From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753928Ab2DSIKh (ORCPT ); Thu, 19 Apr 2012 04:10:37 -0400 Received: from mail-qc0-f174.google.com ([209.85.216.174]:35380 "EHLO mail-qc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752475Ab2DSIKQ (ORCPT ); Thu, 19 Apr 2012 04:10:16 -0400 Date: Thu, 19 Apr 2012 16:10:02 +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: <20120419081002.GB3963@zhy> Reply-To: Yong Zhang References: <1334805958-29119-1-git-send-email-sboyd@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1334805958-29119-1-git-send-email-sboyd@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 Wed, Apr 18, 2012 at 08:25:57PM -0700, Stephen Boyd wrote: > If a workqueue is flushed but the work item is not scheduled to > run, lockdep checking will be circumvented. For example: > > static DEFINE_MUTEX(mutex); > > static void my_work(struct work_struct *w) > { > mutex_lock(&mutex); > mutex_unlock(&mutex); > } > > static DECLARE_WORK(work, my_work); > > static int __init start_test_module(void) > { > schedule_work(&work); > return 0; > } > module_init(start_test_module); > > static void __exit stop_test_module(void) > { > mutex_lock(&mutex); > flush_work(&work); > mutex_unlock(&mutex); > } > module_exit(stop_test_module); > > would only print a warning if the work item was actively running > when flush_work() was called. Otherwise flush_work() returns > early. In this trivial example nothing could go wrong, but if the > work item is schedule via an interrupt we could potentially have a > scenario where the work item is running just at the time flush_work() You mean flush_work() could be called in interupt? I don't it is possible. > is called. This could become a classic AB-BA locking problem. I don't see how the deadlock happen, could you please be more specific? Thanks, Yong > > Add a lockdep hint in flush_work() in the "work not running" case > so that we always catch this potential deadlock scenario. > > Signed-off-by: Stephen Boyd > --- > kernel/workqueue.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 66ec08d..eb800df 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -2513,8 +2513,11 @@ bool flush_work(struct work_struct *work) > wait_for_completion(&barr.done); > destroy_work_on_stack(&barr.work); > return true; > - } else > + } else { > + lock_map_acquire(&work->lockdep_map); > + lock_map_release(&work->lockdep_map); > return false; > + } > } > EXPORT_SYMBOL_GPL(flush_work); > > -- > Sent by an employee of the Qualcomm Innovation Center, Inc. > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Only stand for myself