From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757456Ab3HMQnV (ORCPT ); Tue, 13 Aug 2013 12:43:21 -0400 Received: from mail-gh0-f179.google.com ([209.85.160.179]:50556 "EHLO mail-gh0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756774Ab3HMQnT (ORCPT ); Tue, 13 Aug 2013 12:43:19 -0400 Date: Tue, 13 Aug 2013 12:43:15 -0400 From: Tejun Heo To: Stephen Boyd Cc: "Rafael J. Wysocki" , linux-kernel@vger.kernel.org Subject: Re: [PATCH] PM / QoS: Fix workqueue deadlock when using pm_qos_update_request_timeout() Message-ID: <20130813164315.GB32719@htj.dyndns.org> References: <1375992837-1673-1-git-send-email-sboyd@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1375992837-1673-1-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 Hello, Stephen. On Thu, Aug 08, 2013 at 01:13:57PM -0700, Stephen Boyd wrote: > pm_qos_update_request_timeout() updates a qos and then schedules > a delayed work item to bring the qos back down to the default > after the timeout. When the work item runs, pm_qos_work_fn() will > call pm_qos_update_request() and deadlock because it tries to > cancel itself via cancel_delayed_work_sync(). Future callers of > that qos will also hang waiting to cancel the work that is > canceling itself. Before ed1ac6e (PM: don't use > [delayed_]work_pending(), 2013-01-11) this didn't happen because > the work function wouldn't try to cancel itself. I see. That must have been racy tho. If the work item execution races someone else queuing the work item, the same deadlock could happen, right? > Let's just do the little bit of pm_qos_update_request() here so > that we don't deadlock. > > Cc: Tejun Heo > Signed-off-by: Stephen Boyd > --- > kernel/power/qos.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/kernel/power/qos.c b/kernel/power/qos.c > index 06fe285..d52d314 100644 > --- a/kernel/power/qos.c > +++ b/kernel/power/qos.c > @@ -308,7 +308,11 @@ static void pm_qos_work_fn(struct work_struct *work) > struct pm_qos_request, > work); > > - pm_qos_update_request(req, PM_QOS_DEFAULT_VALUE); > + if (PM_QOS_DEFAULT_VALUE != req->node.prio) > + pm_qos_update_target( > + pm_qos_array[req->pm_qos_class]->constraints, > + &req->node, PM_QOS_UPDATE_REQ, > + PM_QOS_DEFAULT_VALUE); Maybe it'd be cleaner to add a param or internal variant of pm_qos_update_request()? Thanks. -- tejun