// 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);
  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 atomic_t watchdog_cpus = ATOMIC_INIT(0);

  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);

  #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;
  }

  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
  ", 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.
  ");

  	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
  ");

  	} else {
  		perf_event_release_kernel(this_cpu_read(watchdog_ev));
  		this_cpu_write(watchdog_ev, NULL);
  	}
  	return ret;
  }