linux-kernel - Re: [PATCH] Fix race between oom kill and task exit

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Message-ID: <20131128183702.GC20740@redhat.com>
Date:	Thu, 28 Nov 2013 19:37:02 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Ma, Xindong" <xindong.ma@...el.com>,
	Sameer Nanda <snanda@...omium.org>
Cc:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mhocko@...e.cz" <mhocko@...e.cz>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"'Peter Zijlstra'" <peterz@...radead.org>,
	"'gregkh@...uxfoundation.org'" <gregkh@...uxfoundation.org>,
	"Tu, Xiaobing" <xiaobing.tu@...el.com>
Subject: Re: [PATCH] Fix race between oom kill and task exit

On 11/28, Ma, Xindong wrote:
>
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -412,16 +412,6 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
>  	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
>  					      DEFAULT_RATELIMIT_BURST);
>  
> -	/*
> -	 * If the task is already exiting, don't alarm the sysadmin or kill
> -	 * its children or threads, just set TIF_MEMDIE so it can die quickly
> -	 */
> -	if (p->flags & PF_EXITING) {
> -		set_tsk_thread_flag(p, TIF_MEMDIE);
> -		put_task_struct(p);
> -		return;
> -	}
> -
>  	if (__ratelimit(&oom_rs))
>  		dump_header(p, gfp_mask, order, memcg, nodemask);
>  
> @@ -437,6 +427,16 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
>  	 * still freeing memory.
>  	 */
>  	read_lock(&tasklist_lock);
> +	/*
> +	 * If the task is already exiting, don't alarm the sysadmin or kill
> +	 * its children or threads, just set TIF_MEMDIE so it can die quickly
> +	 */
> +	if (p->flags & PF_EXITING) {
> +		set_tsk_thread_flag(p, TIF_MEMDIE);
> +		put_task_struct(p);
> +		read_unlock(&tasklist_lock);
> +		return;
> +	}

I got lost... didn't we recently discussed the similar patch from Sameer?

This one doesn't look right. find_lock_task_mm() after unlock(tasklist)
can hit the same problem.

I belive the patch from Sameer was correct.

Oleg.

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