From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756444Ab2DFLfI (ORCPT ); Fri, 6 Apr 2012 07:35:08 -0400 Received: from terminus.zytor.com ([198.137.202.10]:42375 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752899Ab2DFLfG (ORCPT ); Fri, 6 Apr 2012 07:35:06 -0400 Date: Fri, 6 Apr 2012 04:34:43 -0700 From: tip-bot for Neal Cardwell Message-ID: Cc: linux-kernel@vger.kernel.org, bsegall@google.com, ncardwell@google.com, hpa@zytor.com, mingo@kernel.org, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@kernel.org, hpa@zytor.com, ncardwell@google.com, bsegall@google.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <1332875377-23014-1-git-send-email-ncardwell@google.com> References: <1332875377-23014-1-git-send-email-ncardwell@google.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:timers/urgent] nohz: Fix stale jiffies update in tick_nohz_restart() Git-Commit-ID: 6f103929f8979d2638e58d7f7fda0beefcb8ee7e X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.6 (terminus.zytor.com [127.0.0.1]); Fri, 06 Apr 2012 04:34:53 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 6f103929f8979d2638e58d7f7fda0beefcb8ee7e Gitweb: http://git.kernel.org/tip/6f103929f8979d2638e58d7f7fda0beefcb8ee7e Author: Neal Cardwell AuthorDate: Tue, 27 Mar 2012 15:09:37 -0400 Committer: Thomas Gleixner CommitDate: Fri, 6 Apr 2012 13:24:17 +0200 nohz: Fix stale jiffies update in tick_nohz_restart() Fix tick_nohz_restart() to not use a stale ktime_t "now" value when calling tick_do_update_jiffies64(now). If we reach this point in the loop it means that we crossed a tick boundary since we grabbed the "now" timestamp, so at this point "now" refers to a time in the old jiffy, so using the old value for "now" is incorrect, and is likely to give us a stale jiffies value. In particular, the first time through the loop the tick_do_update_jiffies64(now) call is always a no-op, since the caller, tick_nohz_restart_sched_tick(), will have already called tick_do_update_jiffies64(now) with that "now" value. Note that tick_nohz_stop_sched_tick() already uses the correct approach: when we notice we cross a jiffy boundary, grab a new timestamp with ktime_get(), and *then* update jiffies. Signed-off-by: Neal Cardwell Cc: Ben Segall Cc: Ingo Molnar Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1332875377-23014-1-git-send-email-ncardwell@google.com Signed-off-by: Thomas Gleixner --- kernel/time/tick-sched.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 3526038..6a3a5b9 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -534,9 +534,9 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) hrtimer_get_expires(&ts->sched_timer), 0)) break; } - /* Update jiffies and reread time */ - tick_do_update_jiffies64(now); + /* Reread time and update jiffies */ now = ktime_get(); + tick_do_update_jiffies64(now); } }