alarmtimers: Change alarmtimer functions to return alarmtimer_restart values

In order to properly fix the denial of service issue with high freq
periodic alarm timers, we need to push the re-arming logic into the
alarm timer handler, much as the hrtimer code does.

This patch introduces alarmtimer_restart enum and changes the
alarmtimer handler declarations to use it as a return value. Further,
to ease following changes, it extends the alarmtimer handler functions
to also take the time at expiration. No logic is yet modified.

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

include/linux/alarmtimer.h

@@ -13,6 +13,11 @@ enum alarmtimer_type {
 	ALARM_NUMTYPE,
 };
 
+enum alarmtimer_restart {
+	ALARMTIMER_NORESTART,
+	ALARMTIMER_RESTART,
+};
+
 /**
  * struct alarm - Alarm timer structure
  * @node:	timerqueue node for adding to the event list this value
@@ -26,14 +31,14 @@ enum alarmtimer_type {
 struct alarm {
 	struct timerqueue_node	node;
 	ktime_t			period;
-	void			(*function)(struct alarm *);
+	enum alarmtimer_restart	(*function)(struct alarm *, ktime_t now);
 	enum alarmtimer_type	type;
 	bool			enabled;
 	void			*data;
 };
 
 void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
-		void (*function)(struct alarm *));
+		enum alarmtimer_restart (*function)(struct alarm *, ktime_t));
 void alarm_start(struct alarm *alarm, ktime_t start, ktime_t period);
 void alarm_cancel(struct alarm *alarm);
 

kernel/time/alarmtimer.c

@@ -196,7 +196,7 @@ static enum hrtimer_restart alarmtimer_fired(struct hrtimer *timer)
 		}
 		spin_unlock_irqrestore(&base->lock, flags);
 		if (alarm->function)
-			alarm->function(alarm);
+			alarm->function(alarm, now);
 		spin_lock_irqsave(&base->lock, flags);
 	}
 
@@ -299,7 +299,7 @@ static void alarmtimer_freezerset(ktime_t absexp, enum alarmtimer_type type)
  * @function: callback that is run when the alarm fires
  */
 void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
-		void (*function)(struct alarm *))
+		enum alarmtimer_restart (*function)(struct alarm *, ktime_t))
 {
 	timerqueue_init(&alarm->node);
 	alarm->period = ktime_set(0, 0);
@@ -365,12 +365,15 @@ static enum alarmtimer_type clock2alarm(clockid_t clockid)
  *
  * Posix timer callback for expired alarm timers.
  */
-static void alarm_handle_timer(struct alarm *alarm)
+static enum alarmtimer_restart alarm_handle_timer(struct alarm *alarm,
+							ktime_t now)
 {
 	struct k_itimer *ptr = container_of(alarm, struct k_itimer,
 						it.alarmtimer);
 	if (posix_timer_event(ptr, 0) != 0)
 		ptr->it_overrun++;
+
+	return ALARMTIMER_NORESTART;
 }
 
 /**
@@ -509,13 +512,15 @@ static int alarm_timer_set(struct k_itimer *timr, int flags,
  *
  * Wakes up the task that set the alarmtimer
  */
-static void alarmtimer_nsleep_wakeup(struct alarm *alarm)
+static enum alarmtimer_restart alarmtimer_nsleep_wakeup(struct alarm *alarm,
+								ktime_t now)
 {
 	struct task_struct *task = (struct task_struct *)alarm->data;
 
 	alarm->data = NULL;
 	if (task)
 		wake_up_process(task);
+	return ALARMTIMER_NORESTART;
 }
 
 /**