From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753661AbaKXNDv (ORCPT ); Mon, 24 Nov 2014 08:03:51 -0500 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:43720 "EHLO e06smtp16.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753516AbaKXNDl (ORCPT ); Mon, 24 Nov 2014 08:03:41 -0500 From: Christian Borntraeger To: linux-kernel@vger.kernel.org Cc: "linux-arch@vger.kernel.org, linux-mips@linux-mips.org, linux-x86_64@vger.kernel.org, linux-s390"@vger.kernel.org, Paolo Bonzini , paulmck@linux.vnet.ibm.com, mingo@kernel.org, torvalds@linux-foundation.org, Catalin Marinas , Will Deacon , Christian Borntraeger Subject: [PATCH/RFC 6/7] arm64: Replace ACCESS_ONCE for spinlock code with barriers Date: Mon, 24 Nov 2014 14:03:29 +0100 Message-Id: <1416834210-61738-7-git-send-email-borntraeger@de.ibm.com> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1416834210-61738-1-git-send-email-borntraeger@de.ibm.com> References: <1416834210-61738-1-git-send-email-borntraeger@de.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14112413-0025-0000-0000-0000028BFFF8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 access the lock with a barrier. Signed-off-by: Christian Borntraeger --- arch/arm64/include/asm/spinlock.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index c45b7b1..f72dc64 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -99,12 +99,15 @@ 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)); + arch_spinlock_t lockval = *lock; + barrier(); + return !arch_spin_value_unlocked(lockval); } static inline int arch_spin_is_contended(arch_spinlock_t *lock) { - arch_spinlock_t lockval = ACCESS_ONCE(*lock); + arch_spinlock_t lockval = *lock; + barrier(); return (lockval.next - lockval.owner) > 1; } #define arch_spin_is_contended arch_spin_is_contended -- 1.9.3