From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B844C282D7 for ; Wed, 30 Jan 2019 21:32:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DEA4218D2 for ; Wed, 30 Jan 2019 21:32:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388178AbfA3Vci (ORCPT ); Wed, 30 Jan 2019 16:32:38 -0500 Received: from eddie.linux-mips.org ([148.251.95.138]:48726 "EHLO cvs.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731978AbfA3Vch (ORCPT ); Wed, 30 Jan 2019 16:32:37 -0500 Received: (from localhost user: 'ladis' uid#1021 fake: STDIN (ladis@eddie.linux-mips.org)) by eddie.linux-mips.org id S23992820AbfA3VcenLVLh (ORCPT + 3 others); Wed, 30 Jan 2019 22:32:34 +0100 Date: Wed, 30 Jan 2019 22:32:33 +0100 From: Ladislav Michl To: "Rafael J. Wysocki" Cc: Vincent Guittot , Linux PM , Linux Kernel Mailing List , Linux ARM , Linux OMAP Mailing List , "Rafael J. Wysocki" , Ulf Hansson , Biju Das , Geert Uytterhoeven , Linux-Renesas Subject: Re: [PATCH v2 ] PM-runtime: fix deadlock with ktime Message-ID: <20190130213233.GA20881@lenoch> References: <1548846984-2044-1-git-send-email-vincent.guittot@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 30, 2019 at 02:06:07PM +0100, Rafael J. Wysocki wrote: > On Wed, Jan 30, 2019 at 12:16 PM Vincent Guittot > wrote: > > > > A deadlock has been seen when swicthing clocksources which use PM runtime. > > The call path is: > > change_clocksource > > ... > > write_seqcount_begin > > ... > > timekeeping_update > > ... > > sh_cmt_clocksource_enable > > ... > > rpm_resume > > pm_runtime_mark_last_busy > > ktime_get > > do > > read_seqcount_begin > > while read_seqcount_retry > > .... > > write_seqcount_end > > > > Although we should be safe because we haven't yet changed the clocksource > > at that time, we can't because of seqcount protection. > > > > Use ktime_get_mono_fast_ns() instead which is lock safe for such case > > > > With ktime_get_mono_fast_ns, the timestamp is not guaranteed to be > > monotonic across an update and as a result can goes backward. According to > > update_fast_timekeeper() description: "In the worst case, this can > > result is a slightly wrong timestamp (a few nanoseconds)". For > > PM runtime autosuspend, this means only that the suspend decision can > > be slightly sub optimal. > > > > Fixes: 8234f6734c5d ("PM-runtime: Switch autosuspend over to using hrtimers") > > Reported-by: Biju Das > > Signed-off-by: Vincent Guittot > > I've queued this one up as a fix for 5.0, but unfortunately it clashes > with the patch from Ladislav Michl at > https://patchwork.kernel.org/patch/10755477/ which has been dropped > now. > > Can you or Ladislav please rebase that patch on top of this one and repost? > > > --- > > > > - v2: Updated commit message to explain the impact of using > > ktime_get_mono_fast_ns() > > > > drivers/base/power/runtime.c | 10 +++++----- > > include/linux/pm_runtime.h | 2 +- > > 2 files changed, 6 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c > > index 457be03..708a13f 100644 > > --- a/drivers/base/power/runtime.c > > +++ b/drivers/base/power/runtime.c > > @@ -130,7 +130,7 @@ u64 pm_runtime_autosuspend_expiration(struct device *dev) > > { > > int autosuspend_delay; > > u64 last_busy, expires = 0; > > - u64 now = ktime_to_ns(ktime_get()); > > + u64 now = ktime_get_mono_fast_ns(); > > > > if (!dev->power.use_autosuspend) > > goto out; > > @@ -909,7 +909,7 @@ static enum hrtimer_restart pm_suspend_timer_fn(struct hrtimer *timer) > > * If 'expires' is after the current time, we've been called > > * too early. > > */ > > - if (expires > 0 && expires < ktime_to_ns(ktime_get())) { > > + if (expires > 0 && expires < ktime_get_mono_fast_ns()) { > > dev->power.timer_expires = 0; > > rpm_suspend(dev, dev->power.timer_autosuspends ? > > (RPM_ASYNC | RPM_AUTO) : RPM_ASYNC); > > @@ -928,7 +928,7 @@ static enum hrtimer_restart pm_suspend_timer_fn(struct hrtimer *timer) > > int pm_schedule_suspend(struct device *dev, unsigned int delay) > > { > > unsigned long flags; > > - ktime_t expires; > > + u64 expires; > > int retval; > > > > spin_lock_irqsave(&dev->power.lock, flags); > > @@ -945,8 +945,8 @@ int pm_schedule_suspend(struct device *dev, unsigned int delay) > > /* Other scheduled or pending requests need to be canceled. */ > > pm_runtime_cancel_pending(dev); > > > > - expires = ktime_add(ktime_get(), ms_to_ktime(delay)); > > - dev->power.timer_expires = ktime_to_ns(expires); > > + expires = ktime_get_mono_fast_ns() + (u64)delay * NSEC_PER_MSEC); Just FYI, this one does not compile ^ I'm going to send updated optimization patch anyway as fixing this one will not break it :) > > + dev->power.timer_expires = expires; > > dev->power.timer_autosuspends = 0; > > hrtimer_start(&dev->power.suspend_timer, expires, HRTIMER_MODE_ABS); > > > > diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h > > index 54af4ee..fed5be7 100644 > > --- a/include/linux/pm_runtime.h > > +++ b/include/linux/pm_runtime.h > > @@ -105,7 +105,7 @@ static inline bool pm_runtime_callbacks_present(struct device *dev) > > > > static inline void pm_runtime_mark_last_busy(struct device *dev) > > { > > - WRITE_ONCE(dev->power.last_busy, ktime_to_ns(ktime_get())); > > + WRITE_ONCE(dev->power.last_busy, ktime_get_mono_fast_ns()); > > } > > > > static inline bool pm_runtime_is_irq_safe(struct device *dev) > > -- > > 2.7.4 > >