From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757536AbYBPNsx (ORCPT ); Sat, 16 Feb 2008 08:48:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754066AbYBPNso (ORCPT ); Sat, 16 Feb 2008 08:48:44 -0500 Received: from www.tglx.de ([62.245.132.106]:36136 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753975AbYBPNsn (ORCPT ); Sat, 16 Feb 2008 08:48:43 -0500 Date: Sat, 16 Feb 2008 14:48:17 +0100 (CET) From: Thomas Gleixner To: Heiko Carstens cc: linux-kernel@vger.kernel.org, mm-commits@vger.kernel.org, buytenh@wantstofly.org, mingo@elte.hu, riku.voipio@movial.fi, stable@kernel.org, schwidefsky@de.ibm.com Subject: Re: + futex-runtime-enable-pi-and-robust-functionality.patch added to -mm tree In-Reply-To: <20080216134155.GB4900@osiris.boeblingen.de.ibm.com> Message-ID: References: <200802150149.m1F1n8Gx013909@imap1.linux-foundation.org> <20080216124248.GA4900@osiris.boeblingen.de.ibm.com> <20080216134155.GB4900@osiris.boeblingen.de.ibm.com> User-Agent: Alpine 1.00 (LFD 882 2007-12-20) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 16 Feb 2008, Heiko Carstens wrote: > > Well, NULL pointer dereferencing is supposed to fail, isn't it ? > > I wasn't sure that this is true for all architectures, but... It's an requirement for futex support. > > > Indeed it does fail with an Oops on s390 since we enable low address > > > protection in the kernel so we get an exception if something within the > > > kernel writes to the first 512 bytes of the kernel address space. > > > Otherwise it would have silently passed the test... > > > > NULL pointer dereferencing faults on all architectures, at least it > > should, but we explicitely disable pagefaults and recover via the > > extable fixup, which is in S390 as well. That returns -EFAULT and > > signals that there is a working implementation, while those which have > > no support return -ENOSYS, which keeps the robust/pi stuff disabled. > > ...one of our exception table entries has an off-by-one bug. > Never mind, I'll go and fix our own stuff instead ;) Maybe we should do such tests on all exception table protected assembler constructs :) Thanks, tglx