watchdog/core: Add watchdog_thresh command line parameter

The hard and soft lockup detector threshold has a default value of 10
seconds which can only be changed via sysctl.

During early boot lockup detection can trigger when noisy debugging emits
a large amount of messages to the console, but there is no way to set a
larger threshold on the kernel command line. The detector can only be
completely disabled.

Add a new watchdog_thresh= command line parameter to allow boot time
control over the threshold. It works in the same way as the sysctl and
affects both the soft and the hard lockup detectors.
Signed-off-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: rdunlap@infradead.org
Cc: prarit@redhat.com
Link: https://lkml.kernel.org/r/1541079018-13953-1-git-send-email-loberman@redhat.com

Documentation/admin-guide/kernel-parameters.txt

@@ -4957,6 +4957,14 @@
 			or other driver-specific files in the
 			Documentation/watchdog/ directory.
 
+	watchdog_thresh=
+			[KNL]
+			Set the hard lockup detector stall duration
+			threshold in seconds. The soft lockup detector
+			threshold is set to twice the value. A value of 0
+			disables both lockup detectors. Default is 10
+			seconds.
+
 	workqueue.watchdog_thresh=
 			If CONFIG_WQ_WATCHDOG is configured, workqueue can
 			warn stall conditions and dump internal state to

kernel/watchdog.c

@@ -199,6 +199,13 @@ static int __init nosoftlockup_setup(char *str)
 }
 __setup("nosoftlockup", nosoftlockup_setup);
 
+static int __init watchdog_thresh_setup(char *str)
+{
+	get_option(&str, &watchdog_thresh);
+	return 1;
+}
+__setup("watchdog_thresh=", watchdog_thresh_setup);
+
 #ifdef CONFIG_SMP
 int __read_mostly sysctl_softlockup_all_cpu_backtrace;