arch/powerpc/kernel/watchdog.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Watchdog support on powerpc systems.
  *
  * Copyright 2017, IBM Corporation.
  *
  * This uses code from arch/sparc/kernel/nmi.c and kernel/watchdog.c
  */

 #define pr_fmt(fmt) "watchdog: " fmt

 #include <linux/kernel.h>
 #include <linux/param.h>
 #include <linux/init.h>
 #include <linux/percpu.h>
 #include <linux/cpu.h>
 #include <linux/nmi.h>
 #include <linux/module.h>
 #include <linux/export.h>
 #include <linux/kprobes.h>
 #include <linux/hardirq.h>
 #include <linux/reboot.h>
 #include <linux/slab.h>
 #include <linux/kdebug.h>
 #include <linux/sched/debug.h>
 #include <linux/delay.h>
 #include <linux/smp.h>

 #include <asm/paca.h>

 /*
  * The powerpc watchdog ensures that each CPU is able to service timers.
  * The watchdog sets up a simple timer on each CPU to run once per timer
  * period, and updates a per-cpu timestamp and a "pending" cpumask. This is
  * the heartbeat.
  *
  * Then there are two systems to check that the heartbeat is still running.
  * The local soft-NMI, and the SMP checker.
  *
  * The soft-NMI checker can detect lockups on the local CPU. When interrupts
  * are disabled with local_irq_disable(), platforms that use soft-masking
  * can leave hardware interrupts enabled and handle them with a masked
  * interrupt handler. The masked handler can send the timer interrupt to the
  * watchdog's soft_nmi_interrupt(), which appears to Linux as an NMI
  * interrupt, and can be used to detect CPUs stuck with IRQs disabled.
  *
  * The soft-NMI checker will compare the heartbeat timestamp for this CPU
  * with the current time, and take action if the difference exceeds the
  * watchdog threshold.
  *
  * The limitation of the soft-NMI watchdog is that it does not work when
  * interrupts are hard disabled or otherwise not being serviced. This is
  * solved by also having a SMP watchdog where all CPUs check all other
  * CPUs heartbeat.
  *
  * The SMP checker can detect lockups on other CPUs. A gobal "pending"
  * cpumask is kept, containing all CPUs which enable the watchdog. Each
  * CPU clears their pending bit in their heartbeat timer. When the bitmask
  * becomes empty, the last CPU to clear its pending bit updates a global
  * timestamp and refills the pending bitmask.
  *
  * In the heartbeat timer, if any CPU notices that the global timestamp has
  * not been updated for a period exceeding the watchdog threshold, then it
  * means the CPU(s) with their bit still set in the pending mask have had
  * their heartbeat stop, and action is taken.
  *
  * Some platforms implement true NMI IPIs, which can by used by the SMP
  * watchdog to detect an unresponsive CPU and pull it out of its stuck
  * state with the NMI IPI, to get crash/debug data from it. This way the
  * SMP watchdog can detect hardware interrupts off lockups.
  */

 static cpumask_t wd_cpus_enabled __read_mostly;

 static u64 wd_panic_timeout_tb __read_mostly; /* timebase ticks until panic */
 static u64 wd_smp_panic_timeout_tb __read_mostly; /* panic other CPUs */

 static u64 wd_timer_period_ms __read_mostly;  /* interval between heartbeat */

 static DEFINE_PER_CPU(struct timer_list, wd_timer);
 static DEFINE_PER_CPU(u64, wd_timer_tb);

 /* SMP checker bits */
 static unsigned long __wd_smp_lock;
 static cpumask_t wd_smp_cpus_pending;
 static cpumask_t wd_smp_cpus_stuck;
 static u64 wd_smp_last_reset_tb;

 static inline void wd_smp_lock(unsigned long *flags)
 {
 	/*
 	 * Avoid locking layers if possible.
 	 * This may be called from low level interrupt handlers at some
 	 * point in future.
 	 */
 	raw_local_irq_save(*flags);
 	hard_irq_disable(); /* Make it soft-NMI safe */
 	while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) {
 		raw_local_irq_restore(*flags);
 		spin_until_cond(!test_bit(0, &__wd_smp_lock));
 		raw_local_irq_save(*flags);
 		hard_irq_disable();
 	}
 }

 static inline void wd_smp_unlock(unsigned long *flags)
 {
 	clear_bit_unlock(0, &__wd_smp_lock);
 	raw_local_irq_restore(*flags);
 }

 static void wd_lockup_ipi(struct pt_regs *regs)
 {
 	pr_emerg("CPU %d Hard LOCKUP\n", raw_smp_processor_id());
 	print_modules();
 	print_irqtrace_events(current);
 	if (regs)
 		show_regs(regs);
 	else
 		dump_stack();

