sparseirq, xen: make sure irq_desc is allocated for interrupts

Impact: fix crash

Make sure all Xen irqs have an irq_desc.
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

drivers/xen/events.c

@@ -233,6 +233,7 @@ static void unmask_evtchn(int port)
 static int find_unbound_irq(void)
 {
 	int irq;
+	struct irq_desc *desc;
 
 	/* Only allocate from dynirq range */
 	for (irq = 0; irq < nr_irqs; irq++)
@@ -242,6 +243,10 @@ static int find_unbound_irq(void)
 	if (irq == nr_irqs)
 		panic("No available IRQ to bind to: increase nr_irqs!\n");
 
+	desc = irq_to_desc_alloc_cpu(irq, 0);
+	if (WARN_ON(desc == NULL))
+		return -1;
+
 	return irq;
 }