Commit 3a981f48 authored Jun 20, 2012 by Hugh Dickins Committed by Linus Torvalds Jun 20, 2012

memcg: fix use_hierarchy css_is_ancestor oops regression



If use_hierarchy is set, reclaim testing soon oopses in css_is_ancestor()
called from __mem_cgroup_same_or_subtree() called from page_referenced():
when processes are exiting, it's easy for mm_match_cgroup() to pass along
a NULL memcg coming from a NULL mm->owner.

Check for that in __mem_cgroup_same_or_subtree().  Return true or false?
False because we cannot know if it was in the hierarchy, but also false
because it's better not to count a reference from an exiting process.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 61eafb00

mm/memcontrol.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1148,7 +1148,7 @@ bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
		{
		if (root_memcg == memcg)
		return true;
		if (!root_memcg->use_hierarchy)
		if (!root_memcg->use_hierarchy \|\| !memcg)
		return false;
		return css_is_ancestor(&memcg->css, &root_memcg->css);
		}