 	/* Do not panic from here because that can recurse into NMI IPI layer */
 }

 static void set_cpumask_stuck(const struct cpumask *cpumask, u64 tb)
 {
 	cpumask_or(&wd_smp_cpus_stuck, &wd_smp_cpus_stuck, cpumask);
 	cpumask_andnot(&wd_smp_cpus_pending, &wd_smp_cpus_pending, cpumask);
 	if (cpumask_empty(&wd_smp_cpus_pending)) {
 		wd_smp_last_reset_tb = tb;
 		cpumask_andnot(&wd_smp_cpus_pending,
 				&wd_cpus_enabled,
 				&wd_smp_cpus_stuck);
 	}
 }
 static void set_cpu_stuck(int cpu, u64 tb)
 {
 	set_cpumask_stuck(cpumask_of(cpu), tb);
 }

 static void watchdog_smp_panic(int cpu, u64 tb)
 {
 	unsigned long flags;
 	int c;

 	wd_smp_lock(&flags);
 	/* Double check some things under lock */
 	if ((s64)(tb - wd_smp_last_reset_tb) < (s64)wd_smp_panic_timeout_tb)
 		goto out;
 	if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending))
 		goto out;
 	if (cpumask_weight(&wd_smp_cpus_pending) == 0)
 		goto out;

 	pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n",
 		 cpu, cpumask_pr_args(&wd_smp_cpus_pending));

 	if (!sysctl_hardlockup_all_cpu_backtrace) {
 		/*
 		 * Try to trigger the stuck CPUs, unless we are going to
 		 * get a backtrace on all of them anyway.
 		 */
 		for_each_cpu(c, &wd_smp_cpus_pending) {
 			if (c == cpu)
 				continue;
 			smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000);
 		}
 		smp_flush_nmi_ipi(1000000);
 	}

 	/* Take the stuck CPUs out of the watch group */
 	set_cpumask_stuck(&wd_smp_cpus_pending, tb);

 	wd_smp_unlock(&flags);

 	printk_safe_flush();
 	/*
 	 * printk_safe_flush() seems to require another print
 	 * before anything actually goes out to console.
 	 */
 	if (sysctl_hardlockup_all_cpu_backtrace)
 		trigger_allbutself_cpu_backtrace();

 	if (hardlockup_panic)
 		nmi_panic(NULL, "Hard LOCKUP");

 	return;

 out:
 	wd_smp_unlock(&flags);
 }

 static void wd_smp_clear_cpu_pending(int cpu, u64 tb)
 {
 	if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) {
 		if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) {
 			unsigned long flags;

 			pr_emerg("CPU %d became unstuck\n", cpu);
 			wd_smp_lock(&flags);
 			cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck);
 			wd_smp_unlock(&flags);
 		}
 		return;
 	}
 	cpumask_clear_cpu(cpu, &wd_smp_cpus_pending);
 	if (cpumask_empty(&wd_smp_cpus_pending)) {
 		unsigned long flags;

 		wd_smp_lock(&flags);
 		if (cpumask_empty(&wd_smp_cpus_pending)) {
 			wd_smp_last_reset_tb = tb;
 			cpumask_andnot(&wd_smp_cpus_pending,
 					&wd_cpus_enabled,
 					&wd_smp_cpus_stuck);
 		}
 		wd_smp_unlock(&flags);
 	}
 }

 static void watchdog_timer_interrupt(int cpu)
 {
 	u64 tb = get_tb();

 	per_cpu(wd_timer_tb, cpu) = tb;

 	wd_smp_clear_cpu_pending(cpu, tb);

 	if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb)
 		watchdog_smp_panic(cpu, tb);
 }

 void soft_nmi_interrupt(struct pt_regs *regs)
 {
 	unsigned long flags;
 	int cpu = raw_smp_processor_id();
 	u64 tb;

 	if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
 		return;

 	nmi_enter();

