From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760648AbXGCTmS (ORCPT ); Tue, 3 Jul 2007 15:42:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756428AbXGCTmF (ORCPT ); Tue, 3 Jul 2007 15:42:05 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:57195 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757221AbXGCTmD (ORCPT ); Tue, 3 Jul 2007 15:42:03 -0400 Date: Tue, 3 Jul 2007 21:41:06 +0200 From: Ingo Molnar To: Thomas Gleixner Cc: Linus Torvalds , LKML , Dave Jones , Andrew Morton , john stultz , Stable Team , "Fortier,Vincent [Montreal]" Subject: Re: [PATCH] NTP: remove clock_was_set() call to prevent deadlock Message-ID: <20070703194106.GA493@elte.hu> References: <1183485920.3291.28.camel@chaos> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1183485920.3291.28.camel@chaos> User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7 -1.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Thomas Gleixner wrote: > 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 looks good to me. Acked-by: Ingo Molnar Ingo