From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753664AbZAEJLM (ORCPT ); Mon, 5 Jan 2009 04:11:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752062AbZAEJK7 (ORCPT ); Mon, 5 Jan 2009 04:10:59 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:40181 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751643AbZAEJK6 (ORCPT ); Mon, 5 Jan 2009 04:10:58 -0500 Date: Mon, 5 Jan 2009 10:10:34 +0100 From: Ingo Molnar To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, andi@firstfloor.org, snakebyte@gmx.de, akpm@linux-foundation.org, dvhltc@us.ibm.com, niv@us.ibm.com, manfred@colorfullife.com, laijs@cn.fujitsu.com Subject: Re: [PATCH] Fix rcutree grace-period-latency bug on small systems Message-ID: <20090105091034.GA5440@elte.hu> References: <20090105043006.GA22049@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090105043006.GA22049@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul E. McKenney wrote: > Kudos to Andi Kleen for finding a grace-period-latency problem! The > problem was that the special-case code for small machines never updated > the ->signaled field to indicate that grace-period initialization had > completed, which prevented force_quiescent_state() from ever expediting > grace periods. This problem resulted in grace periods extending for more > than 20 seconds. Not subtle. I introduced this bug during my inspection > process when I fixed a race between grace-period initialization and > force_quiescent_state() execution. > > The following patch properly updates the ->signaled field for the > "small"-system case (no more than 32 CPUs for 32-bit kernels and no more > than 64 CPUs for 64-bit kernels). > > I believe that this patch should be included for 2.6.29. > > Located-by: Andi Kleen > Tested-by: Andi Kleen > Signed-off-by: Paul E. McKenney > --- > > rcutree.c | 1 + > 1 file changed, 1 insertion(+) Applied to tip/core/urgent, thanks guys! Ingo