);
			freezer->state &= ~CGROUP_FROZEN;
			clear_frozen = true;
		}
	}

	/* propagate FROZEN clearing upwards */
	while (clear_frozen && (freezer = parent_freezer(freezer))) {
		freezer->state &= ~CGROUP_FROZEN;
		clear_frozen = freezer->state & CGROUP_FREEZING;
	}

	mutex_unlock(&freezer_mutex);
}

/**
 * freezer_fork - cgroup post fork callback
 * @task: a task which has just been forked
 *
 * @task has just been created and should conform to the current state of
 * the cgroup_freezer it belongs to.  This function may race against
 * freezer_attach().  Losing to freezer_attach() means that we don't have
 * to do anything as freezer_attach() will put @task into the appropriate
 * state.
 */
static void freezer_fork(struct task_struct *task)
{
	struct freezer *freezer;

	/*
	 * The root cgroup is non-freezable, so we can skip locking the
	 * freezer.  This is safe regardless of race with task migration.
	 * If we didn't race or won, skipping is obviously the right thing
	 * to do.  If we lost and root is the new cgroup, noop is still the
	 * right thing to do.
	 */
	if (task_css_is_root(task, freezer_cgrp_id))
		return;

	mutex_lock(&freezer_mutex);
	rcu_read_lock();

	freezer = task_freezer(task);
	if (freezer->state & CGROUP_FREEZING)
		freeze_task(task);

	rcu_read_unlock();
	mutex_unlock(&freezer_mutex);
}

/**
 * update_if_frozen - update whether a cgroup finished freezing
 * @css: css of interest
 *
 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
 * calling this function.  If the current state is FREEZING but not FROZEN,
 * this function checks whether all tasks of this cgroup and the descendant
 * cgroups finished freezing and, if so, sets FROZEN.
 *
 * The caller is responsible for grabbing RCU read lock and calling
 * update_if_frozen() on all descendants prior to invoking this function.
 *
 * Task states and freezer state might disagree while tasks are being
 * migrated into or out of @css, so we can't verify task states against
 * @freezer state here.  See freezer_attach() for details.
 */
static void update_if_frozen(struct cgroup_subsys_state *css)
{
	struct freezer *freezer = css_freezer(css);
	struct cgroup_subsys_state *pos;
	struct css_task_iter it;
	struct task_struct *task;

	lockdep_assert_held(&freezer_mutex);

	if (!(freezer->state & CGROUP_FREEZING) ||
	    (freezer->state & CGROUP_FROZEN))
		return;

	/* are all (live) children frozen? */
	rcu_read_lock();
	css_for_each_child(pos, css) {
		struct freezer *child = css_freezer(pos);

		if ((child->state & CGROUP_FREEZER_ONLINE) &&
		    !(child->state & CGROUP_FROZEN)) {
			rcu_read_unlock();
			return;
		}
	}
	rcu_read_unlock();

	/* are all tasks frozen? */
	css_task_iter_start(css, &it);

	while ((task = css_task_iter_next(&it))) {
		if (freezing(task)) {
			/*
			 * freezer_should_skip() indicates that the task
			 * should be skipped when determining freezing
			 * completion.  Consider it frozen in addition to
			 * the usual frozen condition.
			 */
			if (!frozen(task) && !freezer_should_skip(task))
				goto out_iter_end;
		}
	}

	freezer->state |= CGROUP_FROZEN;
out_iter_end:
	css_task_iter_end(&it);
}

static int freezer_read(struct seq_file *m, void *v)
{
	struct cgroup_subsys_state *css = seq_css(m), *pos;

	mutex_lock(&freezer_mutex);
	rcu_read_lock();

