1 files changed, 261 insertions, 0 deletions
diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c
new file mode 100644
index 0000000000..8ea00c4a24
--- /dev/null
+++ b/kernel/watchdog_perf.c
@@ -0,0 +1,261 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Detect hard lockups on a system using perf
+ *
+ * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
+ *
+ * Note: Most of this code is borrowed heavily from the original softlockup
+ * detector, so thanks to Ingo for the initial implementation.
+ * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
+ * to those contributors as well.
+ */
+
+#define pr_fmt(fmt) "NMI watchdog: " fmt
+
+#include <linux/nmi.h>
+#include <linux/atomic.h>
+#include <linux/module.h>
+#include <linux/sched/debug.h>
+
+#include <asm/irq_regs.h>
+#include <linux/perf_event.h>
+
+static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
+static DEFINE_PER_CPU(struct perf_event *, dead_event);
+static struct cpumask dead_events_mask;
+
+static atomic_t watchdog_cpus = ATOMIC_INIT(0);
+
+#ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
+static DEFINE_PER_CPU(ktime_t, last_timestamp);
+static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
+static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
+
+void watchdog_update_hrtimer_threshold(u64 period)
+{
+	/*
+	 * The hrtimer runs with a period of (watchdog_threshold * 2) / 5
+	 *
+	 * So it runs effectively with 2.5 times the rate of the NMI
+	 * watchdog. That means the hrtimer should fire 2-3 times before
+	 * the NMI watchdog expires. The NMI watchdog on x86 is based on
+	 * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
+	 * might run way faster than expected and the NMI fires in a
+	 * smaller period than the one deduced from the nominal CPU
+	 * frequency. Depending on the Turbo-Mode factor this might be fast
+	 * enough to get the NMI period smaller than the hrtimer watchdog
+	 * period and trigger false positives.
+	 *
+	 * The sample threshold is used to check in the NMI handler whether
+	 * the minimum time between two NMI samples has elapsed. That
+	 * prevents false positives.
+	 *
+	 * Set this to 4/5 of the actual watchdog threshold period so the
+	 * hrtimer is guaranteed to fire at least once within the real
+	 * watchdog threshold.
+	 */
+	watchdog_hrtimer_sample_threshold = period * 2;
+}
+
+static bool watchdog_check_timestamp(void)
+{
+	ktime_t delta, now = ktime_get_mono_fast_ns();
+
+	delta = now - __this_cpu_read(last_timestamp);
+	if (delta < watchdog_hrtimer_sample_threshold) {
+		/*
+		 * If ktime is jiffies based, a stalled timer would prevent
+		 * jiffies from being incremented and the filter would look
+		 * at a stale timestamp and never trigger.
+		 */
+		if (__this_cpu_inc_return(nmi_rearmed) < 10)
+			return false;
+	}
+	__this_cpu_write(nmi_rearmed, 0);
+	__this_cpu_write(last_timestamp, now);
+	return true;
+}
+#else
+static inline bool watchdog_check_timestamp(void)
+{
+	return true;
+}
+#endif
+
+static struct perf_event_attr wd_hw_attr = {
+	.type		= PERF_TYPE_HARDWARE,
+	.config		= PERF_COUNT_HW_CPU_CYCLES,
+	.size		= sizeof(struct perf_event_attr),
+	.pinned		= 1,
+	.disabled	= 1,
+};
+
+/* Callback function for perf event subsystem */
+static void watchdog_overflow_callback(struct perf_event *event,
+				       struct perf_sample_data *data,
+				       struct pt_regs *regs)
+{
+	/* Ensure the watchdog never gets throttled */
+	event->hw.interrupts = 0;
+
+	if (!watchdog_check_timestamp())
+		return;
+
+	watchdog_hardlockup_check(smp_processor_id(), regs);
+}
+
+static int hardlockup_detector_event_create(void)
+{
+	unsigned int cpu;
+	struct perf_event_attr *wd_attr;
+	struct perf_event *evt;
+
+	/*
+	 * Preemption is not disabled because memory will be allocated.
+	 * Ensure CPU-locality by calling this in per-CPU kthread.
