/*
   * Detect hard and soft 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/mm.h>
  #include <linux/cpu.h>
  #include <linux/nmi.h>
  #include <linux/init.h>

  #include <linux/module.h>
  #include <linux/sysctl.h>

  #include <linux/smpboot.h>

  #include <linux/sched/rt.h>

  #include <linux/tick.h>

  
  #include <asm/irq_regs.h>

  #include <linux/kvm_para.h>

  #include <linux/perf_event.h>

  /*
   * The run state of the lockup detectors is controlled by the content of the
   * 'watchdog_enabled' variable. Each lockup detector has its dedicated bit -
   * bit 0 for the hard lockup detector and bit 1 for the soft lockup detector.
   *
   * 'watchdog_user_enabled', 'nmi_watchdog_enabled' and 'soft_watchdog_enabled'
   * are variables that are only used as an 'interface' between the parameters
   * in /proc/sys/kernel and the internal state bits in 'watchdog_enabled'. The
   * 'watchdog_thresh' variable is handled differently because its value is not
   * boolean, and the lockup detectors are 'suspended' while 'watchdog_thresh'
   * is equal zero.
   */
  #define NMI_WATCHDOG_ENABLED_BIT   0
  #define SOFT_WATCHDOG_ENABLED_BIT  1
  #define NMI_WATCHDOG_ENABLED      (1 << NMI_WATCHDOG_ENABLED_BIT)
  #define SOFT_WATCHDOG_ENABLED     (1 << SOFT_WATCHDOG_ENABLED_BIT)

  static DEFINE_MUTEX(watchdog_proc_mutex);

  #ifdef CONFIG_HARDLOCKUP_DETECTOR
  static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED;
  #else
  static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
  #endif
  int __read_mostly nmi_watchdog_enabled;
  int __read_mostly soft_watchdog_enabled;
  int __read_mostly watchdog_user_enabled;

  int __read_mostly watchdog_thresh = 10;

  #ifdef CONFIG_SMP
  int __read_mostly sysctl_softlockup_all_cpu_backtrace;
  #else
  #define sysctl_softlockup_all_cpu_backtrace 0
  #endif

  static struct cpumask watchdog_cpumask __read_mostly;
  unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
  
  /* Helper for online, unparked cpus. */
  #define for_each_watchdog_cpu(cpu) \
  	for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)

  static int __read_mostly watchdog_running;

  static u64 __read_mostly sample_period;

  
  static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
  static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
  static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
  static DEFINE_PER_CPU(bool, softlockup_touch_sync);

  static DEFINE_PER_CPU(bool, soft_watchdog_warn);

  static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
  static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);

  static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  static DEFINE_PER_CPU(bool, hard_watchdog_warn);
  static DEFINE_PER_CPU(bool, watchdog_nmi_touch);

  static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
  static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
  #endif

  static unsigned long soft_lockup_nmi_warn;

  /* boot commands */
  /*
   * Should we panic when a soft-lockup or hard-lockup occurs:
   */

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  static int hardlockup_panic =
  			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;

  /*
   * We may not want to enable hard lockup detection by default in all cases,
   * for example when running the kernel as a guest on a hypervisor. In these
   * cases this function can be called to disable hard lockup detection. This
   * function should only be executed once by the boot processor before the
   * kernel command line parameters are parsed, because otherwise it is not
   * possible to override this in hardlockup_panic_setup().
   */

  void hardlockup_detector_disable(void)

  {

  	watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;

  }

  static int __init hardlockup_panic_setup(char *str)
  {
  	if (!strncmp(str, "panic", 5))
  		hardlockup_panic = 1;

  	else if (!strncmp(str, "nopanic", 7))
  		hardlockup_panic = 0;

  	else if (!strncmp(str, "0", 1))

  		watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
  	else if (!strncmp(str, "1", 1))
  		watchdog_enabled |= NMI_WATCHDOG_ENABLED;

  	return 1;
  }
  __setup("nmi_watchdog=", hardlockup_panic_setup);
  #endif
  
  unsigned int __read_mostly softlockup_panic =
  			CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  
  static int __init softlockup_panic_setup(char *str)
  {
  	softlockup_panic = simple_strtoul(str, NULL, 0);
  
  	return 1;
  }
  __setup("softlockup_panic=", softlockup_panic_setup);
  
  static int __init nowatchdog_setup(char *str)
  {

  	watchdog_enabled = 0;

  	return 1;
  }
  __setup("nowatchdog", nowatchdog_setup);

  static int __init nosoftlockup_setup(char *str)
  {

  	watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;

  	return 1;
  }
  __setup("nosoftlockup", nosoftlockup_setup);

