[PATCH] x86-64: survive having no irq mapping for a vector

Occasionally the kernel has bugs that result in no irq being found for a
given cpu vector.  If we acknowledge the irq the system has a good chance
of continuing even though we dropped an irq message.  If we continue to
simply print a message and not acknowledge the irq the system is likely to
become non-responsive shortly there after.

AK: Fixed compilation for UP kernels
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: "Luigi Genoni" <luigi.genoni@pirelli.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/x86_64/kernel/irq.c

@@ -18,6 +18,7 @@
 #include <asm/uaccess.h>
 #include <asm/io_apic.h>
 #include <asm/idle.h>
+#include <asm/smp.h>
 
 atomic_t irq_err_count;
 
@@ -120,9 +121,14 @@ asmlinkage unsigned int do_IRQ(struct pt_regs *regs)
 
 	if (likely(irq < NR_IRQS))
 		generic_handle_irq(irq);
-	else if (printk_ratelimit())
+	else {
+		if (!disable_apic)
+			ack_APIC_irq();
+
+		if (printk_ratelimit())
 			printk(KERN_EMERG "%s: %d.%d No irq handler for vector\n",
 				__func__, smp_processor_id(), vector);
+	}
 
 	irq_exit();