From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422837AbcFMLTr (ORCPT ); Mon, 13 Jun 2016 07:19:47 -0400 Received: from mail-wm0-f49.google.com ([74.125.82.49]:34067 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161113AbcFMLTq (ORCPT ); Mon, 13 Jun 2016 07:19:46 -0400 Date: Mon, 13 Jun 2016 13:19:43 +0200 From: Michal Hocko To: Tetsuo Handa Cc: linux-mm@kvack.org, rientjes@google.com, oleg@redhat.com, vdavydov@parallels.com, mgorman@techsingularity.net, hughd@google.com, riel@redhat.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: mm, oom_reaper: How to handle race with oom_killer_disable() ? Message-ID: <20160613111943.GB6518@dhcp22.suse.cz> References: <201606102323.BCC73478.FtOJHFQMSVFLOO@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201606102323.BCC73478.FtOJHFQMSVFLOO@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 10-06-16 23:23:36, Tetsuo Handa wrote: [...] > (1) freeze_processes() starts freezing user space threads. > (2) Somebody (maybe a kenrel thread) calls out_of_memory(). > (3) The OOM killer calls mark_oom_victim() on a user space thread > P1 which is already in __refrigerator(). > (4) oom_killer_disable() sets oom_killer_disabled = true. > (5) P1 leaves __refrigerator() and enters do_exit(). > (6) The OOM reaper calls exit_oom_victim(P1) before P1 can call > exit_oom_victim(P1). > (7) oom_killer_disable() returns while P1 is not yet frozen > again (i.e. not yet marked as PF_FROZEN). > (8) P1 perform IO/interfere with the freezer. You are right. I missed that kernel threads are still alive when writing e26796066fdf929c ("oom: make oom_reaper freezable"). I am trying to remember why we are disabling oom killer before kernel threads are frozen but not really sure about that right away. I guess it has something to do with freeze_kernel_threads being called from different contexts as well so freeze_processes was just more convinient and was OK for correctness at the time. > try_to_freeze_tasks(false) from freeze_kernel_threads() will freeze > P1 again, but it seems to me that freeze_kernel_threads() is not > always called when freeze_processes() suceeded. > > Therefore, we need to do like > > - exit_oom_victim(tsk); > + mutex_lock(&oom_lock); > + if (!oom_killer_disabled) > + exit_oom_victim(tsk); > + mutex_unlock(&oom_lock); > > in oom_reap_task(), don't we? I do not like this very much. I would rather make sure that all freezable kernel threads are frozen when disabling the oom killer. [...] > But we might be able to do like below patch rather than above patch. > If below approach is OK, "[PATCH 10/10] mm, oom: hide mm which is shared > with kthread or global init" will be able to call exit_oom_victim() when > can_oom_reap became false. I believe this is not really needed. I will follow up on the 10/10 later. -- Michal Hocko SUSE Labs