linux-kernel - Re: [patch 1/2] mm: memcontrol: handle potential crash when rmap races with task exit

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Message-ID: <20121004184958.GG27536@dhcp22.suse.cz>
Date:	Thu, 4 Oct 2012 20:49:58 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] mm: memcontrol: handle potential crash when rmap
 races with task exit

On Thu 04-10-12 14:09:16, Johannes Weiner wrote:
> page_referenced() counts only references of mm's that are associated
> with the memcg hierarchy that is being reclaimed.  However, if it
> races with the owner of the mm exiting, mm->owner may be NULL.  Don't
> crash, just ignore the reference.

This seems to be fixed by Hugh's patch 3a981f48 "memcg: fix use_hierarchy
css_is_ancestor oops regression" which seems to be merged already.

> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Cc: stable@...nel.org [3.5]
> ---
>  include/linux/memcontrol.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 8d9489f..8686294 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -91,7 +91,7 @@ int mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *cgroup)
>  
>  	rcu_read_lock();
>  	memcg = mem_cgroup_from_task(rcu_dereference((mm)->owner));
> -	match = __mem_cgroup_same_or_subtree(cgroup, memcg);
> +	match = memcg && __mem_cgroup_same_or_subtree(cgroup, memcg);
>  	rcu_read_unlock();
>  	return match;
>  }
> -- 
> 1.7.11.4
> 

-- 
Michal Hocko
SUSE Labs
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