[linux.git] / kernel / watchdog_hld.c

/*
 * 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/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);
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 unsigned long hardlockup_allcpu_dumped;
static bool hardlockup_detector_disabled;

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);

#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 (__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", 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();

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

		__this_cpu_write(hard_watchdog_warn, true);
		return;
	}

	__this_cpu_write(hard_watchdog_warn, false);
	return;
}

/*
 * People like the simple clean cpu node info on boot.
 * Reduce the watchdog noise by only printing messages
 * that are different from what cpu0 displayed.
 */
static unsigned long firstcpu_err;
static atomic_t watchdog_cpus;

int watchdog_nmi_enable(unsigned int cpu)
{
	struct perf_event_attr *wd_attr;
	struct perf_event *event = per_cpu(watchdog_ev, cpu);
	int firstcpu = 0;

	/* nothing to do if the hard lockup detector is disabled */
	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
		goto out;

	/* A failure disabled the hardlockup detector permanently */
	if (hardlockup_detector_disabled)
		return -ENODEV;

	/* is it already setup and enabled? */
	if (event && event->state > PERF_EVENT_STATE_OFF)
		goto out;

	/* it is setup but not enabled */
	if (event != NULL)
		goto out_enable;

	if (atomic_inc_return(&watchdog_cpus) == 1)
		firstcpu = 1;

	wd_attr = &wd_hw_attr;
	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);

	/* Try to register using hardware perf events */
	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);

	/* save the first cpu's error for future comparision */
	if (firstcpu && IS_ERR(event))
		firstcpu_err = PTR_ERR(event);

	if (!IS_ERR(event)) {
		/* only print for the first cpu initialized */
		if (firstcpu || firstcpu_err)
			pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
		goto out_save;
	}

	/* skip displaying the same error again */
	if (!firstcpu && (PTR_ERR(event) == firstcpu_err))
		return PTR_ERR(event);

	/* vary the KERN level based on the returned errno */
	if (PTR_ERR(event) == -EOPNOTSUPP)
		pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
	else if (PTR_ERR(event) == -ENOENT)
		pr_warn("disabled (cpu%i): hardware events not enabled\n",
			 cpu);
	else
		pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
			cpu, PTR_ERR(event));

	pr_info("Disabling hard lockup detector permanently\n");
	hardlockup_detector_disabled = true;

	return PTR_ERR(event);

	/* success path */
out_save:
	per_cpu(watchdog_ev, cpu) = event;
out_enable:
	perf_event_enable(per_cpu(watchdog_ev, cpu));
out:
	return 0;
}

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_info("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;

	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);

		/* watchdog_nmi_enable() expects this to be zero initially. */
		if (atomic_dec_and_test(&watchdog_cpus))
			firstcpu_err = 0;
	}
}

/**
 * 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);

