From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932819AbXHKTJU (ORCPT ); Sat, 11 Aug 2007 15:09:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763252AbXHKS7j (ORCPT ); Sat, 11 Aug 2007 14:59:39 -0400 Received: from 1wt.eu ([62.212.114.60]:1618 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762390AbXHKS7f (ORCPT ); Sat, 11 Aug 2007 14:59:35 -0400 From: Willy Tarreau Message-Id: <20070811184857.%N@1wt.eu> References: <20070811184752.%N@1wt.eu> User-Agent: quilt/0.46-1 Date: Sat, 11 Aug 2007 21:48:19 +0200 To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: Thomas Gleixner , john stultz , Dave Jones , Ingo Molnar , Vincent Fortier , Chris Wright , Greg Kroah-Hartman Subject: [2.6.20.16 review 27/28] NTP: remove clock_was_set() call to prevent deadlock Content-Disposition: inline; filename=0027-NTP-remove-clock_was_set-call-to-prevent-deadlock.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org The clock_was_set() call in seconds_overflow() which happens only when leap seconds are inserted / deleted is wrong in two aspects: 1. it results in a call to on_each_cpu() with interrupts disabled 2. it is potential deadlock source vs. call_lock in smp_call_function() The only possible side effect of the removal might be, that an absolute CLOCK_REALTIME timer fires 1 second too late, in the rare case of leap second deletion and an absolute CLOCK_REALTIME timer which expires in the affected time frame. It will never fire too early. This was probably observed by the reporter of a June 30th -> July 1st hang: http://lkml.org/lkml/2007/7/3/ A similar problem was observed by Dave Jones, who provided a screen shot with a lockdep back trace, which allowed to analyse the problem. Signed-off-by: Thomas Gleixner Cc: john stultz Cc: Dave Jones Cc: Ingo Molnar Cc: Vincent Fortier Signed-off-by: Chris Wright Signed-off-by: Greg Kroah-Hartman --- kernel/time/ntp.c | 2 -- 1 files changed, 0 insertions(+), 2 deletions(-) diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index 3afeaa3..64744bb 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -116,7 +116,6 @@ void second_overflow(void) */ time_interpolator_update(-NSEC_PER_SEC); time_state = TIME_OOP; - clock_was_set(); printk(KERN_NOTICE "Clock: inserting leap second " "23:59:60 UTC "); } @@ -131,7 +130,6 @@ void second_overflow(void) */ time_interpolator_update(NSEC_PER_SEC); time_state = TIME_WAIT; - clock_was_set(); printk(KERN_NOTICE "Clock: deleting leap second " "23:59:59 UTC "); } -- 1.5.2.4 --