[PATCH 4.19 120/134] watchdog: Respect watchdog cpumask on CPU hotplug

[Greg Kroah-Hartman]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit 7dd47617114921fdd8c095509e5e7b4373cc44a1 upstream.

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. As a consequence the watchdog can become unstoppable.

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

Fixes: 9cf57731b63e ("watchdog/softlockup: Replace "watchdog/%u" threads with cpu_stop_work")
Reported-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1903262245490.1789@xxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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;
 }