From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752075AbdHAMOQ (ORCPT ); Tue, 1 Aug 2017 08:14:16 -0400 Received: from mx2.suse.de ([195.135.220.15]:53503 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751789AbdHAMOP (ORCPT ); Tue, 1 Aug 2017 08:14:15 -0400 Date: Tue, 1 Aug 2017 14:14:12 +0200 From: Michal Hocko To: Tetsuo Handa Cc: mjaggi@caviumnetworks.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: Possible race condition in oom-killer Message-ID: <20170801121411.GG15774@dhcp22.suse.cz> References: <20170728130723.GP2274@dhcp22.suse.cz> <201707282215.AGI69210.VFOHQFtOFSOJML@I-love.SAKURA.ne.jp> <20170728132952.GQ2274@dhcp22.suse.cz> <201707282255.BGI87015.FSFOVQtMOHLJFO@I-love.SAKURA.ne.jp> <20170728140706.GT2274@dhcp22.suse.cz> <201707291331.JGI18780.OtJVLFMHFOFSOQ@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201707291331.JGI18780.OtJVLFMHFOFSOQ@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 29-07-17 13:31:44, Tetsuo Handa wrote: [...] > @@ -806,6 +799,20 @@ static bool task_will_free_mem(struct task_struct *task) > } > rcu_read_unlock(); > > + /* > + * It is possible that current thread fails to try allocation from > + * memory reserves if the OOM reaper set MMF_OOM_SKIP on this mm before > + * current thread calls out_of_memory() in order to get TIF_MEMDIE. > + * In that case, allow current thread to try TIF_MEMDIE allocation > + * before start selecting next OOM victims. > + */ > + if (ret && test_bit(MMF_OOM_SKIP, &mm->flags)) { > + if (task == current && !task->oom_kill_free_check_raced) > + task->oom_kill_free_check_raced = true; > + else > + ret = false; > + } > + > return ret; > } I was going to argue that this will not work because we could mark a former OOM victim again after it passed exit_oom_victim but this seems impossible because task_will_free_mem checks task->mm and that will be NULL by that time. This is still an ugly hack and it doesn't provide any additional guarantee. 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 -- Michal Hocko SUSE Labs