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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS 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 23251C282D7 for ; Wed, 30 Jan 2019 13:06:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E850C2084A for ; Wed, 30 Jan 2019 13:06:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548853586; bh=lG3iBNnE9kMDwCgxZmiVlgf8X6un2FKcxIOuyu5Zdbw=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=onNuL1olpQgnlb78iV8bS/D1y0opYe9MteyRwAQoUdraSxOoNQk280pBvRLjUNEvn bzbIolzzGjn3aTEssPXbLOD4ZAnSv4QCCo0qTe4rDJ2l7/7Vo0h0xw2NkPpUpl9iYH sIp+NQXJNfxscfERD9g58kvhJujmLH6bK3D+7Tz0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730980AbfA3NGU (ORCPT ); Wed, 30 Jan 2019 08:06:20 -0500 Received: from mail-ot1-f68.google.com ([209.85.210.68]:44638 "EHLO mail-ot1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730907AbfA3NGU (ORCPT ); Wed, 30 Jan 2019 08:06:20 -0500 Received: by mail-ot1-f68.google.com with SMTP id g16so17012274otg.11; Wed, 30 Jan 2019 05:06:19 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=L/xB8+fKGsHNHqt+qw739geAKACge/qKuZW9F1aYPGU=; b=HS63VeKg69LtxjRvwLMVZpTM126QaSLPRfWwv4oHoQLAV2squ+R7f1CYHjQZ5JBce9 zQ3+Bv2b27+Og5OUZNKYkANqQO2NG/LuZ+4DEt+RqkAp0o9mlZlPBtz9RDMct1I2eFk3 bdK1Hqt/Wt9Cpk6JlcDzpXtdg4Xv3q3hTdIMDGpcAZ8OOFg6cC/FE8yYmbrA0bF3T88B 1vhlE7yaljuWFaX6CSBsoboIvR7etjXTOA1J7RX9E57n3ueZxA3pZalj365gxPuagloo wHaoemIR6+3SgkO1hxop5jeuQETbiTOhBnpo6YAy3irTHozYPuBmiKR09CbrYg6BrhkA SDpA== X-Gm-Message-State: AJcUukdzosQ2ZOETGnV3V+V01pDyV/hKnj6RCi60Vz6N+JlM9TJYsSng WkJjaiZ36l8YCSOryLffstMGEQDpK9NwyAK+fGY= X-Google-Smtp-Source: ALg8bN6Ty+Fh1ghF2ukWnelA6x0UzMZrPDCzhSDkSe54qYG+eYjZ+xTo79yOyzGKpEBSvadJ2z5deMxrHbIxP9Bb3wQ= X-Received: by 2002:a9d:63c1:: with SMTP id e1mr21471175otl.119.1548853579044; Wed, 30 Jan 2019 05:06:19 -0800 (PST) MIME-Version: 1.0 References: <1548846984-2044-1-git-send-email-vincent.guittot@linaro.org> In-Reply-To: <1548846984-2044-1-git-send-email-vincent.guittot@linaro.org> From: "Rafael J. Wysocki" Date: Wed, 30 Jan 2019 14:06:07 +0100 Message-ID: Subject: Re: [PATCH v2 ] PM-runtime: fix deadlock with ktime To: Vincent Guittot Cc: Linux PM , Linux Kernel Mailing List , Linux ARM , Linux OMAP Mailing List , "Rafael J. Wysocki" , Ulf Hansson , Biju Das , Geert Uytterhoeven , Linux-Renesas , Ladislav Michl Content-Type: text/plain; charset="UTF-8" Sender: linux-renesas-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org 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); > + 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 >