		per_cpu(dead_event, cpu) = NULL;
		perf_event_release_kernel(event);
	}
	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 permanetely disabled\n");
	} else {
		perf_event_release_kernel(this_cpu_read(watchdog_ev));
		this_cpu_write(watchdog_ev, NULL);
	}
	return ret;
}
Commit	Line	Data
73ce0511 BM	1	/*
	2	* Detect hard lockups on a system
	3	*
	4	* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
	5	*
	6	* Note: Most of this code is borrowed heavily from the original softlockup
	7	* detector, so thanks to Ingo for the initial implementation.
	8	* Some chunks also taken from the old x86-specific nmi watchdog code, thanks
	9	* to those contributors as well.
	10	*/
	11
	12	#define pr_fmt(fmt) "NMI watchdog: " fmt
	13
	14	#include <linux/nmi.h>
	15	#include <linux/module.h>
b17b0153 IM	16	#include <linux/sched/debug.h>
b17b0153 IM	17
73ce0511 BM	18	#include <asm/irq_regs.h>
	19	#include <linux/perf_event.h>
	20
	21	static DEFINE_PER_CPU(bool, hard_watchdog_warn);
	22	static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
	23	static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
941154bd TG	24	static DEFINE_PER_CPU(struct perf_event *, dead_event);
941154bd TG	25	static struct cpumask dead_events_mask;
73ce0511	26
73ce0511	27	static unsigned long hardlockup_allcpu_dumped;
20d853fd	28	static bool hardlockup_detector_disabled;
73ce0511	29
f2e0cff8	30	void arch_touch_nmi_watchdog(void)
73ce0511 BM	31	{
	32	/*
	33	* Using __raw here because some code paths have
	34	* preemption enabled. If preemption is enabled
	35	* then interrupts should be enabled too, in which
	36	* case we shouldn't have to worry about the watchdog
	37	* going off.
	38	*/
	39	raw_cpu_write(watchdog_nmi_touch, true);
73ce0511	40	}
f2e0cff8	41	EXPORT_SYMBOL(arch_touch_nmi_watchdog);
73ce0511	42
7edaeb68 TG	43	#ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
	44	static DEFINE_PER_CPU(ktime_t, last_timestamp);
	45	static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
	46	static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
	47
	48	void watchdog_update_hrtimer_threshold(u64 period)
	49	{
	50	/*
	51	* The hrtimer runs with a period of (watchdog_threshold * 2) / 5
	52	*
	53	* So it runs effectively with 2.5 times the rate of the NMI
	54	* watchdog. That means the hrtimer should fire 2-3 times before
	55	* the NMI watchdog expires. The NMI watchdog on x86 is based on
	56	* unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
	57	* might run way faster than expected and the NMI fires in a
	58	* smaller period than the one deduced from the nominal CPU
	59	* frequency. Depending on the Turbo-Mode factor this might be fast
	60	* enough to get the NMI period smaller than the hrtimer watchdog
	61	* period and trigger false positives.
	62	*
	63	* The sample threshold is used to check in the NMI handler whether
	64	* the minimum time between two NMI samples has elapsed. That
	65	* prevents false positives.
	66	*
	67	* Set this to 4/5 of the actual watchdog threshold period so the
	68	* hrtimer is guaranteed to fire at least once within the real
	69	* watchdog threshold.
	70	*/
	71	watchdog_hrtimer_sample_threshold = period * 2;
	72	}
	73
	74	static bool watchdog_check_timestamp(void)
	75	{
	76	ktime_t delta, now = ktime_get_mono_fast_ns();
	77
	78	delta = now - __this_cpu_read(last_timestamp);
	79	if (delta < watchdog_hrtimer_sample_threshold) {
	80	/*
	81	* If ktime is jiffies based, a stalled timer would prevent
	82	* jiffies from being incremented and the filter would look
	83	* at a stale timestamp and never trigger.
	84	*/
	85	if (__this_cpu_inc_return(nmi_rearmed) < 10)
	86	return false;
	87	}
	88	__this_cpu_write(nmi_rearmed, 0);
	89	__this_cpu_write(last_timestamp, now);
	90	return true;
	91	}
	92	#else
	93	static inline bool watchdog_check_timestamp(void)
	94	{
	95	return true;
	96	}
	97	#endif
	98
73ce0511 BM	99	static struct perf_event_attr wd_hw_attr = {
	100	.type = PERF_TYPE_HARDWARE,
