Let smp_call_function_single return -EBUSY on UP

All architectures that have an implementation of smp_call_function_single
let it return -EBUSY if it is asked to execute func on the current cpu.
(akpm: except for x86_64).  Therefore the UP version must always return
-EBUSY.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/smp.h

@@ -6,6 +6,7 @@
  *		Alan Cox. <alan@redhat.com>
  */
 
+#include <linux/errno.h>
 
 extern void cpu_idle(void);
 
@@ -101,9 +102,7 @@ static inline void smp_send_reschedule(int cpu) { }
 static inline int smp_call_function_single(int cpuid, void (*func) (void *info),
 					   void *info, int retry, int wait)
 {
-	/* Disable interrupts here? */
-	func(info);
-	return 0;
+	return -EBUSY;
 }
 
 #endif /* !SMP */