watchdog: export lockup_detector_reconfigure

In some circumstances it may be interesting to reconfigure the watchdog
from inside the kernel.

On PowerPC, this may helpful before and after a LPAR migration (LPM) is
initiated, because it implies some latencies, watchdog, and especially NMI
watchdog is expected to be triggered during this operation. Reconfiguring
the watchdog with a factor, would prevent it to happen too frequently
during LPM.

Rename lockup_detector_reconfigure() as __lockup_detector_reconfigure() and
create a new function lockup_detector_reconfigure() calling
__lockup_detector_reconfigure() under the protection of watchdog_mutex.
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
[mpe: Squash in build fix from Laurent, reported by Sachin]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220713154729.80789-3-ldufour@linux.ibm.com

include/linux/nmi.h

@@ -122,6 +122,8 @@ int watchdog_nmi_probe(void);
 int watchdog_nmi_enable(unsigned int cpu);
 void watchdog_nmi_disable(unsigned int cpu);
 
+void lockup_detector_reconfigure(void);
+
 /**
  * touch_nmi_watchdog - restart NMI watchdog timeout.
  *

kernel/watchdog.c

@@ -541,7 +541,7 @@ int lockup_detector_offline_cpu(unsigned int cpu)
 	return 0;
 }
 
-static void lockup_detector_reconfigure(void)
+static void __lockup_detector_reconfigure(void)
 {
 	cpus_read_lock();
 	watchdog_nmi_stop();
@@ -561,6 +561,13 @@ static void lockup_detector_reconfigure(void)
 	__lockup_detector_cleanup();
 }
 
+void lockup_detector_reconfigure(void)
+{
+	mutex_lock(&watchdog_mutex);
+	__lockup_detector_reconfigure();
+	mutex_unlock(&watchdog_mutex);
+}
+
 /*
  * Create the watchdog infrastructure and configure the detector(s).
  */
@@ -577,13 +584,13 @@ static __init void lockup_detector_setup(void)
 		return;
 
 	mutex_lock(&watchdog_mutex);
-	lockup_detector_reconfigure();
+	__lockup_detector_reconfigure();
 	softlockup_initialized = true;
 	mutex_unlock(&watchdog_mutex);
 }
 
 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
-static void lockup_detector_reconfigure(void)
+static void __lockup_detector_reconfigure(void)
 {
 	cpus_read_lock();
 	watchdog_nmi_stop();
@@ -591,9 +598,13 @@ static void lockup_detector_reconfigure(void)
 	watchdog_nmi_start();
 	cpus_read_unlock();
 }
+void lockup_detector_reconfigure(void)
+{
+	__lockup_detector_reconfigure();
+}
 static inline void lockup_detector_setup(void)
 {
-	lockup_detector_reconfigure();
+	__lockup_detector_reconfigure();
 }
 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
 
@@ -633,7 +644,7 @@ static void proc_watchdog_update(void)
 {
 	/* Remove impossible cpus to keep sysctl output clean. */
 	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
-	lockup_detector_reconfigure();
+	__lockup_detector_reconfigure();
 }
 
 /*