+	 */
+	WARN_ON(!is_percpu_thread());
+	cpu = raw_smp_processor_id();
+	wd_attr = &wd_hw_attr;
+	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
+
+	/* Try to register using hardware perf events */
+	evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
+					       watchdog_overflow_callback, NULL);
+	if (IS_ERR(evt)) {
+		pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,
+			 PTR_ERR(evt));
+		return PTR_ERR(evt);
+	}
+	this_cpu_write(watchdog_ev, evt);
+	return 0;
+}
+
+/**
+ * watchdog_hardlockup_enable - Enable the local event
+ *
+ * @cpu: The CPU to enable hard lockup on.
+ */
+void watchdog_hardlockup_enable(unsigned int cpu)
+{
+	WARN_ON_ONCE(cpu != smp_processor_id());
+
+	if (hardlockup_detector_event_create())
+		return;
+
+	/* use original value for check */
+	if (!atomic_fetch_inc(&watchdog_cpus))
+		pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
+
+	perf_event_enable(this_cpu_read(watchdog_ev));
+}
+
+/**
+ * watchdog_hardlockup_disable - Disable the local event
+ *
+ * @cpu: The CPU to enable hard lockup on.
+ */
+void watchdog_hardlockup_disable(unsigned int cpu)
+{
+	struct perf_event *event = this_cpu_read(watchdog_ev);
+
+	WARN_ON_ONCE(cpu != smp_processor_id());
+
+	if (event) {
+		perf_event_disable(event);
+		this_cpu_write(watchdog_ev, NULL);
+		this_cpu_write(dead_event, event);
+		cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
+		atomic_dec(&watchdog_cpus);
+	}
+}
+
+/**
+ * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
+ *
+ * Called from lockup_detector_cleanup(). Serialized by the caller.
+ */
+void hardlockup_detector_perf_cleanup(void)
+{
+	int cpu;
+
+	for_each_cpu(cpu, &dead_events_mask) {
+		struct perf_event *event = per_cpu(dead_event, cpu);
+
+		/*
+		 * Required because for_each_cpu() reports  unconditionally
+		 * CPU0 as set on UP kernels. Sigh.
+		 */
+		if (event)
+			perf_event_release_kernel(event);
+		per_cpu(dead_event, cpu) = NULL;
+	}
+	cpumask_clear(&dead_events_mask);
+}
+
+/**
+ * hardlockup_detector_perf_stop - Globally stop watchdog events
+ *
+ * Special interface for x86 to handle the perf HT bug.
+ */
+void __init hardlockup_detector_perf_stop(void)
+{
+	int cpu;
+
+	lockdep_assert_cpus_held();
+
+	for_each_online_cpu(cpu) {
+		struct perf_event *event = per_cpu(watchdog_ev, cpu);
+
+		if (event)
+			perf_event_disable(event);
+	}
+}
+
+/**
+ * hardlockup_detector_perf_restart - Globally restart watchdog events
+ *
+ * Special interface for x86 to handle the perf HT bug.
+ */
+void __init hardlockup_detector_perf_restart(void)
+{
+	int cpu;
+
+	lockdep_assert_cpus_held();
+
+	if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED))
+		return;
+
+	for_each_online_cpu(cpu) {
+		struct perf_event *event = per_cpu(watchdog_ev, cpu);
+
+		if (event)
+			perf_event_enable(event);
+	}
+}
+
+bool __weak __init arch_perf_nmi_is_available(void)
+{
+	return true;
+}
+
+/**
+ * watchdog_hardlockup_probe - Probe whether NMI event is available at all
+ */
+int __init watchdog_hardlockup_probe(void)
+{
+	int ret;
+
+	if (!arch_perf_nmi_is_available())
+		return -ENODEV;
+
+	ret = hardlockup_detector_event_create();
+
+	if (ret) {
+		pr_info("Perf NMI watchdog permanently disabled\n");
+	} else {
+		perf_event_release_kernel(this_cpu_read(watchdog_ev));
+		this_cpu_write(watchdog_ev, NULL);
+	}
+	return ret;
+}