[PATCH] x86_64: cpu hotplug changes kills nmi watchdog

When the x86_64 cpu hotplug changes went in it added a check in
default_do_nmi() which kills NMI delivery on any CPU but the BSP.

The NMI watchdog is brought up quite some time before the online bit is set
in num_online_cpus so this won't work very well.  The nmi watchdogs on cpus
that are not BSP will never be reprogrammed and no NMIs.

Why was this check added? How does an offlined cpu receive an NMI?
Signed-off-by: NAlexander Nyberg <alexn@telia.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Cc: <ashok.raj@intel.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/traps.c

@@ -594,9 +594,6 @@ asmlinkage void default_do_nmi(struct pt_regs *regs)
 	if (!cpu)
 		reason = get_nmi_reason();
 
-	if (!cpu_online(cpu))
-		return;
-
 	if (!(reason & 0xc0)) {
 		if (notify_die(DIE_NMI_IPI, "nmi_ipi", regs, reason, 0, SIGINT)
 								== NOTIFY_STOP)