From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423531AbcBQOjV (ORCPT ); Wed, 17 Feb 2016 09:39:21 -0500 Received: from mail-wm0-f54.google.com ([74.125.82.54]:34478 "EHLO mail-wm0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964898AbcBQOjU (ORCPT ); Wed, 17 Feb 2016 09:39:20 -0500 Date: Wed, 17 Feb 2016 15:39:17 +0100 From: Michal Hocko To: Tetsuo Handa Cc: akpm@linux-foundation.org, rientjes@google.com, mgorman@suse.de, oleg@redhat.com, torvalds@linux-foundation.org, hughd@google.com, andrea@kernel.org, riel@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Johannes Weiner Subject: Re: [PATCH v2] mm,oom: don't abort on exiting processes when selecting a victim. Message-ID: <20160217143917.GP29196@dhcp22.suse.cz> References: <1455719485-7730-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1455719485-7730-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 17-02-16 23:31:25, Tetsuo Handa wrote: > Currently, oom_scan_process_thread() returns OOM_SCAN_ABORT when there is > a thread which is exiting. But it is possible that that thread is blocked > at down_read(&mm->mmap_sem) in exit_mm() called from do_exit() whereas > one of threads sharing that memory is doing a GFP_KERNEL allocation > between down_write(&mm->mmap_sem) and up_write(&mm->mmap_sem) > (e.g. mmap()). > > ---------- > T1 T2 > Calls mmap() > Calls _exit(0) > Arrives at vm_mmap_pgoff() > Arrives at do_exit() > Gets PF_EXITING via exit_signals() > Calls down_write(&mm->mmap_sem) > Calls do_mmap_pgoff() > Calls down_read(&mm->mmap_sem) from exit_mm() > Calls out of memory via a GFP_KERNEL allocation but > oom_scan_process_thread(T1) returns OOM_SCAN_ABORT > ---------- > > down_read(&mm->mmap_sem) by T1 is waiting for up_write(&mm->mmap_sem) by > T2 while oom_scan_process_thread() by T2 is waiting for T1 to set > T1->mm = NULL. Under such situation, the OOM killer does not choose > a victim, which results in silent OOM livelock problem. > > This patch changes oom_scan_process_thread() not to return OOM_SCAN_ABORT > when there is a thread which is exiting. Thank you for the updated changelog. This makes much more sense now. This problem exists for quite some time but I would be hesitant to mark it for stable because the side effects are quite hard to evaluate. We could e.g. see a premature OOM killer invocation while the currently exiting task just didn't get to finish and release its mm. > Signed-off-by: Tetsuo Handa > Signed-off-by: Johannes Weiner Acked-by: Michal Hocko > --- > mm/oom_kill.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index cf87153..6e6abaf 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -292,9 +292,6 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc, > if (oom_task_origin(task)) > return OOM_SCAN_SELECT; > > - if (task_will_free_mem(task) && !is_sysrq_oom(oc)) > - return OOM_SCAN_ABORT; > - > return OOM_SCAN_OK; > } > > -- > 1.8.3.1 -- Michal Hocko SUSE Labs