[RFC PATCH 22/23] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter

From: Ricardo Neri
Date: Tue Jun 12 2018 - 21:01:51 EST

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

Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: Andi Kleen <andi.kleen@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Babu Moger <babu.moger@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Philippe Ombredanne <pombredanne@xxxxxxxx>
Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Cc: Byungchul Park <byungchul.park@xxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Christoffer Dall <cdall@xxxxxxxxxx>
Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
Cc: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
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.
Documentation/admin-guide/kernel-parameters.txt | 5 ++++-
kernel/watchdog.c | 2 +-
kernel/watchdog_hld_hpet.c | 13 +++++++++++++
3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f2040d4..a8833c7 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2577,7 +2577,7 @@
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
@@ -2587,6 +2587,9 @@
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.

These settings can be accessed at runtime via
the nmi_watchdog and hardlockup_panic sysctls.
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index b94bbe3..b5ce6e4 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -84,7 +84,7 @@ 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);

diff --git a/kernel/watchdog_hld_hpet.c b/kernel/watchdog_hld_hpet.c
index ebb820d..12e5937 100644
--- a/kernel/watchdog_hld_hpet.c
+++ b/kernel/watchdog_hld_hpet.c
@@ -17,6 +17,7 @@
#define pr_fmt(fmt) "NMI hpet watchdog: " fmt

static struct hpet_hld_data *hld_data;
+static bool hardlockup_use_hpet;

* get_count() - Get the current count of the HPET timer
@@ -488,6 +489,15 @@ static void hardlockup_detector_hpet_stop(void)

+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
@@ -502,6 +512,9 @@ static int __init hardlockup_detector_hpet_init(void)
int ret;

+ if (!hardlockup_use_hpet)
+ return -EINVAL;
if (!is_hpet_enabled())
return -ENODEV;