From c155f6499f9797f200aa46eb3ccbf198f4206970 Mon Sep 17 00:00:00 2001 From: Vincent Guittot Date: Mon, 4 Feb 2019 17:25:52 +0100 Subject: [PATCH] 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: a08c2a5a3194 ("PM-runtime: Replace jiffies-based accounting with ktime-based accounting") Reported-by: Biju Das Signed-off-by: Vincent Guittot Reviewed-by: Ulf Hansson [ rjw: Subject, changelog, comment cleanup ] Signed-off-by: Rafael J. Wysocki --- 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 1caa3944898f..6a58bb77a018 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 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__); }