// SPDX-License-Identifier: GPL-2.0

  /*
   * 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) "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/tick.h>

  #include <linux/sched/clock.h>

  #include <linux/sched/debug.h>

  #include <linux/sched/isolation.h>

  #include <linux/stop_machine.h>

  
  #include <asm/irq_regs.h>

  #include <linux/kvm_para.h>

  static DEFINE_MUTEX(watchdog_mutex);

  #if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)

  # define WATCHDOG_DEFAULT	(SOFT_WATCHDOG_ENABLED | NMI_WATCHDOG_ENABLED)
  # define NMI_WATCHDOG_DEFAULT	1

  #else

  # define WATCHDOG_DEFAULT	(SOFT_WATCHDOG_ENABLED)
  # define NMI_WATCHDOG_DEFAULT	0

  #endif

  unsigned long __read_mostly watchdog_enabled;
  int __read_mostly watchdog_user_enabled = 1;
  int __read_mostly nmi_watchdog_user_enabled = NMI_WATCHDOG_DEFAULT;
  int __read_mostly soft_watchdog_user_enabled = 1;

  int __read_mostly watchdog_thresh = 10;

  static int __read_mostly nmi_watchdog_available;

  struct cpumask watchdog_cpumask __read_mostly;
  unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  
  # ifdef CONFIG_SMP
  int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
  # endif /* CONFIG_SMP */

  /*
   * Should we panic when a soft-lockup or hard-lockup occurs:
   */
  unsigned int __read_mostly 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 __init hardlockup_detector_disable(void)

  {

  	nmi_watchdog_user_enabled = 0;

  }
  
  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))

  		nmi_watchdog_user_enabled = 0;

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

  		nmi_watchdog_user_enabled = 1;

  	return 1;
  }
  __setup("nmi_watchdog=", hardlockup_panic_setup);

  #endif /* CONFIG_HARDLOCKUP_DETECTOR */

  /*

   * These functions can be overridden if an architecture implements its
   * own hardlockup detector.

   *
   * watchdog_nmi_enable/disable can be implemented to start and stop when
   * softlockup watchdog threads start and stop. The arch must select the
   * SOFTLOCKUP_DETECTOR Kconfig.

   */
  int __weak watchdog_nmi_enable(unsigned int cpu)
  {

  	hardlockup_detector_perf_enable();

  	return 0;
  }

  void __weak watchdog_nmi_disable(unsigned int cpu)
  {

  	hardlockup_detector_perf_disable();

  }

  /* Return 0, if a NMI watchdog is available. Error code otherwise */
  int __weak __init watchdog_nmi_probe(void)
  {
  	return hardlockup_detector_perf_init();
  }

  /**

   * watchdog_nmi_stop - Stop the watchdog for reconfiguration

   *

   * The reconfiguration steps are:
   * watchdog_nmi_stop();

   * update_variables();

   * watchdog_nmi_start();
   */
  void __weak watchdog_nmi_stop(void) { }
  
  /**
   * watchdog_nmi_start - Start the watchdog after reconfiguration

   *

   * Counterpart to watchdog_nmi_stop().
   *
   * The following variables have been updated in update_variables() and
   * contain the currently valid configuration:

   * - watchdog_enabled

   * - watchdog_thresh
   * - watchdog_cpumask

   */

  void __weak watchdog_nmi_start(void) { }

  /**
   * lockup_detector_update_enable - Update the sysctl enable bit
   *
   * Caller needs to make sure that the NMI/perf watchdogs are off, so this
   * can't race with watchdog_nmi_disable().
   */
  static void lockup_detector_update_enable(void)
  {
  	watchdog_enabled = 0;
  	if (!watchdog_user_enabled)
  		return;

  	if (nmi_watchdog_available && nmi_watchdog_user_enabled)

  		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
  	if (soft_watchdog_user_enabled)
  		watchdog_enabled |= SOFT_WATCHDOG_ENABLED;
  }

