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Mon, 04 Feb 2019 08:25:58 -0800 (PST) Received: from localhost.localdomain ([2a01:e0a:f:6020:70b6:b9c6:89e2:36a]) by smtp.gmail.com with ESMTPSA id a4sm1251992wrt.37.2019.02.04.08.25.57 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 04 Feb 2019 08:25:57 -0800 (PST) From: Vincent Guittot To: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, rjw@rjwysocki.net, ulf.hansson@linaro.org, biju.das@bp.renesas.com Subject: [PATCH 1/2] PM-runtime: move runtime accounting on ktime_get_mono_fast_ns() Date: Mon, 4 Feb 2019 17:25:52 +0100 Message-Id: <1549297553-17647-2-git-send-email-vincent.guittot@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1549297553-17647-1-git-send-email-vincent.guittot@linaro.org> References: <1549297553-17647-1-git-send-email-vincent.guittot@linaro.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190204_082600_236772_4DD0F786 X-CRM114-Status: GOOD ( 14.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-renesas-soc@vger.kernel.org, Vincent Guittot , geert@linux-m68k.org, thara.gopinath@linaro.org, linux-arm-kernel@lists.infradead.org MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Similarly to what happened whith autosuspend, a deadlock has been raised with runtime accounting in the sequence: change_clocksource ... write_seqcount_begin ... timekeeping_update ... sh_cmt_clocksource_enable ... rpm_resume update_pm_runtime_accounting ktime_get do read_seqcount_begin while read_seqcount_retry .... write_seqcount_end Move runtime accounting on ktime_get_mono_fast_ns() With ktime_get_mono_fast_ns, the timestamp is not guaranteed to be monotonic across an update of timekeeping and as a result time can goes backward. Add a test to skip accounting for such situation which should stay exceptional. Fixes: a08c2a5a3194 ("PM-runtime: Replace jiffies-based accounting with ktime-based accounting") Reported-by: Biju Das Signed-off-by: Vincent Guittot Reviewed-by: Ulf Hansson --- drivers/base/power/runtime.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c index 1caa394..50740da 100644 --- a/drivers/base/power/runtime.c +++ b/drivers/base/power/runtime.c @@ -66,13 +66,22 @@ static int rpm_suspend(struct device *dev, int rpmflags); */ void update_pm_runtime_accounting(struct device *dev) { - u64 now = ktime_to_ns(ktime_get()); + u64 now = ktime_get_mono_fast_ns(); + u64 last = dev->power.accounting_timestamp; u64 delta; - delta = now - dev->power.accounting_timestamp; - dev->power.accounting_timestamp = now; + /* + * Because ktime_get_mono_fast_ns() is not monotonic during + * timekeeping update, we must ensure that now is after the last saved + * timesptamp + */ + if (now < last) + return; + + delta = now - last; + if (dev->power.disable_depth > 0) return; @@ -1312,7 +1321,7 @@ void pm_runtime_enable(struct device *dev) /* About to enable runtime pm, set accounting_timestamp to now */ if (!dev->power.disable_depth) - dev->power.accounting_timestamp = ktime_to_ns(ktime_get()); + dev->power.accounting_timestamp = ktime_get_mono_fast_ns(); } else { dev_warn(dev, "Unbalanced %s!\n", __func__); }