From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760375AbXGCSFb (ORCPT ); Tue, 3 Jul 2007 14:05:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755802AbXGCSFY (ORCPT ); Tue, 3 Jul 2007 14:05:24 -0400 Received: from www.osadl.org ([213.239.205.134]:54289 "EHLO mail.tglx.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754659AbXGCSFX (ORCPT ); Tue, 3 Jul 2007 14:05:23 -0400 Subject: [PATCH] NTP: remove clock_was_set() call to prevent deadlock From: Thomas Gleixner To: Linus Torvalds Cc: LKML , Dave Jones , Andrew Morton , john stultz , Ingo Molnar , Stable Team , "Fortier,Vincent [Montreal]" Content-Type: text/plain Date: Tue, 03 Jul 2007 20:05:20 +0200 Message-Id: <1183485920.3291.28.camel@chaos> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 (2.10.1-4.fc7) Content-Transfer-Encoding: 7bit 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 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -122,7 +122,6 @@ 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\n"); } @@ -137,7 +136,6 @@ 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\n"); }