linux-kernel - Re: [PATCH 3/9] oom: oom_kill_process() doesn't select kthread child

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Date:	Thu, 17 Jun 2010 00:02:32 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 3/9] oom: oom_kill_process() doesn't select kthread
 child

On Wed, Jun 16, 2010 at 08:32:08PM +0900, KOSAKI Motohiro wrote:
> Now, select_bad_process() have PF_KTHREAD check, but oom_kill_process
> doesn't. It mean oom_kill_process() may choose wrong task, especially,
> when the child are using use_mm().
Now oom_kill_process is called by three place. 

1. mem_cgroup_out_of_memory
2. out_of_memory with sysctl_oom_kill_allocating_task
3. out_of_memory with non-sysctl_oom_kill_allocating_task

I think it's no problem in 1 and 3 since select_bad_process already checks
PF_KTHREAD. The problem in in 2. 
So How about put the check before calling oom_kill_process in case of
sysctl_oom_kill_allocating task?

if (sysctl_oom_kill_allocating_task) {
        if (!current->flags & PF_KTHREAD)
                oom_kill_process();
                        
It can remove duplicated PF_KTHREAD check in select_bad_process and
oom_kill_process. 

-- 
Kind regards,
Minchan Kim
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