| Message ID | 1548846984-2044-1-git-send-email-vincent.guittot@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] PM-runtime: fix deadlock with ktime | expand |
On Wed, Jan 30, 2019 at 02:06:07PM +0100, Rafael J. Wysocki wrote: > On Wed, Jan 30, 2019 at 12:16 PM Vincent Guittot > <vincent.guittot@linaro.org> wrote: > > > > 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> > > I've queued this one up as a fix for 5.0, but unfortunately it clashes > with the patch from Ladislav Michl at > https://patchwork.kernel.org/patch/10755477/ which has been dropped > now. > > Can you or Ladislav please rebase that patch on top of this one and repost? > > > --- > > > > - 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..708a13f 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); Just FYI, this one does not compile ^ I'm going to send updated optimization patch anyway as fixing this one will not break it :) > > + 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 > >
diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c index 457be03..708a13f 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)
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> --- - 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(-) -- 2.7.4