From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755500AbaIHX30 (ORCPT ); Mon, 8 Sep 2014 19:29:26 -0400 Received: from mail-oi0-f53.google.com ([209.85.218.53]:41899 "EHLO mail-oi0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755213AbaIHX3Z (ORCPT ); Mon, 8 Sep 2014 19:29:25 -0400 MIME-Version: 1.0 In-Reply-To: <4809128.C6aPga5IjQ@vostro.rjw.lan> References: <1409869842-10807-1-git-send-email-xiyou.wangcong@gmail.com> <1609685.fbsF6EQ3X7@vostro.rjw.lan> <4809128.C6aPga5IjQ@vostro.rjw.lan> Date: Mon, 8 Sep 2014 16:29:24 -0700 Message-ID: Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen From: Cong Wang To: "Rafael J. Wysocki" Cc: Tejun Heo , LKML , David Rientjes , Michal Hocko , Andrew Morton 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 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 will put the following as a comment: >> >> /* OOM killer may decide to kill this process after it is frozen, >> in this case SIGKILL can never be handled, so we should check >> TIF_MEMDIE and if it is set, thaw and let SIGKILL kill it. >> But for PM freeze, it is not allowed to get out even for a while, >> so we have to keep it being frozen. */ >> >> Let me know if it looks good to you. > > Well, it reflects the reality, so it's good enough. But please adhere to the > coding style rules for comments. > Sure thing. Thanks!