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Commit aa226ff4 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: make sure a parent css isn't offlined before its children 



There are three subsystem callbacks in css shutdown path -
css_offline(), css_released() and css_free().  Except for
css_released(), cgroup core didn't guarantee the order of invocation.
css_offline() or css_free() could be called on a parent css before its
children.  This behavior is unexpected and led to bugs in cpu and
memory controller.

This patch updates offline path so that a parent css is never offlined
before its children.  Each css keeps online_cnt which reaches zero iff
itself and all its children are offline and offline_css() is invoked
only after online_cnt reaches zero.

This fixes the memory controller bug and allows the fix for cpu
controller.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-and-tested-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Reported-by: default avatarBrian Christiansen <brian.o.christiansen@gmail.com>
Link: http://lkml.kernel.org/g/5698A023.9070703@de.ibm.com
Link: http://lkml.kernel.org/g/CAKB58ikDkzc8REt31WBkD99+hxNzjK4+FBmhkgS+NVrC9vjMSg@mail.gmail.com
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
parent e93ad19d

include/linux/cgroup-defs.h

+6 −0
Original line number Diff line number Diff line
@@ -127,6 +127,12 @@ struct cgroup_subsys_state { 
	 */

	u64 serial_nr;



	/*

	 * Incremented by online self and children.  Used to guarantee that

	 * parents are not offlined before their children.

	 */

	atomic_t online_cnt;



	/* percpu_ref killing and RCU release */

	struct rcu_head rcu_head;

	struct work_struct destroy_work;

kernel/cgroup.c

+17 −5
Original line number Diff line number Diff line
@@ -4760,6 +4760,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css, 
	INIT_LIST_HEAD(&css->sibling);

	INIT_LIST_HEAD(&css->children);

	css->serial_nr = css_serial_nr_next++;

	atomic_set(&css->online_cnt, 0);



	if (cgroup_parent(cgrp)) {

		css->parent = cgroup_css(cgroup_parent(cgrp), ss);
@@ -4782,6 +4783,10 @@ static int online_css(struct cgroup_subsys_state *css) 
	if (!ret) {

		css->flags |= CSS_ONLINE;

		rcu_assign_pointer(css->cgroup->subsys[ss->id], css);



		atomic_inc(&css->online_cnt);

		if (css->parent)

			atomic_inc(&css->parent->online_cnt);

	}

	return ret;

}
@@ -5019,10 +5024,15 @@ static void css_killed_work_fn(struct work_struct *work) 
		container_of(work, struct cgroup_subsys_state, destroy_work);



	mutex_lock(&cgroup_mutex);

	offline_css(css);

	mutex_unlock(&cgroup_mutex);



	do {

		offline_css(css);

		css_put(css);

		/* @css can't go away while we're holding cgroup_mutex */

		css = css->parent;

	} while (css && atomic_dec_and_test(&css->online_cnt));



	mutex_unlock(&cgroup_mutex);

}



/* css kill confirmation processing requires process context, bounce */
@@ -5031,9 +5041,11 @@ static void css_killed_ref_fn(struct percpu_ref *ref) 
	struct cgroup_subsys_state *css =

		container_of(ref, struct cgroup_subsys_state, refcnt);



	if (atomic_dec_and_test(&css->online_cnt)) {

		INIT_WORK(&css->destroy_work, css_killed_work_fn);

		queue_work(cgroup_destroy_wq, &css->destroy_work);

	}

}



/**

 * kill_css - destroy a css