/*
   * Detect Soft Lockups
   *

   * started by Ingo Molnar, Copyright (C) 2005, 2006 Red Hat, Inc.

   *
   * this code detects soft lockups: incidents in where on a CPU
   * the kernel does not reschedule for 10 seconds or more.
   */

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

  #include <asm/irq_regs.h>

  static DEFINE_SPINLOCK(print_lock);

  static DEFINE_PER_CPU(unsigned long, touch_timestamp);
  static DEFINE_PER_CPU(unsigned long, print_timestamp);

  static DEFINE_PER_CPU(struct task_struct *, watchdog_task);

  static int __read_mostly did_panic;
  unsigned long __read_mostly softlockup_thresh = 60;

  
  static int
  softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)

  {
  	did_panic = 1;
  
  	return NOTIFY_DONE;
  }
  
  static struct notifier_block panic_block = {
  	.notifier_call = softlock_panic,
  };

  /*
   * 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 */

  }

  void touch_softlockup_watchdog(void)
  {

  	int this_cpu = raw_smp_processor_id();
  
  	__raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);

  }
  EXPORT_SYMBOL(touch_softlockup_watchdog);

  void touch_all_softlockup_watchdogs(void)
  {
  	int cpu;
  
  	/* Cause each CPU to re-update its timestamp rather than complain */
  	for_each_online_cpu(cpu)
  		per_cpu(touch_timestamp, cpu) = 0;
  }
  EXPORT_SYMBOL(touch_all_softlockup_watchdogs);

  /*
   * This callback runs from the timer interrupt, and checks
   * whether the watchdog thread has hung or not:
   */

  void softlockup_tick(void)

  {
  	int this_cpu = smp_processor_id();

  	unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);

  	unsigned long print_timestamp;

  	struct pt_regs *regs = get_irq_regs();

  	unsigned long now;

  	if (touch_timestamp == 0) {
  		touch_softlockup_watchdog();

  		return;

  	}

  
  	print_timestamp = per_cpu(print_timestamp, this_cpu);
  
  	/* report at most once a second */

  	if ((print_timestamp >= touch_timestamp &&
  			print_timestamp < (touch_timestamp + 1)) ||
  			did_panic || !per_cpu(watchdog_task, this_cpu)) {

  		return;

  	}

  	/* do not print during early bootup: */
  	if (unlikely(system_state != SYSTEM_RUNNING)) {
  		touch_softlockup_watchdog();

  		return;

  	}

  	now = get_timestamp(this_cpu);

  	/* Wake up the high-prio watchdog task every second: */
  	if (now > (touch_timestamp + 1))
  		wake_up_process(per_cpu(watchdog_task, this_cpu));

  	/* Warn about unreasonable delays: */

  	if (now <= (touch_timestamp + softlockup_thresh))

  		return;

  	per_cpu(print_timestamp, this_cpu) = touch_timestamp;
  
  	spin_lock(&print_lock);

  	printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]
  ",
  			this_cpu, now - touch_timestamp,

  			current->comm, task_pid_nr(current));

  	if (regs)
  		show_regs(regs);
  	else

  		dump_stack();

  	spin_unlock(&print_lock);

  }
  
  /*

   * Have a reasonable limit on the number of tasks checked:
   */

  unsigned long __read_mostly sysctl_hung_task_check_count = 1024;

  
  /*
   * Zero means infinite timeout - no checking done:
   */

  unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;

  unsigned long __read_mostly sysctl_hung_task_warnings = 10;

  
  /*
   * Only do the hung-tasks check on one CPU:
   */
  static int check_cpu __read_mostly = -1;
  
  static void check_hung_task(struct task_struct *t, unsigned long now)
  {
  	unsigned long switch_count = t->nvcsw + t->nivcsw;
  
  	if (t->flags & PF_FROZEN)
  		return;
  
  	if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
  		t->last_switch_count = switch_count;
  		t->last_switch_timestamp = now;
  		return;
  	}
  	if ((long)(now - t->last_switch_timestamp) <
  					sysctl_hung_task_timeout_secs)
  		return;
  	if (sysctl_hung_task_warnings < 0)
  		return;
  	sysctl_hung_task_warnings--;
  
