Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 15efb47d authored by Vincent Guittot's avatar Vincent Guittot Committed by Rafael J. Wysocki
Browse files

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: 8234f673 ("PM-runtime: Switch autosuspend over to using hrtimers")
Reported-by: default avatarBiju Das <biju.das@bp.renesas.com>
Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent f17b5f06

drivers/base/power/runtime.c

+5 −5
Original line number Diff line number Diff line
@@ -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);

include/linux/pm_runtime.h

+1 −1
Original line number Diff line number Diff line
@@ -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)