Commit c155f649 authored Feb 04, 2019 by Vincent Guittot Committed by Rafael J. Wysocki Feb 05, 2019

PM-runtime: Switch accounting over to ktime_get_mono_fast_ns()



Similar to what happened whith autosuspend, a deadlock has been
reported with PM-runtime accounting in the call path:

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

Make PM-runtime accounting use ktime_get_mono_fast_ns() to avoid this
problem.

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 go
backward. Add a test to skip accounting for such situation which should
stay exceptional.

Fixes: a08c2a5a ("PM-runtime: Replace jiffies-based accounting with ktime-based accounting")
Reported-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
[ rjw: Subject, changelog, comment cleanup ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

parent f800ea32

drivers/base/power/runtime.c

+13 −4

Original line number	Diff line number	Diff line
		@@ -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 updates, 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__);
		}

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