[RFC PATCH v2 13/14] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter

[Ricardo Neri]

Keep the HPET-based hardlockup detector disabled unless explicitly enabled
via a command line argument. If such parameter is not given, the hardlockup
detector will fallback to use the perf-based implementation.

The function hardlockup_panic_setup() is updated to return 0 in order to
to allow __setup functions of specific hardlockup detectors (in this case
hardlockup_detector_hpet_setup()) to inspect the nmi_watchdog boot
parameter.

Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: Andi Kleen <andi.kleen@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Clemens Ladisch <clemens@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Philippe Ombredanne <pombredanne@xxxxxxxx>
Cc: Kate Stewart <kstewart@xxxxxxxxxxxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
Cc: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Nayna Jain <nayna@xxxxxxxxxxxxx>
Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>

--
checkpatch gives the following warning:

CHECK: __setup appears un-documented -- check Documentation/admin-guide/kernel-parameters.rst
+__setup("nmi_watchdog=", hardlockup_detector_hpet_setup);

This is a false-positive as the option nmi_watchdog is already
documented. The option is re-evaluated in this file as well.
---
 .../admin-guide/kernel-parameters.txt         |  6 +++++-
 arch/x86/kernel/watchdog_hld_hpet.c           | 20 +++++++++++++++++++
 kernel/watchdog.c                             |  2 +-
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cf8f5877d85f..c6270ddeb130 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2739,7 +2739,7 @@
 			Format: [state][,regs][,debounce][,die]
 
 	nmi_watchdog=	[KNL,BUGS=X86] Debugging features for SMP kernels
-			Format: [panic,][nopanic,][num]
+			Format: [panic,][nopanic,][num,][hpet]
 			Valid num: 0 or 1
 			0 - turn hardlockup detector in nmi_watchdog off
 			1 - turn hardlockup detector in nmi_watchdog on
@@ -2749,6 +2749,10 @@
 			please see 'nowatchdog'.
 			This is useful when you use a panic=... timeout and
 			need the box quickly up again.
+			When hpet is specified, the NMI watchdog will be driven
+			by an HPET timer, if available in the system. Otherwise,
+			the perf-based implementation will be used. Specifying
+			hpet implies that nmi_watchdog is on.
 
 			These settings can be accessed at runtime via
 			the nmi_watchdog and hardlockup_panic sysctls.
diff --git a/arch/x86/kernel/watchdog_hld_hpet.c b/arch/x86/kernel/watchdog_hld_hpet.c
index 65b4699f249a..4402deff4b77 100644
--- a/arch/x86/kernel/watchdog_hld_hpet.c
+++ b/arch/x86/kernel/watchdog_hld_hpet.c
@@ -20,6 +20,7 @@
 #include <asm/hpet.h>
 
 static struct hpet_hld_data *hld_data;
+static bool hardlockup_use_hpet;
 
 /**
  * get_count() - Get the current count of the HPET timer
@@ -391,6 +392,22 @@ void hardlockup_detector_hpet_stop(void)
 	disable_timer(hld_data);
 }
 
+/**
+ * hardlockup_detector_hpet_setup() - Parse command-line parameters
+ * @str:	A string containing the kernel command line
+ *
+ * Parse the nmi_watchdog parameter from the kernel command line. If
+ * selected by the user, use this implementation to detect hardlockups.
+ */
+static int __init hardlockup_detector_hpet_setup(char *str)
+{
+	if (strstr(str, "hpet"))
+		hardlockup_use_hpet = true;
+
+	return 0;
+}
+__setup("nmi_watchdog=", hardlockup_detector_hpet_setup);
+
 /**
  * hardlockup_detector_hpet_init() - Initialize the hardlockup detector
  *
@@ -405,6 +422,9 @@ int __init hardlockup_detector_hpet_init(void)
 {
 	int ret;
 
+	if (!hardlockup_use_hpet)
+		return -ENODEV;
+
 	if (!is_hpet_enabled())
 		return -ENODEV;
 
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 367aa81294ef..28cad7310378 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -78,7 +78,7 @@ static int __init hardlockup_panic_setup(char *str)
 		nmi_watchdog_user_enabled = 0;
 	else if (!strncmp(str, "1", 1))
 		nmi_watchdog_user_enabled = 1;
-	return 1;
+	return 0;
 }
 __setup("nmi_watchdog=", hardlockup_panic_setup);
 
-- 
2.17.1