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 * hangcheck-timer.c
 * Driver for a little io fencing timer.
 * Copyright (C) 2002, 2003 Oracle.  All rights reserved.
 * Author: Joel Becker <>
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License version 2 as published by the Free Software Foundation.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * General Public License for more details.
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.

 * 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 paramter 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
 * alloted 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/smp_lock.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <asm/uaccess.h>
#include <linux/sysrq.h>

#define VERSION_STR "0.9.0"

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

/* 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 */

#if defined(CONFIG_X86) || defined(CONFIG_X86_64)
# define TIMER_FREQ 1000000000ULL
#elif defined(CONFIG_ARCH_S390)
/* FA240000 is 1 Second in the IBM time universe (Page 4-38 Principles of Op for zSeries */
# define TIMER_FREQ 0xFA240000ULL
#elif defined(CONFIG_IA64)
# define TIMER_FREQ ((unsigned long long)local_cpu_data->itc_freq)
#elif defined(CONFIG_PPC64)
# define TIMER_FREQ (HZ*loops_per_jiffy)

extern unsigned long long monotonic_clock(void);
static inline unsigned long long monotonic_clock(void)
# ifdef __s390__
	/* returns the TOD.  see 4-38 Principles of Op of zSeries */
	return get_clock();
# else
	return get_cycles();
# endif  /* __s390__ */
#endif  /* HAVE_MONOTONIC */

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

static void hangcheck_fire(unsigned long);

static struct timer_list hangcheck_ticktock =
		TIMER_INITIALIZER(hangcheck_fire, 0, 0);

static void hangcheck_fire(unsigned long data)
	unsigned long long cur_tsc, tsc_diff;

	cur_tsc = monotonic_clock();

	if (cur_tsc > hangcheck_tsc)
		tsc_diff = cur_tsc - hangcheck_tsc;
		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:\n");
			handle_sysrq('t', NULL, NULL);
#endif  /* CONFIG_MAGIC_SYSRQ */
		if (hangcheck_reboot) {
			printk(KERN_CRIT "Hangcheck: hangcheck is restarting the machine.\n");
		} else {
			printk(KERN_CRIT "Hangcheck: hangcheck value past margin!\n");
	mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));
	hangcheck_tsc = monotonic_clock();

static int __init hangcheck_init(void)
	printk("Hangcheck: starting hangcheck timer %s (tick is %d seconds, margin is %d seconds).\n",
	       VERSION_STR, hangcheck_tick, hangcheck_margin);
#if defined (HAVE_MONOTONIC)
	printk("Hangcheck: Using monotonic_clock().\n");
#elif defined(__s390__)
	printk("Hangcheck: Using TOD.\n");
	printk("Hangcheck: Using get_cycles().\n");
#endif  /* HAVE_MONOTONIC */
	hangcheck_tsc_margin =
		(unsigned long long)(hangcheck_margin + hangcheck_tick);
	hangcheck_tsc_margin *= (unsigned long long)TIMER_FREQ;

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

	return 0;

static void __exit hangcheck_exit(void)
        printk("Hangcheck: Stopped hangcheck timer.\n");