	/* update states bottom-up */
	css_for_each_descendant_post(pos, css) {
		if (!css_tryget_online(pos))
			continue;
		rcu_read_unlock();

		update_if_frozen(pos);

		rcu_read_lock();
		css_put(pos);
	}

	rcu_read_unlock();
	mutex_unlock(&freezer_mutex);

	seq_puts(m, freezer_state_strs(css_freezer(css)->state));
	seq_putc(m, '\n');
	return 0;
}

static void freeze_cgroup(struct freezer *freezer)
{
	struct css_task_iter it;
	struct task_struct *task;

	css_task_iter_start(&freezer->css, &it);
	while ((task = css_task_iter_next(&it)))
		freeze_task(task);
	css_task_iter_end(&it);
}

static void unfreeze_cgroup(struct freezer *freezer)
{
	struct css_task_iter it;
	struct task_struct *task;

	css_task_iter_start(&freezer->css, &it);
	while ((task = css_task_iter_next(&it)))
		__thaw_task(task);
	css_task_iter_end(&it);
}

/**
 * freezer_apply_state - apply state change to a single cgroup_freezer
 * @freezer: freezer to apply state change to
 * @freeze: whether to freeze or unfreeze
 * @state: CGROUP_FREEZING_* flag to set or clear
 *
 * Set or clear @state on @cgroup according to @freeze, and perform
 * freezing or thawing as necessary.
 */
static void freezer_apply_state(struct freezer *freezer, bool freeze,
				unsigned int state)
{
	/* also synchronizes against task migration, see freezer_attach() */
	lockdep_assert_held(&freezer_mutex);

	if (!(freezer->state & CGROUP_FREEZER_ONLINE))
		return;

	if (freeze) {
		if (!(freezer->state & CGROUP_FREEZING))
			atomic_inc(&system_freezing_cnt);
		freezer->state |= state;
		freeze_cgroup(freezer);
	} else {
		bool was_freezing = freezer->state & CGROUP_FREEZING;

		freezer->state &= ~state;

		if (!(freezer->state & CGROUP_FREEZING)) {
			if (was_freezing)
				atomic_dec(&system_freezing_cnt);
			freezer->state &= ~CGROUP_FROZEN;
			unfreeze_cgroup(freezer);
		}
	}
}

/**
 * freezer_change_state - change the freezing state of a cgroup_freezer
 * @freezer: freezer of interest
 * @freeze: whether to freeze or thaw
 *
 * Freeze or thaw @freezer according to @freeze.  The operations are
 * recursive - all descendants of @freezer will be affected.
 */
static void freezer_change_state(struct freezer *freezer, bool freeze)
{
	struct cgroup_subsys_state *pos;

	/*
	 * Update all its descendants in pre-order traversal.  Each
	 * descendant will try to inherit its parent's FREEZING state as
	 * CGROUP_FREEZING_PARENT.
	 */
	mutex_lock(&freezer_mutex);
	rcu_read_lock();
	css_for_each_descendant_pre(pos, &freezer->css) {
		struct freezer *pos_f = css_freezer(pos);
		struct freezer *parent = parent_freezer(pos_f);

		if (!css_tryget_online(pos))
			continue;
		rcu_read_unlock();

		if (pos_f == freezer)
			freezer_apply_state(pos_f, freeze,
					    CGROUP_FREEZING_SELF);
		else
			freezer_apply_state(pos_f,
					    parent->state & CGROUP_FREEZING,
					    CGROUP_FREEZING_PARENT);

		rcu_read_lock();
		css_put(pos);
	}
	rcu_read_unlock();
	mutex_unlock(&freezer_mutex);
}

static ssize_t freezer_write(struct kernfs_open_file *of,
			     char *buf, size_t nbytes, loff_t off)
{
	bool freeze;

	buf = strstrip(buf);

	if (strcmp(buf, freezer_state_strs(0)) == 0)
		freeze = false;
	else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
		freeze = true;
	else
		return -EINVAL;

	freezer_change_state(css_freezer(of_css(of)), freeze);
	return nbytes;
}

static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
				      struct cftype *cft)
{
	struct freezer *freezer = css_freezer(css);

	return (bool)(freezer->state & CGROUP_FREEZING_SELF);
}

static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
					struct cftype *cft)
{
	struct freezer *freezer = css_freezer(css);

	return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
}

static struct cftype files[] = {
	{
		.name = "state",
		.flags = CFTYPE_NOT_ON_ROOT,
		.seq_show = freezer_read,
		.write = freezer_write,
	},
	{
		.name = "self_freezing",
		.flags = CFTYPE_NOT_ON_ROOT,
		.read_u64 = freezer_self_freezing_read,
	},
	{
		.name = "parent_freezing",
		.flags = CFTYPE_NOT_ON_ROOT,
		.read_u64 = freezer_parent_freezing_read,
	},
	{ }	/* terminate */
};

