From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755167AbZLBB10 (ORCPT ); Tue, 1 Dec 2009 20:27:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753357AbZLBB1Z (ORCPT ); Tue, 1 Dec 2009 20:27:25 -0500 Received: from kroah.org ([198.145.64.141]:50506 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753300AbZLBB1Z (ORCPT ); Tue, 1 Dec 2009 20:27:25 -0500 Date: Tue, 1 Dec 2009 17:21:00 -0800 From: Greg KH To: Ingo Molnar Cc: Kenji Kaneshige , stable kernel team , Peter Zijlstra , Rusty Russell , linux-kernel@vger.kernel.org Subject: Re: [stable] Kernel oops in resched_task() with 2.6.31.5 Message-ID: <20091202012100.GD30050@kroah.com> References: <4AF80B8B.8080203@jp.fujitsu.com> <1257770720.4108.195.camel@laptop> <4AF810C5.4010505@jp.fujitsu.com> <4AF8F63B.1040402@jp.fujitsu.com> <20091110051537.GF7897@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091110051537.GF7897@elte.hu> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 10, 2009 at 06:15:37AM +0100, Ingo Molnar wrote: > > * Kenji Kaneshige wrote: > > > Kenji Kaneshige wrote: > > >Peter Zijlstra wrote: > > >>On Mon, 2009-11-09 at 21:31 +0900, Kenji Kaneshige wrote: > > >>>Hi, > > >>> > > >>>I frequently encounter the kernel oops attached below in resched_task() > > >>>with 2.6.31.5. This kernel oops happens also with 2.6.32-rc5. I don't > > >>>know about other kernel. > > >>> > > >>>Here is my analysis: > > >>> > > >>>The immediate cause of this kernel oops is that NULL was passed to > > >>>resched_task() from resched_cpu(). From my investigation, this was > > >>>caused as follows: > > >>> > > >>>- trigger_load_balance() caluculated cpu number of idle load balancer > > >>> using find_new_ilb(), and find_new_ilb() returned *offline* CPU > > >>> number (16 in my case). Note that I didn't do any CPU hotplug > > >>> operation. On my system, present, online and offline under > > >>> /sys/devices/system/cpu/ are > > >>> > > >>> [kanesige@localhost ~]$ cat /sys/devices/system/cpu/present > > >>> 0-15 > > >>> [kanesige@localhost ~]$ cat /sys/devices/system/cpu/online > > >>> 0-15 > > >>> [kanesige@localhost ~]$ cat /sys/devices/system/cpu/offline > > >>> 16-255 > > >>> > > >>> And nr_cpu_ids is 256. > > >>> > > >>>- resched_cpu() calculated current task by cpu_curr() with offline CPU > > >>> number. > > >>> > > >>>So this kernel oops seems to be caused by invalid CPU number returned > > >>>from find_new_ilb(). I don't know the find_new_ilb() implementation, > > >>>but I suspect the initialization of cpumasks used by find_new_ilb(). > > >>>The patch attached below seems to fix the problem (With this patch, > > >>>the kernel oops doesn't happen). But I don't know if this is the > > >>>correct fix. > > >> > > >>Please send patches against -tip. > > >> > > >>You might find that Rusty has already fixed a similar issue there in > > >>commit: 49557e620339cb134127b5bfbcfecc06b77d0232. > > >> > > >>Now, Rusty's patch does not clear the ilb mask, so maybe it doesn't > > >>fully cover your issue, please test. > > >> > > > > > >Thank you for quick response. > > > > > >I didn't notice Rusty's fix. > > >I'll look at and test it tomorrow. > > > > > > > I tested Rusty's patch and confirmed it fixes the problem. > > Thanks. > > -stable team, please cherry-pick this upstream commit for .31.x: > > 49557e6: sched: Fix boot crash by zalloc()ing most of the cpu masks Now queued up. thanks, greg k-h