watchdog/softlockup: Enforce that timestamp is valid on boot

[ Upstream commit 11e31f608b499f044f24b20be73f1dcab3e43f8a ]

Robert reported that during boot the watchdog timestamp is set to 0 for one
second which is the indicator for a watchdog reset.

The reason for this is that the timestamp is in seconds and the time is
taken from sched clock and divided by ~1e9. sched clock starts at 0 which
means that for the first second during boot the watchdog timestamp is 0,
i.e. reset.

Use ULONG_MAX as the reset indicator value so the watchdog works correctly
right from the start. ULONG_MAX would only conflict with a real timestamp
if the system reaches an uptime of 136 years on 32bit and almost eternity
on 64bit.

Reported-by: Robert Richter <rrichter@marvell.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/87o8v3uuzl.fsf@nanos.tec.linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index bbc4940..6d60701 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -161,6 +161,8 @@ static void lockup_detector_update_enable(void)
 
 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
 
+#define SOFTLOCKUP_RESET       ULONG_MAX
+
 /* Global variables, exported for sysctl */
 unsigned int __read_mostly softlockup_panic =
                        CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
@@ -267,7 +269,7 @@ notrace void touch_softlockup_watchdog_sched(void)
         * Preemption can be enabled.  It doesn't matter which CPU's timestamp
         * gets zeroed here, so use the raw_ operation.
         */
-       raw_cpu_write(watchdog_touch_ts, 0);
+       raw_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET);
 }
 
 notrace void touch_softlockup_watchdog(void)
@@ -291,14 +293,14 @@ void touch_all_softlockup_watchdogs(void)
         * the softlockup check.
         */
        for_each_cpu(cpu, &watchdog_allowed_mask)
-               per_cpu(watchdog_touch_ts, cpu) = 0;
+               per_cpu(watchdog_touch_ts, cpu) = SOFTLOCKUP_RESET;
        wq_watchdog_touch(-1);
 }
 
 void touch_softlockup_watchdog_sync(void)
 {
        __this_cpu_write(softlockup_touch_sync, true);
-       __this_cpu_write(watchdog_touch_ts, 0);
+       __this_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET);
 }
 
 static int is_softlockup(unsigned long touch_ts)
@@ -376,7 +378,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
        /* .. and repeat */
        hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 
-       if (touch_ts == 0) {
+       if (touch_ts == SOFTLOCKUP_RESET) {
                if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
                        /*
                         * If the time stamp was touched atomically