/*
   * Detect hard and soft lockups on a system
   *
   * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
   *
   * this code detects hard lockups: incidents in where on a CPU
   * the kernel does not respond to anything except NMI.
   *
   * Note: Most of this code is borrowed heavily from softlockup.c,
   * so thanks to Ingo for the initial implementation.
   * Some chunks also taken from arch/x86/kernel/apic/nmi.c, thanks
   * to those contributors as well.
   */
  
  #include <linux/mm.h>
  #include <linux/cpu.h>
  #include <linux/nmi.h>
  #include <linux/init.h>
  #include <linux/delay.h>
  #include <linux/freezer.h>
  #include <linux/kthread.h>
  #include <linux/lockdep.h>
  #include <linux/notifier.h>
  #include <linux/module.h>
  #include <linux/sysctl.h>
  
  #include <asm/irq_regs.h>
  #include <linux/perf_event.h>

  int watchdog_enabled = 1;

  int __read_mostly watchdog_thresh = 10;

  
  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);

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

  /* 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;

  
  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 = 0;

  	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);
  
  /* deprecated */
  static int __init nosoftlockup_setup(char *str)
  {

  	watchdog_enabled = 0;

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

  /*
   * 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()
  {
  	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(int this_cpu)
  {
  	return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
  }
  
  static unsigned long get_sample_period(void)
  {
  	/*

  	 * convert watchdog_thresh from seconds to ns

  	 * the divide by 5 is to give hrtimer 5 chances to
  	 * increment before the hardlockup detector generates
  	 * a warning
  	 */

  	return get_softlockup_thresh() * (NSEC_PER_SEC / 5);

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

  	int this_cpu = smp_processor_id();

  	__this_cpu_write(watchdog_touch_ts, get_timestamp(this_cpu));

  }

  void touch_softlockup_watchdog(void)

  {

  	__this_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_online_cpu(cpu)
  		per_cpu(watchdog_touch_ts, cpu) = 0;
  }

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  void touch_nmi_watchdog(void)
  {

  	if (watchdog_enabled) {
  		unsigned cpu;
  
  		for_each_present_cpu(cpu) {
  			if (per_cpu(watchdog_nmi_touch, cpu) != true)
  				per_cpu(watchdog_nmi_touch, cpu) = true;
  		}
  	}

  	touch_softlockup_watchdog();

  }
  EXPORT_SYMBOL(touch_nmi_watchdog);

  #endif

  void touch_softlockup_watchdog_sync(void)
  {
  	__raw_get_cpu_var(softlockup_touch_sync) = true;
  	__raw_get_cpu_var(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(smp_processor_id());

  
  	/* 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, int nmi,

  		 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;
  }
  static void watchdog_interrupt_count(void)
  {

  	__this_cpu_inc(hrtimer_interrupts);

  }
  #else
  static inline void watchdog_interrupt_count(void) { return; }

  #endif /* CONFIG_HARDLOCKUP_DETECTOR */

  
  /* 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;
  
  	/* 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(get_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();
  		}
  		__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)) {
  		/* only warn once */

  		if (__this_cpu_read(soft_watchdog_warn) == true)

  			return HRTIMER_RESTART;
  
  		printk(KERN_ERR "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_panic)
  			panic("softlockup: hung tasks");

  		__this_cpu_write(soft_watchdog_warn, true);

  	} else

  		__this_cpu_write(soft_watchdog_warn, false);

  
  	return HRTIMER_RESTART;
  }
  
  
  /*
   * The watchdog thread - touches the timestamp.
   */

  static int watchdog(void *unused)

  {

  	static struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };

  	struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);

  
  	sched_setscheduler(current, SCHED_FIFO, &param);
  
  	/* initialize timestamp */
  	__touch_watchdog();
  
  	/* kick off the timer for the hardlockup detector */
  	/* done here because hrtimer_start can only pin to smp_processor_id() */
  	hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
  		      HRTIMER_MODE_REL_PINNED);
  
  	set_current_state(TASK_INTERRUPTIBLE);
  	/*
  	 * Run briefly once per second to reset the softlockup timestamp.
  	 * If this gets delayed for more than 60 seconds then the

  	 * debug-printout triggers in watchdog_timer_fn().

  	 */
  	while (!kthread_should_stop()) {
  		__touch_watchdog();
  		schedule();
  
  		if (kthread_should_stop())
  			break;
  
  		set_current_state(TASK_INTERRUPTIBLE);
  	}
  	__set_current_state(TASK_RUNNING);
  
  	return 0;
  }

  #ifdef CONFIG_HARDLOCKUP_DETECTOR

  static int watchdog_nmi_enable(int cpu)
  {
  	struct perf_event_attr *wd_attr;
  	struct perf_event *event = per_cpu(watchdog_ev, cpu);
  
  	/* 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;
  
  	/* Try to register using hardware perf events */
  	wd_attr = &wd_hw_attr;

  	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);

  	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback);

  	if (!IS_ERR(event)) {
  		printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.
  ");
  		goto out_save;
  	}

