Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756791AbYGHKYn (ORCPT ); Tue, 8 Jul 2008 06:24:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753855AbYGHKYg (ORCPT ); Tue, 8 Jul 2008 06:24:36 -0400 Received: from ns1.suse.de ([195.135.220.2]:32938 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753783AbYGHKYf (ORCPT ); Tue, 8 Jul 2008 06:24:35 -0400 From: Andreas Schwab To: Johannes Weiner Cc: Rusty Russell , Mike Travis , linux-kernel@vger.kernel.org, "H. Anvin" , Christoph Lameter , Ingo Molnar Subject: Re: Dangerous code in cpumask_of_cpu? References: <200807081816.40623.rusty@rustcorp.com.au> <87myksn587.fsf@saeurebad.de> X-Yow: I'm also pre-POURED pre-MEDITATED and pre-RAPHAELITE!! Date: Tue, 08 Jul 2008 12:24:22 +0200 In-Reply-To: <87myksn587.fsf@saeurebad.de> (Johannes Weiner's message of "Tue, 08 Jul 2008 10:35:20 +0200") Message-ID: User-Agent: Gnus/5.110009 (No Gnus v0.9) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1684 Lines: 50 Johannes Weiner writes: > Hi, > > Rusty Russell writes: > >> Hi Christoph/Mike, >> >> Looked at cpumask_of_cpu as introduced in >> 9f0e8d0400d925c3acd5f4e01dbeb736e4011882 (x86: convert cpumask_of_cpu macro >> to allocated array), and I don't think it's safe: >> >> #define cpumask_of_cpu(cpu) \ >> (*({ \ >> typeof(_unused_cpumask_arg_) m; \ >> if (sizeof(m) == sizeof(unsigned long)) { \ >> m.bits[0] = 1UL<<(cpu); \ >> } else { \ >> cpus_clear(m); \ >> cpu_set((cpu), m); \ >> } \ >> &m; \ >> })) >> >> Referring to &m once out of scope is invalid, and I can't find any evidence >> that it's legal here. In particular, the change >> b53e921ba1cff8453dc9a87a84052fa12d5b30bd (generic: reduce stack pressure in >> sched_affinity) which passes &m to other functions seems highly risky. >> >> I'm surprised this hasn't already hit us, but perhaps gcc isn't as clever as >> it could be? > > You don't refer to &m outside scope. Look at the character below the > first e of #define :) The scope of m ends with the outmost braces, and the dereference is done outside of it. Andreas. -- Andreas Schwab, SuSE Labs, schwab@suse.de SuSE Linux Products GmbH, Maxfeldstra?e 5, 90409 N?rnberg, Germany PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different." -- 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/