kernel/watchdog_hld.c - manifest_repos/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Detect hard lockups on a system
  *
  * 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(bool, hard_watchdog_warn);
 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
 #ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
 static cpumask_t __read_mostly watchdog_cpus;
 #endif
 #ifndef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
 static DEFINE_PER_CPU(struct perf_event *, dead_event);
 static struct cpumask dead_events_mask;
 #else
 DECLARE_PER_CPU(unsigned long, hrtimer_interrupts);
 DECLARE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 #endif

 static unsigned long __maybe_unused hardlockup_allcpu_dumped;
 #ifndef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
 static atomic_t watchdog_cpus = ATOMIC_INIT(0);
 #endif

 #ifndef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
 notrace void arch_touch_nmi_watchdog(void)
 {
 	/*
 	 * Using __raw here because some code paths have
 	 * preemption enabled.  If preemption is enabled
 	 * then interrupts should be enabled too, in which
 	 * case we shouldn't have to worry about the watchdog
 	 * going off.
 	 */
 	raw_cpu_write(watchdog_nmi_touch, true);
 }
 EXPORT_SYMBOL(arch_touch_nmi_watchdog);
 #endif

 #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

 #ifndef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
 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 (__this_cpu_read(watchdog_nmi_touch) == true) {
 		__this_cpu_write(watchdog_nmi_touch, false);
 		return;
 	}

 	if (!watchdog_check_timestamp())
 		return;

 	/* check for a hardlockup
 	 * This is done by making sure our timer interrupt
 	 * is incrementing.  The timer interrupt should have
 	 * fired multiple times before we overflow'd.  If it hasn't
 	 * then this is a good indication the cpu is stuck
 	 */
 	if (is_hardlockup()) {
 		int this_cpu = smp_processor_id();

 		/* only print hardlockups once */
 		if (__this_cpu_read(hard_watchdog_warn) == true)
 			return;

 		pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n",
 			 this_cpu);
 		print_modules();
 		print_irqtrace_events(current);
 		if (regs)
 			show_regs(regs);
 		else
 			dump_stack();

 		/*
 		 * Perform all-CPU dump only once to avoid multiple hardlockups
 		 * generating interleaving traces
 		 */
 		if (sysctl_hardlockup_all_cpu_backtrace &&
 				!test_and_set_bit(0, &hardlockup_allcpu_dumped))
 			trigger_allbutself_cpu_backtrace();

 #ifdef CONFIG_AMLOGIC_DEBUG_LOCKUP
 		pr_lockup_info(this_cpu);
 #endif

 		if (hardlockup_panic)
 			nmi_panic(regs, "Hard LOCKUP");

 		__this_cpu_write(hard_watchdog_warn, true);
 		return;
 	}

 	__this_cpu_write(hard_watchdog_warn, false);
 	return;
 }
 #endif

 #ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
 static unsigned int watchdog_next_cpu(unsigned int cpu)
 {
 	cpumask_t cpus = watchdog_cpus;
 	unsigned int next_cpu;

 	next_cpu = cpumask_next(cpu, &cpus);
 	if (next_cpu >= nr_cpu_ids)
 		next_cpu = cpumask_first(&cpus);

 	if (next_cpu == cpu)
 		return nr_cpu_ids;

 	return next_cpu;
 }

 static int is_hardlockup_other_cpu(unsigned int cpu)
 {
 	unsigned long hrint = per_cpu(hrtimer_interrupts, cpu);

 	if (per_cpu(hrtimer_interrupts_saved, cpu) == hrint)
 		return 1;

 	per_cpu(hrtimer_interrupts_saved, cpu) = hrint;
 	return 0;
 }

 void watchdog_check_hardlockup_other_cpu(void)
 {
 	unsigned int next_cpu;

 	/*
 	 * Test for hardlockups every 3 samples.  The sample period is
 	 *  watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over
 	 *  watchdog_thresh (over by 20%).
 	 */
 	if (__this_cpu_read(hrtimer_interrupts) % 3 != 0)
 		return;

