arch/i386/kernel/nmi.c - maze/linux - Git at Google

 /*
  *  linux/arch/i386/nmi.c
  *
  *  NMI watchdog support on APIC systems
  *
  *  Started by Ingo Molnar <mingo@redhat.com>
  *
  *  Fixes:
  *  Mikael Pettersson	: AMD K7 support for local APIC NMI watchdog.
  *  Mikael Pettersson	: Power Management for local APIC NMI watchdog.
  *  Mikael Pettersson	: Pentium 4 support for local APIC NMI watchdog.
  *  Pavel Machek and
  *  Mikael Pettersson	: PM converted to driver model. Disable/enable API.
  */

 #include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/nmi.h>
 #include <linux/sysdev.h>
 #include <linux/sysctl.h>
 #include <linux/percpu.h>
 #include <linux/kprobes.h>
 #include <linux/cpumask.h>
 #include <linux/kernel_stat.h>

 #include <asm/smp.h>
 #include <asm/nmi.h>
 #include <asm/kdebug.h>

 #include "mach_traps.h"

 int unknown_nmi_panic;
 int nmi_watchdog_enabled;

 static cpumask_t backtrace_mask = CPU_MASK_NONE;

 /* nmi_active:
  * >0: the lapic NMI watchdog is active, but can be disabled
  * <0: the lapic NMI watchdog has not been set up, and cannot
  *     be enabled
  *  0: the lapic NMI watchdog is disabled, but can be enabled
  */
 atomic_t nmi_active = ATOMIC_INIT(0);		/* oprofile uses this */

 unsigned int nmi_watchdog = NMI_DEFAULT;
 static unsigned int nmi_hz = HZ;

 static DEFINE_PER_CPU(short, wd_enabled);

 /* local prototypes */
 static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu);

 static int endflag __initdata = 0;

 #ifdef CONFIG_SMP
 /* The performance counters used by NMI_LOCAL_APIC don't trigger when
  * the CPU is idle. To make sure the NMI watchdog really ticks on all
  * CPUs during the test make them busy.
  */
 static __init void nmi_cpu_busy(void *data)
 {
 	local_irq_enable_in_hardirq();
 	/* Intentionally don't use cpu_relax here. This is
 	   to make sure that the performance counter really ticks,
 	   even if there is a simulator or similar that catches the
 	   pause instruction. On a real HT machine this is fine because
 	   all other CPUs are busy with "useless" delay loops and don't
 	   care if they get somewhat less cycles. */
 	while (endflag == 0)
 		mb();
 }
 #endif

 static int __init check_nmi_watchdog(void)
 {
 	unsigned int *prev_nmi_count;
 	int cpu;

 	if ((nmi_watchdog == NMI_NONE) || (nmi_watchdog == NMI_DEFAULT))
 		return 0;

 	if (!atomic_read(&nmi_active))
 		return 0;

 	prev_nmi_count = kmalloc(NR_CPUS * sizeof(int), GFP_KERNEL);
 	if (!prev_nmi_count)
 		return -1;

 	printk(KERN_INFO "Testing NMI watchdog ... ");

 	if (nmi_watchdog == NMI_LOCAL_APIC)
 		smp_call_function(nmi_cpu_busy, (void *)&endflag, 0, 0);

 	for_each_possible_cpu(cpu)
 		prev_nmi_count[cpu] = per_cpu(irq_stat, cpu).__nmi_count;
 	local_irq_enable();
 	mdelay((20*1000)/nmi_hz); // wait 20 ticks

 	for_each_possible_cpu(cpu) {
 #ifdef CONFIG_SMP
 		/* Check cpu_callin_map here because that is set
 		   after the timer is started. */
 		if (!cpu_isset(cpu, cpu_callin_map))
 			continue;
 #endif
 		if (!per_cpu(wd_enabled, cpu))
 			continue;
 		if (nmi_count(cpu) - prev_nmi_count[cpu] <= 5) {
 			printk("CPU#%d: NMI appears to be stuck (%d->%d)!\n",
 				cpu,
 				prev_nmi_count[cpu],
 				nmi_count(cpu));
 			per_cpu(wd_enabled, cpu) = 0;
 			atomic_dec(&nmi_active);
 		}
 	}
 	if (!atomic_read(&nmi_active)) {
 		kfree(prev_nmi_count);
 		atomic_set(&nmi_active, -1);
 		return -1;
 	}
 	endflag = 1;
 	printk("OK.\n");

