Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752115Ab1DVHAh (ORCPT ); Fri, 22 Apr 2011 03:00:37 -0400 Received: from cantor.suse.de ([195.135.220.2]:48377 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751829Ab1DVHAf (ORCPT ); Fri, 22 Apr 2011 03:00:35 -0400 Date: Fri, 22 Apr 2011 09:00:33 +0200 From: Michal Hocko To: Jens Axboe 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 Message-ID: <20110422070032.GA3575@tiehlicka.suse.cz> 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> <4DB07ECA.5050309@fusionio.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4DB07ECA.5050309@fusionio.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1864 Lines: 49 On Thu 21-04-11 21:00:26, Jens Axboe wrote: > 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. Great. I can boot just fine with the current Linus tree (2.6.39-rc4-00149-g91e8549). Thanks a lot! -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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/