From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761622AbZAUHUE (ORCPT ); Wed, 21 Jan 2009 02:20:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754150AbZAUHTx (ORCPT ); Wed, 21 Jan 2009 02:19:53 -0500 Received: from mail.suse.de ([195.135.220.2]:32853 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753752AbZAUHTw (ORCPT ); Wed, 21 Jan 2009 02:19:52 -0500 Date: Wed, 21 Jan 2009 08:19:50 +0100 From: Nick Piggin To: Vegard Nossum Cc: Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Linux Kernel Mailing List Subject: Re: lockdep and debug objects together are broken? Message-ID: <20090121071950.GM24891@wotan.suse.de> References: <20090120085559.GB19505@wotan.suse.de> <19f34abd0901201311t2425056dia6182812f7270297@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <19f34abd0901201311t2425056dia6182812f7270297@mail.gmail.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 20, 2009 at 10:11:47PM +0100, Vegard Nossum wrote: > On Tue, Jan 20, 2009 at 9:55 AM, Nick Piggin wrote: > > Hi, > > > > I've had a problem frustrating my testing because lockdep was silently turning > > itself off... I patched out the code to disable lockdep after the first error, > > and it started showing up weird errors. kernel/fork.c:990 seemed to be the > > first to trigger (hard irqs disabled) from a call_usermodehelper call. Later, > > migration thread was reported to try to unlock rq->lock although it was > > holding no locks. Then init was reported to return to userspace without > > releasing an objectdebug hash lock. > > > > All that went away and everything seemed to work properly with debug objects > > configured out. > > > > I didn't get too far in trying to debug the problem. But it should be easy > > enough to reproduce (if not, I can post traces or test patches). > > I just built a kernel with lockdep and debugobjects enabled, and > everything seemed fine. I think you should post your kernel version, > config, and the lockdep patch (if needed -- it didn't seem to turn > itself off here). Are you sure? Ie. sysrq+D a still works properly? In that case, you wouldn't need the lockdep patch because it just prevents the feature from being switched off. I'll have to dig a bit further, then. The annoying thing is that lockdep turns itself off at the drop of a hat (and this particular problem seems to happen without any backtraces), so it invalidates all your lockdep testing if you don't realise it has turned itself off. Is there a way to re-arm lockdep? That would be neat.