Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761274AbXHQFlt (ORCPT ); Fri, 17 Aug 2007 01:41:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756928AbXHQFlj (ORCPT ); Fri, 17 Aug 2007 01:41:39 -0400 Received: from ozlabs.org ([203.10.76.45]:56066 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756898AbXHQFlh (ORCPT ); Fri, 17 Aug 2007 01:41:37 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18117.13576.93583.222760@cargo.ozlabs.ibm.com> Date: Fri, 17 Aug 2007 15:41:28 +1000 From: Paul Mackerras To: Herbert Xu Cc: Stefan Richter , Satyam Sharma , Christoph Lameter , "Paul E. McKenney" , Chris Snook , Linux Kernel Mailing List , linux-arch@vger.kernel.org, Linus Torvalds , netdev@vger.kernel.org, Andrew Morton , ak@suse.de, heiko.carstens@de.ibm.com, davem@davemloft.net, schwidefsky@de.ibm.com, wensong@linux-vs.org, horms@verge.net.au, wjiang@resilience.com, cfriesen@nortel.com, zlynx@acm.org, rpjday@mindspring.com, jesper.juhl@gmail.com, segher@kernel.crashing.org Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures In-Reply-To: <20070817053200.GA15457@gondor.apana.org.au> References: <18115.45316.702491.681906@cargo.ozlabs.ibm.com> <18115.52863.638655.658466@cargo.ozlabs.ibm.com> <20070816053945.GB32442@gondor.apana.org.au> <18115.62741.807704.969977@cargo.ozlabs.ibm.com> <20070816070907.GA964@gondor.apana.org.au> <46C40587.7050708@s5r6.in-berlin.de> <20070816081049.GA1431@gondor.apana.org.au> <18117.11685.431347.996767@cargo.ozlabs.ibm.com> <20070817053200.GA15457@gondor.apana.org.au> X-Mailer: VM 7.19 under Emacs 21.4.1 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1082 Lines: 31 Herbert Xu writes: > On Fri, Aug 17, 2007 at 03:09:57PM +1000, Paul Mackerras wrote: > > Herbert Xu writes: > > > > > Can you find an actual atomic_read code snippet there that is > > > broken without the volatile modifier? > > > > There are some in arch-specific code, for example line 1073 of > > arch/mips/kernel/smtc.c. On mips, cpu_relax() is just barrier(), so > > the empty loop body is ok provided that atomic_read actually does the > > load each time around the loop. > > A barrier() is all you need to force the compiler to reread > the value. > > The people advocating volatile in this thread are talking > about code that doesn't use barrier()/cpu_relax(). Did you look at it? Here it is: /* Someone else is initializing in parallel - let 'em finish */ while (atomic_read(&idle_hook_initialized) < 1000) ; Paul. - 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/