Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754126AbYC0Xuv (ORCPT ); Thu, 27 Mar 2008 19:50:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752550AbYC0Xun (ORCPT ); Thu, 27 Mar 2008 19:50:43 -0400 Received: from mail.gmx.net ([213.165.64.20]:57733 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752333AbYC0Xum (ORCPT ); Thu, 27 Mar 2008 19:50:42 -0400 X-Authenticated: #5039886 X-Provags-ID: V01U2FsdGVkX1/kudc+79TkxU70RZUPPJfUcWxuM0dl6OocKtIFXL ox3ehBFFWmT/qX Date: Fri, 28 Mar 2008 00:50:39 +0100 From: =?iso-8859-1?Q?Bj=F6rn?= Steinbrink To: Thomas Gleixner Cc: Andrew Morton , Christian Kujau , LKML , Markus Rehbach , "Rafael J. Wysocki" , Ingo Molnar Subject: Re: 2.6.25-rc6: BUG: unable to handle kernel NULL pointer dereference Message-ID: <20080327235039.GA26291@atjola.homenet> References: <20080325233357.17d6ac41.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.17+20080114 (2008-01-14) X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2300 Lines: 70 On 2008.03.27 16:20:53 +0100, Thomas Gleixner wrote: > On Tue, 25 Mar 2008, Andrew Morton wrote: > > > Code: 53 c0 e8 20 08 fc ff c1 e3 02 8b 14 33 89 54 24 20 8b 44 24 20 85 c0 75 10 eb 51 8b 12 89 54 24 20 8b 44 24 20 85 c0 74 43 8b 02 <0f> 18 00 90 8d 5a d8 39 6b 34 75 e4 8b 7c 24 0c 39 7b 30 75 db > > It faults in a prefetch. > > > Markus reported what looks to be the same thing here: > > http://lkml.org/lkml/2008/3/21/202 and it's already in the regresison list. > > Same here. And both are AMD X2 early stepping machines. > > > I guess you've confirmed that this wasn't a mystery > > once-off-on-that-machine. > > > > I can't think what we did to cause this. > > I had a lengthy bug decoding session with Ingo and we found the root > cause: > > A dropped workaround for the prefetch bug in early X2s and > Opterons. Patch below. > > Thanks, > > tglx > > ---------------> > Subject: x86: fix prefetch workaround > From: Ingo Molnar > Date: Thu Mar 27 15:58:28 CET 2008 > > some early Athlon XP's and Opterons generate bogus faults on prefetch ^^ Umh, XP? Didn't you say X2 above? And looking at the patch, X2 seems more plausible as well, I don't think that the XP supported the NX bit, did it? Bj?rn > instructions. The workaround for this regressed over .24 - reinstate it. > > Signed-off-by: Ingo Molnar > Signed-off-by: Thomas Gleixner > > --- > arch/x86/mm/fault.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > Index: linux-x86.q/arch/x86/mm/fault.c > =================================================================== > --- linux-x86.q.orig/arch/x86/mm/fault.c > +++ linux-x86.q/arch/x86/mm/fault.c > @@ -104,7 +104,8 @@ static int is_prefetch(struct pt_regs *r > unsigned char *max_instr; > > #ifdef CONFIG_X86_32 > - if (!(__supported_pte_mask & _PAGE_NX)) > + /* Catch an obscure case of prefetch inside an NX page: */ > + if ((__supported_pte_mask & _PAGE_NX) && (error_code & 16)) > return 0; > #endif > > > -- 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/