From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753854AbaKXNFz (ORCPT ); Mon, 24 Nov 2014 08:05:55 -0500 Received: from e06smtp15.uk.ibm.com ([195.75.94.111]:47224 "EHLO e06smtp15.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753525AbaKXNDl (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 3/7] x86: Rework ACCESS_ONCE for spinlock code Date: Mon, 24 Nov 2014 14:03:26 +0100 Message-Id: <1416834210-61738-4-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: 14112413-0021-0000-0000-000001E3D229 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 union members with ACCESS_ONCE to avoid this problem. Signed-off-by: Christian Borntraeger --- arch/x86/include/asm/spinlock.h | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index 9295016..168eb59 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -8,6 +8,7 @@ #include #include #include +#include /* * Your basic SMP spinlocks, allowing only a single CPU anywhere @@ -105,7 +106,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock) { arch_spinlock_t old, new; - old.tickets = ACCESS_ONCE(lock->tickets); + old.head_tail = ACCESS_ONCE(lock->head_tail); if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG)) return 0; @@ -162,16 +163,19 @@ 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); + arch_spinlock_t tmp = {}; - return tmp.tail != tmp.head; + tmp.head_tail =ACCESS_ONCE(lock->head_tail); + return tmp.tickets.tail != tmp.tickets.head; } static inline int arch_spin_is_contended(arch_spinlock_t *lock) { - struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets); + arch_spinlock_t tmp = {}; + + tmp.head_tail = ACCESS_ONCE(lock->head_tail); + return (__ticket_t)(tmp.tickets.tail - tmp.tickets.head) > TICKET_LOCK_INC; - return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC; } #define arch_spin_is_contended arch_spin_is_contended -- 1.9.3