From patchwork Tue Jul 31 02:51:04 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 1256931 Return-Path: X-Original-To: patchwork-linux-pm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id A5D1ADF24C for ; Tue, 31 Jul 2012 02:51:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754123Ab2GaCvZ (ORCPT ); Mon, 30 Jul 2012 22:51:25 -0400 Received: from cantor2.suse.de ([195.135.220.15]:53754 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751847Ab2GaCvY (ORCPT ); Mon, 30 Jul 2012 22:51:24 -0400 Received: from relay1.suse.de (unknown [195.135.220.254]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx2.suse.de (Postfix) with ESMTP id B2F61A3421; Tue, 31 Jul 2012 04:51:20 +0200 (CEST) Date: Tue, 31 Jul 2012 12:51:04 +1000 From: NeilBrown To: "Rafael J. Wysocki" Cc: Alessandro Zummo , rtc-linux@googlegroups.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Paul Fox Subject: Re: [PATCH] RTC: Avoid races between RTC alarm wakeup and suspend. Message-ID: <20120731125104.7a07f251@notabene.brown> In-Reply-To: <201207302301.49972.rjw@sisk.pl> References: <20120730113547.2c425ea9@notabene.brown> <201207302301.49972.rjw@sisk.pl> X-Mailer: Claws Mail 3.7.10 (GTK+ 2.24.7; x86_64-suse-linux-gnu) Mime-Version: 1.0 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Mon, 30 Jul 2012 23:01:49 +0200 "Rafael J. Wysocki" wrote: > 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. Here is the revised patch. NeilBrown ========== Subject: [PATCH] RTC: Avoid races between RTC alarm wakeup and suspend. 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. This makes the pm_wakeup_event() call in cmos_interrupt unnecessary as it provides suspend protection for all RTCs that use rtc_update_irq. Cc: Paul Fox Signed-off-by: NeilBrown 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))) { diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c index 132333d..4267789 100644 --- a/drivers/rtc/rtc-cmos.c +++ b/drivers/rtc/rtc-cmos.c @@ -568,7 +568,6 @@ static irqreturn_t cmos_interrupt(int irq, void *p) hpet_mask_rtc_irq_bit(RTC_AIE); CMOS_READ(RTC_INTR_FLAGS); - pm_wakeup_event(cmos_rtc.dev, 0); } spin_unlock(&rtc_lock);