  #ifdef CONFIG_SOFTLOCKUP_DETECTOR

  #define SOFTLOCKUP_RESET	ULONG_MAX

  #ifdef CONFIG_SMP
  int __read_mostly sysctl_softlockup_all_cpu_backtrace;
  #endif

  static struct cpumask watchdog_allowed_mask __read_mostly;

  /* Global variables, exported for sysctl */
  unsigned int __read_mostly softlockup_panic =
  			CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;

  static bool softlockup_initialized __read_mostly;

  static u64 __read_mostly sample_period;

  
  static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);

  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, hrtimer_interrupts_saved);

  static unsigned long soft_lockup_nmi_warn;

  static int __init nowatchdog_setup(char *str)
  {

  	watchdog_user_enabled = 0;

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

  static int __init nosoftlockup_setup(char *str)
  {

  	soft_watchdog_user_enabled = 0;

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

  static int __init watchdog_thresh_setup(char *str)
  {
  	get_option(&str, &watchdog_thresh);
  	return 1;
  }
  __setup("watchdog_thresh=", watchdog_thresh_setup);

  static void __lockup_detector_cleanup(void);

  /*
   * 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);

  	watchdog_update_hrtimer_threshold(sample_period);

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

  	__this_cpu_write(watchdog_touch_ts, get_timestamp());

  }

  /**
   * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
   *
   * Call when the scheduler may have stalled for legitimate reasons
   * preventing the watchdog task from executing - e.g. the scheduler
   * entering idle state.  This should only be used for scheduler events.
   * Use touch_softlockup_watchdog() for everything else.
   */

  notrace void touch_softlockup_watchdog_sched(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, SOFTLOCKUP_RESET);

  }

  notrace void touch_softlockup_watchdog(void)

  {
  	touch_softlockup_watchdog_sched();

  	wq_watchdog_touch(raw_smp_processor_id());

  }

  EXPORT_SYMBOL(touch_softlockup_watchdog);

  void touch_all_softlockup_watchdogs(void)

  {
  	int cpu;
  
  	/*

  	 * watchdog_mutex cannpt be taken here, as this might be called
  	 * from (soft)interrupt context, so the access to
  	 * watchdog_allowed_cpumask might race with a concurrent update.
  	 *
  	 * The watchdog time stamp can race against a concurrent real
  	 * update as well, the only side effect might be a cycle delay for
  	 * the softlockup check.

  	 */

  	for_each_cpu(cpu, &watchdog_allowed_mask)

  		per_cpu(watchdog_touch_ts, cpu) = SOFTLOCKUP_RESET;

  	wq_watchdog_touch(-1);

  }

  void touch_softlockup_watchdog_sync(void)
  {

  	__this_cpu_write(softlockup_touch_sync, true);

  	__this_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET);

  }

  static int is_softlockup(unsigned long touch_ts)

  {

  	unsigned long now = get_timestamp();

  	if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){

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

  	return 0;
  }

  /* watchdog detector functions */
  bool is_hardlockup(void)

  {

  	unsigned long hrint = __this_cpu_read(hrtimer_interrupts);

  	if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
  		return true;
  
  	__this_cpu_write(hrtimer_interrupts_saved, hrint);
  	return false;

  }

  
  static void watchdog_interrupt_count(void)

  {

  	__this_cpu_inc(hrtimer_interrupts);

  }

  static DEFINE_PER_CPU(struct completion, softlockup_completion);
  static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);

  /*
   * 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 int softlockup_fn(void *data)
  {

  	__touch_watchdog();

  	complete(this_cpu_ptr(&softlockup_completion));

  
  	return 0;
  }

  /* 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;

  	if (!watchdog_enabled)

  		return HRTIMER_NORESTART;

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

  	if (completion_done(this_cpu_ptr(&softlockup_completion))) {
  		reinit_completion(this_cpu_ptr(&softlockup_completion));
  		stop_one_cpu_nowait(smp_processor_id(),
  				softlockup_fn, NULL,
  				this_cpu_ptr(&softlockup_stop_work));
  	}

  
  	/* .. and repeat */

  	hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));

  	if (touch_ts == SOFTLOCKUP_RESET) {

  		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)

  			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));
  		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_enable(unsigned int cpu)