 	__this_cpu_inc(irq_stat.soft_nmi_irqs);

 	tb = get_tb();
 	if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) {
 		per_cpu(wd_timer_tb, cpu) = tb;

 		wd_smp_lock(&flags);
 		if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) {
 			wd_smp_unlock(&flags);
 			goto out;
 		}
 		set_cpu_stuck(cpu, tb);

 		pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n", cpu, (void *)regs->nip);
 		print_modules();
 		print_irqtrace_events(current);
 		show_regs(regs);

 		wd_smp_unlock(&flags);

 		if (sysctl_hardlockup_all_cpu_backtrace)
 			trigger_allbutself_cpu_backtrace();

 		if (hardlockup_panic)
 			nmi_panic(regs, "Hard LOCKUP");
 	}
 	if (wd_panic_timeout_tb < 0x7fffffff)
 		mtspr(SPRN_DEC, wd_panic_timeout_tb);

 out:
 	nmi_exit();
 }

 static void wd_timer_reset(unsigned int cpu, struct timer_list *t)
 {
 	t->expires = jiffies + msecs_to_jiffies(wd_timer_period_ms);
 	if (wd_timer_period_ms > 1000)
 		t->expires = __round_jiffies_up(t->expires, cpu);
 	add_timer_on(t, cpu);
 }

 static void wd_timer_fn(struct timer_list *t)
 {
 	int cpu = smp_processor_id();

 	watchdog_timer_interrupt(cpu);

 	wd_timer_reset(cpu, t);
 }

 void arch_touch_nmi_watchdog(void)
 {
 	unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000;
 	int cpu = smp_processor_id();
 	u64 tb = get_tb();

 	if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) {
 		per_cpu(wd_timer_tb, cpu) = tb;
 		wd_smp_clear_cpu_pending(cpu, tb);
 	}
 }
 EXPORT_SYMBOL(arch_touch_nmi_watchdog);

 static void start_watchdog_timer_on(unsigned int cpu)
 {
 	struct timer_list *t = per_cpu_ptr(&wd_timer, cpu);

 	per_cpu(wd_timer_tb, cpu) = get_tb();

 	timer_setup(t, wd_timer_fn, TIMER_PINNED);
 	wd_timer_reset(cpu, t);
 }

 static void stop_watchdog_timer_on(unsigned int cpu)
 {
 	struct timer_list *t = per_cpu_ptr(&wd_timer, cpu);

 	del_timer_sync(t);
 }

 static int start_wd_on_cpu(unsigned int cpu)
 {
 	unsigned long flags;

 	if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) {
 		WARN_ON(1);
 		return 0;
 	}

 	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 		return 0;

 	if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
 		return 0;

 	wd_smp_lock(&flags);
 	cpumask_set_cpu(cpu, &wd_cpus_enabled);
 	if (cpumask_weight(&wd_cpus_enabled) == 1) {
 		cpumask_set_cpu(cpu, &wd_smp_cpus_pending);
 		wd_smp_last_reset_tb = get_tb();
 	}
 	wd_smp_unlock(&flags);

 	start_watchdog_timer_on(cpu);

 	return 0;
 }

 static int stop_wd_on_cpu(unsigned int cpu)
 {
 	unsigned long flags;

 	if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
 		return 0; /* Can happen in CPU unplug case */

 	stop_watchdog_timer_on(cpu);

 	wd_smp_lock(&flags);
 	cpumask_clear_cpu(cpu, &wd_cpus_enabled);
 	wd_smp_unlock(&flags);

 	wd_smp_clear_cpu_pending(cpu, get_tb());

 	return 0;
 }

 static void watchdog_calc_timeouts(void)
 {
 	wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq;

 	/* Have the SMP detector trigger a bit later */
 	wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2;

 	/* 2/5 is the factor that the perf based detector uses */
 	wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5;
 }

 void watchdog_nmi_stop(void)
 {
 	int cpu;

 	for_each_cpu(cpu, &wd_cpus_enabled)
 		stop_wd_on_cpu(cpu);
 }

 void watchdog_nmi_start(void)
 {
 	int cpu;

 	watchdog_calc_timeouts();
 	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
 		start_wd_on_cpu(cpu);
 }

 /*
  * Invoked from core watchdog init.
  */
 int __init watchdog_nmi_probe(void)
 {
 	int err;

