From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752316AbXDWUDI (ORCPT ); Mon, 23 Apr 2007 16:03:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751727AbXDWUCf (ORCPT ); Mon, 23 Apr 2007 16:02:35 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:34424 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751707AbXDWUCe (ORCPT ); Mon, 23 Apr 2007 16:02:34 -0400 From: "Rafael J. Wysocki" To: Pavel Machek Subject: Re: [RFC][PATCH -mm 3/3] freezer: Fix problem with kthread_stop Date: Mon, 23 Apr 2007 21:50:30 +0200 User-Agent: KMail/1.9.5 Cc: Andrew Morton , Ingo Molnar , ego@in.ibm.com, Oleg Nesterov , linux-kernel@vger.kernel.org, vatsa@in.ibm.com, paulmck@us.ibm.com References: <20070419120131.GB13435@in.ibm.com> <200704222141.00680.rjw@sisk.pl> <20070423104024.GB5635@elf.ucw.cz> In-Reply-To: <20070423104024.GB5635@elf.ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200704232150.31310.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Monday, 23 April 2007 12:40, Pavel Machek wrote: > Hi! > > > Fix the problem with kthread_stop() that causes the freezer to fail if a > > freezable thread is attempting to stop a frozen one and that may cause the > > freezer to fail if the thread being stopped is freezable and > > try_to_freeze_tasks() is running concurrently with kthread_stop(). > > Parse error. OK, will fix. > > Index: linux-2.6.21-rc6-mm1/kernel/kthread.c > > =================================================================== > > --- linux-2.6.21-rc6-mm1.orig/kernel/kthread.c 2007-04-09 15:23:48.000000000 +0200 > > +++ linux-2.6.21-rc6-mm1/kernel/kthread.c 2007-04-22 19:05:29.000000000 +0200 > > @@ -232,6 +233,14 @@ int kthread_stop(struct task_struct *k) > > > > /* Now set kthread_should_stop() to true, and wake it up. */ > > kthread_stop_info.k = k; > > + if (!freezer_should_exempt(current)) { > > + /* We are freezable, so we must make sure that the thread being > > + * stopped is not frozen and will not be frozen until it dies > > + */ > > + freezer_exempt(k); > > + if (frozen(k)) > > + clear_frozen_flag(k); > > + } > > wake_up_process(k); > > put_task_struct(k); > > > > Do we need to take some locks to access other process' flags? Or do > frozen_exempt() etc take enough locks, already? After the previous patch we only use set_bit(), clear_bit() and test_bit() to access freezer_falgs, so no special locking is needed to protect them. Greetings, Rafael