  {

  	struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);

  	struct completion *done = this_cpu_ptr(&softlockup_completion);

  	WARN_ON_ONCE(cpu != smp_processor_id());

  	init_completion(done);
  	complete(done);

  	/*
  	 * Start the timer first to prevent the NMI watchdog triggering
  	 * before the timer has a chance to fire.
  	 */

  	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);

  	hrtimer->function = watchdog_timer_fn;

  	hrtimer_start(hrtimer, ns_to_ktime(sample_period),

  		      HRTIMER_MODE_REL_PINNED_HARD);

  	/* Initialize timestamp */
  	__touch_watchdog();

  	/* Enable the perf event */

  	if (watchdog_enabled & NMI_WATCHDOG_ENABLED)
  		watchdog_nmi_enable(cpu);

  }

  static void watchdog_disable(unsigned int cpu)
  {

  	struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);

  	WARN_ON_ONCE(cpu != smp_processor_id());

  	/*
  	 * Disable the perf event first. That prevents that a large delay
  	 * between disabling the timer and disabling the perf event causes
  	 * the perf NMI to detect a false positive.
  	 */

  	watchdog_nmi_disable(cpu);

  	hrtimer_cancel(hrtimer);

  	wait_for_completion(this_cpu_ptr(&softlockup_completion));

  }

  static int softlockup_stop_fn(void *data)

  {

  	watchdog_disable(smp_processor_id());
  	return 0;

  }

  static void softlockup_stop_all(void)

  {

  	int cpu;
  
  	if (!softlockup_initialized)
  		return;
  
  	for_each_cpu(cpu, &watchdog_allowed_mask)
  		smp_call_on_cpu(cpu, softlockup_stop_fn, NULL, false);
  
  	cpumask_clear(&watchdog_allowed_mask);

  }

  static int softlockup_start_fn(void *data)

  {

  	watchdog_enable(smp_processor_id());
  	return 0;

  }

  static void softlockup_start_all(void)

  {

  	int cpu;

  	cpumask_copy(&watchdog_allowed_mask, &watchdog_cpumask);
  	for_each_cpu(cpu, &watchdog_allowed_mask)
  		smp_call_on_cpu(cpu, softlockup_start_fn, NULL, false);

  }

  int lockup_detector_online_cpu(unsigned int cpu)

  {

  	if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
  		watchdog_enable(cpu);

  	return 0;

  }

  int lockup_detector_offline_cpu(unsigned int cpu)

  {

  	if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
  		watchdog_disable(cpu);

  	return 0;

  }

  static void lockup_detector_reconfigure(void)

  {

  	cpus_read_lock();

  	watchdog_nmi_stop();

  
  	softlockup_stop_all();

  	set_sample_period();

  	lockup_detector_update_enable();
  	if (watchdog_enabled && watchdog_thresh)

  		softlockup_start_all();

  	watchdog_nmi_start();

  	cpus_read_unlock();
  	/*
  	 * Must be called outside the cpus locked section to prevent
  	 * recursive locking in the perf code.
  	 */
  	__lockup_detector_cleanup();

  }
  
  /*

   * Create the watchdog thread infrastructure and configure the detector(s).

   *
   * The threads are not unparked as watchdog_allowed_mask is empty.  When

   * the threads are successfully initialized, take the proper locks and

   * unpark the threads in the watchdog_cpumask if the watchdog is enabled.
   */

  static __init void lockup_detector_setup(void)

  {

  	/*
  	 * If sysctl is off and watchdog got disabled on the command line,
  	 * nothing to do here.
  	 */

  	lockup_detector_update_enable();

  	if (!IS_ENABLED(CONFIG_SYSCTL) &&
  	    !(watchdog_enabled && watchdog_thresh))
  		return;

  	mutex_lock(&watchdog_mutex);

  	lockup_detector_reconfigure();

  	softlockup_initialized = true;

  	mutex_unlock(&watchdog_mutex);
  }

  #else /* CONFIG_SOFTLOCKUP_DETECTOR */

  static void lockup_detector_reconfigure(void)

