From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755794AbZKIMyA (ORCPT ); Mon, 9 Nov 2009 07:54:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755741AbZKIMx7 (ORCPT ); Mon, 9 Nov 2009 07:53:59 -0500 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:56875 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755738AbZKIMx7 (ORCPT ); Mon, 9 Nov 2009 07:53:59 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Message-ID: <4AF810C5.4010505@jp.fujitsu.com> Date: Mon, 09 Nov 2009 21:53:25 +0900 From: Kenji Kaneshige User-Agent: Thunderbird 2.0.0.23 (Windows/20090812) MIME-Version: 1.0 To: Peter Zijlstra CC: mingo@elte.hu, linux-kernel@vger.kernel.org, Rusty Russell Subject: Re: Kernel oops in resched_task() with 2.6.31.5 References: <4AF80B8B.8080203@jp.fujitsu.com> <1257770720.4108.195.camel@laptop> In-Reply-To: <1257770720.4108.195.camel@laptop> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks, Kenji Kaneshige