From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752704AbaLDAMJ (ORCPT ); Wed, 3 Dec 2014 19:12:09 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:50895 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751896AbaLDAMH (ORCPT ); Wed, 3 Dec 2014 19:12:07 -0500 Date: Wed, 3 Dec 2014 16:12:02 -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 7/9] arm/spinlock: Replace ACCESS_ONCE with READ_ONCE Message-ID: <20141204001202.GD25340@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1417645821-54731-1-git-send-email-borntraeger@de.ibm.com> <1417645821-54731-8-git-send-email-borntraeger@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1417645821-54731-8-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: 14120400-0021-0000-0000-000006A31DD7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 03, 2014 at 11:30:19PM +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/arm/include/asm/spinlock.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h > index ac4bfae..0fa4184 100644 > --- a/arch/arm/include/asm/spinlock.h > +++ b/arch/arm/include/asm/spinlock.h > @@ -120,12 +120,12 @@ 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) > { > - struct __raw_tickets tickets = ACCESS_ONCE(lock->tickets); > + struct __raw_tickets tickets = READ_ONCE(lock->tickets); > return (tickets.next - tickets.owner) > 1; > } > #define arch_spin_is_contended arch_spin_is_contended > -- > 1.9.3 >