linux-kernel - Re: [PATCH 1/4] freezer: Do not freeze tasks killed by OOM killer

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Date:	Tue, 21 Oct 2014 14:04 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Cong Wang <xiyou.wangcong@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 1/4] freezer: Do not freeze tasks killed by OOM killer

On Tuesday, October 21, 2014 09:27:12 AM Michal Hocko wrote:
> From: Cong Wang <xiyou.wangcong@...il.com>
> 
> Since f660daac474c6f (oom: thaw threads if oom killed thread is frozen
> before deferring) OOM killer relies on being able to thaw a frozen task
> to handle OOM situation but a3201227f803 (freezer: make freezing() test
> freeze conditions in effect instead of TIF_FREEZE) has reorganized the
> code and stopped clearing freeze flag in __thaw_task. This means that
> the target task only wakes up and goes into the fridge again because the
> freezing condition hasn't changed for it. This reintroduces the bug
> fixed by f660daac474c6f.
> 
> Fix the issue by checking for TIF_MEMDIE thread flag in
> freezing_slow_path and exclude the task from freezing completely. If a
> task was already frozen it would get woken by __thaw_task from OOM killer
> and get out of freezer after rechecking freezing().
> 
> Changes since v1
> - put TIF_MEMDIE check into freezing_slowpath rather than in __refrigerator
>   as per Oleg
> - return __thaw_task into oom_scan_process_thread because
>   oom_kill_process will not wake task in the fridge because it is
>   sleeping uninterruptible
> 
> [mhocko@...e.cz: rewrote the changelog]
> Fixes: a3201227f803 (freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE)
> Cc: stable@...r.kernel.org # 3.3+
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Michal Hocko <mhocko@...e.cz>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> Acked-by: Oleg Nesterov <oleg@...hat.com>

ACK

> ---
>  kernel/freezer.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index aa6a8aadb911..8f9279b9c6d7 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -42,6 +42,9 @@ bool freezing_slow_path(struct task_struct *p)
>  	if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
>  		return false;
>  
> +	if (test_thread_flag(TIF_MEMDIE))
> +		return false;
> +
>  	if (pm_nosig_freezing || cgroup_freezing(p))
>  		return true;
>  
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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