[PATCH] x86_64: make touch_nmi_watchdog() not touch impossible cpus' private data

Along with that, also suppress the memory touching altogether when the
watchdog is not running, to eliminate needless crosstalk. Plus ad a call
to it to make things consistent (one could also consider removing the call
in enable_timer_nmi_watchdog()).
Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/nmi.c

@@ -236,6 +236,7 @@ static void enable_lapic_nmi_watchdog(void)
 {
 	if (nmi_active < 0) {
 		nmi_watchdog = NMI_LOCAL_APIC;
+		touch_nmi_watchdog();
 		setup_apic_nmi_watchdog();
 	}
 }
@@ -456,15 +457,17 @@ static DEFINE_PER_CPU(int, nmi_touch);
 
 void touch_nmi_watchdog (void)
 {
-	int i;
+	if (nmi_watchdog > 0) {
+		unsigned cpu;
 
 		/*
  		 * Tell other CPUs to reset their alert counters. We cannot
 		 * do it ourselves because the alert count increase is not
 		 * atomic.
 		 */
-	for (i = 0; i < NR_CPUS; i++)
-		per_cpu(nmi_touch, i) = 1;
+		for_each_present_cpu (cpu)
+			per_cpu(nmi_touch, cpu) = 1;
+	}
 
  	touch_softlockup_watchdog();
 }