	101	.config = PERF_COUNT_HW_CPU_CYCLES,
	102	.size = sizeof(struct perf_event_attr),
	103	.pinned = 1,
	104	.disabled = 1,
	105	};
	106
	107	/* Callback function for perf event subsystem */
	108	static void watchdog_overflow_callback(struct perf_event *event,
01f0a027 TG	109	struct perf_sample_data *data,
01f0a027 TG	110	struct pt_regs *regs)
73ce0511 BM	111	{
	112	/* Ensure the watchdog never gets throttled */
	113	event->hw.interrupts = 0;
	114
	115	if (__this_cpu_read(watchdog_nmi_touch) == true) {
	116	__this_cpu_write(watchdog_nmi_touch, false);
	117	return;
	118	}
	119
7edaeb68 TG	120	if (!watchdog_check_timestamp())
	121	return;
	122
73ce0511 BM	123	/* check for a hardlockup
	124	* This is done by making sure our timer interrupt
	125	* is incrementing. The timer interrupt should have
	126	* fired multiple times before we overflow'd. If it hasn't
	127	* then this is a good indication the cpu is stuck
	128	*/
	129	if (is_hardlockup()) {
	130	int this_cpu = smp_processor_id();
	131
	132	/* only print hardlockups once */
	133	if (__this_cpu_read(hard_watchdog_warn) == true)
	134	return;
	135
	136	pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
	137	print_modules();
	138	print_irqtrace_events(current);
	139	if (regs)
	140	show_regs(regs);
	141	else
	142	dump_stack();
	143
	144	/*
	145	* Perform all-CPU dump only once to avoid multiple hardlockups
	146	* generating interleaving traces
	147	*/
	148	if (sysctl_hardlockup_all_cpu_backtrace &&
	149	!test_and_set_bit(0, &hardlockup_allcpu_dumped))
	150	trigger_allbutself_cpu_backtrace();
	151
	152	if (hardlockup_panic)
	153	nmi_panic(regs, "Hard LOCKUP");
	154
	155	__this_cpu_write(hard_watchdog_warn, true);
	156	return;
	157	}
	158
	159	__this_cpu_write(hard_watchdog_warn, false);
	160	return;
	161	}
	162
	163	/*
	164	* People like the simple clean cpu node info on boot.
	165	* Reduce the watchdog noise by only printing messages
	166	* that are different from what cpu0 displayed.
	167	*/
8dcde9de PB	168	static unsigned long firstcpu_err;
8dcde9de PB	169	static atomic_t watchdog_cpus;
73ce0511 BM	170
	171	int watchdog_nmi_enable(unsigned int cpu)
	172	{
	173	struct perf_event_attr *wd_attr;
	174	struct perf_event *event = per_cpu(watchdog_ev, cpu);
8dcde9de	175	int firstcpu = 0;
73ce0511 BM	176
	177	/* nothing to do if the hard lockup detector is disabled */
	178	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
	179	goto out;
	180
20d853fd TG	181	/* A failure disabled the hardlockup detector permanently */
	182	if (hardlockup_detector_disabled)
	183	return -ENODEV;
	184
73ce0511 BM	185	/* is it already setup and enabled? */
	186	if (event && event->state > PERF_EVENT_STATE_OFF)
	187	goto out;
	188
	189	/* it is setup but not enabled */
	190	if (event != NULL)
	191	goto out_enable;
	192
8dcde9de PB	193	if (atomic_inc_return(&watchdog_cpus) == 1)
	194	firstcpu = 1;
	195
73ce0511 BM	196	wd_attr = &wd_hw_attr;
	197	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
	198
	199	/* Try to register using hardware perf events */
	200	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
	201
8dcde9de PB	202	/* save the first cpu's error for future comparision */
	203	if (firstcpu && IS_ERR(event))
	204	firstcpu_err = PTR_ERR(event);
73ce0511 BM	205
73ce0511 BM	206	if (!IS_ERR(event)) {
8dcde9de PB	207	/* only print for the first cpu initialized */
8dcde9de PB	208	if (firstcpu \|\| firstcpu_err)
73ce0511 BM	209	pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
	210	goto out_save;
	211	}
	212
73ce0511	213	/* skip displaying the same error again */
8dcde9de	214	if (!firstcpu && (PTR_ERR(event) == firstcpu_err))
73ce0511 BM	215	return PTR_ERR(event);
	216
	217	/* vary the KERN level based on the returned errno */
	218	if (PTR_ERR(event) == -EOPNOTSUPP)
	219	pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
	220	else if (PTR_ERR(event) == -ENOENT)
	221	pr_warn("disabled (cpu%i): hardware events not enabled\n",
