From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753228Ab0DAGD5 (ORCPT ); Thu, 1 Apr 2010 02:03:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1936 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752942Ab0DAGDv (ORCPT ); Thu, 1 Apr 2010 02:03:51 -0400 Message-ID: <4BB4381C.8010800@redhat.com> Date: Thu, 01 Apr 2010 14:07:24 +0800 From: Cong Wang User-Agent: Thunderbird 2.0.0.23 (X11/20091001) MIME-Version: 1.0 To: Tejun Heo CC: Oleg Nesterov , linux-kernel@vger.kernel.org, Rusty Russell , akpm@linux-foundation.org, Ingo Molnar Subject: Re: [Patch] workqueue: move lockdep annotations up to destroy_workqueue() References: <20100331105534.5601.50813.sendpatchset@localhost.localdomain> <20100331112559.GA17747@redhat.com> <4BB408AF.4080908@redhat.com> <4BB41988.1030400@kernel.org> <4BB41C72.3090909@redhat.com> <4BB41DAE.3010605@kernel.org> <4BB420D6.7050401@redhat.com> <4BB42822.30607@kernel.org> <4BB42D05.4060207@redhat.com> <4BB437B8.9060802@redhat.com> In-Reply-To: <4BB437B8.9060802@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Cong Wang wrote: > Cong Wang wrote: >> Tejun Heo wrote: >>> Hello, >>> >>> On 04/01/2010 01:28 PM, Cong Wang wrote: >>>>> Hmmm... can you please try to see whether this circular locking >>>>> warning involving wq->lockdep_map is reproducible w/ the bonding >>>>> locking fixed? I still can't see where wq -> cpu_add_remove_lock >>>>> dependency is created. >>>>> >>>> I thought this is obvious. >>>> >>>> Here it is: >>>> >>>> void destroy_workqueue(struct workqueue_struct *wq) >>>> { >>>> const struct cpumask *cpu_map = wq_cpu_map(wq); >>>> int cpu; >>>> >>>> cpu_maps_update_begin(); <----------------- Hold >>>> cpu_add_remove_lock here >>>> spin_lock(&workqueue_lock); >>>> list_del(&wq->list); >>>> spin_unlock(&workqueue_lock); >>>> >>>> for_each_cpu(cpu, cpu_map) >>>> cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, >>>> cpu)); <------ See below >>>> cpu_maps_update_done(); <----------------- Release >>>> cpu_add_remove_lock here >>>> >>>> ... >>>> static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq) >>>> { >>>> /* >>>> * Our caller is either destroy_workqueue() or CPU_POST_DEAD, >>>> * cpu_add_remove_lock protects cwq->thread. >>>> */ >>>> if (cwq->thread == NULL) >>>> return; >>>> >>>> lock_map_acquire(&cwq->wq->lockdep_map); <-------------- >>>> Lockdep >>>> complains here. >>>> lock_map_release(&cwq->wq->lockdep_map); >>>> ... >>> >>> Yeap, the above is cpu_add_remove_lock -> wq->lockdep_map dependency. >>> I can see that but I'm failing to see where the dependency the other >>> direction is created. >>> >> >> Hmm, it looks like I misunderstand lock_map_acquire()? From the >> changelog, >> I thought it was added to complain its caller is holding a lock when >> invoking >> it, thus cpu_add_remove_lock is not an exception. >> > > Oh, I see, wq->lockdep_map is acquired again in run_workqueue(), so I > was wrong. :) > I think you and Oleg are right, the lockdep warning is not irrelevant. > Oops, typo, I meant "is irrelevant." ;)