From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755209AbZBNVRX (ORCPT ); Sat, 14 Feb 2009 16:17:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754627AbZBNVOo (ORCPT ); Sat, 14 Feb 2009 16:14:44 -0500 Received: from casper.infradead.org ([85.118.1.10]:46193 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754606AbZBNVOl (ORCPT ); Sat, 14 Feb 2009 16:14:41 -0500 Subject: Re: [PATCH 1.5/2] generic-smp: fix initial quiesent count. From: Peter Zijlstra To: Linus Torvalds Cc: Nick Piggin , Jens Axboe , "Paul E. McKenney" , Ingo Molnar , Rusty Russell , linux-kernel@vger.kernel.org, Oleg Nesterov In-Reply-To: <1234622792.4698.31.camel@laptop> References: <20090212223200.979433820@chello.nl> <20090212223750.295581470@chello.nl> <1234622474.4698.25.camel@laptop> <1234622792.4698.31.camel@laptop> Content-Type: text/plain Date: Sat, 14 Feb 2009 22:14:16 +0100 Message-Id: <1234646056.4695.10.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.25.90 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2009-02-14 at 15:46 +0100, Peter Zijlstra wrote: > first compile, then send out... > > --- > Subject: generic-smp: fix initial quiesent count. > From: Peter Zijlstra > Date: Sat Feb 14 15:36:07 CET 2009 > > If we start with a quiesent sequence count of 0, we'll match the initial stamp > values of the cfd_data, and never make any progress. > > To avoid getting stuck in this situation, start out with an increased quiesent > sequence count. OK, so this is not going to fix the problem in generic. Its still possible to end up with the original issue. We'd need a callback list to free used entries, much like regular RCU, this quiesent sequence count's wrapping just seems too brittle.