 	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
 					"powerpc/watchdog:online",
 					start_wd_on_cpu, stop_wd_on_cpu);
 	if (err < 0) {
 		pr_warn("could not be initialized");
 		return err;
 	}
 	return 0;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Watchdog support on powerpc systems.
	*
	* Copyright 2017, IBM Corporation.
	*
	* This uses code from arch/sparc/kernel/nmi.c and kernel/watchdog.c
	*/

	#define pr_fmt(fmt) "watchdog: " fmt

	#include <linux/kernel.h>
	#include <linux/param.h>
	#include <linux/init.h>
	#include <linux/percpu.h>
	#include <linux/cpu.h>
	#include <linux/nmi.h>
	#include <linux/module.h>
	#include <linux/export.h>
	#include <linux/kprobes.h>
	#include <linux/hardirq.h>
	#include <linux/reboot.h>
	#include <linux/slab.h>
	#include <linux/kdebug.h>
	#include <linux/sched/debug.h>
	#include <linux/delay.h>
	#include <linux/smp.h>

	#include <asm/paca.h>

	/*
	* The powerpc watchdog ensures that each CPU is able to service timers.
	* The watchdog sets up a simple timer on each CPU to run once per timer
	* period, and updates a per-cpu timestamp and a "pending" cpumask. This is
	* the heartbeat.
	*
	* Then there are two systems to check that the heartbeat is still running.
	* The local soft-NMI, and the SMP checker.
	*
	* The soft-NMI checker can detect lockups on the local CPU. When interrupts
	* are disabled with local_irq_disable(), platforms that use soft-masking
	* can leave hardware interrupts enabled and handle them with a masked
	* interrupt handler. The masked handler can send the timer interrupt to the
	* watchdog's soft_nmi_interrupt(), which appears to Linux as an NMI
	* interrupt, and can be used to detect CPUs stuck with IRQs disabled.
	*
	* The soft-NMI checker will compare the heartbeat timestamp for this CPU
	* with the current time, and take action if the difference exceeds the
	* watchdog threshold.
	*
	* The limitation of the soft-NMI watchdog is that it does not work when
	* interrupts are hard disabled or otherwise not being serviced. This is
	* solved by also having a SMP watchdog where all CPUs check all other
	* CPUs heartbeat.
	*
	* The SMP checker can detect lockups on other CPUs. A gobal "pending"
	* cpumask is kept, containing all CPUs which enable the watchdog. Each
	* CPU clears their pending bit in their heartbeat timer. When the bitmask
	* becomes empty, the last CPU to clear its pending bit updates a global
	* timestamp and refills the pending bitmask.
	*
	* In the heartbeat timer, if any CPU notices that the global timestamp has
	* not been updated for a period exceeding the watchdog threshold, then it
	* means the CPU(s) with their bit still set in the pending mask have had
	* their heartbeat stop, and action is taken.
	*
	* Some platforms implement true NMI IPIs, which can by used by the SMP
	* watchdog to detect an unresponsive CPU and pull it out of its stuck
	* state with the NMI IPI, to get crash/debug data from it. This way the
	* SMP watchdog can detect hardware interrupts off lockups.
	*/

	static cpumask_t wd_cpus_enabled __read_mostly;

	static u64 wd_panic_timeout_tb __read_mostly; /* timebase ticks until panic */
	static u64 wd_smp_panic_timeout_tb __read_mostly; /* panic other CPUs */

	static u64 wd_timer_period_ms __read_mostly; /* interval between heartbeat */

	static DEFINE_PER_CPU(struct timer_list, wd_timer);
	static DEFINE_PER_CPU(u64, wd_timer_tb);

	/* SMP checker bits */
	static unsigned long __wd_smp_lock;
	static cpumask_t wd_smp_cpus_pending;
	static cpumask_t wd_smp_cpus_stuck;
	static u64 wd_smp_last_reset_tb;

	static inline void wd_smp_lock(unsigned long *flags)
	{
	/*
	* Avoid locking layers if possible.
	* This may be called from low level interrupt handlers at some
	* point in future.
	*/
	raw_local_irq_save(*flags);
	hard_irq_disable(); /* Make it soft-NMI safe */
	while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) {
	raw_local_irq_restore(*flags);
	spin_until_cond(!test_bit(0, &__wd_smp_lock));
	raw_local_irq_save(*flags);
	hard_irq_disable();
	}
	}

	static inline void wd_smp_unlock(unsigned long *flags)
	{
	clear_bit_unlock(0, &__wd_smp_lock);
	raw_local_irq_restore(*flags);
	}

	static void wd_lockup_ipi(struct pt_regs *regs)
	{
	pr_emerg("CPU %d Hard LOCKUP\n", raw_smp_processor_id());
	print_modules();
	print_irqtrace_events(current);
	if (regs)
	show_regs(regs);
	else
	dump_stack();

