Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932731AbXHPBdJ (ORCPT ); Wed, 15 Aug 2007 21:33:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752959AbXHPBcx (ORCPT ); Wed, 15 Aug 2007 21:32:53 -0400 Received: from gate.crashing.org ([63.228.1.57]:38087 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751712AbXHPBcw (ORCPT ); Wed, 15 Aug 2007 21:32:52 -0400 In-Reply-To: <20070815235125.GT9645@linux.vnet.ibm.com> References: <46C32618.2080108@redhat.com> <20070815234021.GA28775@gondor.apana.org.au> <20070815235125.GT9645@linux.vnet.ibm.com> Mime-Version: 1.0 (Apple Message framework v623) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: <0de0c3d833b6f543bd75f74bb17a124b@kernel.crashing.org> Content-Transfer-Encoding: 7bit Cc: heiko.carstens@de.ibm.com, horms@verge.net.au, linux-kernel@vger.kernel.org, rpjday@mindspring.com, ak@suse.de, netdev@vger.kernel.org, cfriesen@nortel.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, jesper.juhl@gmail.com, linux-arch@vger.kernel.org, zlynx@acm.org, satyam@infradead.org, clameter@sgi.com, schwidefsky@de.ibm.com, Chris Snook , Herbert Xu , davem@davemloft.net, wensong@linux-vs.org, wjiang@resilience.com From: Segher Boessenkool Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Date: Thu, 16 Aug 2007 03:30:44 +0200 To: paulmck@linux.vnet.ibm.com X-Mailer: Apple Mail (2.623) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 961 Lines: 26 >>> Part of the motivation here is to fix heisenbugs. If I knew where >>> they >> >> By the same token we should probably disable optimisations >> altogether since that too can create heisenbugs. > > Precisely the point -- use of volatile (whether in casts or on asms) > in these cases are intended to disable those optimizations likely to > result in heisenbugs. The only thing volatile on an asm does is create a side effect on the asm statement; in effect, it tells the compiler "do not remove this asm even if you don't need any of its outputs". It's not disabling optimisation likely to result in bugs, heisen- or otherwise; _not_ putting the volatile on an asm that needs it simply _is_ a bug :-) Segher - 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/