  #ifdef CONFIG_SMP
  static int __init softlockup_all_cpu_backtrace_setup(char *str)
  {
  	sysctl_softlockup_all_cpu_backtrace =
  		!!simple_strtol(str, NULL, 0);
  	return 1;
  }
  __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
  #endif

  /*
   * Hard-lockup warnings should be triggered after just a few seconds. Soft-
   * lockups can have false positives under extreme conditions. So we generally
   * want a higher threshold for soft lockups than for hard lockups. So we couple
   * the thresholds with a factor: we make the soft threshold twice the amount of
   * time the hard threshold is.
   */

  static int get_softlockup_thresh(void)

  {
  	return watchdog_thresh * 2;
  }

  
  /*
   * Returns seconds, approximately.  We don't need nanosecond
   * resolution, and we don't need to waste time with a big divide when
   * 2^30ns == 1.074s.
   */

  static unsigned long get_timestamp(void)

  {

  	return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */

  }

  static void set_sample_period(void)

  {
  	/*

  	 * convert watchdog_thresh from seconds to ns

  	 * the divide by 5 is to give hrtimer several chances (two
  	 * or three with the current relation between the soft
  	 * and hard thresholds) to increment before the
  	 * hardlockup detector generates a warning

  	 */

  	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);

  }
  
  /* Commands for resetting the watchdog */
  static void __touch_watchdog(void)
  {

  	__this_cpu_write(watchdog_touch_ts, get_timestamp());

  }

  void touch_softlockup_watchdog(void)

  {

  	/*
  	 * Preemption can be enabled.  It doesn't matter which CPU's timestamp
  	 * gets zeroed here, so use the raw_ operation.
  	 */
  	raw_cpu_write(watchdog_touch_ts, 0);

  }

  EXPORT_SYMBOL(touch_softlockup_watchdog);

  void touch_all_softlockup_watchdogs(void)

  {
  	int cpu;
  
  	/*
  	 * this is done lockless
  	 * do we care if a 0 races with a timestamp?
  	 * all it means is the softlock check starts one cycle later
  	 */

  	for_each_watchdog_cpu(cpu)

  		per_cpu(watchdog_touch_ts, cpu) = 0;
  }

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  void 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);

  	touch_softlockup_watchdog();

  }
  EXPORT_SYMBOL(touch_nmi_watchdog);

  #endif

  void touch_softlockup_watchdog_sync(void)
  {

  	__this_cpu_write(softlockup_touch_sync, true);
  	__this_cpu_write(watchdog_touch_ts, 0);

  }

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  /* watchdog detector functions */

  static int is_hardlockup(void)

  {

  	unsigned long hrint = __this_cpu_read(hrtimer_interrupts);

  	if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)

  		return 1;

  	__this_cpu_write(hrtimer_interrupts_saved, hrint);

  	return 0;
  }
  #endif

  static int is_softlockup(unsigned long touch_ts)

  {

  	unsigned long now = get_timestamp();

  	if (watchdog_enabled & SOFT_WATCHDOG_ENABLED) {
  		/* Warn about unreasonable delays. */
  		if (time_after(now, touch_ts + get_softlockup_thresh()))
  			return now - touch_ts;
  	}

  	return 0;
  }

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  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;
  	}
  
  	/* 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;
  
  		if (hardlockup_panic)

  			panic("Watchdog detected hard LOCKUP on cpu %d",
  			      this_cpu);

  		else

  			WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
  			     this_cpu);

  		__this_cpu_write(hard_watchdog_warn, true);

  		return;
  	}

  	__this_cpu_write(hard_watchdog_warn, false);

  	return;
  }

  #endif /* CONFIG_HARDLOCKUP_DETECTOR */

  static void watchdog_interrupt_count(void)
  {

  	__this_cpu_inc(hrtimer_interrupts);

  }

  
  static int watchdog_nmi_enable(unsigned int cpu);
  static void watchdog_nmi_disable(unsigned int cpu);

  
  /* watchdog kicker functions */
  static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
  {

  	unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);

  	struct pt_regs *regs = get_irq_regs();
  	int duration;

  	int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;

