linux-kernel - Re: Possible race condition in oom-killer

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Message-Id: <201708012316.CFF21387.VMFtLFJHFOQOOS@I-love.SAKURA.ne.jp>
Date:   Tue, 1 Aug 2017 23:16:13 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     mhocko@...nel.org
Cc:     mjaggi@...iumnetworks.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: Possible race condition in oom-killer

Michal Hocko wrote:
>                       Once we merge [1] then the oom victim wouldn't
> need to get TIF_MEMDIE to access memory reserves.
> 
> [1] http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org

False. We are not setting oom_mm to all thread groups (!CLONE_THREAD) sharing
that mm (CLONE_VM). Thus, one thread from each thread group sharing that mm
will have to call out_of_memory() in order to set oom_mm, and they will find
task_will_free_mem() returning false due to MMF_OOM_SKIP already set, and
after all goes to next OOM victim selection.