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Commit 22b4e111 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup_freezer: prepare for removal of TIF_FREEZE 



TIF_FREEZE will be removed soon and freezing() will directly test
whether any freezing condition is in effect.  Make the following
changes in preparation.

* Rename cgroup_freezing_or_frozen() to cgroup_freezing() and make it
  return bool.

* Make cgroup_freezing() access task_freezer() under rcu read lock
  instead of task_lock().  This makes the state dereferencing racy
  against task moving to another cgroup; however, it was already racy
  without this change as ->state dereference wasn't synchronized.
  This will be later dealt with using attach hooks.

* freezer->state is now set before trying to push tasks into the
  target state.

-v2: Oleg pointed out that freeze_change_state() was setting
     freeze->state incorrectly to CGROUP_FROZEN instead of
     CGROUP_FREEZING.  Fixed.

-v3: Matt pointed out that setting CGROUP_FROZEN used to always invoke
     try_to_freeze_cgroup() regardless of the current state.  Patch
     updated such that the actual freeze/thaw operations are always
     performed on invocation.  This shouldn't make any difference
     unless something is broken.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarPaul Menage <paul@paulmenage.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
parent 03afed8b

include/linux/freezer.h

+3 −3
Original line number Diff line number Diff line
@@ -63,11 +63,11 @@ static inline bool try_to_freeze(void) 
extern bool freeze_task(struct task_struct *p, bool sig_only);



#ifdef CONFIG_CGROUP_FREEZER

extern int cgroup_freezing_or_frozen(struct task_struct *task);

extern bool cgroup_freezing(struct task_struct *task);

#else /* !CONFIG_CGROUP_FREEZER */

static inline int cgroup_freezing_or_frozen(struct task_struct *task)

static inline bool cgroup_freezing(struct task_struct *task)

{

	return 0;

	return false;

}

#endif /* !CONFIG_CGROUP_FREEZER */

kernel/cgroup_freezer.c

+13 −27
Original line number Diff line number Diff line
@@ -48,19 +48,17 @@ static inline struct freezer *task_freezer(struct task_struct *task) 
			    struct freezer, css);

}



static inline int __cgroup_freezing_or_frozen(struct task_struct *task)

bool cgroup_freezing(struct task_struct *task)

{

	enum freezer_state state = task_freezer(task)->state;

	return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN);

}

	enum freezer_state state;

	bool ret;



int cgroup_freezing_or_frozen(struct task_struct *task)

{

	int result;

	task_lock(task);

	result = __cgroup_freezing_or_frozen(task);

	task_unlock(task);

	return result;

	rcu_read_lock();

	state = task_freezer(task)->state;

	ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN;

	rcu_read_unlock();



	return ret;

}



/*
@@ -102,9 +100,6 @@ struct cgroup_subsys freezer_subsys; 
 * 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)
@@ -177,13 +172,7 @@ static int freezer_can_attach(struct cgroup_subsys *ss, 


static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)

{

	rcu_read_lock();

	if (__cgroup_freezing_or_frozen(tsk)) {

		rcu_read_unlock();

		return -EBUSY;

	}

	rcu_read_unlock();

	return 0;

	return cgroup_freezing(tsk) ? -EBUSY : 0;

}



static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
@@ -279,7 +268,6 @@ static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) 
	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))
@@ -303,8 +291,6 @@ static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) 
	while ((task = cgroup_iter_next(cgroup, &it)))

		__thaw_task(task);

	cgroup_iter_end(cgroup, &it);



	freezer->state = CGROUP_THAWED;

}



static int freezer_change_state(struct cgroup *cgroup,
@@ -318,20 +304,20 @@ static int freezer_change_state(struct cgroup *cgroup, 
	spin_lock_irq(&freezer->lock);



	update_if_frozen(cgroup, freezer);

	if (goal_state == freezer->state)

		goto out;



	switch (goal_state) {

	case CGROUP_THAWED:

		freezer->state = CGROUP_THAWED;

		unfreeze_cgroup(cgroup, freezer);

		break;

	case CGROUP_FROZEN:

		freezer->state = CGROUP_FREEZING;

		retval = try_to_freeze_cgroup(cgroup, freezer);

		break;

	default:

		BUG();

	}

out:



	spin_unlock_irq(&freezer->lock);



	return retval;

kernel/power/process.c

+1 −1
Original line number Diff line number Diff line
@@ -170,7 +170,7 @@ void thaw_processes(void) 


	read_lock(&tasklist_lock);

	do_each_thread(g, p) {

		if (cgroup_freezing_or_frozen(p))

		if (cgroup_freezing(p))

			continue;



		__thaw_task(p);