Commit 2bd9bb20 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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memcg: clean up waiting move acct 



Now, for checking a memcg is under task-account-moving, we do css_tryget()
against mc.to and mc.from.  But this is just complicating things.  This
patch makes the check easier.

This patch adds a spinlock to move_charge_struct and guard modification of
mc.to and mc.from.  By this, we don't have to think about complicated
races arount this not-critical path.

[balbir@linux.vnet.ibm.com: don't crash on a null memcg being passed]
Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarBalbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4b534334

mm/memcontrol.c

+29 −22
Original line number Diff line number Diff line
@@ -268,6 +268,7 @@ enum move_type { 


/* "mc" and its members are protected by cgroup_mutex */

static struct move_charge_struct {

	spinlock_t	  lock; /* for from, to, moving_task */

	struct mem_cgroup *from;

	struct mem_cgroup *to;

	unsigned long precharge;
@@ -276,6 +277,7 @@ static struct move_charge_struct { 
	struct task_struct *moving_task;	/* a task moving charges */

	wait_queue_head_t waitq;		/* a waitq for other context */

} mc = {

	.lock = __SPIN_LOCK_UNLOCKED(mc.lock),

	.waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),

};
@@ -1051,26 +1053,24 @@ static unsigned int get_swappiness(struct mem_cgroup *memcg) 


static bool mem_cgroup_under_move(struct mem_cgroup *mem)

{

	struct mem_cgroup *from = mc.from;

	struct mem_cgroup *to = mc.to;

	struct mem_cgroup *from;

	struct mem_cgroup *to;

	bool ret = false;



	if (from == mem || to == mem)

		return true;



	if (!from || !to || !mem->use_hierarchy)

		return false;



	rcu_read_lock();

	if (css_tryget(&from->css)) {

		ret = css_is_ancestor(&from->css, &mem->css);

		css_put(&from->css);

	}

	if (!ret && css_tryget(&to->css)) {

		ret = css_is_ancestor(&to->css,	&mem->css);

		css_put(&to->css);

	}

	rcu_read_unlock();

	/*

	 * Unlike task_move routines, we access mc.to, mc.from not under

	 * mutual exclusion by cgroup_mutex. Here, we take spinlock instead.

	 */

	spin_lock(&mc.lock);

	from = mc.from;

	to = mc.to;

	if (!from)

		goto unlock;

	if (from == mem || to == mem

	    || (mem->use_hierarchy && css_is_ancestor(&from->css, &mem->css))

	    || (mem->use_hierarchy && css_is_ancestor(&to->css,	&mem->css)))

		ret = true;

unlock:

	spin_unlock(&mc.lock);

	return ret;

}
@@ -1406,7 +1406,7 @@ static void memcg_wakeup_oom(struct mem_cgroup *mem) 


static void memcg_oom_recover(struct mem_cgroup *mem)

{

	if (atomic_read(&mem->oom_lock))

	if (mem && atomic_read(&mem->oom_lock))

		memcg_wakeup_oom(mem);

}
@@ -4441,11 +4441,13 @@ static int mem_cgroup_precharge_mc(struct mm_struct *mm) 


static void mem_cgroup_clear_mc(void)

{

	struct mem_cgroup *from = mc.from;

	struct mem_cgroup *to = mc.to;



	/* we must uncharge all the leftover precharges from mc.to */

	if (mc.precharge) {

		__mem_cgroup_cancel_charge(mc.to, mc.precharge);

		mc.precharge = 0;

		memcg_oom_recover(mc.to);

	}

	/*

	 * we didn't uncharge from mc.from at mem_cgroup_move_account(), so
@@ -4454,7 +4456,6 @@ static void mem_cgroup_clear_mc(void) 
	if (mc.moved_charge) {

		__mem_cgroup_cancel_charge(mc.from, mc.moved_charge);

		mc.moved_charge = 0;

		memcg_oom_recover(mc.from);

	}

	/* we must fixup refcnts and charges */

	if (mc.moved_swap) {
@@ -4479,9 +4480,13 @@ static void mem_cgroup_clear_mc(void) 


		mc.moved_swap = 0;

	}

	spin_lock(&mc.lock);

	mc.from = NULL;

	mc.to = NULL;

	mc.moving_task = NULL;

	spin_unlock(&mc.lock);

	memcg_oom_recover(from);

	memcg_oom_recover(to);

	wake_up_all(&mc.waitq);

}
@@ -4510,12 +4515,14 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss, 
			VM_BUG_ON(mc.moved_charge);

			VM_BUG_ON(mc.moved_swap);

			VM_BUG_ON(mc.moving_task);

			spin_lock(&mc.lock);

			mc.from = from;

			mc.to = mem;

			mc.precharge = 0;

			mc.moved_charge = 0;

			mc.moved_swap = 0;

			mc.moving_task = current;

			spin_unlock(&mc.lock);



			ret = mem_cgroup_precharge_mc(mm);

			if (ret)

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