  
  	/* kick the hardlockup detector */
  	watchdog_interrupt_count();
  
  	/* kick the softlockup detector */

  	wake_up_process(__this_cpu_read(softlockup_watchdog));

  
  	/* .. and repeat */

  	hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));

  
  	if (touch_ts == 0) {

  		if (unlikely(__this_cpu_read(softlockup_touch_sync))) {

  			/*
  			 * If the time stamp was touched atomically
  			 * make sure the scheduler tick is up to date.
  			 */

  			__this_cpu_write(softlockup_touch_sync, false);

  			sched_clock_tick();
  		}

  
  		/* Clear the guest paused flag on watchdog reset */
  		kvm_check_and_clear_guest_paused();

  		__touch_watchdog();
  		return HRTIMER_RESTART;
  	}
  
  	/* check for a softlockup
  	 * This is done by making sure a high priority task is
  	 * being scheduled.  The task touches the watchdog to
  	 * indicate it is getting cpu time.  If it hasn't then
  	 * this is a good indication some task is hogging the cpu
  	 */

  	duration = is_softlockup(touch_ts);

  	if (unlikely(duration)) {

  		/*
  		 * If a virtual machine is stopped by the host it can look to
  		 * the watchdog like a soft lockup, check to see if the host
  		 * stopped the vm before we issue the warning
  		 */
  		if (kvm_check_and_clear_guest_paused())
  			return HRTIMER_RESTART;

  		/* only warn once */

  		if (__this_cpu_read(soft_watchdog_warn) == true) {
  			/*
  			 * When multiple processes are causing softlockups the
  			 * softlockup detector only warns on the first one
  			 * because the code relies on a full quiet cycle to
  			 * re-arm.  The second process prevents the quiet cycle
  			 * and never gets reported.  Use task pointers to detect
  			 * this.
  			 */
  			if (__this_cpu_read(softlockup_task_ptr_saved) !=
  			    current) {
  				__this_cpu_write(soft_watchdog_warn, false);
  				__touch_watchdog();
  			}

  			return HRTIMER_RESTART;

  		}

  		if (softlockup_all_cpu_backtrace) {
  			/* Prevent multiple soft-lockup reports if one cpu is already
  			 * engaged in dumping cpu back traces
  			 */
  			if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
  				/* Someone else will report us. Let's give up */
  				__this_cpu_write(soft_watchdog_warn, true);
  				return HRTIMER_RESTART;
  			}
  		}

  		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]
  ",

  			smp_processor_id(), duration,

  			current->comm, task_pid_nr(current));

  		__this_cpu_write(softlockup_task_ptr_saved, current);

  		print_modules();
  		print_irqtrace_events(current);
  		if (regs)
  			show_regs(regs);
  		else
  			dump_stack();

  		if (softlockup_all_cpu_backtrace) {
  			/* Avoid generating two back traces for current
  			 * given that one is already made above
  			 */
  			trigger_allbutself_cpu_backtrace();
  
  			clear_bit(0, &soft_lockup_nmi_warn);
  			/* Barrier to sync with other cpus */
  			smp_mb__after_atomic();
  		}

  		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);

  		if (softlockup_panic)
  			panic("softlockup: hung tasks");

  		__this_cpu_write(soft_watchdog_warn, true);

  	} else

  		__this_cpu_write(soft_watchdog_warn, false);

  
  	return HRTIMER_RESTART;
  }

  static void watchdog_set_prio(unsigned int policy, unsigned int prio)
  {
  	struct sched_param param = { .sched_priority = prio };

  	sched_setscheduler(current, policy, &param);
  }
  
  static void watchdog_enable(unsigned int cpu)

  {

  	struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);

  	/* kick off the timer for the hardlockup detector */
  	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
  	hrtimer->function = watchdog_timer_fn;

  	/* Enable the perf event */
  	watchdog_nmi_enable(cpu);

  	/* done here because hrtimer_start can only pin to smp_processor_id() */

  	hrtimer_start(hrtimer, ns_to_ktime(sample_period),

  		      HRTIMER_MODE_REL_PINNED);

  	/* initialize timestamp */
  	watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
  	__touch_watchdog();
  }

  static void watchdog_disable(unsigned int cpu)
  {

  	struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);

  	watchdog_set_prio(SCHED_NORMAL, 0);
  	hrtimer_cancel(hrtimer);
  	/* disable the perf event */
  	watchdog_nmi_disable(cpu);

