From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760393Ab3B1PQM (ORCPT ); Thu, 28 Feb 2013 10:16:12 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:42052 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756760Ab3B1Or1 (ORCPT ); Thu, 28 Feb 2013 09:47:27 -0500 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Joonsoo Kim , Russell King , Luis Henriques Subject: [PATCH 040/139] ARM: 7643/1: sched: correct update_sched_clock() Date: Thu, 28 Feb 2013 14:43:10 +0000 Message-Id: <1362062689-2567-41-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1362062689-2567-1-git-send-email-luis.henriques@canonical.com> References: <1362062689-2567-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.5.7.7 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Joonsoo Kim commit 7c4e9ced424be4d36df6a3e3825763e97ee97607 upstream. If we want load epoch_cyc and epoch_ns atomically, we should update epoch_cyc_copy first of all. This notify reader that updating is in progress. If we update epoch_cyc first like as current implementation, there is subtle error case. Look at the below example. cyc = 9 ns = 900 cyc_copy = 9 == CASE 1 == write cyc = 10 read cyc = 10 read ns = 900 write ns = 1000 write cyc_copy = 10 read cyc_copy = 10 output = (10, 900) == CASE 2 == read cyc = 9 write cyc = 10 write ns = 1000 read ns = 1000 read cyc_copy = 9 write cyc_copy = 10 output = (9, 1000) If atomic read is ensured, output should be (9, 900) or (10, 1000). But, output in example case are not. So, change updating sequence in order to correct this problem. Signed-off-by: Joonsoo Kim Signed-off-by: Russell King Signed-off-by: Luis Henriques --- arch/arm/kernel/sched_clock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm/kernel/sched_clock.c b/arch/arm/kernel/sched_clock.c index 27d186a..6bbf936 100644 --- a/arch/arm/kernel/sched_clock.c +++ b/arch/arm/kernel/sched_clock.c @@ -84,11 +84,11 @@ static void notrace update_sched_clock(void) * detectable in cyc_to_fixed_sched_clock(). */ raw_local_irq_save(flags); - cd.epoch_cyc = cyc; + cd.epoch_cyc_copy = cyc; smp_wmb(); cd.epoch_ns = ns; smp_wmb(); - cd.epoch_cyc_copy = cyc; + cd.epoch_cyc = cyc; raw_local_irq_restore(flags); } -- 1.8.1.2