1 files changed, 38 insertions, 7 deletions

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index fbb1f85327bf..af0b8bae4502 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -929,8 +929,11 @@ static struct timer_base *lock_timer_base(struct timer_list *timer,
 	}
 }
 
+#define MOD_TIMER_PENDING_ONLY		0x01
+#define MOD_TIMER_REDUCE		0x02
+
 static inline int
-__mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
+__mod_timer(struct timer_list *timer, unsigned long expires, unsigned int options)
 {
 	struct timer_base *base, *new_base;
 	unsigned int idx = UINT_MAX;
@@ -950,7 +953,11 @@ __mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
 		 * larger granularity than you would get from adding a new
 		 * timer with this expiry.
 		 */
-		if (timer->expires == expires)
+		long diff = timer->expires - expires;
+
+		if (!diff)
+			return 1;
+		if (options & MOD_TIMER_REDUCE && diff <= 0)
 			return 1;
 
 		/*
@@ -962,6 +969,12 @@ __mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
 		base = lock_timer_base(timer, &flags);
 		forward_timer_base(base);
 
+		if (timer_pending(timer) && (options & MOD_TIMER_REDUCE) &&
+		    time_before_eq(timer->expires, expires)) {
+			ret = 1;
+			goto out_unlock;
+		}
+
 		clk = base->clk;
 		idx = calc_wheel_index(expires, clk);
 
@@ -971,7 +984,10 @@ __mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
 		 * subsequent call will exit in the expires check above.
 		 */
 		if (idx == timer_get_idx(timer)) {
-			timer->expires = expires;
+			if (!(options & MOD_TIMER_REDUCE))
+				timer->expires = expires;
+			else if (time_after(timer->expires, expires))
+				timer->expires = expires;
 			ret = 1;
 			goto out_unlock;
 		}
@@ -981,7 +997,7 @@ __mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
 	}
 
 	ret = detach_if_pending(timer, base, false);
-	if (!ret && pending_only)
+	if (!ret && (options & MOD_TIMER_PENDING_ONLY))
 		goto out_unlock;
 
 	debug_activate(timer, expires);
@@ -1042,7 +1058,7 @@ out_unlock:
  */
 int mod_timer_pending(struct timer_list *timer, unsigned long expires)
 {
-	return __mod_timer(timer, expires, true);
+	return __mod_timer(timer, expires, MOD_TIMER_PENDING_ONLY);
 }
 EXPORT_SYMBOL(mod_timer_pending);
 
@@ -1068,11 +1084,26 @@ EXPORT_SYMBOL(mod_timer_pending);
  */
 int mod_timer(struct timer_list *timer, unsigned long expires)
 {
-	return __mod_timer(timer, expires, false);
+	return __mod_timer(timer, expires, 0);
 }
 EXPORT_SYMBOL(mod_timer);
 
 /**
+ * timer_reduce - Modify a timer's timeout if it would reduce the timeout
+ * @timer:	The timer to be modified
+ * @expires:	New timeout in jiffies
+ *
+ * timer_reduce() is very similar to mod_timer(), except that it will only
+ * modify a running timer if that would reduce the expiration time (it will
+ * start a timer that isn't running).
+ */
+int timer_reduce(struct timer_list *timer, unsigned long expires)
+{
+	return __mod_timer(timer, expires, MOD_TIMER_REDUCE);
+}
+EXPORT_SYMBOL(timer_reduce);
+
+/**
  * add_timer - start a timer
  * @timer: the timer to be added
  *
@@ -1754,7 +1785,7 @@ signed long __sched schedule_timeout(signed long timeout)
 
 	timer.task = current;
 	timer_setup_on_stack(&timer.timer, process_timeout, 0);
-	__mod_timer(&timer.timer, expire, false);
+	__mod_timer(&timer.timer, expire, 0);
 	schedule();
 	del_singleshot_timer_sync(&timer.timer);