 	/* check for a hardlockup on the next cpu */
 	next_cpu = watchdog_next_cpu(smp_processor_id());
 	if (next_cpu >= nr_cpu_ids)
 		return;

 	/*mem barrier*/
 	smp_rmb();

 	if (per_cpu(watchdog_nmi_touch, next_cpu) == true) {
 		per_cpu(watchdog_nmi_touch, next_cpu) = false;
 		return;
 	}

 	if (is_hardlockup_other_cpu(next_cpu)) {
 		/* only warn once */
 		if (per_cpu(hard_watchdog_warn, next_cpu) == true)
 			return;

 #ifdef CONFIG_AMLOGIC_DEBUG_LOCKUP
 	pr_lockup_info(next_cpu);
 #endif

 		if (hardlockup_panic)
 			panic("Watchdog detected hard LOCKUP on cpu %u",
 			      next_cpu);
 		else
 			WARN(1, "Watchdog detected hard LOCKUP on cpu %u",
 			     next_cpu);

 		per_cpu(hard_watchdog_warn, next_cpu) = true;
 	} else {
 		per_cpu(hard_watchdog_warn, next_cpu) = false;
 	}
 }
 #else
 static inline void watchdog_check_hardlockup_other_cpu(void) { return; }
 #endif

 #ifdef CONFIG_HAVE_NMI_WATCHDOG
 static int hardlockup_detector_event_create(void)
 {
 	unsigned int cpu = smp_processor_id();
 	struct perf_event_attr *wd_attr;
 	struct perf_event *evt;

 	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;
 }

 /**
  * hardlockup_detector_perf_enable - Enable the local event
  */
 void hardlockup_detector_perf_enable(void)
 {
 	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));
 }

 /**
  * hardlockup_detector_perf_disable - Disable the local event
  */
 void hardlockup_detector_perf_disable(void)
 {
 	struct perf_event *event = this_cpu_read(watchdog_ev);

 	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 & NMI_WATCHDOG_ENABLED))
 		return;

 	for_each_online_cpu(cpu) {
 		struct perf_event *event = per_cpu(watchdog_ev, cpu);

 		if (event)
 			perf_event_enable(event);
 	}
 }

 /**
  * hardlockup_detector_perf_init - Probe whether NMI event is available at all
  */
 int __init hardlockup_detector_perf_init(void)
 {
 	int 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;
 }
 #else
 #ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
 int watchdog_nmi_enable(unsigned int cpu)
 {
 	/*
 	 * The new cpu will be marked online before the first hrtimer interrupt
 	 * runs on it.  If another cpu tests for a hardlockup on the new cpu
 	 * before it has run its first hrtimer, it will get a false positive.
 	 * Touch the watchdog on the new cpu to delay the first check for at
 	 * least 3 sampling periods to guarantee one hrtimer has run on the new
 	 * cpu.
 	 */
 	per_cpu(watchdog_nmi_touch, cpu) = true;
 	/*mem barrier*/
 	smp_wmb();
 	cpumask_set_cpu(cpu, &watchdog_cpus);
 	return 0;
 }

 void watchdog_nmi_disable(unsigned int cpu)
 {
 	unsigned int next_cpu = watchdog_next_cpu(cpu);