 	/* now that we know it works we can reduce NMI frequency to
 	   something more reasonable; makes a difference in some configs */
 	if (nmi_watchdog == NMI_LOCAL_APIC)
 		nmi_hz = lapic_adjust_nmi_hz(1);

 	kfree(prev_nmi_count);
 	return 0;
 }
 /* This needs to happen later in boot so counters are working */
 late_initcall(check_nmi_watchdog);

 static int __init setup_nmi_watchdog(char *str)
 {
 	int nmi;

 	get_option(&str, &nmi);

 	if ((nmi >= NMI_INVALID) || (nmi < NMI_NONE))
 		return 0;

 	nmi_watchdog = nmi;
 	return 1;
 }

 __setup("nmi_watchdog=", setup_nmi_watchdog);


 /* Suspend/resume support */

 #ifdef CONFIG_PM

 static int nmi_pm_active; /* nmi_active before suspend */

 static int lapic_nmi_suspend(struct sys_device *dev, pm_message_t state)
 {
 	/* only CPU0 goes here, other CPUs should be offline */
 	nmi_pm_active = atomic_read(&nmi_active);
 	stop_apic_nmi_watchdog(NULL);
 	BUG_ON(atomic_read(&nmi_active) != 0);
 	return 0;
 }

 static int lapic_nmi_resume(struct sys_device *dev)
 {
 	/* only CPU0 goes here, other CPUs should be offline */
 	if (nmi_pm_active > 0) {
 		setup_apic_nmi_watchdog(NULL);
 		touch_nmi_watchdog();
 	}
 	return 0;
 }


 static struct sysdev_class nmi_sysclass = {
 	set_kset_name("lapic_nmi"),
 	.resume		= lapic_nmi_resume,
 	.suspend	= lapic_nmi_suspend,
 };

 static struct sys_device device_lapic_nmi = {
 	.id	= 0,
 	.cls	= &nmi_sysclass,
 };

 static int __init init_lapic_nmi_sysfs(void)
 {
 	int error;

 	/* should really be a BUG_ON but b/c this is an
 	 * init call, it just doesn't work.  -dcz
 	 */
 	if (nmi_watchdog != NMI_LOCAL_APIC)
 		return 0;

 	if (atomic_read(&nmi_active) < 0)
 		return 0;

 	error = sysdev_class_register(&nmi_sysclass);
 	if (!error)
 		error = sysdev_register(&device_lapic_nmi);
 	return error;
 }
 /* must come after the local APIC's device_initcall() */
 late_initcall(init_lapic_nmi_sysfs);

 #endif	/* CONFIG_PM */

 static void __acpi_nmi_enable(void *__unused)
 {
 	apic_write_around(APIC_LVT0, APIC_DM_NMI);
 }

 /*
  * Enable timer based NMIs on all CPUs:
  */
 void acpi_nmi_enable(void)
 {
 	if (atomic_read(&nmi_active) && nmi_watchdog == NMI_IO_APIC)
 		on_each_cpu(__acpi_nmi_enable, NULL, 0, 1);
 }

 static void __acpi_nmi_disable(void *__unused)
 {
 	apic_write(APIC_LVT0, APIC_DM_NMI | APIC_LVT_MASKED);
 }

 /*
  * Disable timer based NMIs on all CPUs:
  */
 void acpi_nmi_disable(void)
 {
 	if (atomic_read(&nmi_active) && nmi_watchdog == NMI_IO_APIC)
 		on_each_cpu(__acpi_nmi_disable, NULL, 0, 1);
 }

 void setup_apic_nmi_watchdog (void *unused)
 {
 	if (__get_cpu_var(wd_enabled))
  		return;

