From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754536AbXDZLLG (ORCPT ); Thu, 26 Apr 2007 07:11:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030621AbXDZLLG (ORCPT ); Thu, 26 Apr 2007 07:11:06 -0400 Received: from mail.screens.ru ([213.234.233.54]:51108 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754536AbXDZLLE (ORCPT ); Thu, 26 Apr 2007 07:11:04 -0400 Date: Thu, 26 Apr 2007 14:15:47 +0400 From: Oleg Nesterov To: Gautham R Shenoy Cc: Andrew Morton , "Rafael J. Wysocki" , "Eric W. Biederman" , LKML Subject: Re: 2.6.21-rc7-mm1: BUG_ON in kthread_bind during _cpu_down Message-ID: <20070426101547.GA97@tv-sign.ru> References: <200704260110.22224.rjw@sisk.pl> <20070425165410.b73443b4.akpm@linux-foundation.org> <20070426100922.GB12892@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070426100922.GB12892@in.ibm.com> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 04/26, Gautham R Shenoy wrote: > > On Wed, Apr 25, 2007 at 04:54:10PM -0700, Andrew Morton wrote: > > On Thu, 26 Apr 2007 01:10:21 +0200 "Rafael J. Wysocki" wrote: > > > > > Hi, > > > > > > The BUG_ON in khthread_bind (line 165 in kthread.c) triggers for me during > > > attempted suspend to disk, when disable_nonboot_cpus() calls _cpu_down() > > > (on x86_64). > > > Caused due to Oleg's patch http://lkml.org/lkml/2007/4/13/93. > > Agreed that most of the time a kthread_create(p) is followed by a > kthread_bind(p), in which case the assertion > WARN_ON(p->state != TASK_UNINTERRUPTIBLE) makes sense. > > But, in cpu hotplug case, we need to rebind the stop_machine_run thread > from the cpu which has just been offlined to any online cpu. > (kernel/cpu.c line 180) I can't understand why do we need to re-bind this thread. We are doing kthread_stop()->wake_up() below, at this point move_task_off_dead_cpu() has already cared about this task, no? > We only need to ensure in kthread_bind that the task which is being > bound is not running or exiting. Doesn't matter if it's sleeping in > TASK_INTERRUPTIBLE or TASK_UNINTERRUPTIBLE state. We need to ensure that this task can't be woken after return from wait_task_inactive(k), otherwise set_task_cpu() after that is not safe. TASK_INTERRUPTIBLE doesn't protect us from freezing. Couldn't we just remove this kthread_bind() ? Oleg.