From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755039AbdBETbK (ORCPT + 2 others); Sun, 5 Feb 2017 14:31:10 -0500 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:28608 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752624AbdBETbI (ORCPT ); Sun, 5 Feb 2017 14:31:08 -0500 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net Cc: Will Deacon , Peter Zijlstra , Catalin Marinas , Willy Tarreau Subject: [PATCH 3.10 060/319] arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb() Date: Sun, 5 Feb 2017 20:20:47 +0100 Message-Id: <1486322486-8024-31-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1486322486-8024-1-git-send-email-w@1wt.eu> References: <1486322486-8024-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: From: Will Deacon commit 872c63fbf9e153146b07f0cece4da0d70b283eeb upstream. smp_mb__before_spinlock() is intended to upgrade a spin_lock() operation to a full barrier, such that prior stores are ordered with respect to loads and stores occuring inside the critical section. Unfortunately, the core code defines the barrier as smp_wmb(), which is insufficient to provide the required ordering guarantees when used in conjunction with our load-acquire-based spinlock implementation. This patch overrides the arm64 definition of smp_mb__before_spinlock() to map to a full smp_mb(). Cc: Peter Zijlstra Reported-by: Alan Stern Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas Signed-off-by: Willy Tarreau --- arch/arm64/include/asm/spinlock.h | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index 0defa07..c3cab6f 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -200,4 +200,14 @@ static inline int arch_read_trylock(arch_rwlock_t *rw) #define arch_read_relax(lock) cpu_relax() #define arch_write_relax(lock) cpu_relax() +/* + * Accesses appearing in program order before a spin_lock() operation + * can be reordered with accesses inside the critical section, by virtue + * of arch_spin_lock being constructed using acquire semantics. + * + * In cases where this is problematic (e.g. try_to_wake_up), an + * smp_mb__before_spinlock() can restore the required ordering. + */ +#define smp_mb__before_spinlock() smp_mb() + #endif /* __ASM_SPINLOCK_H */ -- 2.8.0.rc2.1.gbe9624a