linux-kernel - Re: [PATCH] memcg: fix oops in oom handling

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Message-Id: <20080414161428.27f3ee59.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 14 Apr 2008 16:14:28 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Paul Menage <menage@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] memcg: fix oops in oom handling

On Mon, 14 Apr 2008 14:52:00 +0800
Li Zefan <lizf@...fujitsu.com> wrote:
> 
> It's reproducable in a x86_64 box, but doesn't happen in x86_32.
> 
> This is because tsk->sighand is not guarded by RCU, so we have to
> hold tasklist_lock, just as what out_of_memory() does.
> 

Good catch! and patch seems good.

Paul, I have one confirmation. Lock hierarchy of
	cgroup_lock()
	->	read_lock(&tasklist_lock)

is ok ? (I think this is ok.)

Thanks,
-Kame

> Signed-off-by: Li Zefan <lizf@...fujitsu>
> ---
>  mm/oom_kill.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index f255eda..beb592f 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -423,7 +423,7 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
>  	struct task_struct *p;
>  
>  	cgroup_lock();
> -	rcu_read_lock();
> +	read_lock(&tasklist_lock);
>  retry:
>  	p = select_bad_process(&points, mem);
>  	if (PTR_ERR(p) == -1UL)
> @@ -436,7 +436,7 @@ retry:
>  				"Memory cgroup out of memory"))
>  		goto retry;
>  out:
> -	rcu_read_unlock();
> +	read_unlock(&tasklist_lock);
>  	cgroup_unlock();
>  }
>  #endif
> -- 1.5.4.rc3 
> 
> 
> 
> 

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