From: Vincent Guittot <vincent.guittot@linaro.org>
To: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org,
rjw@rjwysocki.net, ulf.hansson@linaro.org,
biju.das@bp.renesas.com
Cc: geert@linux-m68k.org, linux-renesas-soc@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>
Subject: [PATCH v3] PM-runtime: fix deadlock with ktime
Date: Wed, 30 Jan 2019 18:26:02 +0100 [thread overview]
Message-ID: <1548869162-6223-1-git-send-email-vincent.guittot@linaro.org> (raw)
In-Reply-To: <CAJZ5v0gunbCHp_9mDTmtwW1i-_GcXPcjTP48NdV2zv-B6UrD4g@mail.gmail.com>
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 because of seqcount protection.
Use ktime_get_mono_fast_ns() instead which is lock safe for such case
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 can
be slightly sub optimal.
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>
---
Hi Rafael,
Sorry, I sent the version with the typo mistake that generated the compilation error
reported by kbuild-test-robot
This version doesn't have the typo.
Regards,
Vincent
- v3: fix typo error that appears while updating commit message
- v2: Updated commit message to explain the impact of using
ktime_get_mono_fast_ns()
drivers/base/power/runtime.c | 10 +++++-----
include/linux/pm_runtime.h | 2 +-
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 457be03..0ea2139 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -130,7 +130,7 @@ u64 pm_runtime_autosuspend_expiration(struct device *dev)
{
int autosuspend_delay;
u64 last_busy, expires = 0;
- u64 now = ktime_to_ns(ktime_get());
+ u64 now = ktime_get_mono_fast_ns();
if (!dev->power.use_autosuspend)
goto out;
@@ -909,7 +909,7 @@ static enum hrtimer_restart pm_suspend_timer_fn(struct hrtimer *timer)
* If 'expires' is after the current time, we've been called
* too early.
*/
- if (expires > 0 && expires < ktime_to_ns(ktime_get())) {
+ if (expires > 0 && expires < ktime_get_mono_fast_ns()) {
dev->power.timer_expires = 0;
rpm_suspend(dev, dev->power.timer_autosuspends ?
(RPM_ASYNC | RPM_AUTO) : RPM_ASYNC);
@@ -928,7 +928,7 @@ static enum hrtimer_restart pm_suspend_timer_fn(struct hrtimer *timer)
int pm_schedule_suspend(struct device *dev, unsigned int delay)
{
unsigned long flags;
- ktime_t expires;
+ u64 expires;
int retval;
spin_lock_irqsave(&dev->power.lock, flags);
@@ -945,8 +945,8 @@ int pm_schedule_suspend(struct device *dev, unsigned int delay)
/* Other scheduled or pending requests need to be canceled. */
pm_runtime_cancel_pending(dev);
- expires = ktime_add(ktime_get(), ms_to_ktime(delay));
- dev->power.timer_expires = ktime_to_ns(expires);
+ expires = ktime_get_mono_fast_ns() + (u64)delay * NSEC_PER_MSEC;
+ dev->power.timer_expires = expires;
dev->power.timer_autosuspends = 0;
hrtimer_start(&dev->power.suspend_timer, expires, HRTIMER_MODE_ABS);
diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
index 54af4ee..fed5be7 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)
--
2.7.4
next prev parent reply other threads:[~2019-01-30 17:26 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-30 11:16 [PATCH v2 ] PM-runtime: fix deadlock with ktime Vincent Guittot
2019-01-30 12:14 ` Ulf Hansson
2019-02-05 13:24 ` Geert Uytterhoeven
2019-02-05 13:40 ` Ulf Hansson
2019-01-30 13:06 ` Rafael J. Wysocki
2019-01-30 13:18 ` Vincent Guittot
2019-01-30 19:39 ` Ladislav Michl
2019-01-30 17:26 ` Vincent Guittot [this message]
2019-01-30 21:53 ` [PATCH v3] " Rafael J. Wysocki
2019-02-01 15:02 ` Biju Das
2019-02-01 15:28 ` Vincent Guittot
2019-02-01 15:44 ` Biju Das
2019-02-01 15:48 ` Vincent Guittot
2019-02-01 15:52 ` Vincent Guittot
2019-02-04 9:29 ` Biju Das
2019-02-01 15:45 ` Vincent Guittot
2019-01-30 21:32 ` [PATCH v2 ] " Ladislav Michl
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