linux-kernel - Re: [PATCH 04/12] memcg, kmem: fix reference count handling on the error path

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Date:	Tue, 09 Apr 2013 11:51:39 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizefan@...wei.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Glauber Costa <glommer@...allels.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 04/12] memcg, kmem: fix reference count handling on the
 error path

(2013/04/08 15:33), Li Zefan wrote:
> From: Michal Hocko <mhocko@...e.cz>
> 
> mem_cgroup_css_online calls mem_cgroup_put if memcg_init_kmem
> fails. This is not correct because only memcg_propagate_kmem takes an
> additional reference while mem_cgroup_sockets_init is allowed to fail as
> well (although no current implementation fails) but it doesn't take any
> reference. This all suggests that it should be memcg_propagate_kmem that
> should clean up after itself so this patch moves mem_cgroup_put over
> there.
> 
> Unfortunately this is not that easy (as pointed out by Li Zefan) because
> memcg_kmem_mark_dead marks the group dead (KMEM_ACCOUNTED_DEAD) if it
> is marked active (KMEM_ACCOUNTED_ACTIVE) which is the case even if
> memcg_propagate_kmem fails so the additional reference is dropped in
> that case in kmem_cgroup_destroy which means that the reference would be
> dropped two times.
> 
> The easiest way then would be to simply remove mem_cgrroup_put from
> mem_cgroup_css_online and rely on kmem_cgroup_destroy doing the right
> thing.
> 
> Signed-off-by: Li Zefan <lizefan@...wei.com>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> Cc: <stable@...r.kernel.org> # 3.8.x

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


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