Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752420Ab1DUTAf (ORCPT ); Thu, 21 Apr 2011 15:00:35 -0400 Received: from mx2.fusionio.com ([64.244.102.31]:35824 "EHLO mx2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750829Ab1DUTAe (ORCPT ); Thu, 21 Apr 2011 15:00:34 -0400 X-ASG-Debug-ID: 1303412430-01de284cf817a270001-xx1T2L X-Barracuda-Envelope-From: JAxboe@fusionio.com Message-ID: <4DB07ECA.5050309@fusionio.com> Date: Thu, 21 Apr 2011 21:00:26 +0200 From: Jens Axboe MIME-Version: 1.0 To: Michal Hocko CC: Linus Torvalds , Jens Axboe , LKML Subject: Re: 2.6.39-rc4 BUG: unable to handle kernel NULL pointer dereference at 0000000c IP: cfq_insert_request+0x1d/0x3f5 References: <20110420125824.GA3507@tiehlicka.suse.cz> <4DAEDBEB.7060904@fusionio.com> <20110420132903.GA13554@tiehlicka.suse.cz> <4DAF18DF.9080205@fusionio.com> <20110421071642.GA3556@tiehlicka.suse.cz> <5F35AAD2-8277-44BD-86B6-B1D7B816071E@kernel.dk> <20110421185112.GA4796@tiehlicka.suse.cz> X-ASG-Orig-Subj: Re: 2.6.39-rc4 BUG: unable to handle kernel NULL pointer dereference at 0000000c IP: cfq_insert_request+0x1d/0x3f5 In-Reply-To: <20110421185112.GA4796@tiehlicka.suse.cz> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Barracuda-Connect: mail1.int.fusionio.com[10.101.1.21] X-Barracuda-Start-Time: 1303412430 X-Barracuda-URL: http://10.101.1.181:8000/cgi-mod/mark.cgi X-Barracuda-Spam-Score: 0.20 X-Barracuda-Spam-Status: No, SCORE=0.20 using global scores of TAG_LEVEL=1000.0 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=9.0 tests=PR0N_SUBJECT X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.2.61526 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- 0.20 PR0N_SUBJECT Subject has letters around special characters (pr0n) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1576 Lines: 40 On 2011-04-21 20:51, Michal Hocko wrote: > On Thu 21-04-11 07:38:57, Linus Torvalds wrote: >> On Thu, Apr 21, 2011 at 12:25 AM, Jens Axboe wrote: >>>> >>>> I am going to bisect, let's see if I can find anything. >>> >>> Thanks, that would be great! >> >> I'd expect it to be very timing-dependent, and thus could easily be >> triggered (or hidden) by unrelated changes. >> >> Just happening to have a request added to the elevator at _just_ the >> same moment that another CPU is changing it and getting rid of the >> data structures for the old one. > > And it really looks like a timing issue. I have bisected down to > e710d7d5a9cab1041b7a3cf9e655b75d92786857. I had to skip[1] some commits > due to compile errors [2]. > At first it looked quite promising because I was able to boot after I > reverted that patch but then I have tried to revert it on top of rc4 > (2f666bcf757cb72549f360ef6da02f03620a48b6) and saw the same problem > again. > > So I do not think that bisecting will help here. It will be timing dependent. If there's no allocated IO requests when the switch happens, it'll work. But the commit that caused this regression is 5e84ea3a. If you revert that, it should work fine. Or just apply the patch I sent (or update to Linus' tree, it's in now) and it'll work as well. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/