xen/time: Free onlined per-cpu data structure if we want to online it again.

If the per-cpu time data structure has been onlined already and
we are trying to online it again, then free the previous copy
before blindly over-writting it.

A developer naturally should not call this function multiple times
but just in case.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/time.c

@@ -401,6 +401,20 @@ static irqreturn_t xen_timer_interrupt(int irq, void *dev_id)
 	return ret;
 }
 
+void xen_teardown_timer(int cpu)
+{
+	struct clock_event_device *evt;
+	BUG_ON(cpu == 0);
+	evt = &per_cpu(xen_clock_events, cpu).evt;
+
+	if (evt->irq >= 0) {
+		unbind_from_irqhandler(evt->irq, NULL);
+		evt->irq = -1;
+		kfree(per_cpu(xen_clock_events, cpu).name);
+		per_cpu(xen_clock_events, cpu).name = NULL;
+	}
+}
+
 void xen_setup_timer(int cpu)
 {
 	char *name;
@@ -409,6 +423,8 @@ void xen_setup_timer(int cpu)
 
 	evt = &per_cpu(xen_clock_events, cpu).evt;
 	WARN(evt->irq >= 0, "IRQ%d for CPU%d is already allocated\n", evt->irq, cpu);
+	if (evt->irq >= 0)
+		xen_teardown_timer(cpu);
 
 	printk(KERN_INFO "installing Xen timer for CPU %d\n", cpu);
 
@@ -429,19 +445,6 @@ void xen_setup_timer(int cpu)
 	per_cpu(xen_clock_events, cpu).name = name;
 }
 
-void xen_teardown_timer(int cpu)
-{
-	struct clock_event_device *evt;
-	BUG_ON(cpu == 0);
-	evt = &per_cpu(xen_clock_events, cpu).evt;
-
-	if (evt->irq >= 0) {
-		unbind_from_irqhandler(evt->irq, NULL);
-		evt->irq = -1;
-		kfree(per_cpu(xen_clock_events, cpu).name);
-		per_cpu(xen_clock_events, cpu).name = NULL;
-	}
-}
 
 void xen_setup_cpu_clockevents(void)
 {