	222	cpu);
	223	else
	224	pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
	225	cpu, PTR_ERR(event));
	226
20d853fd TG	227	pr_info("Disabling hard lockup detector permanently\n");
20d853fd TG	228	hardlockup_detector_disabled = true;
73ce0511 BM	229
	230	return PTR_ERR(event);
	231
	232	/* success path */
	233	out_save:
	234	per_cpu(watchdog_ev, cpu) = event;
	235	out_enable:
	236	perf_event_enable(per_cpu(watchdog_ev, cpu));
	237	out:
	238	return 0;
	239	}
	240
178b9f7a TG	241	static int hardlockup_detector_event_create(void)
	242	{
	243	unsigned int cpu = smp_processor_id();
	244	struct perf_event_attr *wd_attr;
	245	struct perf_event *evt;
	246
	247	wd_attr = &wd_hw_attr;
	248	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
	249
	250	/* Try to register using hardware perf events */
	251	evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
	252	watchdog_overflow_callback, NULL);
	253	if (IS_ERR(evt)) {
	254	pr_info("Perf event create on CPU %d failed with %ld\n", cpu,
	255	PTR_ERR(evt));
	256	return PTR_ERR(evt);
	257	}
	258	this_cpu_write(watchdog_ev, evt);
	259	return 0;
	260	}
	261
2a1b8ee4 TG	262	/**
	263	* hardlockup_detector_perf_enable - Enable the local event
	264	*/
	265	void hardlockup_detector_perf_enable(void)
	266	{
	267	if (hardlockup_detector_event_create())
	268	return;
	269
	270	perf_event_enable(this_cpu_read(watchdog_ev));
	271	}
	272
941154bd TG	273	/**
	274	* hardlockup_detector_perf_disable - Disable the local event
	275	*/
	276	void hardlockup_detector_perf_disable(void)
73ce0511	277	{
941154bd	278	struct perf_event *event = this_cpu_read(watchdog_ev);
73ce0511 BM	279
	280	if (event) {
	281	perf_event_disable(event);
941154bd TG	282	this_cpu_write(watchdog_ev, NULL);
	283	this_cpu_write(dead_event, event);
	284	cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
8dcde9de	285
73ce0511	286	/* watchdog_nmi_enable() expects this to be zero initially. */
8dcde9de PB	287	if (atomic_dec_and_test(&watchdog_cpus))
8dcde9de PB	288	firstcpu_err = 0;
73ce0511 BM	289	}
73ce0511 BM	290	}
d0b6e0a8	291
941154bd TG	292	/**
	293	* hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
	294	*
	295	* Called from lockup_detector_cleanup(). Serialized by the caller.
	296	*/
	297	void hardlockup_detector_perf_cleanup(void)
	298	{
	299	int cpu;
	300
	301	for_each_cpu(cpu, &dead_events_mask) {
	302	struct perf_event *event = per_cpu(dead_event, cpu);
	303
	304	per_cpu(dead_event, cpu) = NULL;
	305	perf_event_release_kernel(event);
	306	}
	307	cpumask_clear(&dead_events_mask);
	308	}
	309
d0b6e0a8 PZ	310	/**
	311	* hardlockup_detector_perf_stop - Globally stop watchdog events
	312	*
	313	* Special interface for x86 to handle the perf HT bug.
	314	*/
	315	void __init hardlockup_detector_perf_stop(void)
	316	{
	317	int cpu;
	318
	319	lockdep_assert_cpus_held();
	320
	321	for_each_online_cpu(cpu) {
	322	struct perf_event *event = per_cpu(watchdog_ev, cpu);
	323
	324	if (event)
	325	perf_event_disable(event);
	326	}
	327	}
	328
	329	/**
	330	* hardlockup_detector_perf_restart - Globally restart watchdog events
	331	*
	332	* Special interface for x86 to handle the perf HT bug.
	333	*/
	334	void __init hardlockup_detector_perf_restart(void)
	335	{
	336	int cpu;
	337
	338	lockdep_assert_cpus_held();
	339
	340	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
	341	return;
	342
	343	for_each_online_cpu(cpu) {
	344	struct perf_event *event = per_cpu(watchdog_ev, cpu);
	345
	346	if (event)
	347	perf_event_enable(event);
	348	}
	349	}
178b9f7a TG	350
	351	/**
	352	* hardlockup_detector_perf_init - Probe whether NMI event is available at all
	353	*/
	354	int __init hardlockup_detector_perf_init(void)
	355	{
	356	int ret = hardlockup_detector_event_create();
	357
	358	if (ret) {
	359	pr_info("Perf NMI watchdog permanetely disabled\n");
	360	} else {
	361	perf_event_release_kernel(this_cpu_read(watchdog_ev));
	362	this_cpu_write(watchdog_ev, NULL);
	363	}
	364	return ret;
	365	}