struct cgroup_subsys freezer_cgrp_subsys = {
	.css_alloc	= freezer_css_alloc,
	.css_online	= freezer_css_online,
	.css_offline	= freezer_css_offline,
	.css_free	= freezer_css_free,
	.attach		= freezer_attach,
	.fork		= freezer_fork,
	.legacy_cftypes	= files,
};
Commit	Line	Data
	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/export.h>
	18	#include <linux/slab.h>
	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	#include <linux/mutex.h>
	25
	26	/*
	27	* A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is
	28	* set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
	29	* for "THAWED". FREEZING_PARENT is set if the parent freezer is FREEZING
	30	* for whatever reason. IOW, a cgroup has FREEZING_PARENT set if one of
	31	* its ancestors has FREEZING_SELF set.
	32	*/
	33	enum freezer_state_flags {
	34	CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */
	35	CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */
	36	CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */
	37	CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */
	38
	39	/* mask for all FREEZING flags */
	40	CGROUP_FREEZING = CGROUP_FREEZING_SELF \| CGROUP_FREEZING_PARENT,
	41	};
	42
	43	struct freezer {
	44	struct cgroup_subsys_state css;
	45	unsigned int state;
	46	};
	47
	48	static DEFINE_MUTEX(freezer_mutex);
	49
	50	static inline struct freezer css_freezer(struct cgroup_subsys_state css)
	51	{
	52	return css ? container_of(css, struct freezer, css) : NULL;
	53	}
	54
	55	static inline struct freezer task_freezer(struct task_struct task)
	56	{
	57	return css_freezer(task_css(task, freezer_cgrp_id));
	58	}
	59
	60	static struct freezer parent_freezer(struct freezer freezer)
	61	{
	62	return css_freezer(freezer->css.parent);
	63	}
	64
	65	bool cgroup_freezing(struct task_struct *task)
	66	{
	67	bool ret;
	68
	69	rcu_read_lock();
	70	ret = task_freezer(task)->state & CGROUP_FREEZING;
	71	rcu_read_unlock();
	72
	73	return ret;
	74	}
	75
	76	static const char *freezer_state_strs(unsigned int state)
	77	{
	78	if (state & CGROUP_FROZEN)
	79	return "FROZEN";
	80	if (state & CGROUP_FREEZING)
	81	return "FREEZING";
	82	return "THAWED";
	83	};
	84
	85	static struct cgroup_subsys_state *
	86	freezer_css_alloc(struct cgroup_subsys_state *parent_css)
	87	{
	88	struct freezer *freezer;
	89
	90	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
	91	if (!freezer)
	92	return ERR_PTR(-ENOMEM);
	93
	94	return &freezer->css;
	95	}
	96
	97	/**
	98	* freezer_css_online - commit creation of a freezer css
	99	* @css: css being created
	100	*
	101	* We're committing to creation of @css. Mark it online and inherit
	102	* parent's freezing state while holding both parent's and our
	103	* freezer->lock.
	104	*/
	105	static int freezer_css_online(struct cgroup_subsys_state *css)
	106	{
	107	struct freezer *freezer = css_freezer(css);
	108	struct freezer *parent = parent_freezer(freezer);
	109
	110	mutex_lock(&freezer_mutex);
	111
	112	freezer->state \|= CGROUP_FREEZER_ONLINE;
	113
	114	if (parent && (parent->state & CGROUP_FREEZING)) {
	115	freezer->state \|= CGROUP_FREEZING_PARENT \| CGROUP_FROZEN;
	116	atomic_inc(&system_freezing_cnt);
	117	}
	118
	119	mutex_unlock(&freezer_mutex);
	120	return 0;
	121	}
	122
	123	/**
	124	* freezer_css_offline - initiate destruction of a freezer css
	125	* @css: css being destroyed
	126	*
	127	* @css is going away. Mark it dead and decrement system_freezing_count if
	128	* it was holding one.
	129	*/
	130	static void freezer_css_offline(struct cgroup_subsys_state *css)
