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[209.132.180.67]) by mx.google.com with ESMTP id a26si1132372pgl.282.2019.01.30.03.16.35; Wed, 30 Jan 2019 03:16:36 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=fdbWLO+0; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730654AbfA3LQe (ORCPT + 31 others); Wed, 30 Jan 2019 06:16:34 -0500 Received: from mail-wm1-f67.google.com ([209.85.128.67]:55571 "EHLO mail-wm1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730060AbfA3LQd (ORCPT ); Wed, 30 Jan 2019 06:16:33 -0500 Received: by mail-wm1-f67.google.com with SMTP id y139so21022919wmc.5 for ; Wed, 30 Jan 2019 03:16:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id; bh=ynD/SKO0NKYF/TZnALi5yaZz+mi8VJz9rkAXrSOgxSg=; b=fdbWLO+0W3s4gxf54oKHr34BvQZE1DTRv1+2imPUtVYqpY5T1J/RczVnUNU8ZucjA/ dkxKQTvDiQ0gKZh7ri4Py9/BqT5Wtceyq9u9lrC6mQl39TVPqaybKqbovIHmD3bhVE17 WwiHuRbEuXfbY4iZ+uLxwqNJfwCOd4UsQKCbA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=ynD/SKO0NKYF/TZnALi5yaZz+mi8VJz9rkAXrSOgxSg=; b=o6H9uXoXfCtY2ozjB7O7g/P/Vbvrt4VwWeR1XTADB6v9IFA8359rHGpyc/OGPZW5CT V+cfrEXBnWwbCpYyk0AMPPGaCiehM7dWobKHlpuBI2Dw5iNxAZMHnOUEuoa6gjtkNBgE clknPb6a6drDLkrXNDPeBj9kYqq0l3G69qKzLWRvdHfZnliha+v8uqDELjjppTYssL1j 1iKcQ5kTTiwRkMSQlIeDrl2npRs/vrEkECFsGOsKdPdcOpQ40QuH2ZTju9k7diV81lO+ DAiv2kTYHpZI3EkZrxYftXLbeKuQIJHAUSC66pE9am68GjvfOYLpfgzX+JeHhu7TPh6b cEfg== X-Gm-Message-State: AJcUukd435jMbCavz940nQxIXjl/tmpf33dh8oRIyyA6MQIXyfEQa/HM rRs6Ogqj/bxnnZjwBsBre8f1TA== X-Received: by 2002:a1c:3282:: with SMTP id y124mr25933459wmy.134.1548846991495; Wed, 30 Jan 2019 03:16:31 -0800 (PST) Received: from localhost.localdomain ([2a01:e0a:f:6020:79e5:6689:e4d2:d212]) by smtp.gmail.com with ESMTPSA id p10sm4502173wmd.14.2019.01.30.03.16.30 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 30 Jan 2019 03:16:30 -0800 (PST) From: Vincent Guittot To: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org, rjw@rjwysocki.net, ulf.hansson@linaro.org, biju.das@bp.renesas.com Cc: geert@linux-m68k.org, linux-renesas-soc@vger.kernel.org, Vincent Guittot Subject: [PATCH v2 ] PM-runtime: fix deadlock with ktime Date: Wed, 30 Jan 2019 12:16:24 +0100 Message-Id: <1548846984-2044-1-git-send-email-vincent.guittot@linaro.org> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- - 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(-) -- 2.7.4 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)