kernel/watchdog_perf.c - linux - Git at Google

 // 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;
 }
	// 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;
	}