  
  	/* vary the KERN level based on the returned errno */
  	if (PTR_ERR(event) == -EOPNOTSUPP)
  		printk(KERN_INFO "NMI watchdog disabled (cpu%i): not supported (no LAPIC?)
  ", cpu);
  	else if (PTR_ERR(event) == -ENOENT)
  		printk(KERN_WARNING "NMI watchdog disabled (cpu%i): hardware events not enabled
  ", cpu);
  	else
  		printk(KERN_ERR "NMI watchdog disabled (cpu%i): unable to create perf event: %ld
  ", cpu, PTR_ERR(event));

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

  #endif /* CONFIG_HARDLOCKUP_DETECTOR */

  
  /* prepare/enable/disable routines */
  static int watchdog_prepare_cpu(int cpu)
  {
  	struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
  
  	WARN_ON(per_cpu(softlockup_watchdog, cpu));
  	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
  	hrtimer->function = watchdog_timer_fn;
  
  	return 0;
  }
  
  static int watchdog_enable(int cpu)
  {
  	struct task_struct *p = per_cpu(softlockup_watchdog, cpu);

  	int err = 0;

  
  	/* enable the perf event */

  	err = watchdog_nmi_enable(cpu);

  
  	/* Regardless of err above, fall through and start softlockup */

  
  	/* create the watchdog thread */
  	if (!p) {
  		p = kthread_create(watchdog, (void *)(unsigned long)cpu, "watchdog/%d", cpu);
  		if (IS_ERR(p)) {
  			printk(KERN_ERR "softlockup watchdog for %i failed
  ", cpu);

  			if (!err) {

  				/* if hardlockup hasn't already set this */
  				err = PTR_ERR(p);

  				/* and disable the perf event */
  				watchdog_nmi_disable(cpu);
  			}

  			goto out;

  		}
  		kthread_bind(p, cpu);
  		per_cpu(watchdog_touch_ts, cpu) = 0;
  		per_cpu(softlockup_watchdog, cpu) = p;
  		wake_up_process(p);
  	}

  out:
  	return err;

  }
  
  static void watchdog_disable(int cpu)
  {
  	struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
  	struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
  
  	/*
  	 * cancel the timer first to stop incrementing the stats
  	 * and waking up the kthread
  	 */
  	hrtimer_cancel(hrtimer);
  
  	/* disable the perf event */
  	watchdog_nmi_disable(cpu);
  
  	/* stop the watchdog thread */
  	if (p) {
  		per_cpu(softlockup_watchdog, cpu) = NULL;
  		kthread_stop(p);
  	}

  }
  
  static void watchdog_enable_all_cpus(void)
  {
  	int cpu;

  
  	watchdog_enabled = 0;

  
  	for_each_online_cpu(cpu)

  		if (!watchdog_enable(cpu))
  			/* if any cpu succeeds, watchdog is considered
  			   enabled for the system */
  			watchdog_enabled = 1;

  	if (!watchdog_enabled)

  		printk(KERN_ERR "watchdog: failed to be enabled on some cpus
  ");
  
  }
  
  static void watchdog_disable_all_cpus(void)
  {
  	int cpu;
  
  	for_each_online_cpu(cpu)
  		watchdog_disable(cpu);
  
  	/* if all watchdogs are disabled, then they are disabled for the system */
  	watchdog_enabled = 0;
  }
  
  
  /* sysctl functions */
  #ifdef CONFIG_SYSCTL
  /*

   * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh

   */

  int proc_dowatchdog(struct ctl_table *table, int write,
  		    void __user *buffer, size_t *lenp, loff_t *ppos)

  {

  	int ret;

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

  	if (ret || !write)
  		goto out;

  	if (watchdog_enabled && watchdog_thresh)

  		watchdog_enable_all_cpus();
  	else
  		watchdog_disable_all_cpus();
  
  out:
  	return ret;

  }

  #endif /* CONFIG_SYSCTL */
  
  
  /*
   * Create/destroy watchdog threads as CPUs come and go:
   */
  static int __cpuinit
  cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
  {
  	int hotcpu = (unsigned long)hcpu;

  	int err = 0;

  
  	switch (action) {
  	case CPU_UP_PREPARE:
  	case CPU_UP_PREPARE_FROZEN:

  		err = watchdog_prepare_cpu(hotcpu);

  		break;
  	case CPU_ONLINE:
  	case CPU_ONLINE_FROZEN:

  		if (watchdog_enabled)
  			err = watchdog_enable(hotcpu);

  		break;
  #ifdef CONFIG_HOTPLUG_CPU
  	case CPU_UP_CANCELED:
  	case CPU_UP_CANCELED_FROZEN:
  		watchdog_disable(hotcpu);
  		break;
  	case CPU_DEAD:
  	case CPU_DEAD_FROZEN:
  		watchdog_disable(hotcpu);
  		break;
  #endif /* CONFIG_HOTPLUG_CPU */
  	}

  
  	/*
  	 * hardlockup and softlockup are not important enough
  	 * to block cpu bring up.  Just always succeed and
  	 * rely on printk output to flag problems.
  	 */
  	return NOTIFY_OK;

  }
  
  static struct notifier_block __cpuinitdata cpu_nfb = {
  	.notifier_call = cpu_callback
  };

  void __init lockup_detector_init(void)

  {
  	void *cpu = (void *)(long)smp_processor_id();
  	int err;

  	err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);

  	WARN_ON(notifier_to_errno(err));

  
  	cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
  	register_cpu_notifier(&cpu_nfb);

  	return;

  }