x86: Don't send RESCHEDULE_VECTOR to offlined cpus

In the x86 native_smp_send_reschedule_function(), don't send the IPI if the
cpu has gone offline already. Warn nevertheless!!

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/smp.c

@@ -118,7 +118,10 @@
  */
 static void native_smp_send_reschedule(int cpu)
 {
-	WARN_ON(cpu_is_offline(cpu));
+	if (unlikely(cpu_is_offline(cpu))) {
+		WARN_ON(1);
+		return;
+	}
 	send_IPI_mask(cpumask_of_cpu(cpu), RESCHEDULE_VECTOR);
 }