From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754229AbcEZO7e (ORCPT ); Thu, 26 May 2016 10:59:34 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:32920 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754095AbcEZO7c (ORCPT ); Thu, 26 May 2016 10:59:32 -0400 Date: Thu, 26 May 2016 16:59:30 +0200 From: Michal Hocko To: Tetsuo Handa Cc: linux-mm@kvack.org, rientjes@google.com, oleg@redhat.com, vdavydov@parallels.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/6] mm, oom: do not loop over all tasks if there are no external tasks sharing mm Message-ID: <20160526145930.GF23675@dhcp22.suse.cz> References: <1464266415-15558-1-git-send-email-mhocko@kernel.org> <1464266415-15558-2-git-send-email-mhocko@kernel.org> <201605262330.EEB52182.OtMFOJHFLOSFVQ@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201605262330.EEB52182.OtMFOJHFLOSFVQ@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 Thu 26-05-16 23:30:06, Tetsuo Handa wrote: > Michal Hocko wrote: > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index 5bb2f7698ad7..0e33e912f7e4 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -820,6 +820,13 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, > > task_unlock(victim); > > > > /* > > + * skip expensive iterations over all tasks if we know that there > > + * are no users outside of threads in the same thread group > > + */ > > + if (atomic_read(&mm->mm_users) <= get_nr_threads(victim)) > > + goto oom_reap; > > Is this really safe? Isn't it possible that victim thread's thread group has > more than atomic_read(&mm->mm_users) threads which are past exit_mm() and blocked > at exit_task_work() which are before __exit_signal() from release_task() from > exit_notify()? You are right. The race window between exit_mm and __exit_signal is really large. I thought about == check instead but that wouldn't work for the same reason, dang, it looked so promissing. Scratch this patch then. -- Michal Hocko SUSE Labs