From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753710Ab1IBRTX (ORCPT ); Fri, 2 Sep 2011 13:19:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11608 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753584Ab1IBRTW (ORCPT ); Fri, 2 Sep 2011 13:19:22 -0400 Date: Fri, 2 Sep 2011 19:15:17 +0200 From: Oleg Nesterov To: Tejun Heo Cc: Matt Helsley , "Rafael J. Wysocki" , Paul Menage , containers@lists.linux-foundation.org, linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH pm-freezer 1/4] cgroup_freezer: fix freezer->state setting bug in freezer_change_state() Message-ID: <20110902171517.GA8247@redhat.com> References: <20110831102100.GA2828@mtj.dyndns.org> <20110902004231.GF1919@count0.beaverton.ibm.com> <20110902165839.GA7478@redhat.com> <20110902170844.GJ2752@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110902170844.GJ2752@htj.dyndns.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/03, Tejun Heo wrote: > > Hello, > > On Fri, Sep 02, 2011 at 06:58:39PM +0200, Oleg Nesterov wrote: > > > This still doesn't look quite right. If the cgroup is FREEZING it should > > > also call try_to_freeze_cgroup(). I think this is what's needed: > > > > > > if (freezer->state == CGROUP_THAWED) > > > atomic_inc(&system_freezing_cnt); > > > freezer->state = CGROUP_FREEZING; > > > retval = try_to_freeze_cgroup(cgroup, freezer); > > > > This is what I mentioned before, to me this looks like a win. > > > > Why do we need try_to_freeze_cgroup() in this case? "for safety" > > could actually mean "hide the bug" ;) > > I guess it depends on the viewpoint. A simple analogy would be using > WARN_ON_ONCE() instead of BUG_ON() so that the mode of failure is > softer. This change isn't likely to make bugs significantly more > difficult to discover so why not? I agree either way. Personally I prefer your current patch. Because it is not clear why do we call try_to_freeze_cgroup() if it was already called. And, the 2nd call can silently hide the problem if we have some bug. But of course, this is up to you and Matt. > > But I agree either way. Rafael, I think 1-4 are fine, but I think > > we need the simple 5/4, will send in a minute... > > Can you please wait a bit? The second one was broken (missing unlock) Yes, I just noticed the small problem too, hopefully we mean the same bug ;) Oleg.