From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758731Ab1IKBf4 (ORCPT ); Sat, 10 Sep 2011 21:35:56 -0400 Received: from mail-pz0-f42.google.com ([209.85.210.42]:51667 "EHLO mail-pz0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755036Ab1IKBfz (ORCPT ); Sat, 10 Sep 2011 21:35:55 -0400 Date: Sun, 11 Sep 2011 10:35:49 +0900 From: Tejun Heo To: Thomas Tuttle Cc: lkml Subject: Re: [PATCH v2] workqueue: lock cwq access in drain_workqueue Message-ID: <20110911013549.GI29319@htj.dyndns.org> References: <20110909152222.GA14705@google.com> <20110909230053.GA28394@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110909230053.GA28394@google.com> 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 Hello, On Fri, Sep 09, 2011 at 07:00:53PM -0400, Thomas Tuttle wrote: > Take cwq->gcwq->lock to avoid racing between drain_workqueue checking > to make sure the workqueues are empty and cwq_dec_nr_in_flight > decrementing and then incrementing nr_active when it activates a > delayed work. Nice catch. Just few minor nits below. > We discovered this when a corner case in one of our drivers resulted in > us trying to destroy a workqueue in which the remaining work would > always requeue itself again in the same workqueue. We would hit this > race condition and trip the BUG_ON on workqueue.c:3080. > > Signed-off-by: Thomas Tuttle > --- > Updated to use bool instead of int (d'oh), and CCed maintainer. > > kernel/workqueue.c | 8 +++++++- > 1 files changed, 7 insertions(+), 1 deletions(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 25fb1b0..0c2e585 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -2412,8 +2412,14 @@ reflush: > > for_each_cwq_cpu(cpu, wq) { > struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); > + bool cwq_flushed; Maybe "drained" would be better? > - if (!cwq->nr_active && list_empty(&cwq->delayed_works)) > + spin_lock_irq(&cwq->gcwq->lock); > + cwq_flushed = !cwq->nr_active > + && list_empty(&cwq->delayed_works); and then this should fit inside 80 column, right? Thanks. -- tejun