 	/* cheap hack to support suspend/resume */
 	/* if cpu0 is not active neither should the other cpus */
 	if ((smp_processor_id() != 0) && (atomic_read(&nmi_active) <= 0))
 		return;

 	switch (nmi_watchdog) {
 	case NMI_LOCAL_APIC:
 		__get_cpu_var(wd_enabled) = 1; /* enable it before to avoid race with handler */
 		if (lapic_watchdog_init(nmi_hz) < 0) {
 			__get_cpu_var(wd_enabled) = 0;
 			return;
 		}
 		/* FALL THROUGH */
 	case NMI_IO_APIC:
 		__get_cpu_var(wd_enabled) = 1;
 		atomic_inc(&nmi_active);
 	}
 }

 void stop_apic_nmi_watchdog(void *unused)
 {
 	/* only support LOCAL and IO APICs for now */
 	if ((nmi_watchdog != NMI_LOCAL_APIC) &&
 	    (nmi_watchdog != NMI_IO_APIC))
 	    	return;
 	if (__get_cpu_var(wd_enabled) == 0)
 		return;
 	if (nmi_watchdog == NMI_LOCAL_APIC)
 		lapic_watchdog_stop();
 	__get_cpu_var(wd_enabled) = 0;
 	atomic_dec(&nmi_active);
 }

 /*
  * the best way to detect whether a CPU has a 'hard lockup' problem
  * is to check it's local APIC timer IRQ counts. If they are not
  * changing then that CPU has some problem.
  *
  * as these watchdog NMI IRQs are generated on every CPU, we only
  * have to check the current processor.
  *
  * since NMIs don't listen to _any_ locks, we have to be extremely
  * careful not to rely on unsafe variables. The printk might lock
  * up though, so we have to break up any console locks first ...
  * [when there will be more tty-related locks, break them up
  *  here too!]
  */

 static unsigned int
 	last_irq_sums [NR_CPUS],
 	alert_counter [NR_CPUS];

 void touch_nmi_watchdog (void)
 {
 	if (nmi_watchdog > 0) {
 		unsigned cpu;

 		/*
 		 * Just reset the alert counters, (other CPUs might be
 		 * spinning on locks we hold):
 		 */
 		for_each_present_cpu (cpu)
 			alert_counter[cpu] = 0;
 	}

 	/*
 	 * Tickle the softlockup detector too:
 	 */
 	touch_softlockup_watchdog();
 }
 EXPORT_SYMBOL(touch_nmi_watchdog);

 extern void die_nmi(struct pt_regs *, const char *msg);

 __kprobes int nmi_watchdog_tick(struct pt_regs * regs, unsigned reason)
 {

 	/*
 	 * Since current_thread_info()-> is always on the stack, and we
 	 * always switch the stack NMI-atomically, it's safe to use
 	 * smp_processor_id().
 	 */
 	unsigned int sum;
 	int touched = 0;
 	int cpu = smp_processor_id();
 	int rc=0;

 	/* check for other users first */
 	if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
 			== NOTIFY_STOP) {
 		rc = 1;
 		touched = 1;
 	}

 	if (cpu_isset(cpu, backtrace_mask)) {
 		static DEFINE_SPINLOCK(lock);	/* Serialise the printks */

 		spin_lock(&lock);
 		printk("NMI backtrace for cpu %d\n", cpu);
 		dump_stack();
 		spin_unlock(&lock);
 		cpu_clear(cpu, backtrace_mask);
 	}

 	/*
 	 * Take the local apic timer and PIT/HPET into account. We don't
 	 * know which one is active, when we have highres/dyntick on
 	 */
 	sum = per_cpu(irq_stat, cpu).apic_timer_irqs + kstat_irqs(0);

 	/* if the none of the timers isn't firing, this cpu isn't doing much */
 	if (!touched && last_irq_sums[cpu] == sum) {
 		/*
 		 * Ayiee, looks like this CPU is stuck ...
 		 * wait a few IRQs (5 seconds) before doing the oops ...
 		 */
 		alert_counter[cpu]++;
 		if (alert_counter[cpu] == 5*nmi_hz)
 			/*
 			 * die_nmi will return ONLY if NOTIFY_STOP happens..
 			 */
 			die_nmi(regs, "BUG: NMI Watchdog detected LOCKUP");
 	} else {
 		last_irq_sums[cpu] = sum;
 		alert_counter[cpu] = 0;
 	}
 	/* see if the nmi watchdog went off */
 	if (!__get_cpu_var(wd_enabled))
 		return rc;
 	switch (nmi_watchdog) {
 	case NMI_LOCAL_APIC:
 		rc |= lapic_wd_event(nmi_hz);
 		break;
 	case NMI_IO_APIC:
 		/* don't know how to accurately check for this.
 		 * just assume it was a watchdog timer interrupt
 		 * This matches the old behaviour.
 		 */
 		rc = 1;
 		break;
 	}
 	return rc;
 }

 int do_nmi_callback(struct pt_regs * regs, int cpu)
 {
 #ifdef CONFIG_SYSCTL
 	if (unknown_nmi_panic)
 		return unknown_nmi_panic_callback(regs, cpu);
 #endif
 	return 0;
 }