  {

  	cpus_read_lock();

  	watchdog_nmi_stop();

  	lockup_detector_update_enable();

  	watchdog_nmi_start();

  	cpus_read_unlock();

  }

  static inline void lockup_detector_setup(void)

  {

  	lockup_detector_reconfigure();

  }

  #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */

  static void __lockup_detector_cleanup(void)
  {
  	lockdep_assert_held(&watchdog_mutex);
  	hardlockup_detector_perf_cleanup();
  }
  
  /**
   * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
   *
   * Caller must not hold the cpu hotplug rwsem.
   */
  void lockup_detector_cleanup(void)
  {
  	mutex_lock(&watchdog_mutex);
  	__lockup_detector_cleanup();
  	mutex_unlock(&watchdog_mutex);
  }

  /**
   * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
   *
   * Special interface for parisc. It prevents lockup detector warnings from
   * the default pm_poweroff() function which busy loops forever.
   */
  void lockup_detector_soft_poweroff(void)
  {
  	watchdog_enabled = 0;
  }

  #ifdef CONFIG_SYSCTL

  /* Propagate any changes to the watchdog threads */

  static void proc_watchdog_update(void)

  {

  	/* Remove impossible cpus to keep sysctl output clean. */
  	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);

  	lockup_detector_reconfigure();

  }
  
  /*

   * common function for watchdog, nmi_watchdog and soft_watchdog parameter
   *

   * caller             | table->data points to      | 'which'
   * -------------------|----------------------------|--------------------------
   * proc_watchdog      | watchdog_user_enabled      | NMI_WATCHDOG_ENABLED |
   *                    |                            | SOFT_WATCHDOG_ENABLED
   * -------------------|----------------------------|--------------------------
   * proc_nmi_watchdog  | nmi_watchdog_user_enabled  | NMI_WATCHDOG_ENABLED
   * -------------------|----------------------------|--------------------------
   * proc_soft_watchdog | soft_watchdog_user_enabled | SOFT_WATCHDOG_ENABLED

   */
  static int proc_watchdog_common(int which, struct ctl_table *table, int write,

  				void *buffer, size_t *lenp, loff_t *ppos)

  {

  	int err, old, *param = table->data;

  	mutex_lock(&watchdog_mutex);

  	if (!write) {

  		/*
  		 * On read synchronize the userspace interface. This is a
  		 * racy snapshot.
  		 */
  		*param = (watchdog_enabled & which) != 0;

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

  		old = READ_ONCE(*param);

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

  		if (!err && old != READ_ONCE(*param))

  			proc_watchdog_update();

  	}

  	mutex_unlock(&watchdog_mutex);

  	return err;
  }
  
  /*

   * /proc/sys/kernel/watchdog
   */
  int proc_watchdog(struct ctl_table *table, int write,

  		  void *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 *buffer, size_t *lenp, loff_t *ppos)

  {

  	if (!nmi_watchdog_available && write)
  		return -ENOTSUPP;

  	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 *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 *buffer, size_t *lenp, loff_t *ppos)

  {

  	int err, old;

  	mutex_lock(&watchdog_mutex);

  	old = READ_ONCE(watchdog_thresh);

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

  	if (!err && write && old != READ_ONCE(watchdog_thresh))
  		proc_watchdog_update();

  	mutex_unlock(&watchdog_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 *buffer, size_t *lenp, loff_t *ppos)

  {
  	int err;

  	mutex_lock(&watchdog_mutex);

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

  	if (!err && write)

  		proc_watchdog_update();

  	mutex_unlock(&watchdog_mutex);

  	return err;
  }

  #endif /* CONFIG_SYSCTL */

  void __init lockup_detector_init(void)

  {

  	if (tick_nohz_full_enabled())

  		pr_info("Disabling watchdog on nohz_full cores by default
  ");

  	cpumask_copy(&watchdog_cpumask,
  		     housekeeping_cpumask(HK_FLAG_TIMER));

  	if (!watchdog_nmi_probe())
  		nmi_watchdog_available = true;

  	lockup_detector_setup();

  }