[PATCH] watchdog: Respect watchdog cpumask on CPU hotplug

[Thomas Gleixner <tglx@linutronix.de>]

The rework of the watchdog core to use cpu_stop_work broke the watchdog
cpumask on CPU hotplug.

The watchdog_enable/disable() functions are now called unconditionally from
the hotplug callback, i.e. even on CPUs which are not in the watchdog
cpumask.

Only invoke them when the plugged CPU is in the watchdog cpumask.

Fixes: 9cf57731b63e ("watchdog/softlockup: Replace "watchdog/%u" threads with cpu_stop_work")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
---
 kernel/watchdog.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -547,13 +547,15 @@ static void softlockup_start_all(void)
 
 int lockup_detector_online_cpu(unsigned int cpu)
 {
-	watchdog_enable(cpu);
+	if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
+		watchdog_enable(cpu);
 	return 0;
 }
 
 int lockup_detector_offline_cpu(unsigned int cpu)
 {
-	watchdog_disable(cpu);
+	if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
+		watchdog_disable(cpu);
 	return 0;
 }