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Date: Wed, 25 Nov 2009 09:00:50 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: stable <stable@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
       linux-mm <linux-mm@kvack.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
       David Rientjes <rientjes@google.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [BUGFIX][PATCH -stable] memcg: avoid oom-killing innocent task
 in case of use_hierarchy
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On Tue, 24 Nov 2009 16:28:54 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> task_in_mem_cgroup(), which is called by select_bad_process() to check whether
> a task can be a candidate for being oom-killed from memcg's limit, checks
> "curr->use_hierarchy"("curr" is the mem_cgroup the task belongs to).
> 
> But this check return true(it's false positive) when:
> 
> 	<some path>/00		use_hierarchy == 0	<- hitting limit
> 	  <some path>/00/aa	use_hierarchy == 1	<- "curr"
> 
> This leads to killing an innocent task in 00/aa. This patch is a fix for this
> bug. And this patch also fixes the arg for mem_cgroup_print_oom_info(). We
> should print information of mem_cgroup which the task being killed, not current,
> belongs to.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> ---
>  mm/memcontrol.c |    2 +-
>  mm/oom_kill.c   |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index fd4529d..3acc226 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -496,7 +496,7 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
>  	task_unlock(task);
>  	if (!curr)
>  		return 0;
> -	if (curr->use_hierarchy)
> +	if (mem->use_hierarchy)
>  		ret = css_is_ancestor(&curr->css, &mem->css);
>  	else
>  		ret = (curr == mem);

Hmm. Maybe not-expected behavior...could you add comment ?

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
(*) I'm sorry I can't work enough in these days.

Thanks,
-Kame

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