 #ifdef CONFIG_SYSCTL

 static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu)
 {
 	unsigned char reason = get_nmi_reason();
 	char buf[64];

 	sprintf(buf, "NMI received for unknown reason %02x\n", reason);
 	die_nmi(regs, buf);
 	return 0;
 }

 /*
  * proc handler for /proc/sys/kernel/nmi
  */
 int proc_nmi_enabled(struct ctl_table *table, int write, struct file *file,
 			void __user *buffer, size_t *length, loff_t *ppos)
 {
 	int old_state;

 	nmi_watchdog_enabled = (atomic_read(&nmi_active) > 0) ? 1 : 0;
 	old_state = nmi_watchdog_enabled;
 	proc_dointvec(table, write, file, buffer, length, ppos);
 	if (!!old_state == !!nmi_watchdog_enabled)
 		return 0;

 	if (atomic_read(&nmi_active) < 0) {
 		printk( KERN_WARNING "NMI watchdog is permanently disabled\n");
 		return -EIO;
 	}

 	if (nmi_watchdog == NMI_DEFAULT) {
 		if (lapic_watchdog_ok())
 			nmi_watchdog = NMI_LOCAL_APIC;
 		else
 			nmi_watchdog = NMI_IO_APIC;
 	}

 	if (nmi_watchdog == NMI_LOCAL_APIC) {
 		if (nmi_watchdog_enabled)
 			enable_lapic_nmi_watchdog();
 		else
 			disable_lapic_nmi_watchdog();
 	} else {
 		printk( KERN_WARNING
 			"NMI watchdog doesn't know what hardware to touch\n");
 		return -EIO;
 	}
 	return 0;
 }

 #endif

 void __trigger_all_cpu_backtrace(void)
 {
 	int i;

 	backtrace_mask = cpu_online_map;
 	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
 	for (i = 0; i < 10 * 1000; i++) {
 		if (cpus_empty(backtrace_mask))
 			break;
 		mdelay(1);
 	}
 }

 EXPORT_SYMBOL(nmi_active);
 EXPORT_SYMBOL(nmi_watchdog);
	/*
	* linux/arch/i386/nmi.c
	*
	* NMI watchdog support on APIC systems
	*
	* Started by Ingo Molnar <mingo@redhat.com>
	*
	* Fixes:
	* Mikael Pettersson : AMD K7 support for local APIC NMI watchdog.
	* Mikael Pettersson : Power Management for local APIC NMI watchdog.
	* Mikael Pettersson : Pentium 4 support for local APIC NMI watchdog.
	* Pavel Machek and
	* Mikael Pettersson : PM converted to driver model. Disable/enable API.
	*/

	#include <linux/delay.h>
	#include <linux/interrupt.h>
	#include <linux/module.h>
	#include <linux/nmi.h>
	#include <linux/sysdev.h>
	#include <linux/sysctl.h>
	#include <linux/percpu.h>
	#include <linux/kprobes.h>
	#include <linux/cpumask.h>
	#include <linux/kernel_stat.h>

	#include <asm/smp.h>
	#include <asm/nmi.h>
	#include <asm/kdebug.h>

	#include "mach_traps.h"

	int unknown_nmi_panic;
	int nmi_watchdog_enabled;

	static cpumask_t backtrace_mask = CPU_MASK_NONE;

	/* nmi_active:
	* >0: the lapic NMI watchdog is active, but can be disabled
	* <0: the lapic NMI watchdog has not been set up, and cannot
	* be enabled
	* 0: the lapic NMI watchdog is disabled, but can be enabled
	*/
	atomic_t nmi_active = ATOMIC_INIT(0); /* oprofile uses this */

	unsigned int nmi_watchdog = NMI_DEFAULT;
	static unsigned int nmi_hz = HZ;

	static DEFINE_PER_CPU(short, wd_enabled);

	/* local prototypes */
	static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu);

	static int endflag __initdata = 0;