  }

  static void watchdog_cleanup(unsigned int cpu, bool online)
  {
  	watchdog_disable(cpu);
  }

  static int watchdog_should_run(unsigned int cpu)
  {
  	return __this_cpu_read(hrtimer_interrupts) !=
  		__this_cpu_read(soft_lockup_hrtimer_cnt);
  }
  
  /*
   * The watchdog thread function - touches the timestamp.
   *

   * It only runs once every sample_period seconds (4 seconds by

   * default) to reset the softlockup timestamp. If this gets delayed
   * for more than 2*watchdog_thresh seconds then the debug-printout
   * triggers in watchdog_timer_fn().
   */
  static void watchdog(unsigned int cpu)
  {
  	__this_cpu_write(soft_lockup_hrtimer_cnt,
  			 __this_cpu_read(hrtimer_interrupts));
  	__touch_watchdog();

  
  	/*
  	 * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
  	 * failure path. Check for failures that can occur asynchronously -
  	 * for example, when CPUs are on-lined - and shut down the hardware
  	 * perf event on each CPU accordingly.
  	 *
  	 * The only non-obvious place this bit can be cleared is through
  	 * watchdog_nmi_enable(), so a pr_info() is placed there.  Placing a
  	 * pr_info here would be too noisy as it would result in a message
  	 * every few seconds if the hardlockup was disabled but the softlockup
  	 * enabled.
  	 */
  	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
  		watchdog_nmi_disable(cpu);

  }

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  /*
   * 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 cpu0_err;

  static int watchdog_nmi_enable(unsigned int cpu)

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

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

  	/* 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;

  	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 cpu0 error for future comparision */
  	if (cpu == 0 && IS_ERR(event))
  		cpu0_err = PTR_ERR(event);

  	if (!IS_ERR(event)) {

  		/* only print for cpu0 or different than cpu0 */
  		if (cpu == 0 || cpu0_err)
  			pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.
  ");

  		goto out_save;
  	}

  	/*
  	 * Disable the hard lockup detector if _any_ CPU fails to set up
  	 * set up the hardware perf event. The watchdog() function checks
  	 * the NMI_WATCHDOG_ENABLED bit periodically.
  	 *
  	 * The barriers are for syncing up watchdog_enabled across all the
  	 * cpus, as clear_bit() does not use barriers.
  	 */
  	smp_mb__before_atomic();
  	clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
  	smp_mb__after_atomic();

  	/* skip displaying the same error again */
  	if (cpu > 0 && (PTR_ERR(event) == cpu0_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?)
  ", cpu);

  	else if (PTR_ERR(event) == -ENOENT)

  		pr_warn("disabled (cpu%i): hardware events not enabled
  ",

  			 cpu);

  	else

  		pr_err("disabled (cpu%i): unable to create perf event: %ld
  ",
  			cpu, PTR_ERR(event));

  
  	pr_info("Shutting down hard lockup detector on all cpus
  ");

  	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 void watchdog_nmi_disable(unsigned int cpu)

  {
  	struct perf_event *event = per_cpu(watchdog_ev, cpu);
  
  	if (event) {
  		perf_event_disable(event);
  		per_cpu(watchdog_ev, cpu) = NULL;
  
  		/* should be in cleanup, but blocks oprofile */
  		perf_event_release_kernel(event);
  	}

  	if (cpu == 0) {
  		/* watchdog_nmi_enable() expects this to be zero initially. */
  		cpu0_err = 0;
  	}

  }

  
  void watchdog_nmi_enable_all(void)
  {
  	int cpu;

  	mutex_lock(&watchdog_proc_mutex);
  
  	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
  		goto unlock;

  
  	get_online_cpus();

  	for_each_watchdog_cpu(cpu)

  		watchdog_nmi_enable(cpu);
  	put_online_cpus();

  
  unlock:

  	mutex_unlock(&watchdog_proc_mutex);

  }
  
  void watchdog_nmi_disable_all(void)
  {
  	int cpu;

  	mutex_lock(&watchdog_proc_mutex);

  	if (!watchdog_running)

  		goto unlock;

  
  	get_online_cpus();

  	for_each_watchdog_cpu(cpu)

  		watchdog_nmi_disable(cpu);
  	put_online_cpus();

  
  unlock:
  	mutex_unlock(&watchdog_proc_mutex);

