From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757968AbYBPOE5 (ORCPT ); Sat, 16 Feb 2008 09:04:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754354AbYBPOEu (ORCPT ); Sat, 16 Feb 2008 09:04:50 -0500 Received: from mtagate6.de.ibm.com ([195.212.29.155]:22512 "EHLO mtagate6.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754111AbYBPOEt (ORCPT ); Sat, 16 Feb 2008 09:04:49 -0500 Date: Sat, 16 Feb 2008 15:04:44 +0100 From: Heiko Carstens To: Thomas Gleixner 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 Message-ID: <20080216140444.GC4900@osiris.boeblingen.de.ibm.com> References: <200802150149.m1F1n8Gx013909@imap1.linux-foundation.org> <20080216124248.GA4900@osiris.boeblingen.de.ibm.com> <20080216134155.GB4900@osiris.boeblingen.de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 16, 2008 at 02:48:17PM +0100, Thomas Gleixner wrote: > 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. To be more precise: dereferencing alone won't cause an exception for NULL pointers on s390. Only writes will do so. That is very architecture specific since we cannot unmap page 0, it contains per-cpu data -- like exception pointers and all such stuff that the cpu needs. Just in case there is any code that relies on the fact that also reads via a NULL pointer are supposed to failed.