The irq vector offset should spread the irq's out evenly, which

implies that it should vary between 0-7, not any further (the
higher bits are done by updating current_vector by 8).

This also means that we don't have any overflow condition.

arch/i386/kernel/io_apic.c

@@ -1116,13 +1116,10 @@ static int __init assign_irq_vector(int irq)
 		goto next;
 
 	if (current_vector > FIRST_SYSTEM_VECTOR) {
-		offset++;
+		offset = (offset + 1) & 7;
 		current_vector = FIRST_DEVICE_VECTOR + offset;
 	}
 
-	if (current_vector == FIRST_SYSTEM_VECTOR)
-		panic("ran out of interrupt sources!");
-
 	IO_APIC_VECTOR(irq) = current_vector;
 	return current_vector;
 }