	#ifdef CONFIG_SMP
	/* The performance counters used by NMI_LOCAL_APIC don't trigger when
	* the CPU is idle. To make sure the NMI watchdog really ticks on all
	* CPUs during the test make them busy.
	*/
	static __init void nmi_cpu_busy(void *data)
	{
	local_irq_enable_in_hardirq();
	/* Intentionally don't use cpu_relax here. This is
	to make sure that the performance counter really ticks,
	even if there is a simulator or similar that catches the
	pause instruction. On a real HT machine this is fine because
	all other CPUs are busy with "useless" delay loops and don't
	care if they get somewhat less cycles. */
	while (endflag == 0)
	mb();
	}
	#endif

	static int __init check_nmi_watchdog(void)
	{
	unsigned int *prev_nmi_count;
	int cpu;

	if ((nmi_watchdog == NMI_NONE) \|\| (nmi_watchdog == NMI_DEFAULT))
	return 0;

	if (!atomic_read(&nmi_active))
	return 0;

	prev_nmi_count = kmalloc(NR_CPUS * sizeof(int), GFP_KERNEL);
	if (!prev_nmi_count)
	return -1;

	printk(KERN_INFO "Testing NMI watchdog ... ");

	if (nmi_watchdog == NMI_LOCAL_APIC)
	smp_call_function(nmi_cpu_busy, (void *)&endflag, 0, 0);

	for_each_possible_cpu(cpu)
	prev_nmi_count[cpu] = per_cpu(irq_stat, cpu).__nmi_count;
	local_irq_enable();
	mdelay((20*1000)/nmi_hz); // wait 20 ticks

	for_each_possible_cpu(cpu) {
	#ifdef CONFIG_SMP
	/* Check cpu_callin_map here because that is set
	after the timer is started. */
	if (!cpu_isset(cpu, cpu_callin_map))
	continue;
	#endif
	if (!per_cpu(wd_enabled, cpu))
	continue;
	if (nmi_count(cpu) - prev_nmi_count[cpu] <= 5) {
	printk("CPU#%d: NMI appears to be stuck (%d->%d)!\n",
	cpu,
	prev_nmi_count[cpu],
	nmi_count(cpu));
	per_cpu(wd_enabled, cpu) = 0;
	atomic_dec(&nmi_active);
	}
	}
	if (!atomic_read(&nmi_active)) {
	kfree(prev_nmi_count);
	atomic_set(&nmi_active, -1);
	return -1;
	}
	endflag = 1;
	printk("OK.\n");

	/* now that we know it works we can reduce NMI frequency to
	something more reasonable; makes a difference in some configs */
	if (nmi_watchdog == NMI_LOCAL_APIC)
	nmi_hz = lapic_adjust_nmi_hz(1);

	kfree(prev_nmi_count);
	return 0;
	}
	/* This needs to happen later in boot so counters are working */
	late_initcall(check_nmi_watchdog);

	static int __init setup_nmi_watchdog(char *str)
	{
	int nmi;

	get_option(&str, &nmi);

	if ((nmi >= NMI_INVALID) \|\| (nmi < NMI_NONE))
	return 0;

	nmi_watchdog = nmi;
	return 1;
	}

	__setup("nmi_watchdog=", setup_nmi_watchdog);


	/* Suspend/resume support */

	#ifdef CONFIG_PM

	static int nmi_pm_active; /* nmi_active before suspend */

	static int lapic_nmi_suspend(struct sys_device *dev, pm_message_t state)
	{
	/* only CPU0 goes here, other CPUs should be offline */
	nmi_pm_active = atomic_read(&nmi_active);
	stop_apic_nmi_watchdog(NULL);
	BUG_ON(atomic_read(&nmi_active) != 0);
	return 0;
	}

	static int lapic_nmi_resume(struct sys_device *dev)
	{
	/* only CPU0 goes here, other CPUs should be offline */
	if (nmi_pm_active > 0) {
	setup_apic_nmi_watchdog(NULL);
	touch_nmi_watchdog();
	}
	return 0;
	}


	static struct sysdev_class nmi_sysclass = {
	set_kset_name("lapic_nmi"),
	.resume = lapic_nmi_resume,
	.suspend = lapic_nmi_suspend,
	};

	static struct sys_device device_lapic_nmi = {
	.id = 0,
	.cls = &nmi_sysclass,
	};

	static int __init init_lapic_nmi_sysfs(void)
	{
	int error;

