kernel/cgroup_freezer.c - kernel/common.git - Git at Google

 /*
  * 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_taskset *tset)
 {
 	struct task_struct *task;
 	struct cgroup_subsys_state *new_css;

 	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, new_css, tset) {
 		struct freezer *freezer = css_freezer(new_css);

 		if (!(freezer->state & CGROUP_FREEZING)) {
 			__thaw_task(task);
 		} else {
 			freeze_task(task);
 			/* clear FROZEN and propagate upwards */
 			while (freezer && (freezer->state & CGROUP_FROZEN)) {
 				freezer->state &= ~CGROUP_FROZEN;
 				freezer = parent_freezer(freezer);
 			}
 		}
 	}

 	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, void *private)
 {
 	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,
 };
	/*
	* 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_taskset *tset)
	{
	struct task_struct *task;
	struct cgroup_subsys_state *new_css;

	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, new_css, tset) {
	struct freezer *freezer = css_freezer(new_css);

	if (!(freezer->state & CGROUP_FREEZING)) {
	__thaw_task(task);
	} else {
	freeze_task(task);
	/* clear FROZEN and propagate upwards */
	while (freezer && (freezer->state & CGROUP_FROZEN)) {
	freezer->state &= ~CGROUP_FROZEN;
	freezer = parent_freezer(freezer);
	}
	}
	}

	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, void private)
	{
	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,
	};