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authorVincent Guittot <vincent.guittot@linaro.org>2019-01-30 18:26:02 +0100
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2019-01-30 22:49:06 +0100
commit15efb47dc560849d0c07db96fdad5121f2cf736e (patch)
tree1f0e4af0f13875be99b3aadd3457d32a65e1d408 /include
parentf17b5f06cb92ef2250513a1e154c47b78df07d40 (diff)
downloadlwn-15efb47dc560849d0c07db96fdad5121f2cf736e.tar.gz
lwn-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.h2
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)