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watchdog/softlockup: Enforce that timestamp is valid on boot 

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
This commit is contained in:
Thomas Gleixner 2020-01-16 19:17:02 +01:00
parent 3a51449b79
commit 11e31f608b
1 changed files with 6 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
kernel/watchdog.c
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@ -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;
@ -272,7 +274,7 @@ 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)
@ -296,14 +298,14 @@ 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)
@ -379,7 +381,7 @@ 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