[PATCH 2/3] PM / Sleep: Fix race conditions related to wakeup source timer function

Rafael J. Wysocki
2012-02-15T22:20:43Z

From: Rafael J. Wysocki <rjw@sisk.pl>

If __pm_wakeup_event() has been used (with a nonzero timeout) to
report a wakeup event and then __pm_relax() immediately followed by
__pm_stay_awake() is called or __pm_wakeup_event() is called once
again for the same wakeup source object before its timer expires, the
timer function pm_wakeup_timer_fn() may still be run as a result of
the previous __pm_wakeup_event() call. In either of those cases it
may mistakenly deactivate the wakeup source that has just been
activated.

To prevent that from happening, make wakeup_source_deactivate()
clear the wakeup source's timer_expires field and make
pm_wakeup_timer_fn() check if timer_expires is different from zero
and if it's not in future before calling wakeup_source_deactivate()
(if timer_expires is 0, it means that the timer has just been
deleted and if timer_expires is in future, it means that the timer
has just been rescheduled to a different time).

Reported-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
drivers/base/power/wakeup.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

Index: linux/drivers/base/power/wakeup.c
===================================================================
--- linux.orig/drivers/base/power/wakeup.c
+++ linux/drivers/base/power/wakeup.c
@@ -433,6 +433,7 @@ static void wakeup_source_deactivate(str
ws->max_time = duration;

del_timer(&ws->timer);
+ ws->timer_expires = 0;

/*
* Increment the counter of registered wakeup events and decrement the
@@ -487,11 +488,22 @@ EXPORT_SYMBOL_GPL(pm_relax);
* pm_wakeup_timer_fn - Delayed finalization of a wakeup event.
* @data: Address of the wakeup source object associated with the event source.
*
- * Call __pm_relax() for the wakeup source whose address is stored in @data.
+ * Call wakeup_source_deactivate() for the wakeup source whose address is stored
+ * in @data if it is currently active and its timer has not been canceled and
+ * the expiration time of the timer is not in future.
*/
static void pm_wakeup_timer_fn(unsigned long data)
{
- __pm_relax((struct wakeup_source *)data);
+ struct wakeup_source *ws = (struct wakeup_source *)data;
+ unsigned long flags;
+
+ spin_lock_irqsave(&ws->lock, flags);
+
+ if (ws->active && ws->timer_expires
+ && time_after_eq(jiffies, ws->timer_expires))
+ wakeup_source_deactivate(ws);
+
+ spin_unlock_irqrestore(&ws->lock, flags);
}

/**