  }

  #else

  static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
  static void watchdog_nmi_disable(unsigned int cpu) { return; }

  void watchdog_nmi_enable_all(void) {}
  void watchdog_nmi_disable_all(void) {}

  #endif /* CONFIG_HARDLOCKUP_DETECTOR */

  static struct smp_hotplug_thread watchdog_threads = {
  	.store			= &softlockup_watchdog,
  	.thread_should_run	= watchdog_should_run,
  	.thread_fn		= watchdog,
  	.thread_comm		= "watchdog/%u",
  	.setup			= watchdog_enable,
  	.cleanup		= watchdog_cleanup,
  	.park			= watchdog_disable,
  	.unpark			= watchdog_enable,
  };

  static void restart_watchdog_hrtimer(void *info)
  {

  	struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);

  	int ret;
  
  	/*
  	 * No need to cancel and restart hrtimer if it is currently executing
  	 * because it will reprogram itself with the new period now.
  	 * We should never see it unqueued here because we are running per-cpu
  	 * with interrupts disabled.
  	 */
  	ret = hrtimer_try_to_cancel(hrtimer);
  	if (ret == 1)
  		hrtimer_start(hrtimer, ns_to_ktime(sample_period),
  				HRTIMER_MODE_REL_PINNED);
  }

  static void update_watchdog(int cpu)

  {

  	/*
  	 * Make sure that perf event counter will adopt to a new
  	 * sampling period. Updating the sampling period directly would
  	 * be much nicer but we do not have an API for that now so
  	 * let's use a big hammer.
  	 * Hrtimer will adopt the new period on the next tick but this
  	 * might be late already so we have to restart the timer as well.
  	 */
  	watchdog_nmi_disable(cpu);

  	smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);

  	watchdog_nmi_enable(cpu);
  }

  static void update_watchdog_all_cpus(void)

  {
  	int cpu;
  
  	get_online_cpus();

  	for_each_watchdog_cpu(cpu)

  		update_watchdog(cpu);

  	put_online_cpus();
  }

  static int watchdog_enable_all_cpus(void)

  {

  	int err = 0;

  	if (!watchdog_running) {

  		err = smpboot_register_percpu_thread(&watchdog_threads);
  		if (err)
  			pr_err("Failed to create watchdog threads, disabled
  ");

  		else {
  			if (smpboot_update_cpumask_percpu_thread(
  				    &watchdog_threads, &watchdog_cpumask))
  				pr_err("Failed to set cpumask for watchdog threads
  ");

  			watchdog_running = 1;

  		}

  	} else {
  		/*
  		 * Enable/disable the lockup detectors or
  		 * change the sample period 'on the fly'.
  		 */
  		update_watchdog_all_cpus();

  	}

  
  	return err;

  }

  /* prepare/enable/disable routines */
  /* sysctl functions */
  #ifdef CONFIG_SYSCTL

  static void watchdog_disable_all_cpus(void)
  {

  	if (watchdog_running) {
  		watchdog_running = 0;

  		smpboot_unregister_percpu_thread(&watchdog_threads);

  	}

  }

  /*

   * Update the run state of the lockup detectors.
   */
  static int proc_watchdog_update(void)
  {
  	int err = 0;
  
  	/*
  	 * Watchdog threads won't be started if they are already active.
  	 * The 'watchdog_running' variable in watchdog_*_all_cpus() takes
  	 * care of this. If those threads are already active, the sample
  	 * period will be updated and the lockup detectors will be enabled
  	 * or disabled 'on the fly'.
  	 */
  	if (watchdog_enabled && watchdog_thresh)

  		err = watchdog_enable_all_cpus();

  	else
  		watchdog_disable_all_cpus();
  
  	return err;
  
  }
  
  /*

   * common function for watchdog, nmi_watchdog and soft_watchdog parameter
   *
   * caller             | table->data points to | 'which' contains the flag(s)
   * -------------------|-----------------------|-----------------------------
   * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
   *                    |                       | with SOFT_WATCHDOG_ENABLED
   * -------------------|-----------------------|-----------------------------
   * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
   * -------------------|-----------------------|-----------------------------
   * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
   */
  static int proc_watchdog_common(int which, struct ctl_table *table, int write,
  				void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	int err, old, new;
  	int *watchdog_param = (int *)table->data;
  
  	mutex_lock(&watchdog_proc_mutex);
  
