From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755186AbaC3X4S (ORCPT ); Sun, 30 Mar 2014 19:56:18 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:37332 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754600AbaC3Xn0 (ORCPT ); Sun, 30 Mar 2014 19:43:26 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Mark Rutland" , "Will Deacon" , "Russell King" Date: Mon, 31 Mar 2014 00:23:35 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 099/200] ARM: 7955/1: spinlock: ensure we have a compiler barrier before sev In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.56-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Will Deacon commit 7c8746a9eb287642deaad0e7c2cdf482dce5e4be upstream. When unlocking a spinlock, we require the following, strictly ordered sequence of events: /* dmb */ /* dsb */ Whilst the code does indeed reflect this in terms of the architecture, the final + have been contracted into a single inline asm without a "memory" clobber, therefore the compiler is at liberty to reorder the unlock to the end of the above sequence. In such a case, a waiting CPU may be woken up before the lock has been unlocked, leading to extremely poor performance. This patch reworks the dsb_sev() function to make use of the dsb() macro and ensure ordering against the unlock. Reported-by: Mark Rutland Signed-off-by: Will Deacon Signed-off-by: Russell King [bwh: Backported to 3.2: 'ishst' variant is not used here] Signed-off-by: Ben Hutchings --- arch/arm/include/asm/spinlock.h | 15 +++------------ 1 file changed, 3 insertions(+), 12 deletions(-) --- a/arch/arm/include/asm/spinlock.h +++ b/arch/arm/include/asm/spinlock.h @@ -44,18 +44,9 @@ static inline void dsb_sev(void) { -#if __LINUX_ARM_ARCH__ >= 7 - __asm__ __volatile__ ( - "dsb\n" - SEV - ); -#else - __asm__ __volatile__ ( - "mcr p15, 0, %0, c7, c10, 4\n" - SEV - : : "r" (0) - ); -#endif + + dsb(); + __asm__(SEV); } /*