[PATCH][v2] watchdog/hardlockup: reassign last_timestamp when enable nmi event

[Li RongQing]

last_timestamp is not initialized and is zero after boot, or stop
to forward when nmi watchdog is disabled; and false positives still
is possible when restart NMI timer after stopping 120 seconds

so reassign last_timestamp always when enable nmi event

Fixes: 7edaeb6841df ("kernel/watchdog: Prevent false positives with turbo modes")
Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
Signed-off-by: Zhang Yu <zhangyu31@xxxxxxxxx>
---

v1-->v2: make it be able to be compiled on no CONFIG_HARDLOCKUP_CHECK_TIMESTAMP platform 

kernel/watchdog_hld.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index 247bf0b1582c..f14d18280387 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -91,11 +91,24 @@ static bool watchdog_check_timestamp(void)
 	__this_cpu_write(last_timestamp, now);
 	return true;
 }
+
+static void watchdog_touch_timestamp(int cpu)
+{
+
+	ktime_t now = ktime_get_mono_fast_ns();
+
+	per_cpu(last_timestamp, cpu) = now;
+}
 #else
 static inline bool watchdog_check_timestamp(void)
 {
 	return true;
 }
+
+static void watchdog_touch_timestamp(int cpu)
+{
+
+}
 #endif
 
 static struct perf_event_attr wd_hw_attr = {
@@ -196,6 +209,7 @@ void hardlockup_detector_perf_enable(void)
 	if (!atomic_fetch_inc(&watchdog_cpus))
 		pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
 
+	watchdog_touch_timestamp(smp_processor_id());
 	perf_event_enable(this_cpu_read(watchdog_ev));
 }
 
@@ -274,8 +288,10 @@ void __init hardlockup_detector_perf_restart(void)
 	for_each_online_cpu(cpu) {
 		struct perf_event *event = per_cpu(watchdog_ev, cpu);
 
-		if (event)
+		if (event) {
+			watchdog_touch_timestamp(cpu);
 			perf_event_enable(event);
+		}
 	}
 }
 
-- 
2.16.2