From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Date: Wed, 15 Aug 2007 19:30:50 -0700 Message-ID: <20070816023050.GC14613@linux.vnet.ibm.com> References: <46C32618.2080108@redhat.com> <20070815234021.GA28775@gondor.apana.org.au> <20070815235125.GT9645@linux.vnet.ibm.com> <0de0c3d833b6f543bd75f74bb17a124b@kernel.crashing.org> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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 To: Segher Boessenkool Return-path: Received: from e6.ny.us.ibm.com ([32.97.182.146]:58469 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937122AbXHPCay (ORCPT ); Wed, 15 Aug 2007 22:30:54 -0400 Content-Disposition: inline In-Reply-To: <0de0c3d833b6f543bd75f74bb17a124b@kernel.crashing.org> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, Aug 16, 2007 at 03:30:44AM +0200, Segher Boessenkool wrote: > >>>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 :-) Yep. And the reason it is a bug is that it fails to disable the relevant compiler optimizations. So I suspect that we might actually be saying the same thing here. Thanx, Paul