[PATCH v3] watchdog: Add warning message when the newcpumask contains nohz_full cores

[Zqiang]

The watchdog default is disabled on nohz_full cores, however when
override the cpumask, if new cpumask contains nohz_full cores,
add warning message.

Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx>
---
 v1->v2:
 if watchdog_cpumask became empty, set housekeeping_cpumask.
 v2->v3:
 only print a warning when a nohz_full CPU is included in new cpumask.

 kernel/watchdog.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index ad912511a0c0..37a978d8ff06 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -629,6 +629,7 @@ static void proc_watchdog_update(void)
 {
 	/* Remove impossible cpus to keep sysctl output clean. */
 	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
+	WARN_ONCE(!cpumask_subset(&watchdog_cpumask, housekeeping_cpumask(HK_FLAG_TIMER)), "Enabling watchdog on nohz_full cores\n");
 	lockup_detector_reconfigure();
 }
 
-- 
2.17.1