	131	{
	132	struct freezer *freezer = css_freezer(css);
	133
	134	mutex_lock(&freezer_mutex);
	135
	136	if (freezer->state & CGROUP_FREEZING)
	137	atomic_dec(&system_freezing_cnt);
	138
	139	freezer->state = 0;
	140
	141	mutex_unlock(&freezer_mutex);
	142	}
	143
	144	static void freezer_css_free(struct cgroup_subsys_state *css)
	145	{
	146	kfree(css_freezer(css));
	147	}
	148
	149	/*
	150	* Tasks can be migrated into a different freezer anytime regardless of its
	151	* current state. freezer_attach() is responsible for making new tasks
	152	* conform to the current state.
	153	*
	154	* Freezer state changes and task migration are synchronized via
	155	* @freezer->lock. freezer_attach() makes the new tasks conform to the
	156	* current state and all following state changes can see the new tasks.
	157	*/
	158	static void freezer_attach(struct cgroup_subsys_state *new_css,
	159	struct cgroup_taskset *tset)
	160	{
	161	struct freezer *freezer = css_freezer(new_css);
	162	struct task_struct *task;
	163	bool clear_frozen = false;
	164
	165	mutex_lock(&freezer_mutex);
	166
	167	/*
	168	* Make the new tasks conform to the current state of @new_css.
	169	* For simplicity, when migrating any task to a FROZEN cgroup, we
	170	* revert it to FREEZING and let update_if_frozen() determine the
	171	* correct state later.
	172	*
	173	* Tasks in @tset are on @new_css but may not conform to its
	174	* current state before executing the following - !frozen tasks may
	175	* be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
	176	*/
	177	cgroup_taskset_for_each(task, tset) {
	178	if (!(freezer->state & CGROUP_FREEZING)) {
	179	__thaw_task(task);
	180	} else {
	181	freeze_task(task);
	182	freezer->state &= ~CGROUP_FROZEN;
	183	clear_frozen = true;
	184	}
	185	}
	186
	187	/* propagate FROZEN clearing upwards */
	188	while (clear_frozen && (freezer = parent_freezer(freezer))) {
	189	freezer->state &= ~CGROUP_FROZEN;
	190	clear_frozen = freezer->state & CGROUP_FREEZING;
	191	}
	192
	193	mutex_unlock(&freezer_mutex);
	194	}
	195
	196	/**
	197	* freezer_fork - cgroup post fork callback
	198	* @task: a task which has just been forked
	199	*
	200	* @task has just been created and should conform to the current state of
	201	* the cgroup_freezer it belongs to. This function may race against
	202	* freezer_attach(). Losing to freezer_attach() means that we don't have
	203	* to do anything as freezer_attach() will put @task into the appropriate
	204	* state.
	205	*/
	206	static void freezer_fork(struct task_struct *task)
	207	{
	208	struct freezer *freezer;
	209
	210	/*
	211	* The root cgroup is non-freezable, so we can skip locking the
	212	* freezer. This is safe regardless of race with task migration.
	213	* If we didn't race or won, skipping is obviously the right thing
	214	* to do. If we lost and root is the new cgroup, noop is still the
	215	* right thing to do.
	216	*/
	217	if (task_css_is_root(task, freezer_cgrp_id))
	218	return;
	219
	220	mutex_lock(&freezer_mutex);
	221	rcu_read_lock();
	222
	223	freezer = task_freezer(task);
	224	if (freezer->state & CGROUP_FREEZING)
	225	freeze_task(task);
	226
	227	rcu_read_unlock();
	228	mutex_unlock(&freezer_mutex);
	229	}
	230
	231	/**
	232	* update_if_frozen - update whether a cgroup finished freezing
	233	* @css: css of interest
	234	*
	235	* Once FREEZING is initiated, transition to FROZEN is lazily updated by
	236	* calling this function. If the current state is FREEZING but not FROZEN,
