From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754982AbaKYMmT (ORCPT ); Tue, 25 Nov 2014 07:42:19 -0500 Received: from e06smtp15.uk.ibm.com ([195.75.94.111]:50549 "EHLO e06smtp15.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754198AbaKYMir (ORCPT ); Tue, 25 Nov 2014 07:38:47 -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 , Alexei Starovoitov , David Howells , Russell King , Christian Borntraeger Subject: [PATCHv2 04/10] x86/spinlock: Replace ACCESS_ONCE with READ_ONCE/ASSIGN_ONCE Date: Tue, 25 Nov 2014 13:38:31 +0100 Message-Id: <1416919117-50652-5-git-send-email-borntraeger@de.ibm.com> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1416919117-50652-1-git-send-email-borntraeger@de.ibm.com> References: <1416919117-50652-1-git-send-email-borntraeger@de.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14112512-0021-0000-0000-000001E7A922 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 replace ACCESS_ONCE with READ_ONCE and ASSIGN_ONCE. Signed-off-by: Christian Borntraeger --- arch/x86/include/asm/spinlock.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index 9295016..af6e673 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -92,7 +92,7 @@ static __always_inline void arch_spin_lock(arch_spinlock_t *lock) unsigned count = SPIN_THRESHOLD; do { - if (ACCESS_ONCE(lock->tickets.head) == inc.tail) + if (ASSIGN_ONCE(inc.tail, lock->tickets.head)) goto out; cpu_relax(); } while (--count); @@ -105,7 +105,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock) { arch_spinlock_t old, new; - old.tickets = ACCESS_ONCE(lock->tickets); + old.tickets = READ_ONCE(lock->tickets); if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG)) return 0; @@ -162,14 +162,14 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock) static inline int arch_spin_is_locked(arch_spinlock_t *lock) { - struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets); + struct __raw_tickets tmp = READ_ONCE(lock->tickets); return tmp.tail != tmp.head; } static inline int arch_spin_is_contended(arch_spinlock_t *lock) { - struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets); + struct __raw_tickets tmp = READ_ONCE(lock->tickets); return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC; } -- 1.9.3