  	/*
  	 * If the parameter is being read return the state of the corresponding
  	 * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
  	 * run state of the lockup detectors.
  	 */
  	if (!write) {
  		*watchdog_param = (watchdog_enabled & which) != 0;
  		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
  	} else {
  		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
  		if (err)
  			goto out;
  
  		/*
  		 * There is a race window between fetching the current value
  		 * from 'watchdog_enabled' and storing the new value. During
  		 * this race window, watchdog_nmi_enable() can sneak in and
  		 * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
  		 * The 'cmpxchg' detects this race and the loop retries.
  		 */
  		do {
  			old = watchdog_enabled;
  			/*
  			 * If the parameter value is not zero set the
  			 * corresponding bit(s), else clear it(them).
  			 */
  			if (*watchdog_param)
  				new = old | which;
  			else
  				new = old & ~which;
  		} while (cmpxchg(&watchdog_enabled, old, new) != old);
  
  		/*
  		 * Update the run state of the lockup detectors.
  		 * Restore 'watchdog_enabled' on failure.
  		 */
  		err = proc_watchdog_update();
  		if (err)
  			watchdog_enabled = old;
  	}
  out:
  	mutex_unlock(&watchdog_proc_mutex);
  	return err;
  }
  
  /*

   * /proc/sys/kernel/watchdog
   */
  int proc_watchdog(struct ctl_table *table, int write,
  		  void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
  				    table, write, buffer, lenp, ppos);
  }
  
  /*
   * /proc/sys/kernel/nmi_watchdog

   */

  int proc_nmi_watchdog(struct ctl_table *table, int write,
  		      void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
  				    table, write, buffer, lenp, ppos);
  }
  
  /*
   * /proc/sys/kernel/soft_watchdog
   */
  int proc_soft_watchdog(struct ctl_table *table, int write,
  			void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
  				    table, write, buffer, lenp, ppos);
  }

  /*
   * /proc/sys/kernel/watchdog_thresh
   */
  int proc_watchdog_thresh(struct ctl_table *table, int write,
  			 void __user *buffer, size_t *lenp, loff_t *ppos)

  {

  	int err, old;

  	mutex_lock(&watchdog_proc_mutex);

  	old = ACCESS_ONCE(watchdog_thresh);

  	err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);

  	if (err || !write)

  		goto out;

  	/*

  	 * Update the sample period.
  	 * Restore 'watchdog_thresh' on failure.

  	 */

  	set_sample_period();
  	err = proc_watchdog_update();
  	if (err)
  		watchdog_thresh = old;

  out:
  	mutex_unlock(&watchdog_proc_mutex);

  	return err;

  }

  
  /*
   * The cpumask is the mask of possible cpus that the watchdog can run
   * on, not the mask of cpus it is actually running on.  This allows the
   * user to specify a mask that will include cpus that have not yet
   * been brought online, if desired.
   */
  int proc_watchdog_cpumask(struct ctl_table *table, int write,
  			  void __user *buffer, size_t *lenp, loff_t *ppos)
  {
  	int err;
  
  	mutex_lock(&watchdog_proc_mutex);
  	err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
  	if (!err && write) {
  		/* Remove impossible cpus to keep sysctl output cleaner. */
  		cpumask_and(&watchdog_cpumask, &watchdog_cpumask,
  			    cpu_possible_mask);
  
  		if (watchdog_running) {
  			/*
  			 * Failure would be due to being unable to allocate
  			 * a temporary cpumask, so we are likely not in a
  			 * position to do much else to make things better.
  			 */
  			if (smpboot_update_cpumask_percpu_thread(
  				    &watchdog_threads, &watchdog_cpumask) != 0)
  				pr_err("cpumask update failed
  ");
  		}
  	}
  	mutex_unlock(&watchdog_proc_mutex);
  	return err;
  }

  #endif /* CONFIG_SYSCTL */

  void __init lockup_detector_init(void)

  {

  	set_sample_period();

  #ifdef CONFIG_NO_HZ_FULL
  	if (tick_nohz_full_enabled()) {
  		if (!cpumask_empty(tick_nohz_full_mask))
  			pr_info("Disabling watchdog on nohz_full cores by default
  ");
  		cpumask_andnot(&watchdog_cpumask, cpu_possible_mask,
  			       tick_nohz_full_mask);
  	} else
  		cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
  #else
  	cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
  #endif

  	if (watchdog_enabled)

  		watchdog_enable_all_cpus();

  }