linux-kernel - Re: [PATCH] memcg: fix use_hierarchy css_is

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Message-ID: <4FD598C2.8020709@jp.fujitsu.com>
Date:	Mon, 11 Jun 2012 16:05:38 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] memcg: fix use_hierarchy css_is_ancestor oops regression

(2012/06/11 3:54), Hugh Dickins wrote:
> 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@...gle.com>

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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