	/* Do not panic from here because that can recurse into NMI IPI layer */
	}

	static void set_cpumask_stuck(const struct cpumask *cpumask, u64 tb)
	{
	cpumask_or(&wd_smp_cpus_stuck, &wd_smp_cpus_stuck, cpumask);
	cpumask_andnot(&wd_smp_cpus_pending, &wd_smp_cpus_pending, cpumask);
	if (cpumask_empty(&wd_smp_cpus_pending)) {
	wd_smp_last_reset_tb = tb;
	cpumask_andnot(&wd_smp_cpus_pending,
	&wd_cpus_enabled,
	&wd_smp_cpus_stuck);
	}
	}
	static void set_cpu_stuck(int cpu, u64 tb)
	{
	set_cpumask_stuck(cpumask_of(cpu), tb);
	}

	static void watchdog_smp_panic(int cpu, u64 tb)
	{
	unsigned long flags;
	int c;

	wd_smp_lock(&flags);
	/* Double check some things under lock */
	if ((s64)(tb - wd_smp_last_reset_tb) < (s64)wd_smp_panic_timeout_tb)
	goto out;
	if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending))
	goto out;
	if (cpumask_weight(&wd_smp_cpus_pending) == 0)
	goto out;

	pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n",
	cpu, cpumask_pr_args(&wd_smp_cpus_pending));

	if (!sysctl_hardlockup_all_cpu_backtrace) {
	/*
	* Try to trigger the stuck CPUs, unless we are going to
	* get a backtrace on all of them anyway.
	*/
	for_each_cpu(c, &wd_smp_cpus_pending) {
	if (c == cpu)
	continue;
	smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000);
	}
	smp_flush_nmi_ipi(1000000);
	}

	/* Take the stuck CPUs out of the watch group */
	set_cpumask_stuck(&wd_smp_cpus_pending, tb);

	wd_smp_unlock(&flags);

	printk_safe_flush();
	/*
	* printk_safe_flush() seems to require another print
	* before anything actually goes out to console.
	*/
	if (sysctl_hardlockup_all_cpu_backtrace)
	trigger_allbutself_cpu_backtrace();

	if (hardlockup_panic)
	nmi_panic(NULL, "Hard LOCKUP");

	return;

	out:
	wd_smp_unlock(&flags);
	}

	static void wd_smp_clear_cpu_pending(int cpu, u64 tb)
	{
	if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) {
	if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) {
	unsigned long flags;

	pr_emerg("CPU %d became unstuck\n", cpu);
	wd_smp_lock(&flags);
	cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck);
	wd_smp_unlock(&flags);
	}
	return;
	}
	cpumask_clear_cpu(cpu, &wd_smp_cpus_pending);
	if (cpumask_empty(&wd_smp_cpus_pending)) {
	unsigned long flags;

	wd_smp_lock(&flags);
	if (cpumask_empty(&wd_smp_cpus_pending)) {
	wd_smp_last_reset_tb = tb;
	cpumask_andnot(&wd_smp_cpus_pending,
	&wd_cpus_enabled,
	&wd_smp_cpus_stuck);
	}
	wd_smp_unlock(&flags);
	}
	}

	static void watchdog_timer_interrupt(int cpu)
	{
	u64 tb = get_tb();

	per_cpu(wd_timer_tb, cpu) = tb;

	wd_smp_clear_cpu_pending(cpu, tb);

	if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb)
	watchdog_smp_panic(cpu, tb);
	}

	void soft_nmi_interrupt(struct pt_regs *regs)
	{
	unsigned long flags;
	int cpu = raw_smp_processor_id();
	u64 tb;

	if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
	return;

	nmi_enter();

