diff options
| author |   Vincent Guittot <vincent.guittot@linaro.org> | 2019-01-30 18:26:02 +0100 |
|---|---|---|
| committer |   Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2019-01-30 22:49:06 +0100 |
| commit | 15efb47dc560849d0c07db96fdad5121f2cf736e (patch) | |
| tree | 1f0e4af0f13875be99b3aadd3457d32a65e1d408 /include | |
| parent | Linux 5.0-rc4 (diff) | |
| download | wireguard-linux-15efb47dc560849d0c07db96fdad5121f2cf736e.tar.xz wireguard-linux-15efb47dc560849d0c07db96fdad5121f2cf736e.zip | |
PM-runtime: Fix deadlock with ktime_get()
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 do that because of seqcount
protection.
Use ktime_get_mono_fast_ns() instead which is lock safe for such
cases.
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 may be slightly suboptimal.
Fixes: 8234f6734c5d ("PM-runtime: Switch autosuspend over to using hrtimers")
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>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/pm_runtime.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h index 54af4eef169f..fed5be706bc9 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) |