From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266717AbUGUUfS (ORCPT ); Wed, 21 Jul 2004 16:35:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266721AbUGUUfS (ORCPT ); Wed, 21 Jul 2004 16:35:18 -0400 Received: from dbl.q-ag.de ([213.172.117.3]:930 "EHLO dbl.q-ag.de") by vger.kernel.org with ESMTP id S266717AbUGUUfD (ORCPT ); Wed, 21 Jul 2004 16:35:03 -0400 Message-ID: <40FED38D.7050401@colorfullife.com> Date: Wed, 21 Jul 2004 22:35:25 +0200 From: Manfred Spraul User-Agent: Mozilla/5.0 (X11; U; Linux i686; fr-FR; rv:1.6) Gecko/20040510 X-Accept-Language: en-us, en MIME-Version: 1.0 To: paulmck@us.ibm.com CC: Manfred Spraul , linux-kernel@vger.kernel.org, lse-tech@lists.sourceforge.net Subject: Re: [Lse-tech] [RFC, PATCH] 5/5 rcu lock update: Hierarchical rcu_cpu_mask bitmap References: <200405250535.i4P5ZO7I017623@dbl.q-ag.de> <20040716233803.GA1293@us.ibm.com> In-Reply-To: <20040716233803.GA1293@us.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Paul E. McKenney wrote: >I don't understand how the following helps, given that the CPU being >offlined is supposed to be completely dead by the time we get here. >Can't see anything that it really hurts other than a bit of delay in >an extremely infrequent operation, but... > > > >>+ spin_unlock_wait(&rcu_state.mutex); >> cpu_quiet(cpu, 1); >> >> I was concerned about a race of cpu_quiet for the dead cpu (last cpu in a group) with a concurrent cpu_quiet for another cpu in another cpu group. A stale bit in either rcu_state.outstanding or rcu_groups[].outstanding would lock up the rcu subsystem. I've thought about it again and I agree with you - there is no race. I agree with most of your other points - the patch is a proof of concept, it definitively needs a big cleanup before is should be considered for merging [+ a system that needs it] -- Manfred