	__this_cpu_inc(irq_stat.soft_nmi_irqs);

	tb = get_tb();
	if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) {
	per_cpu(wd_timer_tb, cpu) = tb;

	wd_smp_lock(&flags);
	if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) {
	wd_smp_unlock(&flags);
	goto out;
	}
	set_cpu_stuck(cpu, tb);

	pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n", cpu, (void *)regs->nip);
	print_modules();
	print_irqtrace_events(current);
	show_regs(regs);

	wd_smp_unlock(&flags);

	if (sysctl_hardlockup_all_cpu_backtrace)
	trigger_allbutself_cpu_backtrace();

	if (hardlockup_panic)
	nmi_panic(regs, "Hard LOCKUP");
	}
	if (wd_panic_timeout_tb < 0x7fffffff)
	mtspr(SPRN_DEC, wd_panic_timeout_tb);

	out:
	nmi_exit();
	}

	static void wd_timer_reset(unsigned int cpu, struct timer_list *t)
	{
	t->expires = jiffies + msecs_to_jiffies(wd_timer_period_ms);
	if (wd_timer_period_ms > 1000)
	t->expires = __round_jiffies_up(t->expires, cpu);
	add_timer_on(t, cpu);
	}

	static void wd_timer_fn(struct timer_list *t)
	{
	int cpu = smp_processor_id();

	watchdog_timer_interrupt(cpu);

	wd_timer_reset(cpu, t);
	}

	void arch_touch_nmi_watchdog(void)
	{
	unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000;
	int cpu = smp_processor_id();
	u64 tb = get_tb();

	if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) {
	per_cpu(wd_timer_tb, cpu) = tb;
	wd_smp_clear_cpu_pending(cpu, tb);
	}
	}
	EXPORT_SYMBOL(arch_touch_nmi_watchdog);

	static void start_watchdog_timer_on(unsigned int cpu)
	{
	struct timer_list *t = per_cpu_ptr(&wd_timer, cpu);

	per_cpu(wd_timer_tb, cpu) = get_tb();

	timer_setup(t, wd_timer_fn, TIMER_PINNED);
	wd_timer_reset(cpu, t);
	}

	static void stop_watchdog_timer_on(unsigned int cpu)
	{
	struct timer_list *t = per_cpu_ptr(&wd_timer, cpu);

	del_timer_sync(t);
	}

	static int start_wd_on_cpu(unsigned int cpu)
	{
	unsigned long flags;

	if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) {
	WARN_ON(1);
	return 0;
	}

	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
	return 0;

	if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
	return 0;

	wd_smp_lock(&flags);
	cpumask_set_cpu(cpu, &wd_cpus_enabled);
	if (cpumask_weight(&wd_cpus_enabled) == 1) {
	cpumask_set_cpu(cpu, &wd_smp_cpus_pending);
	wd_smp_last_reset_tb = get_tb();
	}
	wd_smp_unlock(&flags);

	start_watchdog_timer_on(cpu);

	return 0;
	}

	static int stop_wd_on_cpu(unsigned int cpu)
	{
	unsigned long flags;

	if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
	return 0; /* Can happen in CPU unplug case */

	stop_watchdog_timer_on(cpu);

	wd_smp_lock(&flags);
	cpumask_clear_cpu(cpu, &wd_cpus_enabled);
	wd_smp_unlock(&flags);

	wd_smp_clear_cpu_pending(cpu, get_tb());

	return 0;
	}

	static void watchdog_calc_timeouts(void)
	{
	wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq;

	/* Have the SMP detector trigger a bit later */
	wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2;

	/* 2/5 is the factor that the perf based detector uses */
	wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5;
	}

	void watchdog_nmi_stop(void)
	{
	int cpu;

	for_each_cpu(cpu, &wd_cpus_enabled)
	stop_wd_on_cpu(cpu);
	}

	void watchdog_nmi_start(void)
	{
	int cpu;

	watchdog_calc_timeouts();
	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
	start_wd_on_cpu(cpu);
	}

	/*
	* Invoked from core watchdog init.
	*/
	int __init watchdog_nmi_probe(void)
	{
	int err;

	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
	"powerpc/watchdog:online",
	start_wd_on_cpu, stop_wd_on_cpu);
	if (err < 0) {
	pr_warn("could not be initialized");
	return err;
	}
	return 0;
	}