From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752572AbaLDAK5 (ORCPT ); Wed, 3 Dec 2014 19:10:57 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:37545 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751430AbaLDAK4 (ORCPT ); Wed, 3 Dec 2014 19:10:56 -0500 Date: Wed, 3 Dec 2014 16:10:51 -0800 From: "Paul E. McKenney" To: Christian Borntraeger Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, torvalds@linux-foundation.org Subject: Re: [PATCH 4/9] x86/gup: Replace ACCESS_ONCE with READ_ONCE Message-ID: <20141204001051.GA25340@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1417645821-54731-1-git-send-email-borntraeger@de.ibm.com> <1417645821-54731-5-git-send-email-borntraeger@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1417645821-54731-5-git-send-email-borntraeger@de.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14120400-0017-0000-0000-000006CBF797 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 03, 2014 at 11:30:16PM +0100, Christian Borntraeger wrote: > ACCESS_ONCE does not work reliably on non-scalar types. For > example gcc 4.6 and 4.7 might remove the volatile tag for such > accesses during the SRA (scalar replacement of aggregates) step > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) > > Change the gup code to replace ACCESS_ONCE with READ_ONCE. > > Signed-off-by: Christian Borntraeger Acked-by: Paul E. McKenney > --- > arch/x86/mm/gup.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c > index 207d9aef..d754782 100644 > --- a/arch/x86/mm/gup.c > +++ b/arch/x86/mm/gup.c > @@ -15,7 +15,7 @@ > static inline pte_t gup_get_pte(pte_t *ptep) > { > #ifndef CONFIG_X86_PAE > - return ACCESS_ONCE(*ptep); > + return READ_ONCE(*ptep); > #else > /* > * With get_user_pages_fast, we walk down the pagetables without taking > -- > 1.9.3 >