	237	* this function checks whether all tasks of this cgroup and the descendant
	238	* cgroups finished freezing and, if so, sets FROZEN.
	239	*
	240	* The caller is responsible for grabbing RCU read lock and calling
	241	* update_if_frozen() on all descendants prior to invoking this function.
	242	*
	243	* Task states and freezer state might disagree while tasks are being
	244	* migrated into or out of @css, so we can't verify task states against
	245	* @freezer state here. See freezer_attach() for details.
	246	*/
	247	static void update_if_frozen(struct cgroup_subsys_state *css)
	248	{
	249	struct freezer *freezer = css_freezer(css);
	250	struct cgroup_subsys_state *pos;
	251	struct css_task_iter it;
	252	struct task_struct *task;
	253
	254	lockdep_assert_held(&freezer_mutex);
	255
	256	if (!(freezer->state & CGROUP_FREEZING) \|\|
	257	(freezer->state & CGROUP_FROZEN))
	258	return;
	259
	260	/* are all (live) children frozen? */
	261	rcu_read_lock();
	262	css_for_each_child(pos, css) {
	263	struct freezer *child = css_freezer(pos);
	264
	265	if ((child->state & CGROUP_FREEZER_ONLINE) &&
	266	!(child->state & CGROUP_FROZEN)) {
	267	rcu_read_unlock();
	268	return;
	269	}
	270	}
	271	rcu_read_unlock();
	272
	273	/* are all tasks frozen? */
	274	css_task_iter_start(css, &it);
	275
	276	while ((task = css_task_iter_next(&it))) {
	277	if (freezing(task)) {
	278	/*
	279	* freezer_should_skip() indicates that the task
	280	* should be skipped when determining freezing
	281	* completion. Consider it frozen in addition to
	282	* the usual frozen condition.
	283	*/
	284	if (!frozen(task) && !freezer_should_skip(task))
	285	goto out_iter_end;
	286	}
	287	}
	288
	289	freezer->state \|= CGROUP_FROZEN;
	290	out_iter_end:
	291	css_task_iter_end(&it);
	292	}
	293
	294	static int freezer_read(struct seq_file m, void v)
	295	{
	296	struct cgroup_subsys_state css = seq_css(m), pos;
	297
	298	mutex_lock(&freezer_mutex);
	299	rcu_read_lock();
	300
	301	/* update states bottom-up */
	302	css_for_each_descendant_post(pos, css) {
	303	if (!css_tryget_online(pos))
	304	continue;
	305	rcu_read_unlock();
	306
	307	update_if_frozen(pos);
	308
	309	rcu_read_lock();
	310	css_put(pos);
	311	}
	312
	313	rcu_read_unlock();
	314	mutex_unlock(&freezer_mutex);
	315
	316	seq_puts(m, freezer_state_strs(css_freezer(css)->state));
	317	seq_putc(m, '\n');
	318	return 0;
	319	}
	320
	321	static void freeze_cgroup(struct freezer *freezer)
	322	{
	323	struct css_task_iter it;
	324	struct task_struct *task;
	325
	326	css_task_iter_start(&freezer->css, &it);
	327	while ((task = css_task_iter_next(&it)))
	328	freeze_task(task);
	329	css_task_iter_end(&it);
	330	}
	331
	332	static void unfreeze_cgroup(struct freezer *freezer)
	333	{
	334	struct css_task_iter it;
	335	struct task_struct *task;
	336
	337	css_task_iter_start(&freezer->css, &it);
	338	while ((task = css_task_iter_next(&it)))
	339	__thaw_task(task);
	340	css_task_iter_end(&it);
	341	}
	342
	343	/**
	344	* freezer_apply_state - apply state change to a single cgroup_freezer
	345	* @freezer: freezer to apply state change to
	346	* @freeze: whether to freeze or unfreeze
	347	* @state: CGROUP_FREEZING_* flag to set or clear
	348	*
	349	* Set or clear @state on @cgroup according to @freeze, and perform
	350	* freezing or thawing as necessary.
	351	*/
	352	static void freezer_apply_state(struct freezer *freezer, bool freeze,
	353	unsigned int state)
	354	{
	355	/* also synchronizes against task migration, see freezer_attach() */
