From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941241AbXGaEjx (ORCPT ); Tue, 31 Jul 2007 00:39:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S940749AbXGaEct (ORCPT ); Tue, 31 Jul 2007 00:32:49 -0400 Received: from canuck.infradead.org ([209.217.80.40]:34731 "EHLO canuck.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S940631AbXGaEcr (ORCPT ); Tue, 31 Jul 2007 00:32:47 -0400 Date: Mon, 30 Jul 2007 21:33:48 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org, torvalds@osdl.org Cc: Justin Forbes , Zwane Mwaikambo , "Theodore Ts'o" , Randy Dunlap , Dave Jones , Chuck Wolber , Chris Wedgwood , Michael Krufky , Chuck Ebbert , Domenico Andreoli , torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, akpm@osdl.org, johnstul@us.ibm.com, mingo@elte.hu, Vincent.Fortier1@EC.GC.CA, Thomas Gleixner , Chris Wright , Greg Kroah-Hartman Subject: [patch 23/26] NTP: remove clock_was_set() call to prevent deadlock Message-ID: <20070731043348.GX3975@kroah.com> References: <20070731042108.546594256@blue.kroah.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline; filename="ntp-remove-clock_was_set-call-to-prevent-deadlock.patch" In-Reply-To: <20070731043047.GA3975@kroah.com> User-Agent: Mutt/1.5.15 (2007-04-06) X-Bad-Reply: References and In-Reply-To but no 'Re:' in Subject. Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org -stable review patch. If anyone has any objections, please let us know. ------------------ 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 file changed, 2 deletions(-) --- linux-2.6.21.6.orig/kernel/time/ntp.c +++ linux-2.6.21.6/kernel/time/ntp.c @@ -120,7 +120,6 @@ 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"); } @@ -135,7 +134,6 @@ 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"); } --