/* * 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 *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 *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 *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 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",		.flags = CFTYPE_NOT_ON_ROOT,		.read_seq_string = freezer_read,		.write_string = freezer_write,	},	{ }	/* terminate */}; struct cgroup_subsys freezer_subsys = {	.name		= "freezer",	.create		= freezer_create,	.destroy	= freezer_destroy,	.subsys_id	= freezer_subsys_id,	.can_attach	= freezer_can_attach,	.fork		= freezer_fork,	.base_cftypes	= files,};