x86_64: Allow smp_call_function_single() to current cpu

This removes the requirement for callers to get_cpu() to check in simple
cases.

Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86_64/kernel/smp.c

@@ -357,7 +357,7 @@ __smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 }
 
 /*
- * smp_call_function_single - Run a function on another CPU
+ * smp_call_function_single - Run a function on a specific CPU
  * @func: The function to run. This must be fast and non-blocking.
  * @info: An arbitrary pointer to pass to the function.
  * @nonatomic: Currently unused.
@@ -374,14 +374,18 @@ int smp_call_function_single (int cpu, void (*func) (void *info), void *info,
 {
 	/* prevent preemption and reschedule on another processor */
 	int me = get_cpu();
+
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	if (cpu == me) {
+		local_irq_disable();
+		func(info);
+		local_irq_enable();
 		put_cpu();
 		return 0;
 	}
 
-	/* Can deadlock when called with interrupts disabled */
-	WARN_ON(irqs_disabled());
-
 	spin_lock_bh(&call_lock);
 	__smp_call_function_single(cpu, func, info, nonatomic, wait);
 	spin_unlock_bh(&call_lock);