From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752649AbaLDALv (ORCPT ); Wed, 3 Dec 2014 19:11:51 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:37826 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752332AbaLDALs (ORCPT ); Wed, 3 Dec 2014 19:11:48 -0500 Date: Wed, 3 Dec 2014 16:11:42 -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 6/9] arm64/spinlock: Replace ACCESS_ONCE READ_ONCE Message-ID: <20141204001142.GC25340@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1417645821-54731-1-git-send-email-borntraeger@de.ibm.com> <1417645821-54731-7-git-send-email-borntraeger@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1417645821-54731-7-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: 14120400-0017-0000-0000-000006CBF87E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 03, 2014 at 11:30:18PM +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 spinlock code to replace ACCESS_ONCE with READ_ONCE. > > Signed-off-by: Christian Borntraeger Acked-by: Paul E. McKenney > --- > arch/arm64/include/asm/spinlock.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h > index c45b7b1..cee1287 100644 > --- a/arch/arm64/include/asm/spinlock.h > +++ b/arch/arm64/include/asm/spinlock.h > @@ -99,12 +99,12 @@ static inline int arch_spin_value_unlocked(arch_spinlock_t lock) > > static inline int arch_spin_is_locked(arch_spinlock_t *lock) > { > - return !arch_spin_value_unlocked(ACCESS_ONCE(*lock)); > + return !arch_spin_value_unlocked(READ_ONCE(*lock)); > } > > static inline int arch_spin_is_contended(arch_spinlock_t *lock) > { > - arch_spinlock_t lockval = ACCESS_ONCE(*lock); > + arch_spinlock_t lockval = READ_ONCE(*lock); > return (lockval.next - lockval.owner) > 1; > } > #define arch_spin_is_contended arch_spin_is_contended > -- > 1.9.3 >