x86, NMI: NMI-selftest should handle the UP case properly

If no remote cpus are online, then just quietly skip the remote
IPI test for now.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: andi@firstfloor.org
Cc: torvalds@linux-foundation.org
Cc: peterz@infradead.org
Cc: robert.richter@amd.com
Link: http://lkml.kernel.org/r/20111206180859.GR1669@redhat.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/nmi_selftest.c

@@ -90,7 +90,8 @@ static void remote_ipi(void)
 {
 	cpumask_copy(to_cpumask(nmi_ipi_mask), cpu_online_mask);
 	cpumask_clear_cpu(smp_processor_id(), to_cpumask(nmi_ipi_mask));
-	test_nmi_ipi(to_cpumask(nmi_ipi_mask));
+	if (!cpumask_empty(nmi_ipi_mask))
+		test_nmi_ipi(to_cpumask(nmi_ipi_mask));
 }
 
 static void local_ipi(void)