[PATCH v6 25/29] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter

[Ricardo Neri <ricardo.neri-calderon@linux.intel.com>]

Keep the HPET-based hardlockup detector disabled unless explicitly enabled
via a command-line argument. If such parameter is not given, the
initialization of the HPET-based hardlockup detector fails and the NMI
watchdog will fall back to use the perf-based implementation.

Implement the command-line parsing using an early_param, as
__setup("nmi_watchdog=") only parses generic options.

Cc: Andi Kleen <ak@linux.intel.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
Cc: iommu@lists.linux-foundation.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: x86@kernel.org
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
--
Changes since v5:
 * None

Changes since v4:
 * None

Changes since v3:
 * None

Changes since v2:
 * Do not imply that using nmi_watchdog=hpet means the detector is
   enabled. Instead, print a warning in such case.

Changes since v1:
 * Added documentation to the function handing the nmi_watchdog
   kernel command-line argument.
---
 .../admin-guide/kernel-parameters.txt         |  8 ++++++-
 arch/x86/kernel/watchdog_hld_hpet.c           | 22 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 269be339d738..89eae950fdb8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3370,7 +3370,7 @@
 			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
@@ -3381,6 +3381,12 @@
 			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,
+			it falls back to the default implementation (perf or
+			architecture-specific). Specifying hpet has no effect
+			if the NMI watchdog is not enabled (either at build time
+			or via the command line).
 
 			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 3effdbf29095..4413d5fb94f4 100644
--- a/arch/x86/kernel/watchdog_hld_hpet.c
+++ b/arch/x86/kernel/watchdog_hld_hpet.c
@@ -379,6 +379,28 @@ void hardlockup_detector_hpet_start(void)
 	enable_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 (!str)
+		return -EINVAL;
+
+	if (parse_option_str(str, "hpet"))
+		hardlockup_use_hpet = true;
+
+	if (!nmi_watchdog_user_enabled && hardlockup_use_hpet)
+		pr_err("Selecting HPET NMI watchdog has no effect with NMI watchdog disabled\n");
+
+	return 0;
+}
+early_param("nmi_watchdog", hardlockup_detector_hpet_setup);
+
 /**
  * hardlockup_detector_hpet_init() - Initialize the hardlockup detector
  *
-- 
2.17.1

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