// 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_TIMESTAMPstatic 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;} static void watchdog_init_timestamp(void){	__this_cpu_write(nmi_rearmed, 0);	__this_cpu_write(last_timestamp, ktime_get_mono_fast_ns());}#elsestatic inline bool watchdog_check_timestamp(void) { return true; }static inline void watchdog_init_timestamp(void) { }#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,}; static struct perf_event_attr fallback_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)) {		wd_attr = &fallback_wd_hw_attr;		wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);		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"); 	watchdog_init_timestamp();	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;} /** * hardlockup_config_perf_event - Overwrite config of wd_hw_attr. * @str: number which identifies the raw perf event to use */void __init hardlockup_config_perf_event(const char *str){	u64 config;	char buf[24];	char *comma = strchr(str, ','); 	if (!comma) {		if (kstrtoull(str, 16, &config))			return;	} else {		unsigned int len = comma - str; 		if (len >= sizeof(buf))			return; 		if (strscpy(buf, str, sizeof(buf)) < 0)			return;		buf[len] = 0;		if (kstrtoull(buf, 16, &config))			return;	} 	wd_hw_attr.type = PERF_TYPE_RAW;	wd_hw_attr.config = config;}