 	/*
 	 * Offlining this cpu will cause the cpu before this one to start
 	 * checking the one after this one.  If this cpu just finished checking
 	 * the next cpu and updating hrtimer_interrupts_saved, and then the
 	 * previous cpu checks it within one sample period, it will trigger a
 	 * false positive.  Touch the watchdog on the next cpu to prevent it.
 	 */
 	if (next_cpu < nr_cpu_ids)
 		per_cpu(watchdog_nmi_touch, next_cpu) = true;
 	/*mem barrier*/
 	smp_wmb();
 	cpumask_clear_cpu(cpu, &watchdog_cpus);
 }
 #else
 int watchdog_nmi_enable(unsigned int cpu) { return 0; }
 void watchdog_nmi_disable(unsigned int cpu) { return; }
 #endif /* CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU */
 #endif /* CONFIG_HAVE_NMI_WATCHDOG*/
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Detect hard lockups on a system
	*
	* 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(bool, hard_watchdog_warn);
	static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
	#ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
	static cpumask_t __read_mostly watchdog_cpus;
	#endif
	#ifndef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
	static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
	static DEFINE_PER_CPU(struct perf_event *, dead_event);
	static struct cpumask dead_events_mask;
	#else
	DECLARE_PER_CPU(unsigned long, hrtimer_interrupts);
	DECLARE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
	#endif

	static unsigned long __maybe_unused hardlockup_allcpu_dumped;
	#ifndef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
	static atomic_t watchdog_cpus = ATOMIC_INIT(0);
	#endif

	#ifndef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
	notrace void arch_touch_nmi_watchdog(void)
	{
	/*
	* Using __raw here because some code paths have
	* preemption enabled. If preemption is enabled
	* then interrupts should be enabled too, in which
	* case we shouldn't have to worry about the watchdog
	* going off.
	*/
	raw_cpu_write(watchdog_nmi_touch, true);
	}
	EXPORT_SYMBOL(arch_touch_nmi_watchdog);
	#endif

	#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

	#ifndef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
	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 (__this_cpu_read(watchdog_nmi_touch) == true) {
	__this_cpu_write(watchdog_nmi_touch, false);
	return;
	}

	if (!watchdog_check_timestamp())
	return;

	/* check for a hardlockup
	* This is done by making sure our timer interrupt
	* is incrementing. The timer interrupt should have
	* fired multiple times before we overflow'd. If it hasn't
	* then this is a good indication the cpu is stuck
	*/
	if (is_hardlockup()) {
	int this_cpu = smp_processor_id();

	/* only print hardlockups once */
	if (__this_cpu_read(hard_watchdog_warn) == true)
	return;

	pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n",
	this_cpu);
	print_modules();
	print_irqtrace_events(current);
	if (regs)
	show_regs(regs);
	else
	dump_stack();

	/*
	* Perform all-CPU dump only once to avoid multiple hardlockups
	* generating interleaving traces
	*/
	if (sysctl_hardlockup_all_cpu_backtrace &&
	!test_and_set_bit(0, &hardlockup_allcpu_dumped))
	trigger_allbutself_cpu_backtrace();

	#ifdef CONFIG_AMLOGIC_DEBUG_LOCKUP
	pr_lockup_info(this_cpu);
	#endif

	if (hardlockup_panic)
	nmi_panic(regs, "Hard LOCKUP");

	__this_cpu_write(hard_watchdog_warn, true);
	return;
	}

	__this_cpu_write(hard_watchdog_warn, false);
	return;
	}
	#endif

	#ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
	static unsigned int watchdog_next_cpu(unsigned int cpu)
	{
	cpumask_t cpus = watchdog_cpus;
	unsigned int next_cpu;

	next_cpu = cpumask_next(cpu, &cpus);
	if (next_cpu >= nr_cpu_ids)
	next_cpu = cpumask_first(&cpus);

	if (next_cpu == cpu)
	return nr_cpu_ids;

	return next_cpu;
	}

	static int is_hardlockup_other_cpu(unsigned int cpu)
	{
	unsigned long hrint = per_cpu(hrtimer_interrupts, cpu);

	if (per_cpu(hrtimer_interrupts_saved, cpu) == hrint)
	return 1;

	per_cpu(hrtimer_interrupts_saved, cpu) = hrint;
	return 0;
	}

	void watchdog_check_hardlockup_other_cpu(void)
	{
	unsigned int next_cpu;

	/*
	* Test for hardlockups every 3 samples. The sample period is
	* watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over
	* watchdog_thresh (over by 20%).
	*/
	if (__this_cpu_read(hrtimer_interrupts) % 3 != 0)
	return;

