linux-kernel - Re: [patch] mm, oom: avoid attempting to kill init sharing same memory

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Date:	Thu, 3 Dec 2015 09:12:01 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, chenjie6@...wei.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	David.Woodhouse@...el.com, zhihui.gao@...wei.com,
	lizefan@...wei.com
Subject: Re: [patch] mm, oom: avoid attempting to kill init sharing same
 memory

On Wed 02-12-15 15:10:28, David Rientjes wrote:
> From: Chen Jie <chenjie6@...wei.com>
> 
> It's possible that an oom killed victim shares an ->mm with the init
> process and thus oom_kill_process() would end up trying to kill init as
> well.
> 
> This has been shown in practice:
> 
> 	Out of memory: Kill process 9134 (init) score 3 or sacrifice child
> 	Killed process 9134 (init) total-vm:1868kB, anon-rss:84kB, file-rss:572kB
> 	Kill process 1 (init) sharing same memory
> 	...
> 	Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
> 
> And this will result in a kernel panic.
> 
> If a process is forked by init and selected for oom kill while still
> sharing init_mm, then it's likely this system is in a recoverable state.
> However, it's better not to try to kill init and allow the machine to
> panic due to unkillable processes.
> 
> [rientjes@...gle.com: rewrote changelog]
> Acked-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Chen Jie <chenjie6@...wei.com>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  I removed stable from this patch since the alternative would most likely
>  be to panic the system for no killable processes anyway.  There's a very
>  small likelihood this patch would allow for a recoverable system.

Agreed.

>  mm/oom_kill.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -608,6 +608,8 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
>  			continue;
>  		if (unlikely(p->flags & PF_KTHREAD))
>  			continue;
> +		if (!is_global_init(p))
> +			continue;
>  		if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
>  			continue;
>  

-- 
Michal Hocko
SUSE Labs
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