Re: [PATCH 3/3] PM / Sleep: Make __pm_stay_awake() delete wakeup source timers

Rafael J. Wysocki
2012-02-16T22:16:55Z

On Thursday, February 16, 2012, Arve Hjønnevåg wrote:
> 2012/2/15 Rafael J. Wysocki <rjw@sisk.pl>:
> ...
> > --- linux.orig/drivers/base/power/wakeup.c
> > +++ linux/drivers/base/power/wakeup.c
> > @@ -365,9 +365,15 @@ void __pm_stay_awake(struct wakeup_sourc
> > return;
> >
> > spin_lock_irqsave(&ws->lock, flags);
> > +
> > + del_timer(&ws->timer);
> > + ws->timer_expires = 0;
>
> timer_expires gets overwritten in wakeup_source_activate,

I actually don't remember why it does that and with the $subject changes
it's just pointless.

> so __pm_relax followed by __pm_stay_awake is still not safe.

Yes, I overlooked that timer_expires modification. Updated patch follows.

> ...
> > @@ -529,8 +535,12 @@ void __pm_wakeup_event(struct wakeup_sou
> > spin_lock_irqsave(&ws->lock, flags);
> >
> > ws->event_count++;
> > - if (!ws->active)
> > + if (ws->active) {
> > + if (!ws->timer_expires)
> > + goto unlock;
> > + } else {
> > wakeup_source_activate(ws);
> > + }
> >
> > if (!msec) {
> > wakeup_source_deactivate(ws);
> >
>
> I suggest dropping this and adding:

Well, what exactly would you like to drop? The above proposed changes I guess?

> - if (time_after(expires, ws->timer_expires)) {
> + if (!ws->timer_expires || time_after(expires, ws->timer_expires)) {

I've tried to follow your suggestion, so that __pm_wakeup_event() always
sets the timer, if msec is positive, or deactivates the wakeup source, if
msec is 0. Please let me know if that's what you wanted. :-)

Thanks,
Rafael

---
From: Rafael J. Wysocki <rjw@sisk.pl>
Subject: PM / Sleep: Make __pm_stay_awake() delete wakeup source timers

If __pm_stay_awake() is called after __pm_wakeup_event() for the same
wakep source object before its timer expires, it won't cancel the
timer, so the wakeup source will be deactivated from the timer
function as scheduled by __pm_wakeup_event(). In that case
__pm_stay_awake() doesn't have any effect beyond incrementing
the wakeup source's event_count field, although it should cancel
the timer and make the wakeup source stay active until __pm_relax()
is called for it.

To fix this problem make __pm_stay_awake() delete the wakeup source's
timer and ensure that it won't be deactivated from the timer funtion
afterwards by clearing its timer_expires field.

Reported-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
drivers/base/power/wakeup.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux/drivers/base/power/wakeup.c
===================================================================
--- linux.orig/drivers/base/power/wakeup.c
+++ linux/drivers/base/power/wakeup.c
@@ -344,7 +344,6 @@ static void wakeup_source_activate(struc
{
ws->active = true;
ws->active_count++;
- ws->timer_expires = jiffies;
ws->last_time = ktime_get();

/* Increment the counter of events in progress. */
@@ -365,9 +364,14 @@ void __pm_stay_awake(struct wakeup_sourc
return;

spin_lock_irqsave(&ws->lock, flags);
+
ws->event_count++;
if (!ws->active)
wakeup_source_activate(ws);
+
+ del_timer(&ws->timer);
+ ws->timer_expires = 0;
+
spin_unlock_irqrestore(&ws->lock, flags);
}
EXPORT_SYMBOL_GPL(__pm_stay_awake);
@@ -541,7 +545,7 @@ void __pm_wakeup_event(struct wakeup_sou
if (!expires)
expires = 1;

- if (time_after(expires, ws->timer_expires)) {
+ if (!ws->timer_expires || time_after(expires, ws->timer_expires)) {
mod_timer(&ws->timer, expires);
ws->timer_expires = expires;
}