  	/*
  	 * Ok, the task did not get scheduled for more than 2 minutes,
  	 * complain:
  	 */
  	printk(KERN_ERR "INFO: task %s:%d blocked for more than "
  			"%ld seconds.
  ", t->comm, t->pid,
  			sysctl_hung_task_timeout_secs);
  	printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
  			" disables this message.
  ");
  	sched_show_task(t);
  	__debug_show_held_locks(t);
  
  	t->last_switch_timestamp = now;
  	touch_nmi_watchdog();
  }
  
  /*
   * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
   * a really long time (120 seconds). If that happens, print out
   * a warning.
   */
  static void check_hung_uninterruptible_tasks(int this_cpu)
  {
  	int max_count = sysctl_hung_task_check_count;
  	unsigned long now = get_timestamp(this_cpu);
  	struct task_struct *g, *t;
  
  	/*
  	 * If the system crashed already then all bets are off,
  	 * do not report extra hung tasks:
  	 */
  	if ((tainted & TAINT_DIE) || did_panic)
  		return;
  
  	read_lock(&tasklist_lock);
  	do_each_thread(g, t) {
  		if (!--max_count)

  			goto unlock;

  		if (t->state & TASK_UNINTERRUPTIBLE)
  			check_hung_task(t, now);
  	} while_each_thread(g, t);

   unlock:

  	read_unlock(&tasklist_lock);
  }
  
  /*

   * The watchdog thread - runs every second and touches the timestamp.
   */

  static int watchdog(void *__bind_cpu)

  {

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

  	int this_cpu = (long)__bind_cpu;

  
  	sched_setscheduler(current, SCHED_FIFO, &param);

  	/* initialize timestamp */
  	touch_softlockup_watchdog();

  	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 softlockup_tick().

  	 */
  	while (!kthread_should_stop()) {

  		touch_softlockup_watchdog();

  		schedule();
  
  		if (kthread_should_stop())
  			break;

  		if (this_cpu == check_cpu) {
  			if (sysctl_hung_task_timeout_secs)
  				check_hung_uninterruptible_tasks(this_cpu);
  		}

  		set_current_state(TASK_INTERRUPTIBLE);

  	}

  	__set_current_state(TASK_RUNNING);

  
  	return 0;
  }
  
  /*
   * 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;
  	struct task_struct *p;
  
  	switch (action) {
  	case CPU_UP_PREPARE:

  	case CPU_UP_PREPARE_FROZEN:

  		BUG_ON(per_cpu(watchdog_task, hotcpu));
  		p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
  		if (IS_ERR(p)) {

  			printk(KERN_ERR "watchdog for %i failed
  ", hotcpu);

  			return NOTIFY_BAD;
  		}

  		per_cpu(touch_timestamp, hotcpu) = 0;
  		per_cpu(watchdog_task, hotcpu) = p;

  		kthread_bind(p, hotcpu);

  		break;

  	case CPU_ONLINE:

  	case CPU_ONLINE_FROZEN:

  		check_cpu = any_online_cpu(cpu_online_map);

  		wake_up_process(per_cpu(watchdog_task, hotcpu));
  		break;
  #ifdef CONFIG_HOTPLUG_CPU

  	case CPU_DOWN_PREPARE:
  	case CPU_DOWN_PREPARE_FROZEN:
  		if (hotcpu == check_cpu) {
  			cpumask_t temp_cpu_online_map = cpu_online_map;
  
  			cpu_clear(hotcpu, temp_cpu_online_map);
  			check_cpu = any_online_cpu(temp_cpu_online_map);
  		}
  		break;

  
  	case CPU_UP_CANCELED:
  	case CPU_UP_CANCELED_FROZEN:
  		if (!per_cpu(watchdog_task, hotcpu))
  			break;
  		/* Unbind so it can run.  Fall thru. */
  		kthread_bind(per_cpu(watchdog_task, hotcpu),
  			     any_online_cpu(cpu_online_map));

  	case CPU_DEAD:

  	case CPU_DEAD_FROZEN:

  		p = per_cpu(watchdog_task, hotcpu);
  		per_cpu(watchdog_task, hotcpu) = NULL;
  		kthread_stop(p);
  		break;
  #endif /* CONFIG_HOTPLUG_CPU */

  	}

  	return NOTIFY_OK;
  }

  static struct notifier_block __cpuinitdata cpu_nfb = {

  	.notifier_call = cpu_callback
  };
  
  __init void spawn_softlockup_task(void)
  {
  	void *cpu = (void *)(long)smp_processor_id();

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

  	BUG_ON(err == NOTIFY_BAD);

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

  	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);

  }