+ watchdog-explicitly-update-timestamp-when-reporting-softlockup.patch added to -mm tree

+ watchdog-explicitly-update-timestamp-when-reporting-softlockup.patch added to -mm tree

[akpm]

The patch titled
     Subject: watchdog: explicitly update timestamp when reporting softlockup
has been added to the -mm tree.  Its filename is
     watchdog-explicitly-update-timestamp-when-reporting-softlockup.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/watchdog-explicitly-update-timestamp-when-reporting-softlockup.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/watchdog-explicitly-update-timestamp-when-reporting-softlockup.patch

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------------------------------------------------------
From: Petr Mladek <pmladek@suse.com>
Subject: watchdog: explicitly update timestamp when reporting softlockup

The softlockup situation might stay for a long time or even forever.  When
it happens, the softlockup debug messages are printed in regular intervals
defined by get_softlockup_thresh().

There is a mystery.  The repeated message is printed after the full
interval that is defined by get_softlockup_thresh().  But the timer
callback is called more often as defined by sample_period.  The code looks
like the soflockup should get reported in every sample_period when it was
once behind the thresh.

It works only by chance.  The watchdog is touched when printing the stall
report, for example, in printk_stack_address().

Make the behavior clear and predictable by explicitly updating the
timestamp in watchdog_timer_fn() when the report gets printed.

Link: https://lkml.kernel.org/r/20210311122130.6788-3-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/watchdog.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/watchdog.c~watchdog-explicitly-update-timestamp-when-reporting-softlockup
+++ a/kernel/watchdog.c
@@ -409,6 +409,9 @@ static enum hrtimer_restart watchdog_tim
 			}
 		}
 
+		/* Start period for the next softlockup warning. */
+		update_touch_ts();
+
 		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 			smp_processor_id(), duration,
 			current->comm, task_pid_nr(current));
_

Patches currently in -mm which might be from pmladek@suse.com are

watchdog-rename-__touch_watchdog-to-a-better-descriptive-name.patch
watchdog-explicitly-update-timestamp-when-reporting-softlockup.patch
watchdog-softlockup-report-the-overall-time-of-softlockups.patch
watchdog-softlockup-remove-logic-that-tried-to-prevent-repeated-reports.patch
watchdog-fix-barriers-when-printing-backtraces-from-all-cpus.patch
watchdog-cleanup-handling-of-false-positives.patch