	/* should really be a BUG_ON but b/c this is an
	* init call, it just doesn't work. -dcz
	*/
	if (nmi_watchdog != NMI_LOCAL_APIC)
	return 0;

	if (atomic_read(&nmi_active) < 0)
	return 0;

	error = sysdev_class_register(&nmi_sysclass);
	if (!error)
	error = sysdev_register(&device_lapic_nmi);
	return error;
	}
	/* must come after the local APIC's device_initcall() */
	late_initcall(init_lapic_nmi_sysfs);

	#endif /* CONFIG_PM */

	static void __acpi_nmi_enable(void *__unused)
	{
	apic_write_around(APIC_LVT0, APIC_DM_NMI);
	}

	/*
	* Enable timer based NMIs on all CPUs:
	*/
	void acpi_nmi_enable(void)
	{
	if (atomic_read(&nmi_active) && nmi_watchdog == NMI_IO_APIC)
	on_each_cpu(__acpi_nmi_enable, NULL, 0, 1);
	}

	static void __acpi_nmi_disable(void *__unused)
	{
	apic_write(APIC_LVT0, APIC_DM_NMI \| APIC_LVT_MASKED);
	}

	/*
	* Disable timer based NMIs on all CPUs:
	*/
	void acpi_nmi_disable(void)
	{
	if (atomic_read(&nmi_active) && nmi_watchdog == NMI_IO_APIC)
	on_each_cpu(__acpi_nmi_disable, NULL, 0, 1);
	}

	void setup_apic_nmi_watchdog (void *unused)
	{
	if (__get_cpu_var(wd_enabled))
	return;

	/* cheap hack to support suspend/resume */
	/* if cpu0 is not active neither should the other cpus */
	if ((smp_processor_id() != 0) && (atomic_read(&nmi_active) <= 0))
	return;

	switch (nmi_watchdog) {
	case NMI_LOCAL_APIC:
	__get_cpu_var(wd_enabled) = 1; /* enable it before to avoid race with handler */
	if (lapic_watchdog_init(nmi_hz) < 0) {
	__get_cpu_var(wd_enabled) = 0;
	return;
	}
	/* FALL THROUGH */
	case NMI_IO_APIC:
	__get_cpu_var(wd_enabled) = 1;
	atomic_inc(&nmi_active);
	}
	}

	void stop_apic_nmi_watchdog(void *unused)
	{
	/* only support LOCAL and IO APICs for now */
	if ((nmi_watchdog != NMI_LOCAL_APIC) &&
	(nmi_watchdog != NMI_IO_APIC))
	return;
	if (__get_cpu_var(wd_enabled) == 0)
	return;
	if (nmi_watchdog == NMI_LOCAL_APIC)
	lapic_watchdog_stop();
	__get_cpu_var(wd_enabled) = 0;
	atomic_dec(&nmi_active);
	}

	/*
	* the best way to detect whether a CPU has a 'hard lockup' problem
	* is to check it's local APIC timer IRQ counts. If they are not
	* changing then that CPU has some problem.
	*
	* as these watchdog NMI IRQs are generated on every CPU, we only
	* have to check the current processor.
	*
	* since NMIs don't listen to _any_ locks, we have to be extremely
	* careful not to rely on unsafe variables. The printk might lock
	* up though, so we have to break up any console locks first ...
	* [when there will be more tty-related locks, break them up
	* here too!]
	*/

	static unsigned int
	last_irq_sums [NR_CPUS],
	alert_counter [NR_CPUS];

	void touch_nmi_watchdog (void)
	{
	if (nmi_watchdog > 0) {
	unsigned cpu;

	/*
	* Just reset the alert counters, (other CPUs might be
	* spinning on locks we hold):
	*/
	for_each_present_cpu (cpu)
	alert_counter[cpu] = 0;
	}

	/*
	* Tickle the softlockup detector too:
	*/
	touch_softlockup_watchdog();
	}
	EXPORT_SYMBOL(touch_nmi_watchdog);

	extern void die_nmi(struct pt_regs , const char msg);

