watchdog/perf: properly initialize the turbo mode timestamp and rearm counter

JIRA: https://issues.redhat.com/browse/RHEL-103375
Conflicts: kernel/watchdog_perf.c doesn't exist in RHEL at this time, so
	   this commit is applied to kernel/watchdog_hld.c

commit f944ffc
Author: Thomas Gleixner <tglx@linutronix.de>
Date:   Thu Jul 11 22:25:21 2024 +0200

    watchdog/perf: properly initialize the turbo mode timestamp and rearm counter

    For systems on which the performance counter can expire early due to turbo
    modes the watchdog handler has a safety net in place which validates that
    since the last watchdog event there has at least 4/5th of the watchdog
    period elapsed.

    This works reliably only after the first watchdog event because the per
    CPU variable which holds the timestamp of the last event is never
    initialized.

    So a first spurious event will validate against a timestamp of 0 which
    results in a delta which is likely to be way over the 4/5 threshold of the
    period.  As this might happen before the first watchdog hrtimer event
    increments the watchdog counter, this can lead to false positives.

    Fix this by initializing the timestamp before enabling the hardware event.
    Reset the rearm counter as well, as that might be non zero after the
    watchdog was disabled and reenabled.

    Link: https://lkml.kernel.org/r/87frsfu15a.ffs@tglx
    Fixes: 7edaeb6 ("kernel/watchdog: Prevent false positives with turbo modes")
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: David Arcari <darcari@redhat.com>

Author: darcari

kernel/watchdog_hld.c

@@ -91,11 +91,15 @@ static bool watchdog_check_timestamp(void)
 	__this_cpu_write(last_timestamp, now);
 	return true;
 }
-#else
-static inline bool watchdog_check_timestamp(void)
+
+static void watchdog_init_timestamp(void)
 {
-	return true;
+	__this_cpu_write(nmi_rearmed, 0);
+	__this_cpu_write(last_timestamp, ktime_get_mono_fast_ns());
 }
+#else
+static inline bool watchdog_check_timestamp(void) { return true; }
+static inline void watchdog_init_timestamp(void) { }
 #endif
 
 static struct perf_event_attr wd_hw_attr = {
@@ -196,6 +200,7 @@ void hardlockup_detector_perf_enable(void)
 	if (!atomic_fetch_inc(&watchdog_cpus))
 		pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
 
+	watchdog_init_timestamp();
 	perf_event_enable(this_cpu_read(watchdog_ev));
 }