alarmtimers: Add try_to_cancel functionality

There's a number of edge cases when cancelling a alarm, so
to be sure we accurately do so, introduce try_to_cancel, which
returns proper failure errors if it cannot. Also modify cancel
to spin until the alarm is properly disabled.

CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 37 insertions, 6 deletions

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 5b14cc29b6a6..bdb7342b6896 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -336,21 +336,49 @@ void alarm_start(struct alarm *alarm, ktime_t start)
 }
 
 /**
- * alarm_cancel - Tries to cancel an alarm timer
+ * alarm_try_to_cancel - Tries to cancel an alarm timer
  * @alarm: ptr to alarm to be canceled
+ *
+ * Returns 1 if the timer was canceled, 0 if it was not running,
+ * and -1 if the callback was running
  */
-void alarm_cancel(struct alarm *alarm)
+int alarm_try_to_cancel(struct alarm *alarm)
 {
         struct alarm_base *base = &alarm_bases[alarm->type];
         unsigned long flags;
-
+        int ret = -1;
         spin_lock_irqsave(&base->lock, flags);
-        if (alarmtimer_is_queued(alarm))
+
+        if (alarmtimer_callback_running(alarm))
+                goto out;
+
+        if (alarmtimer_is_queued(alarm)) {
                 alarmtimer_remove(base, alarm);
+                ret = 1;
+        } else
+                ret = 0;
+out:
         spin_unlock_irqrestore(&base->lock, flags);
+        return ret;
 }
 
 
+/**
+ * alarm_cancel - Spins trying to cancel an alarm timer until it is done
+ * @alarm: ptr to alarm to be canceled
+ *
+ * Returns 1 if the timer was canceled, 0 if it was not active.
+ */
+int alarm_cancel(struct alarm *alarm)
+{
+        for (;;) {
+                int ret = alarm_try_to_cancel(alarm);
+                if (ret >= 0)
+                        return ret;
+                cpu_relax();
+        }
+}
+
 
 u64 alarm_forward(struct alarm *alarm, ktime_t now, ktime_t interval)
 {
@@ -510,7 +538,9 @@ static int alarm_timer_del(struct k_itimer *timr)
         if (!rtcdev)
                 return -ENOTSUPP;
 
-        alarm_cancel(&timr->it.alarm.alarmtimer);
+        if (alarm_try_to_cancel(&timr->it.alarm.alarmtimer) < 0)
+                return TIMER_RETRY;
+
         return 0;
 }
 
@@ -534,7 +564,8 @@ static int alarm_timer_set(struct k_itimer *timr, int flags,
                 alarm_timer_get(timr, old_setting);
 
         /* If the timer was already set, cancel it */
-        alarm_cancel(&timr->it.alarm.alarmtimer);
+        if (alarm_try_to_cancel(&timr->it.alarm.alarmtimer) < 0)
+                return TIMER_RETRY;
 
         /* start the timer */
         timr->it.alarm.interval = timespec_to_ktime(new_setting->it_interval);