Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757691AbXJCQIB (ORCPT ); Wed, 3 Oct 2007 12:08:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754272AbXJCQHw (ORCPT ); Wed, 3 Oct 2007 12:07:52 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:58194 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753243AbXJCQHw (ORCPT ); Wed, 3 Oct 2007 12:07:52 -0400 Date: Wed, 3 Oct 2007 18:07:43 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Linux Kernel Mailing List , Greg KH , Alexander Viro , Peter Zijlstra Subject: Re: [bug] crash when reading /proc/mounts (was: Re: Linux 2.6.23-rc9 and a heads-up for the 2.6.24 series..) Message-ID: <20071003160743.GA22782@elte.hu> References: <20071003084607.GC32218@elte.hu> <20071003154914.GA21690@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071003154914.GA21690@elte.hu> User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7-deb -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1789 Lines: 55 * Ingo Molnar wrote: > > * Linus Torvalds wrote: > > > Your compiler generates > > > > movl -16(%ebp),%edx > > movl (%edx),%edi /* this is _totally_ bogus! */ > > incl %edx > > movl %edx,-16(%ebp) > > movl %edi,%ecx > > testb %cl,%cl > > je ... > > ah, ok. > > > while I get (gcc version 4.1.2 20070925 (Red Hat 4.1.2-28)): > > > > movl -16(%ebp), %eax # p, > > movzbl (%eax), %edi #, c /* not bogus! */ > > movl %edi, %edx # c, > > testb %dl, %dl # > > je .L64 #, > > incl %eax # > > movsbl %dl,%ebx #, D.12414 > > movl %eax, -16(%ebp) #, p > > > > where the difference (apart from doing the increment differently and > > different register allocation) is that I have a "movzbl" (correct), > > while you have a "movl" (pure and utter crap). > > i'll try with another compiler in a minute. i just tried: gcc version 4.1.2 20070626 (Red Hat 4.1.2-13) and indeed the crash is gone. So you are completely right, it's a compiler bug in 4.0.2 (it's vanilla gcc 4.0.2 built by me, not a distro compiler). It should not affect normal kernels too much this bug needs CONFIG_DEBUG_PAGEALLOC. (or it needs a _really_ unlucky allocation being at the far upper end of RAM - but those are usually taken up by boot-time allocations anyway). i also just re-tried the other config as well - and crash is gone there too. (not surprisingly) Ingo - 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/