[patch 22/29] lockup_detector: Make watchdog_nmi_reconfigure() two stage

[patch 22/29] lockup_detector: Make watchdog_nmi_reconfigure() two stage

[Thomas Gleixner]

Both the perf reconfiguration and the powerpc watchdog_nmi_reconfigure()
need to be done in two steps.

     1) Stop all NMIs
     2) Read the new parameters and start NMIs

Right now watchdog_nmi_reconfigure() is a combination of both. To allow a
clean reconfiguration add a 'run' argument and split the functionality in
powerpc.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org
---
 arch/powerpc/kernel/watchdog.c |   17 +++++++++--------
 include/linux/nmi.h            |    2 ++
 kernel/watchdog.c              |   31 ++++++++++++++++++++++---------
 3 files changed, 33 insertions(+), 17 deletions(-)

--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -352,17 +352,18 @@ static void watchdog_calc_timeouts(void)
 	wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5;
 }
 
-void watchdog_nmi_reconfigure(void)
+void watchdog_nmi_reconfigure(bool stop)
 {
 	int cpu;
 
-	watchdog_calc_timeouts();
-
-	for_each_cpu(cpu, &wd_cpus_enabled)
-		stop_wd_on_cpu(cpu);
-
-	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
-		start_wd_on_cpu(cpu);
+	if (stop) {
+		for_each_cpu(cpu, &wd_cpus_enabled)
+			stop_wd_on_cpu(cpu);
+	} else {
+		watchdog_calc_timeouts();
+		for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
+			start_wd_on_cpu(cpu);
+	}
 }
 
 /*
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -103,6 +103,8 @@ static inline void arch_touch_nmi_watchd
 #endif
 #endif
 
+void watchdog_nmi_reconfigure(bool run);
+
 /**
  * touch_nmi_watchdog - restart NMI watchdog timeout.
  *
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -105,17 +105,25 @@ static int __init hardlockup_all_cpu_bac
 int __weak watchdog_nmi_enable(unsigned int cpu) { return 0; }
 void __weak watchdog_nmi_disable(unsigned int cpu) { }
 
-/*
- * watchdog_nmi_reconfigure can be implemented to be notified after any
- * watchdog configuration change. The arch hardlockup watchdog should
- * respond to the following variables:
+/**
+ * watchdog_nmi_reconfigure - Optional function to reconfigure NMI watchdogs
+ * @stop:	If true stop the watchdogs on all enabled CPUs
+ *		If false start the watchdogs on all enabled CPUs
+ *
+ * The core call order is:
+ * watchdog_nmi_reconfigure(true);
+ * update_variables();
+ * watchdog_nmi_reconfigure(false);
+ *
+ * The second call which starts the watchdogs again guarantees that the
+ * following variables are stable across the call.
  * - watchdog_enabled
  * - watchdog_thresh
  * - watchdog_cpumask
- * - sysctl_hardlockup_all_cpu_backtrace
- * - hardlockup_panic
+ *
+ * After the call the variables can be changed again.
  */
-void __weak watchdog_nmi_reconfigure(void) { }
+void __weak watchdog_nmi_reconfigure(bool stop) { }
 
 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
 
@@ -509,10 +517,12 @@ static void softlockup_unpark_threads(vo
 
 static void softlockup_reconfigure_threads(bool enabled)
 {
+	watchdog_nmi_reconfigure(false);
 	softlockup_park_all_threads();
 	set_sample_period();
 	if (enabled)
 		softlockup_unpark_threads();
+	watchdog_nmi_reconfigure(true);
 }
 
 /*
@@ -553,7 +563,11 @@ static inline void watchdog_unpark_threa
 static inline int watchdog_enable_all_cpus(void) { return 0; }
 static inline void watchdog_disable_all_cpus(void) { }
 static inline void softlockup_init_threads(void) { }
-static inline void softlockup_reconfigure_threads(bool enabled) { }
+static void softlockup_reconfigure_threads(bool enabled)
+{
+	watchdog_nmi_reconfigure(false);
+	watchdog_nmi_reconfigure(true);
+}
 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
 
 static void __lockup_detector_cleanup(void)
@@ -593,7 +607,6 @@ static void proc_watchdog_update(void)
 	/* Remove impossible cpus to keep sysctl output clean. */
 	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
 	softlockup_reconfigure_threads(watchdog_enabled && watchdog_thresh);
-	watchdog_nmi_reconfigure();
 }
 
 /*

[patch 29/29] lockup_detector: Cleanup hotplug locking mess

[Thomas Gleixner]

All watchdog thread related functions are delegated to the smpboot thread
infrastructure, which handles serialization against CPU hotplug correctly.

The sysctl interface is completely decoupled from anything which requires
CPU hotplug protection.

No need to protect the sysctl writes against cpu hotplug anymore. Remove it
and add the now required protection to the powerpc arch_nmi_watchdog
implementation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org
---
 arch/powerpc/kernel/watchdog.c |    2 ++
 kernel/watchdog.c              |    6 ------
 2 files changed, 2 insertions(+), 6 deletions(-)

--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -356,6 +356,7 @@ void watchdog_nmi_reconfigure(bool stop)
 {
 	int cpu;
 
+	cpus_read_lock();
 	if (stop) {
 		for_each_cpu(cpu, &wd_cpus_enabled)
 			stop_wd_on_cpu(cpu);
@@ -364,6 +365,7 @@ void watchdog_nmi_reconfigure(bool stop)
 		for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
 			start_wd_on_cpu(cpu);
 	}
+	cpus_read_unlock();
 }
 
 /*
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -652,7 +652,6 @@ static int proc_watchdog_common(int whic
 {
 	int err, old, *param = table->data;
 
-	cpu_hotplug_disable();
 	mutex_lock(&watchdog_mutex);
 
 	if (!write) {
@@ -669,7 +668,6 @@ static int proc_watchdog_common(int whic
 			proc_watchdog_update();
 	}
 	mutex_unlock(&watchdog_mutex);
-	cpu_hotplug_enable();
 	return err;
 }
 
@@ -713,7 +711,6 @@ int proc_watchdog_thresh(struct ctl_tabl
 {
 	int err, old;
 
-	cpu_hotplug_disable();
 	mutex_lock(&watchdog_mutex);
 
 	old = READ_ONCE(watchdog_thresh);
@@ -723,7 +720,6 @@ int proc_watchdog_thresh(struct ctl_tabl
 		proc_watchdog_update();
 
 	mutex_unlock(&watchdog_mutex);
-	cpu_hotplug_enable();
 	return err;
 }
 
@@ -738,7 +734,6 @@ int proc_watchdog_cpumask(struct ctl_tab
 {
 	int err;
 
-	cpu_hotplug_disable();
 	mutex_lock(&watchdog_mutex);
 
 	err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
@@ -746,7 +741,6 @@ int proc_watchdog_cpumask(struct ctl_tab
 		proc_watchdog_update();
 
 	mutex_unlock(&watchdog_mutex);
-	cpu_hotplug_enable();
 	return err;
 }
 #endif /* CONFIG_SYSCTL */