On Tue, 5 Feb 2019 at 09:10, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Mon, 4 Feb 2019 at 17:25, Vincent Guittot <vincent.guittot@xxxxxxxxxx> wrote:
> >
> > 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 <biju.das@xxxxxxxxxxxxxx>
> > Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
>
> Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Thanks
>
> Kind regards
> Uffe
>
>
> > ---
> > 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__);
> > }
> > --
> > 2.7.4
> >