	__kprobes int nmi_watchdog_tick(struct pt_regs * regs, unsigned reason)
	{

	/*
	* Since current_thread_info()-> is always on the stack, and we
	* always switch the stack NMI-atomically, it's safe to use
	* smp_processor_id().
	*/
	unsigned int sum;
	int touched = 0;
	int cpu = smp_processor_id();
	int rc=0;

	/* check for other users first */
	if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
	== NOTIFY_STOP) {
	rc = 1;
	touched = 1;
	}

	if (cpu_isset(cpu, backtrace_mask)) {
	static DEFINE_SPINLOCK(lock); /* Serialise the printks */

	spin_lock(&lock);
	printk("NMI backtrace for cpu %d\n", cpu);
	dump_stack();
	spin_unlock(&lock);
	cpu_clear(cpu, backtrace_mask);
	}

	/*
	* Take the local apic timer and PIT/HPET into account. We don't
	* know which one is active, when we have highres/dyntick on
	*/
	sum = per_cpu(irq_stat, cpu).apic_timer_irqs + kstat_irqs(0);

	/* if the none of the timers isn't firing, this cpu isn't doing much */
	if (!touched && last_irq_sums[cpu] == sum) {
	/*
	* Ayiee, looks like this CPU is stuck ...
	* wait a few IRQs (5 seconds) before doing the oops ...
	*/
	alert_counter[cpu]++;
	if (alert_counter[cpu] == 5*nmi_hz)
	/*
	* die_nmi will return ONLY if NOTIFY_STOP happens..
	*/
	die_nmi(regs, "BUG: NMI Watchdog detected LOCKUP");
	} else {
	last_irq_sums[cpu] = sum;
	alert_counter[cpu] = 0;
	}
	/* see if the nmi watchdog went off */
	if (!__get_cpu_var(wd_enabled))
	return rc;
	switch (nmi_watchdog) {
	case NMI_LOCAL_APIC:
	rc \|= lapic_wd_event(nmi_hz);
	break;
	case NMI_IO_APIC:
	/* don't know how to accurately check for this.
	* just assume it was a watchdog timer interrupt
	* This matches the old behaviour.
	*/
	rc = 1;
	break;
	}
	return rc;
	}

	int do_nmi_callback(struct pt_regs * regs, int cpu)
	{
	#ifdef CONFIG_SYSCTL
	if (unknown_nmi_panic)
	return unknown_nmi_panic_callback(regs, cpu);
	#endif
	return 0;
	}

	#ifdef CONFIG_SYSCTL

	static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu)
	{
	unsigned char reason = get_nmi_reason();
	char buf[64];

	sprintf(buf, "NMI received for unknown reason %02x\n", reason);
	die_nmi(regs, buf);
	return 0;
	}

	/*
	* proc handler for /proc/sys/kernel/nmi
	*/
	int proc_nmi_enabled(struct ctl_table table, int write, struct file file,
	void __user buffer, size_t length, loff_t *ppos)
	{
	int old_state;

	nmi_watchdog_enabled = (atomic_read(&nmi_active) > 0) ? 1 : 0;
	old_state = nmi_watchdog_enabled;
	proc_dointvec(table, write, file, buffer, length, ppos);
	if (!!old_state == !!nmi_watchdog_enabled)
	return 0;

	if (atomic_read(&nmi_active) < 0) {
	printk( KERN_WARNING "NMI watchdog is permanently disabled\n");
	return -EIO;
	}

	if (nmi_watchdog == NMI_DEFAULT) {
	if (lapic_watchdog_ok())
	nmi_watchdog = NMI_LOCAL_APIC;
	else
	nmi_watchdog = NMI_IO_APIC;
	}

	if (nmi_watchdog == NMI_LOCAL_APIC) {
	if (nmi_watchdog_enabled)
	enable_lapic_nmi_watchdog();
	else
	disable_lapic_nmi_watchdog();
	} else {
	printk( KERN_WARNING
	"NMI watchdog doesn't know what hardware to touch\n");
	return -EIO;
	}
	return 0;
	}

	#endif

	void __trigger_all_cpu_backtrace(void)
	{
	int i;

	backtrace_mask = cpu_online_map;
	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
	for (i = 0; i < 10 * 1000; i++) {
	if (cpus_empty(backtrace_mask))
	break;
	mdelay(1);
	}
	}

	EXPORT_SYMBOL(nmi_active);
	EXPORT_SYMBOL(nmi_watchdog);