Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756269AbXHIRya (ORCPT ); Thu, 9 Aug 2007 13:54:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751073AbXHIRyU (ORCPT ); Thu, 9 Aug 2007 13:54:20 -0400 Received: from mtagate7.de.ibm.com ([195.212.29.156]:52953 "EHLO mtagate7.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750920AbXHIRyS (ORCPT ); Thu, 9 Aug 2007 13:54:18 -0400 Subject: Re: [PATCH] make atomic_t volatile on all architectures From: Martin Schwidefsky Reply-To: schwidefsky@de.ibm.com To: Chuck Ebbert Cc: Chris Snook , Linus Torvalds , akpm@linux-foundation.org, ak@suse.de, heiko.carstens@de.ibm.com, davem@davemloft.net, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, wensong@linux-vs.org, horms@verge.net.au, wjiang@resilience.com, cfriesen@nortel.com, zlynx@acm.org In-Reply-To: <46BB508B.7050601@redhat.com> References: <20070808230733.GA17270@shell.boston.redhat.com> <46BAC2BE.1090106@redhat.com> <46BB508B.7050601@redhat.com> Content-Type: text/plain Organization: IBM Corporation Date: Thu, 09 Aug 2007 19:57:55 +0200 Message-Id: <1186682275.9669.12.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.10.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 883 Lines: 33 On Thu, 2007-08-09 at 13:36 -0400, Chuck Ebbert wrote: > > Fair enough. Casting to (volatile int *) will give us the behavior > > people expect when using atomic_t without needing to use inefficient > > barriers. > > > > You can use this forget() macro to make the compiler reread a > variable: > > #define forget(var) asm volatile ("" : "=m"(var)) You need to specify a "m"(var) input constraint as well. Without it the compiler might remove the initialization of var. E.g. void fn(void) { int var = 0; forget(var); /* now var can have any value. */ } -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. - 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/