[PATCH 1/4] watchdog/hardlockup: Always update saved interrupts during check

[Mayank Rungta via B4 Relay]

From: Mayank Rungta <mrungta@xxxxxxxxxx>

Currently, arch_touch_nmi_watchdog() causes an early return that
skips updating hrtimer_interrupts_saved. This leads to stale
comparisons and delayed lockup detection.

Update the saved interrupt count before checking the touched flag
to ensure detection timeliness.

Signed-off-by: Mayank Rungta <mrungta@xxxxxxxxxx>
---
 kernel/watchdog.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 7d675781bc917d709aa3fb499629eeac86934f55..b71aa814edcf9ad8f73644eb5bcd1eeb3264e4ed 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -186,7 +186,21 @@ static void watchdog_hardlockup_kick(void)
 
 void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
 {
+	bool is_hl;
 	int hardlockup_all_cpu_backtrace;
+	/*
+	 * Check for a hardlockup by making sure the CPU's timer
+	 * interrupt is incrementing. The timer interrupt should have
+	 * fired multiple times before we overflow'd. If it hasn't
+	 * then this is a good indication the cpu is stuck
+	 *
+	 * Purposely check this _before_ checking watchdog_hardlockup_touched
+	 * so we make sure we still update the saved value of the interrupts.
+	 * Without that we'll take an extra round through this function before
+	 * we can detect a lockup.
+	 */
+
+	is_hl = is_hardlockup(cpu);
 
 	if (per_cpu(watchdog_hardlockup_touched, cpu)) {
 		per_cpu(watchdog_hardlockup_touched, cpu) = false;
@@ -195,13 +209,8 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
 
 	hardlockup_all_cpu_backtrace = (hardlockup_si_mask & SYS_INFO_ALL_BT) ?
 					1 : sysctl_hardlockup_all_cpu_backtrace;
-	/*
-	 * Check for a hardlockup by making sure the CPU's timer
-	 * interrupt is incrementing. The timer interrupt should have
-	 * fired multiple times before we overflow'd. If it hasn't
-	 * then this is a good indication the cpu is stuck
-	 */
-	if (is_hardlockup(cpu)) {
+
+	if (is_hl) {
 		unsigned int this_cpu = smp_processor_id();
 		unsigned long flags;
 

-- 
2.53.0.273.g2a3d683680-goog