From: Hugh Dickins <hughd@google.com>
Date: Wed, 20 Jun 2012 19:52:58 +0000 (-0700)
Subject: memcg: fix use_hierarchy css_is_ancestor oops regression
X-Git-Tag: v3.5-rc4~20^2~16
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3a981f482cc29f7d0aeab509e51ea15519a6e961;p=pandora-kernel.git

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>
---

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