diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index c027d4f602f18276f73694a593cefb6ea77bc3a0..e4c699dfa4e8776ee3ed9e671922e962002b6a06 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -182,7 +182,10 @@ void clockevents_register_device(struct clock_event_device *dev)
 	unsigned long flags;
 
 	BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
-	BUG_ON(!dev->cpumask);
+	if (!dev->cpumask) {
+		WARN_ON(num_possible_cpus() > 1);
+		dev->cpumask = cpumask_of(smp_processor_id());
+	}
 
 	raw_spin_lock_irqsave(&clockevents_lock, flags);
 
diff --git a/kernel/timer.c b/kernel/timer.c
index fd6198692b57b16e47132d1eb5183bafd98b050e..8cff36119e4d50f7336a06e8d01e59e8b162e694 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -749,16 +749,15 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires)
 	unsigned long expires_limit, mask;
 	int bit;
 
-	expires_limit = expires;
-
 	if (timer->slack >= 0) {
 		expires_limit = expires + timer->slack;
 	} else {
-		unsigned long now = jiffies;
+		long delta = expires - jiffies;
+
+		if (delta < 256)
+			return expires;
 
-		/* No slack, if already expired else auto slack 0.4% */
-		if (time_after(expires, now))
-			expires_limit = expires + (expires - now)/256;
+		expires_limit = expires + delta / 256;
 	}
 	mask = expires ^ expires_limit;
 	if (mask == 0)
@@ -795,6 +794,8 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires)
  */
 int mod_timer(struct timer_list *timer, unsigned long expires)
 {
+	expires = apply_slack(timer, expires);
+
 	/*
 	 * This is a common optimization triggered by the
 	 * networking code - if the timer is re-modified
@@ -803,8 +804,6 @@ int mod_timer(struct timer_list *timer, unsigned long expires)
 	if (timer_pending(timer) && timer->expires == expires)
 		return 1;
 
-	expires = apply_slack(timer, expires);
-
 	return __mod_timer(timer, expires, false, TIMER_NOT_PINNED);
 }
 EXPORT_SYMBOL(mod_timer);