linux-kernel - Re: [PATCH] mm: memcontrol: fix possible css ref leak on oom

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Date:	Mon, 23 May 2016 19:44:43 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memcontrol: fix possible css ref leak on oom

On Mon 23-05-16 19:02:10, Vladimir Davydov wrote:
> mem_cgroup_oom may be invoked multiple times while a process is handling
> a page fault, in which case current->memcg_in_oom will be overwritten
> leaking the previously taken css reference.

Have you seen this happening? I was under impression that the page fault
paths that have oom enabled will not retry allocations.
 
> Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>

That being said I do not have anything against the patch. It is a good
safety net I am just not sure this might happen right now and so the
patch is not stable candidate.

After clarification
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5b48cd25951b..ef8797d34039 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1608,7 +1608,7 @@ static void memcg_oom_recover(struct mem_cgroup *memcg)
>  
>  static void mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
>  {
> -	if (!current->memcg_may_oom)
> +	if (!current->memcg_may_oom || current->memcg_in_oom)
>  		return;
>  	/*
>  	 * We are in the middle of the charge context here, so we
> -- 
> 2.1.4

-- 
Michal Hocko
SUSE Labs