From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755475Ab2DTHSL (ORCPT ); Fri, 20 Apr 2012 03:18:11 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:45707 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752557Ab2DTHSJ (ORCPT ); Fri, 20 Apr 2012 03:18:09 -0400 Date: Fri, 20 Apr 2012 15:18:00 +0800 From: Yong Zhang To: Stephen Boyd Cc: linux-kernel@vger.kernel.org, Tejun Heo , netdev@vger.kernel.org, Ben Dooks Subject: Re: [PATCH 1/2] workqueue: Catch more locking problems with flush_work() Message-ID: <20120420071759.GA17846@zhy> Reply-To: Yong Zhang References: <1334805958-29119-1-git-send-email-sboyd@codeaurora.org> <20120419081002.GB3963@zhy> <4F905B30.4080501@codeaurora.org> <20120420052633.GA16219@zhy> <20120420060101.GA16563@zhy> <4F9101A7.5010100@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <4F9101A7.5010100@codeaurora.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 19, 2012 at 11:26:47PM -0700, Stephen Boyd wrote: > complain in the case where the work is not queued. That case is not a > false positive. We will get a lockdep warning if the work is running IIRC, flush_work() is just a nop when a work is not queued nor running. > (when start_flush_work() returns true) solely with the > lock_map_acquire() on cwq->wq->lockdep_map. Yeah, that is the point we use lockdep to detect deadlock for workqueue. But when looking at start_flush_work(), for some case !(cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER), lock_map_acquire_read() is called, but recursive read is not added to the chain list. So when lock_map_acquire_read(&cwq->wq->lockdep_map) is called, deadlock will not be detected. I hope you don't hit that special case. Thanks, Yong