linux-kernel - Re: [PATCH 1/1] oom: fix the unsafe usage of badness() in proc_oom

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Date:	Thu, 1 Apr 2010 12:03:39 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	anfei <anfei.zhou@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	nishimura@....nes.nec.co.jp,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH 1/1] oom: fix the unsafe usage of badness() in
 proc_oom_score()

On Thu, 1 Apr 2010, Oleg Nesterov wrote:

> proc_oom_score(task) have a reference to task_struct, but that is all.
> If this task was already released before we take tasklist_lock
> 
> 	- we can't use task->group_leader, it points to nowhere
> 
> 	- it is not safe to call badness() even if this task is
> 	  ->group_leader, has_intersects_mems_allowed() assumes
> 	  it is safe to iterate over ->thread_group list.
> 
> 	- even worse, badness() can hit ->signal == NULL
> 
> Add the pid_alive() check to ensure __unhash_process() was not called.
> 
> Also, use "task" instead of task->group_leader. badness() should return
> the same result for any sub-thread. Currently this is not true, but
> this should be changed anyway.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: David Rientjes <rientjes@...gle.com>

Andrew, this is 2.6.34 material and should be backported to stable.  It's 
not introduced by the recent oom killer rewrite pending in -mm, but it 
will require a trivial merge resolution on that work.
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