From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752237AbaIJXSx (ORCPT ); Wed, 10 Sep 2014 19:18:53 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:62920 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750970AbaIJXSw (ORCPT ); Wed, 10 Sep 2014 19:18:52 -0400 From: "Rafael J. Wysocki" To: Cong Wang Cc: Tejun Heo , LKML , David Rientjes , Michal Hocko , Andrew Morton Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen Date: Thu, 11 Sep 2014 01:38:21 +0200 Message-ID: <2606659.qXoKHWVyLl@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.16.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: References: <1409869842-10807-1-git-send-email-xiyou.wangcong@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday, September 10, 2014 01:30:25 PM Cong Wang wrote: > On Mon, Sep 8, 2014 at 4:29 PM, Cong Wang wrote: > > On Mon, Sep 8, 2014 at 4:42 PM, Rafael J. Wysocki wrote: > >> On Monday, September 08, 2014 04:16:15 PM Cong Wang wrote: > >>> On Mon, Sep 8, 2014 at 4:23 PM, Rafael J. Wysocki wrote: > >>> > > >>> > The reason why it matters for the suspend-time freezing is that we freeze tasks > >>> > to take them out of the picture entirely until they are thawed. Therefore we > >>> > can't allow them to go back to the picture just for a while until they are > >>> > killed. Frozen tasks are not supposed to get back to the picture at all. > >>> > > >>> > >>> > >>> Ok, then checking TIF_MEMDIE is unsafe for PM freeze, we should > >>> keep the cgroup_freezing() test to make sure freeze request is from > >>> cgroup not PM. Question got answered. :) > >> > >> Do I think correctly that cgroups freezing and system suspend are > >> mutually exclusive? If not, then this still is problematic. > > > > Good point! Although rare, but it is possible we freeze a process both from > > cgroup and PM. Hmm, this means we have to explicitly exclude PM rather > > just checking cgroup freeze? Interesting, but I am not familiar with PM. > > > > I am wondering if the folllowing check makes any sense with regarding > to rule out PM freeze: > > if ((!pm_nosig_freezing && !pm_freezing) && > cgroup_freezing(current) && test_thread_flag(TIF_MEMDIE)) > return true; > > PM will not freeze the process again if it is already frozen by cgroup, > so here we just make sure that it will not thaw if PM freeze is in progress. > > Am I missing anything? And where exactly would you like to put this check? Into __refrigerator()? -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.