From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932196AbWHVMgn (ORCPT ); Tue, 22 Aug 2006 08:36:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932209AbWHVMgn (ORCPT ); Tue, 22 Aug 2006 08:36:43 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:25250 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S932196AbWHVMgn (ORCPT ); Tue, 22 Aug 2006 08:36:43 -0400 Subject: Re: Lockdep message on workqueue_mutex From: Arjan van de Ven To: Heiko Carstens Cc: Andrew Morton , Greg KH , Dave Jones , linux-kernel@vger.kernel.org In-Reply-To: <20060822121042.GA29577@osiris.boeblingen.de.ibm.com> References: <20060822121042.GA29577@osiris.boeblingen.de.ibm.com> Content-Type: text/plain Organization: Intel International BV Date: Tue, 22 Aug 2006 14:36:32 +0200 Message-Id: <1156250192.2976.47.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2006-08-22 at 14:10 +0200, Heiko Carstens wrote: > git commit 9b41ea7289a589993d3daabc61f999b4147872c4 causes the lockdep > message below on cpu hotplug (git kernel of today). > > We have: > > cpu_down (takes cpu_add_remove_lock) > [CPU_DOWN_PREPARE] > blocking_notifier_call_chain (takes (cpu_chain).rwsem) > workqueue_cpu_callback (takes workqueue_mutex) > blocking_notifier_call_chain (releases (cpu_chain).rwsem) > [CPU_DEAD] > blocking_notifier_call_chain (takes (cpu_chain).rwsem) > ^^^^^^^^^^^^^^^^^^^^^^^ > -> reverse locking order, since we still hold workqueue_mutex. > > But since all of this is protected by the cpu_add_remove_lock this looks > legal. Well, at least it's safe as long as no other cpu callback function > does anything that will take the workqueue_mutex as well. so you're saying this locking is entirely redundant ? ;-)