x86, ioapic: Throw BUG instead of NULL dereference

Instead of plain NULL deref we better throw error
message with a backtrace. Actually we need more
gracious error handling here. Meanwhile leave it
as is.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: yinghai@kernel.org
LKML-Reference: <20090801075435.769301745@openvz.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/apic/io_apic.c

@@ -503,6 +503,10 @@ static void add_pin_to_irq_node(struct irq_cfg *cfg, int node, int apic, int pin
 	}
 
 	entry = get_one_free_irq_2_pin(node);
+	if (!entry) {
+		printk(KERN_ERR "can not alloc irq_pin_list\n");
+		BUG_ON(1);
+	}
 	entry->apic = apic;
 	entry->pin = pin;