	356	lockdep_assert_held(&freezer_mutex);
	357
	358	if (!(freezer->state & CGROUP_FREEZER_ONLINE))
	359	return;
	360
	361	if (freeze) {
	362	if (!(freezer->state & CGROUP_FREEZING))
	363	atomic_inc(&system_freezing_cnt);
	364	freezer->state \|= state;
	365	freeze_cgroup(freezer);
	366	} else {
	367	bool was_freezing = freezer->state & CGROUP_FREEZING;
	368
	369	freezer->state &= ~state;
	370
	371	if (!(freezer->state & CGROUP_FREEZING)) {
	372	if (was_freezing)
	373	atomic_dec(&system_freezing_cnt);
	374	freezer->state &= ~CGROUP_FROZEN;
	375	unfreeze_cgroup(freezer);
	376	}
	377	}
	378	}
	379
	380	/**
	381	* freezer_change_state - change the freezing state of a cgroup_freezer
	382	* @freezer: freezer of interest
	383	* @freeze: whether to freeze or thaw
	384	*
	385	* Freeze or thaw @freezer according to @freeze. The operations are
	386	* recursive - all descendants of @freezer will be affected.
	387	*/
	388	static void freezer_change_state(struct freezer *freezer, bool freeze)
	389	{
	390	struct cgroup_subsys_state *pos;
	391
	392	/*
	393	* Update all its descendants in pre-order traversal. Each
	394	* descendant will try to inherit its parent's FREEZING state as
	395	* CGROUP_FREEZING_PARENT.
	396	*/
	397	mutex_lock(&freezer_mutex);
	398	rcu_read_lock();
	399	css_for_each_descendant_pre(pos, &freezer->css) {
	400	struct freezer *pos_f = css_freezer(pos);
	401	struct freezer *parent = parent_freezer(pos_f);
	402
	403	if (!css_tryget_online(pos))
	404	continue;
	405	rcu_read_unlock();
	406
	407	if (pos_f == freezer)
	408	freezer_apply_state(pos_f, freeze,
	409	CGROUP_FREEZING_SELF);
	410	else
	411	freezer_apply_state(pos_f,
	412	parent->state & CGROUP_FREEZING,
	413	CGROUP_FREEZING_PARENT);
	414
	415	rcu_read_lock();
	416	css_put(pos);
	417	}
	418	rcu_read_unlock();
	419	mutex_unlock(&freezer_mutex);
	420	}
	421
	422	static ssize_t freezer_write(struct kernfs_open_file *of,
	423	char *buf, size_t nbytes, loff_t off)
	424	{
	425	bool freeze;
	426
	427	buf = strstrip(buf);
	428
	429	if (strcmp(buf, freezer_state_strs(0)) == 0)
	430	freeze = false;
	431	else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
	432	freeze = true;
	433	else
	434	return -EINVAL;
	435
	436	freezer_change_state(css_freezer(of_css(of)), freeze);
	437	return nbytes;
	438	}
	439
	440	static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
	441	struct cftype *cft)
	442	{
	443	struct freezer *freezer = css_freezer(css);
	444
	445	return (bool)(freezer->state & CGROUP_FREEZING_SELF);
	446	}
	447
	448	static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
	449	struct cftype *cft)
	450	{
	451	struct freezer *freezer = css_freezer(css);
	452
	453	return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
	454	}
	455
	456	static struct cftype files[] = {
	457	{
	458	.name = "state",
	459	.flags = CFTYPE_NOT_ON_ROOT,
	460	.seq_show = freezer_read,
	461	.write = freezer_write,
	462	},
	463	{
	464	.name = "self_freezing",
	465	.flags = CFTYPE_NOT_ON_ROOT,
	466	.read_u64 = freezer_self_freezing_read,
	467	},
	468	{
	469	.name = "parent_freezing",
	470	.flags = CFTYPE_NOT_ON_ROOT,
	471	.read_u64 = freezer_parent_freezing_read,
	472	},
	473	{ } /* terminate */
	474	};
	475
	476	struct cgroup_subsys freezer_cgrp_subsys = {
	477	.css_alloc = freezer_css_alloc,
	478	.css_online = freezer_css_online,
	479	.css_offline = freezer_css_offline,
	480	.css_free = freezer_css_free,
	481	.attach = freezer_attach,
	482	.fork = freezer_fork,
	483	.legacy_cftypes = files,
	484	};