kernel/cgroup_freezer.c - maze/linux - 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>

 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);
 }

 bool cgroup_freezing(struct task_struct *task)
 {
 	enum freezer_state state;
 	bool ret;

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

 	return ret;
 }

 /*
  * 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)
  *
  * 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_task(), 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)
 {
 	struct freezer *freezer = cgroup_freezer(cgroup);

 	if (freezer->state != CGROUP_THAWED)
 		atomic_dec(&system_freezing_cnt);
 	kfree(freezer);
 }

 /* 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 cgroup_taskset *tset)
 {
 	struct freezer *freezer;
 	struct task_struct *task;

 	/*
 	 * Anything frozen can't move or be moved to/from.
 	 */
 	cgroup_taskset_for_each(task, new_cgroup, tset)
 		if (cgroup_freezing(task))
 			return -EBUSY;

 	freezer = cgroup_freezer(new_cgroup);
 	if (freezer->state != CGROUP_THAWED)
 		return -EBUSY;

 	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);
 	spin_unlock_irq(&freezer->lock);
 }

 /*
  * caller must hold freezer->lock
  */
 static void update_if_frozen(struct cgroup *cgroup,
 				 struct freezer *freezer)
 {
 	struct cgroup_iter it;
 	struct task_struct *task;
 	unsigned int nfrozen = 0, ntotal = 0;
 	enum freezer_state old_state = freezer->state;

 	cgroup_iter_start(cgroup, &it);
 	while ((task = cgroup_iter_next(cgroup, &it))) {
 		ntotal++;
 		if (freezing(task) && is_task_frozen_enough(task))
 			nfrozen++;
 	}

 	if (old_state == CGROUP_THAWED) {
 		BUG_ON(nfrozen > 0);
 	} else if (old_state == CGROUP_FREEZING) {
 		if (nfrozen == ntotal)
 			freezer->state = CGROUP_FROZEN;
 	} else { /* old_state == CGROUP_FROZEN */
 		BUG_ON(nfrozen != ntotal);
 	}

 	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_if_frozen(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;

 	cgroup_iter_start(cgroup, &it);
 	while ((task = cgroup_iter_next(cgroup, &it))) {
 		if (!freeze_task(task))
 			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_task(task);
 	cgroup_iter_end(cgroup, &it);
 }

 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_if_frozen(cgroup, freezer);

 	switch (goal_state) {
 	case CGROUP_THAWED:
 		if (freezer->state != CGROUP_THAWED)
 			atomic_dec(&system_freezing_cnt);
 		freezer->state = CGROUP_THAWED;
 		unfreeze_cgroup(cgroup, freezer);
 		break;
 	case CGROUP_FROZEN:
 		if (freezer->state == CGROUP_THAWED)
 			atomic_inc(&system_freezing_cnt);
 		freezer->state = CGROUP_FREEZING;
 		retval = try_to_freeze_cgroup(cgroup, freezer);
 		break;
 	default:
 		BUG();
 	}

 	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,
 	.fork		= freezer_fork,
 };
	/*
	* 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>

	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);
	}

	bool cgroup_freezing(struct task_struct *task)
	{
	enum freezer_state state;
	bool ret;

	rcu_read_lock();
	state = task_freezer(task)->state;
	ret = state == CGROUP_FREEZING \|\| state == CGROUP_FROZEN;
	rcu_read_unlock();

	return ret;
	}

	/*
	* 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)
	*
	* 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_task(), 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)
	{
	struct freezer *freezer = cgroup_freezer(cgroup);

	if (freezer->state != CGROUP_THAWED)
	atomic_dec(&system_freezing_cnt);
	kfree(freezer);
	}

	/* 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 cgroup_taskset *tset)
	{
	struct freezer *freezer;
	struct task_struct *task;

	/*
	* Anything frozen can't move or be moved to/from.
	*/
	cgroup_taskset_for_each(task, new_cgroup, tset)
	if (cgroup_freezing(task))
	return -EBUSY;

	freezer = cgroup_freezer(new_cgroup);
	if (freezer->state != CGROUP_THAWED)
	return -EBUSY;

	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);
	spin_unlock_irq(&freezer->lock);
	}

	/*
	* caller must hold freezer->lock
	*/
	static void update_if_frozen(struct cgroup *cgroup,
	struct freezer *freezer)
	{
	struct cgroup_iter it;
	struct task_struct *task;
	unsigned int nfrozen = 0, ntotal = 0;
	enum freezer_state old_state = freezer->state;

	cgroup_iter_start(cgroup, &it);
	while ((task = cgroup_iter_next(cgroup, &it))) {
	ntotal++;
	if (freezing(task) && is_task_frozen_enough(task))
	nfrozen++;
	}

	if (old_state == CGROUP_THAWED) {
	BUG_ON(nfrozen > 0);
	} else if (old_state == CGROUP_FREEZING) {
	if (nfrozen == ntotal)
	freezer->state = CGROUP_FROZEN;
	} else { /* old_state == CGROUP_FROZEN */
	BUG_ON(nfrozen != ntotal);
	}

	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_if_frozen(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;

	cgroup_iter_start(cgroup, &it);
	while ((task = cgroup_iter_next(cgroup, &it))) {
	if (!freeze_task(task))
	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_task(task);
	cgroup_iter_end(cgroup, &it);
	}

	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_if_frozen(cgroup, freezer);

	switch (goal_state) {
	case CGROUP_THAWED:
	if (freezer->state != CGROUP_THAWED)
	atomic_dec(&system_freezing_cnt);
	freezer->state = CGROUP_THAWED;
	unfreeze_cgroup(cgroup, freezer);
	break;
	case CGROUP_FROZEN:
	if (freezer->state == CGROUP_THAWED)
	atomic_inc(&system_freezing_cnt);
	freezer->state = CGROUP_FREEZING;
	retval = try_to_freeze_cgroup(cgroup, freezer);
	break;
	default:
	BUG();
	}

	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,
	.fork = freezer_fork,
	};