From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751445Ab0CAPnh (ORCPT ); Mon, 1 Mar 2010 10:43:37 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36026 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751020Ab0CAPng (ORCPT ); Mon, 1 Mar 2010 10:43:36 -0500 Date: Mon, 1 Mar 2010 16:41:44 +0100 From: Oleg Nesterov To: Tejun Heo Cc: torvalds@linux-foundation.org, mingo@elte.hu, peterz@infradead.org, awalls@radix.net, linux-kernel@vger.kernel.org, jeff@garzik.org, akpm@linux-foundation.org, jens.axboe@oracle.com, rusty@rustcorp.com.au, cl@linux-foundation.org, dhowells@redhat.com, arjan@linux.intel.com, avi@redhat.com, johannes@sipsolutions.net, andi@firstfloor.org Subject: Re: [PATCH 10/43] stop_machine: reimplement without using workqueue Message-ID: <20100301154144.GB11090@redhat.com> References: <1267187000-18791-1-git-send-email-tj@kernel.org> <1267187000-18791-11-git-send-email-tj@kernel.org> <20100228143405.GA13236@redhat.com> <4B8BD934.4050908@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B8BD934.4050908@kernel.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/02, Tejun Heo wrote: > > Hello, again. > > On 02/28/2010 11:34 PM, Oleg Nesterov wrote: > > On 02/26, Tejun Heo wrote: > >> > >> @@ -164,19 +259,18 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) > >> idle.fn = chill; > >> idle.data = NULL; > >> > >> + smp_wmb(); /* -> stop_cpu()::set_current_state() */ > >> ... > >> + for_each_online_cpu(i) > >> + wake_up_process(*per_cpu_ptr(stop_machine_threads, i)); > > > > Afaics, this smp_wmb() is not needed, wake_up_process() (try_to_wake_up) > > should ensure we can't race with set_current_state() + check_condition. > > It does, note the wmb() in try_to_wake_up(). > > Yeap, the initial version was like that and it was awkward to explain > in the comment in stop_cpu() so I basically put it there as a > documentation anchor. OK, > Do you think removing it would be better? No, I just wanted to understand what I have missed. This applies to all my questions in this thread ;) Thanks, Oleg.