linux-kernel - Re: [PATCH] oom, oom_reaper: Do not enqueue task if it is on the oom_reaper

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Message-Id: <201603292152.IBF60927.FJOHMVtOFOFSQL@I-love.SAKURA.ne.jp>
Date:	Tue, 29 Mar 2016 21:52:20 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mhocko@...nel.org, akpm@...ux-foundation.org
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, mhocko@...e.com
Subject: Re: [PATCH] oom, oom_reaper: Do not enqueue task if it is on the oom_reaper_list head

Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> bb29902a7515 ("oom, oom_reaper: protect oom_reaper_list using simpler
> way") has simplified the check for tasks already enqueued for the oom
> reaper by checking tsk->oom_reaper_list != NULL. This check is not
> sufficient because the tsk might be the head of the queue without any
> other tasks queued and then we would simply lockup looping on the same
> task. Fix the condition by checking for the head as well.

Indeed, oom_reaper_list is initially NULL.

> 
> Fixes: bb29902a7515 ("oom, oom_reaper: protect oom_reaper_list using simpler way")
> Signed-off-by: Michal Hocko <mhocko@...e.com>
Acked-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

> ---
> Hi,
> I have just noticed this after I started consolidating other oom_reaper
> related changes I have here locally. I should have caught this during
> the review already and I really feel ashamed I haven't because this is
> really a trivial bug that should be obvious see...