// SPDX-License-Identifier: GPL-2.0-only

  /*
   * hangcheck-timer.c
   *
   * Driver for a little io fencing timer.
   *

   * Copyright (C) 2002, 2003 Oracle.  All rights reserved.

   *
   * Author: Joel Becker <joel.becker@oracle.com>

   */
  
  /*
   * The hangcheck-timer driver uses the TSC to catch delays that
   * jiffies does not notice.  A timer is set.  When the timer fires, it
   * checks whether it was delayed and if that delay exceeds a given

   * margin of error.  The hangcheck_tick module parameter takes the timer

   * duration in seconds.  The hangcheck_margin parameter defines the
   * margin of error, in seconds.  The defaults are 60 seconds for the
   * timer and 180 seconds for the margin of error.  IOW, a timer is set
   * for 60 seconds.  When the timer fires, the callback checks the
   * actual duration that the timer waited.  If the duration exceeds the

   * allotted time and margin (here 60 + 180, or 240 seconds), the machine

   * is restarted.  A healthy machine will have the duration match the
   * expected timeout very closely.
   */
  
  #include <linux/module.h>
  #include <linux/moduleparam.h>
  #include <linux/types.h>
  #include <linux/kernel.h>
  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/reboot.h>
  #include <linux/init.h>

  #include <linux/delay.h>

  #include <linux/uaccess.h>

  #include <linux/sysrq.h>

  #include <linux/timer.h>

  #include <linux/hrtimer.h>

  #define VERSION_STR "0.9.1"

  
  #define DEFAULT_IOFENCE_MARGIN 60	/* Default fudge factor, in seconds */
  #define DEFAULT_IOFENCE_TICK 180	/* Default timer timeout, in seconds */
  
  static int hangcheck_tick = DEFAULT_IOFENCE_TICK;
  static int hangcheck_margin = DEFAULT_IOFENCE_MARGIN;
  static int hangcheck_reboot;  /* Defaults to not reboot */

  static int hangcheck_dump_tasks;  /* Defaults to not dumping SysRQ T */

  /* options - modular */

  module_param(hangcheck_tick, int, 0);
  MODULE_PARM_DESC(hangcheck_tick, "Timer delay.");
  module_param(hangcheck_margin, int, 0);
  MODULE_PARM_DESC(hangcheck_margin, "If the hangcheck timer has been delayed more than hangcheck_margin seconds, the driver will fire.");
  module_param(hangcheck_reboot, int, 0);
  MODULE_PARM_DESC(hangcheck_reboot, "If nonzero, the machine will reboot when the timer margin is exceeded.");

  module_param(hangcheck_dump_tasks, int, 0);
  MODULE_PARM_DESC(hangcheck_dump_tasks, "If nonzero, the machine will dump the system task state when the timer margin is exceeded.");

  MODULE_AUTHOR("Oracle");

  MODULE_DESCRIPTION("Hangcheck-timer detects when the system has gone out to lunch past a certain margin.");
  MODULE_LICENSE("GPL");

  MODULE_VERSION(VERSION_STR);
  
  /* options - nonmodular */
  #ifndef MODULE
  
  static int __init hangcheck_parse_tick(char *str)
  {
  	int par;
  	if (get_option(&str,&par))
  		hangcheck_tick = par;
  	return 1;
  }
  
  static int __init hangcheck_parse_margin(char *str)
  {
  	int par;
  	if (get_option(&str,&par))
  		hangcheck_margin = par;
  	return 1;
  }
  
  static int __init hangcheck_parse_reboot(char *str)
  {
  	int par;
  	if (get_option(&str,&par))
  		hangcheck_reboot = par;
  	return 1;
  }
  
  static int __init hangcheck_parse_dump_tasks(char *str)
  {
  	int par;
  	if (get_option(&str,&par))
  		hangcheck_dump_tasks = par;
  	return 1;
  }
  
  __setup("hcheck_tick", hangcheck_parse_tick);
  __setup("hcheck_margin", hangcheck_parse_margin);
  __setup("hcheck_reboot", hangcheck_parse_reboot);
  __setup("hcheck_dump_tasks", hangcheck_parse_dump_tasks);
  #endif /* not MODULE */

  #define TIMER_FREQ 1000000000ULL

  
  /* Last time scheduled */
  static unsigned long long hangcheck_tsc, hangcheck_tsc_margin;

  static void hangcheck_fire(struct timer_list *);

  static DEFINE_TIMER(hangcheck_ticktock, hangcheck_fire);

  static void hangcheck_fire(struct timer_list *unused)

  {
  	unsigned long long cur_tsc, tsc_diff;

  	cur_tsc = ktime_get_ns();

  
  	if (cur_tsc > hangcheck_tsc)
  		tsc_diff = cur_tsc - hangcheck_tsc;
  	else
  		tsc_diff = (cur_tsc + (~0ULL - hangcheck_tsc)); /* or something */
  
  	if (tsc_diff > hangcheck_tsc_margin) {

  		if (hangcheck_dump_tasks) {
  			printk(KERN_CRIT "Hangcheck: Task state:
  ");
  #ifdef CONFIG_MAGIC_SYSRQ

  			handle_sysrq('t');

  #endif  /* CONFIG_MAGIC_SYSRQ */
  		}

  		if (hangcheck_reboot) {
  			printk(KERN_CRIT "Hangcheck: hangcheck is restarting the machine.
  ");

  			emergency_restart();

  		} else {
  			printk(KERN_CRIT "Hangcheck: hangcheck value past margin!
  ");
  		}
  	}

  #if 0
  	/*
  	 * Enable to investigate delays in detail
  	 */
  	printk("Hangcheck: called %Ld ns since last time (%Ld ns overshoot)
  ",
  			tsc_diff, tsc_diff - hangcheck_tick*TIMER_FREQ);
  #endif

  	mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));

  	hangcheck_tsc = ktime_get_ns();

  }
  
  
  static int __init hangcheck_init(void)
  {
  	printk("Hangcheck: starting hangcheck timer %s (tick is %d seconds, margin is %d seconds).
  ",
  	       VERSION_STR, hangcheck_tick, hangcheck_margin);

  	hangcheck_tsc_margin =

  		(unsigned long long)hangcheck_margin + hangcheck_tick;
  	hangcheck_tsc_margin *= TIMER_FREQ;

  	hangcheck_tsc = ktime_get_ns();

  	mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));
  
  	return 0;
  }
  
  
  static void __exit hangcheck_exit(void)
  {
  	del_timer_sync(&hangcheck_ticktock);

          printk("Hangcheck: Stopped hangcheck timer.
  ");

  }
  
  module_init(hangcheck_init);
  module_exit(hangcheck_exit);