	/* check for a hardlockup on the next cpu */
	next_cpu = watchdog_next_cpu(smp_processor_id());
	if (next_cpu >= nr_cpu_ids)
	return;

	/mem barrier/
	smp_rmb();

	if (per_cpu(watchdog_nmi_touch, next_cpu) == true) {
	per_cpu(watchdog_nmi_touch, next_cpu) = false;
	return;
	}

	if (is_hardlockup_other_cpu(next_cpu)) {
	/* only warn once */
	if (per_cpu(hard_watchdog_warn, next_cpu) == true)
	return;

	#ifdef CONFIG_AMLOGIC_DEBUG_LOCKUP
	pr_lockup_info(next_cpu);
	#endif

	if (hardlockup_panic)
	panic("Watchdog detected hard LOCKUP on cpu %u",
	next_cpu);
	else
	WARN(1, "Watchdog detected hard LOCKUP on cpu %u",
	next_cpu);

	per_cpu(hard_watchdog_warn, next_cpu) = true;
	} else {
	per_cpu(hard_watchdog_warn, next_cpu) = false;
	}
	}
	#else
	static inline void watchdog_check_hardlockup_other_cpu(void) { return; }
	#endif

	#ifdef CONFIG_HAVE_NMI_WATCHDOG
	static int hardlockup_detector_event_create(void)
	{
	unsigned int cpu = smp_processor_id();
	struct perf_event_attr *wd_attr;
	struct perf_event *evt;

	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;
	}

	/**
	* hardlockup_detector_perf_enable - Enable the local event
	*/
	void hardlockup_detector_perf_enable(void)
	{
	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));
	}

	/**
	* hardlockup_detector_perf_disable - Disable the local event
	*/
	void hardlockup_detector_perf_disable(void)
	{
	struct perf_event *event = this_cpu_read(watchdog_ev);

	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 & NMI_WATCHDOG_ENABLED))
	return;

	for_each_online_cpu(cpu) {
	struct perf_event *event = per_cpu(watchdog_ev, cpu);

	if (event)
	perf_event_enable(event);
	}
	}

	/**
	* hardlockup_detector_perf_init - Probe whether NMI event is available at all
	*/
	int __init hardlockup_detector_perf_init(void)
	{
	int 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;
	}
	#else
	#ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
	int watchdog_nmi_enable(unsigned int cpu)
	{
	/*
	* The new cpu will be marked online before the first hrtimer interrupt
	* runs on it. If another cpu tests for a hardlockup on the new cpu
	* before it has run its first hrtimer, it will get a false positive.
	* Touch the watchdog on the new cpu to delay the first check for at
	* least 3 sampling periods to guarantee one hrtimer has run on the new
	* cpu.
	*/
	per_cpu(watchdog_nmi_touch, cpu) = true;
	/mem barrier/
	smp_wmb();
	cpumask_set_cpu(cpu, &watchdog_cpus);
	return 0;
	}

	void watchdog_nmi_disable(unsigned int cpu)
	{
	unsigned int next_cpu = watchdog_next_cpu(cpu);

	/*
	* Offlining this cpu will cause the cpu before this one to start
	* checking the one after this one. If this cpu just finished checking
	* the next cpu and updating hrtimer_interrupts_saved, and then the
	* previous cpu checks it within one sample period, it will trigger a
	* false positive. Touch the watchdog on the next cpu to prevent it.
	*/
	if (next_cpu < nr_cpu_ids)
	per_cpu(watchdog_nmi_touch, next_cpu) = true;
	/mem barrier/
	smp_wmb();
	cpumask_clear_cpu(cpu, &watchdog_cpus);
	}
	#else
	int watchdog_nmi_enable(unsigned int cpu) { return 0; }
	void watchdog_nmi_disable(unsigned int cpu) { return; }
	#endif /* CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU */
	#endif /* CONFIG_HAVE_NMI_WATCHDOG*/