linux-kernel - Re: [RFC 2/2] OOM, PM: make OOM detection in the freezer path raceless

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Date:	Thu, 4 Dec 2014 18:18:22 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	linux-pm@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"\\\"Rafael J. Wysocki\\\"" <rjw@...ysocki.net>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [RFC 2/2] OOM, PM: make OOM detection in the freezer path
 raceless

On Thu 04-12-14 17:56:01, Michal Hocko wrote:
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 1d55ab12792f..032be9d2a239 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -408,7 +408,7 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
>   * Number of OOM victims in flight
>   */
>  static atomic_t oom_victims = ATOMIC_INIT(0);
> -static DECLARE_COMPLETION(oom_victims_wait);
> +static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
>  
>  bool oom_killer_disabled __read_mostly;
>  static DECLARE_RWSEM(oom_sem);
> @@ -435,7 +435,7 @@ void unmark_tsk_oom_victim(void)
>  	 * is nobody who cares.
>  	 */
>  	if (!atomic_dec_return(&oom_victims) && oom_killer_disabled)
> -		complete_all(&oom_victims_wait);
> +		wake_up_all(&oom_victims_wait);
>  	up_read(&oom_sem);
>  }
>  
> @@ -464,16 +464,11 @@ bool oom_killer_disable(void)
>  		return false;
>  	}
>  
> -	/* unmark_tsk_oom_victim is calling complete_all */
> -	if (!oom_killer_disable)
> -		reinit_completion(&oom_victims_wait);
> -
>  	oom_killer_disabled = true;
> -	count = atomic_read(&oom_victims);
>  	up_write(&oom_sem);
>  
>  	if (count)

whithout this count test obviously

> -		wait_for_completion(&oom_victims_wait);
> +		wait_event(oom_victims_wait, atomic_read(&oom_victims));
>  
>  	return true;
>  }
-- 
Michal Hocko
SUSE Labs
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