From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933289AbXCBJNe (ORCPT ); Fri, 2 Mar 2007 04:13:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933294AbXCBJNe (ORCPT ); Fri, 2 Mar 2007 04:13:34 -0500 Received: from www.osadl.org ([213.239.205.134]:45841 "EHLO mail.tglx.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933289AbXCBJNd (ORCPT ); Fri, 2 Mar 2007 04:13:33 -0500 Subject: Re: [BUG 2.6.21-rc2] divide error: 0000 From: Thomas Gleixner Reply-To: tglx@linutronix.de To: Willy Tarreau Cc: Sean Young , linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton In-Reply-To: <20070302061149.GF943@1wt.eu> References: <20070301231241.GA32630@atlantis.8hz.com> <20070302061149.GF943@1wt.eu> Content-Type: text/plain Date: Fri, 02 Mar 2007 10:19:17 +0100 Message-Id: <1172827157.24738.29.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2007-03-02 at 07:11 +0100, Willy Tarreau wrote: > > Call Trace: > > [] posix_cpu_clock_get+0x47/0xdc > > [] sys_clock_gettime+0x80/0x82 > > [] syscall_call+0x7/0xb > > [] svc_ioctl+0xc2/0x261 > > ======================= > > Code: 0b eb fe 57 56 53 89 cb 89 d1 8b 74 24 10 83 e0 03 83 f8 02 74 0c 89 f2 89 c8 5b 5e 5f e9 ee 3f ff ff bf 00 ca 9a 3b 89 d0 89 da f7 89 56 04 89 06 5b 5e 5f c3 55 57 56 53 89 c7 89 d6 89 cb > > EIP: [] sample_to_timespec+0x28/0x33 SS:ESP 0068:d4a56f74 > > > > The instruction is: > > > > div %edi > > > > And edi is 1e9 (0x3b9aca00). I don't understand why this results in an > > divide error. > > It does this because 'div' does an unsigned divide of edx:eax by edi. > Here, edx=fffffffa and eax is 63b5a669. Clearly, such a number cannot > be divided by 1e9 to return a 32 bits value. > > Given the values we see here, I suspect the code should have used an > integer divide (idiv). This means that something in the code implies > that the result is unsigned while it should be signed. The question is why do we have this negative value in the dividend. I suspect this is related to http://marc.theaimsgroup.com/?l=linux-kernel&m=117210430112543&w=2 Sean, can you please retest with that patch applied, which hit mainline after 2.6.21-rc2 tglx