[hrtimer] Enforce resolution as lower limit of intervals

Roman Zippel pointed out that the missing lower limit of intervals
leads to an accounting error in the overrun count. Enforce the lower
limit of intervals to resolution in the timer forwarding code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/hrtimer.h

@@ -122,8 +122,7 @@ static inline int hrtimer_active(const struct hrtimer *timer)
 }
 
 /* Forward a hrtimer so it expires after now: */
-extern unsigned long hrtimer_forward(struct hrtimer *timer,
-				     const ktime_t interval);
+extern unsigned long hrtimer_forward(struct hrtimer *timer, ktime_t interval);
 
 /* Precise sleep: */
 extern long hrtimer_nanosleep(struct timespec *rqtp,

kernel/hrtimer.c

@@ -275,7 +275,7 @@ void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
  * The number of overruns is added to the overrun field.
  */
 unsigned long
-hrtimer_forward(struct hrtimer *timer, const ktime_t interval)
+hrtimer_forward(struct hrtimer *timer, ktime_t interval)
 {
 	unsigned long orun = 1;
 	ktime_t delta, now;
@@ -287,6 +287,9 @@ hrtimer_forward(struct hrtimer *timer, const ktime_t interval)
 	if (delta.tv64 < 0)
 		return 0;
 
+	if (interval.tv64 < timer->base->resolution.tv64)
+		interval.tv64 = timer->base->resolution.tv64;
+
 	if (unlikely(delta.tv64 >= interval.tv64)) {
 		nsec_t incr = ktime_to_ns(interval);