From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755487Ab1IHXcF (ORCPT ); Thu, 8 Sep 2011 19:32:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49185 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755166Ab1IHXb7 (ORCPT ); Thu, 8 Sep 2011 19:31:59 -0400 Date: Thu, 8 Sep 2011 19:59:26 +0200 From: Oleg Nesterov To: Tejun Heo Cc: "Rafael J. Wysocki" , matthltc@us.ibm.com, paul@paulmenage.org, containers@lists.linux-foundation.org, linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] freezer: fix wait_event_freezable/__thaw_task races Message-ID: <20110908175926.GA26986@redhat.com> References: <20110904184626.GA30101@redhat.com> <20110905023315.GB9807@htj.dyndns.org> <20110905162012.GA4445@redhat.com> <20110906032846.GA18425@mtj.dyndns.org> <20110906151836.GA15568@redhat.com> <20110906152539.GA16899@redhat.com> <20110906155332.GF18425@mtj.dyndns.org> <20110907182156.GA13909@redhat.com> <20110907182217.GB13909@redhat.com> <20110908010530.GD3987@mtj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110908010530.GD3987@mtj.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 Hi, On 09/08, Tejun Heo wrote: > > Hello, > > On Wed, Sep 07, 2011 at 08:22:17PM +0200, Oleg Nesterov wrote: > > wait_event_freezable() and wait_event_freezable_timeout() stop > > the waiting if try_to_freeze() fails. This is not right, we can > > race with __thaw_task() and in this case > > > > - wait_event_freezable() returns the wrong ERESTARTSYS > > > > - wait_event_freezable_timeout() can return the positive > > value while condition == F > > Indeed, nice catch. This one actually is pretty dangerous. We > probably want to make a separate fix for this and backport it to > -stable? And I forgot to mention that wait_event_freezable_timeout() doesn't handle -ERESTARTSYS at all. But I don't think -stable needs this fix. According to grep, nobody check the returned value, and none of the callers plays with signals. > > Change the code to always check __retval/condition before return. > > > > Note: with or without this patch the timeout logic looks strange, > > probably we should recalc timeout if try_to_freeze() returns T. > > > > Signed-off-by: Oleg Nesterov > > Yeap, with freezable_with_signal gone, this looks correct & simpler to > me I don't really understand this... set_freezable_with_signal() has a lot of problems, yes... But even if it wasn't removed this fix makes sense anyway, afaics. If freezable_with_signal caller does wait_event_freezable_timeout(), __retval becomes -ERESTARTSYS after freeze_task(). The next iteration will return 0 with the KERN_ERR message from schedule_timeout(). > but it would be nice if you can sprinkle some documentation while > at it. :) But they already have the comment ;) What can I add? Oleg.