linux-kernel - [PATCH v2 2/7] watchdog: Explicitly update timestamp when reporting softlockup

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Date:   Thu, 11 Mar 2021 13:21:25 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Laurence Oberman <loberman@...hat.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH v2 2/7] 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.

Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 kernel/watchdog.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index c58244064de8..7776d53a015c 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -409,6 +409,9 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 			}
 		}

+		/* 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));
-- 
2.26.2