From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754629Ab2G3U4U (ORCPT ); Mon, 30 Jul 2012 16:56:20 -0400 Received: from ogre.sisk.pl ([193.178.161.156]:35312 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754267Ab2G3U4S (ORCPT ); Mon, 30 Jul 2012 16:56:18 -0400 From: "Rafael J. Wysocki" To: NeilBrown Subject: Re: [PATCH] RTC: Avoid races between RTC alarm wakeup and suspend. Date: Mon, 30 Jul 2012 23:01:49 +0200 User-Agent: KMail/1.13.6 (Linux/3.5.0+; KDE/4.6.0; x86_64; ; ) Cc: Alessandro Zummo , rtc-linux@googlegroups.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20120730113547.2c425ea9@notabene.brown> In-Reply-To: <20120730113547.2c425ea9@notabene.brown> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-2" Content-Transfer-Encoding: 7bit Message-Id: <201207302301.49972.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday, July 30, 2012, NeilBrown wrote: > > If an RTC alarm fires just as suspend is happening, it is possible for > suspend to complete and the alarm to be missed. > > To avoid the race, we must register the event with the PM core. > > As the event is made visible to userspace through a thread which is > only scheduled by the interrupt, we need a pm_stay_awake/pm_relax > pair preventing suspend from the interrupt until the thread completes > its work. > > Signed-off-by: NeilBrown > > -- > This makes the pm_wakeup_event() call in cmos_interrupt unnecessary as it > provides suspend protection for all RTCs that use rtc_update_irq. Care to remove the call in cmos_interrupt(), then? > I think the pm_stay_awake//pm_relax is needed - just pm_wakup_event() is > theoretically not sufficient. > > This is because there is no guarantee (that I know of) that the workqueue > thread will actually get scheduled before 'suspend' takes over. I think you are right. Thanks, Rafael > diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c > index eb415bd..9592b93 100644 > --- a/drivers/rtc/interface.c > +++ b/drivers/rtc/interface.c > @@ -582,6 +582,7 @@ enum hrtimer_restart rtc_pie_update_irq(struct hrtimer *timer) > void rtc_update_irq(struct rtc_device *rtc, > unsigned long num, unsigned long events) > { > + pm_stay_awake(rtc->dev.parent); > schedule_work(&rtc->irqwork); > } > EXPORT_SYMBOL_GPL(rtc_update_irq); > @@ -844,6 +845,7 @@ void rtc_timer_do_work(struct work_struct *work) > > mutex_lock(&rtc->ops_lock); > again: > + pm_relax(rtc->dev.parent); > __rtc_read_time(rtc, &tm); > now = rtc_tm_to_ktime(tm); > while ((next = timerqueue_getnext(&rtc->timerqueue))) { >