[RFC PATCH 18/23] watchdog/hardlockup/hpet: Add the NMI watchdog operations

[Ricardo Neri]

Implement the start, stop and disable operations of the HPET-based NMI
watchdog. Given that a single timer is used to monitor all the CPUs in
the system, it is necessary to define a cpumask that keeps track of the
CPUs that can be monitored. This cpumask is protected with a spin lock.

As individual CPUs are put online and offline, this cpumask is updated.
CPUs are unconditionally cleared from the mask when going offline. When
going online, the CPU is set in the mask only if is one of the CPUs allowed
to be monitored by the watchdog.

It is not necessary to implement a start function. The NMI watchdog will
be enabled when there is at least one CPU to monitor.

The disable function clears the CPU mask and disables the timer.

Cc: Ashok Raj <ashok.raj at intel.com>
Cc: Andi Kleen <andi.kleen at intel.com>
Cc: Tony Luck <tony.luck at intel.com>
Cc: Borislav Petkov <bp at suse.de>
Cc: Jacob Pan <jacob.jun.pan at intel.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki at intel.com>
Cc: Don Zickus <dzickus at redhat.com>
Cc: Nicholas Piggin <npiggin at gmail.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Frederic Weisbecker <frederic at kernel.org>
Cc: Alexei Starovoitov <ast at kernel.org>
Cc: Babu Moger <babu.moger at oracle.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Cc: Masami Hiramatsu <mhiramat at kernel.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Philippe Ombredanne <pombredanne at nexb.com>
Cc: Colin Ian King <colin.king at canonical.com>
Cc: Byungchul Park <byungchul.park at lge.com>
Cc: "Paul E. McKenney" <paulmck at linux.vnet.ibm.com>
Cc: "Luis R. Rodriguez" <mcgrof at kernel.org>
Cc: Waiman Long <longman at redhat.com>
Cc: Josh Poimboeuf <jpoimboe at redhat.com>
Cc: Randy Dunlap <rdunlap at infradead.org>
Cc: Davidlohr Bueso <dave at stgolabs.net>
Cc: Christoffer Dall <cdall at linaro.org>
Cc: Marc Zyngier <marc.zyngier at arm.com>
Cc: Kai-Heng Feng <kai.heng.feng at canonical.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Cc: David Rientjes <rientjes at google.com>
Cc: "Ravi V. Shankar" <ravi.v.shankar at intel.com>
Cc: x86 at kernel.org
Cc: iommu at lists.linux-foundation.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon at linux.intel.com>
---
 arch/x86/include/asm/hpet.h |  2 +
 include/linux/nmi.h         |  1 +
 kernel/watchdog_hld_hpet.c  | 98 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 101 insertions(+)

diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h
index 33309b7..6ace2d1 100644
--- a/arch/x86/include/asm/hpet.h
+++ b/arch/x86/include/asm/hpet.h
@@ -124,6 +124,8 @@ struct hpet_hld_data {
 	u32		irq;
 	u32		flags;
 	u64		ticks_per_second;
+	struct cpumask	monitored_mask;
+	spinlock_t	lock; /* serialized access to monitored_mask */
 };
 
 extern struct hpet_hld_data *hpet_hardlockup_detector_assign_timer(void);
diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index e608762..23e20d2 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -129,6 +129,7 @@ struct nmi_watchdog_ops {
 };
 
 extern struct nmi_watchdog_ops hardlockup_detector_perf_ops;
+extern struct nmi_watchdog_ops hardlockup_detector_hpet_ops;
 
 void watchdog_nmi_stop(void);
 void watchdog_nmi_start(void);
diff --git a/kernel/watchdog_hld_hpet.c b/kernel/watchdog_hld_hpet.c
index 3bedffa..857e051 100644
--- a/kernel/watchdog_hld_hpet.c
+++ b/kernel/watchdog_hld_hpet.c
@@ -345,6 +345,91 @@ static int setup_hpet_irq(struct hpet_hld_data *hdata)
 }
 
 /**
+ * hardlockup_detector_hpet_enable() - Enable the hardlockup detector
+ *
+ * The hardlockup detector is enabled for the CPU that executes the
+ * function. It is only enabled if such CPU is allowed to be monitored
+ * by the lockup detector.
+ *
+ * Returns:
+ *
+ * None
+ *
+ */
+static void hardlockup_detector_hpet_enable(void)
+{
+	struct cpumask *allowed = watchdog_get_allowed_cpumask();
+	unsigned int cpu = smp_processor_id();
+
+	if (!hld_data)
+		return;
+
+	if (!cpumask_test_cpu(cpu, allowed))
+		return;
+
+	spin_lock(&hld_data->lock);
+
+	cpumask_set_cpu(cpu, &hld_data->monitored_mask);
+
+	/*
+	 * If this is the first CPU to be monitored, set everything in motion:
+	 * move the interrupt to this CPU, kick and enable the timer.
+	 */
+	if (cpumask_weight(&hld_data->monitored_mask) == 1) {
+		if (irq_set_affinity(hld_data->irq, cpumask_of(cpu))) {
+			spin_unlock(&hld_data->lock);
+			pr_err("Unable to enable on CPU %d.!\n", cpu);
+			return;
+		}
+
+		kick_timer(hld_data);
+		enable(hld_data);
+	}
+
+	spin_unlock(&hld_data->lock);
+}
+
+/**
+ * hardlockup_detector_hpet_disable() - Disable the hardlockup detector
+ *
+ * The hardlockup detector is disabled for the CPU that executes the
+ * function.
+ *
+ * None
+ */
+static void hardlockup_detector_hpet_disable(void)
+{
+	if (!hld_data)
+		return;
+
+	spin_lock(&hld_data->lock);
+
+	cpumask_clear_cpu(smp_processor_id(), &hld_data->monitored_mask);
+
+	/* Only disable the timer if there are no more CPUs to monitor. */
+	if (!cpumask_weight(&hld_data->monitored_mask))
+		disable(hld_data);
+
+	spin_unlock(&hld_data->lock);
+}
+
+/**
+ * hardlockup_detector_hpet_stop() - Stop the NMI watchdog on all CPUs
+ *
+ * Returns:
+ *
+ * None
+ */
+static void hardlockup_detector_hpet_stop(void)
+{
+	disable(hld_data);
+
+	spin_lock(&hld_data->lock);
+	cpumask_clear(&hld_data->monitored_mask);
+	spin_unlock(&hld_data->lock);
+}
+
+/**
  * hardlockup_detector_hpet_init() - Initialize the hardlockup detector
  *
  * Only initialize and configure the detector if an HPET is available on the
@@ -383,5 +468,18 @@ static int __init hardlockup_detector_hpet_init(void)
 	 */
 	disable(hld_data);
 
+	spin_lock_init(&hld_data->lock);
+
+	spin_lock(&hld_data->lock);
+	cpumask_clear(&hld_data->monitored_mask);
+	spin_unlock(&hld_data->lock);
+
 	return 0;
 }
+
+struct nmi_watchdog_ops hardlockup_detector_hpet_ops = {
+	.init		= hardlockup_detector_hpet_init,
+	.enable		= hardlockup_detector_hpet_enable,
+	.disable	= hardlockup_detector_hpet_disable,
+	.stop		= hardlockup_detector_hpet_stop
+};
-- 
2.7.4