kernel/watchdog_hld.c - arm/linux - Git at Google

 /*
  * Detect hard lockups on a system
  *
  * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
  *
  * Note: Most of this code is borrowed heavily from the original softlockup
  * detector, so thanks to Ingo for the initial implementation.
  * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
  * to those contributors as well.
  */

 #define pr_fmt(fmt) "NMI watchdog: " fmt

 #include <linux/nmi.h>
 #include <linux/module.h>
 #include <linux/sched/debug.h>

 #include <asm/irq_regs.h>
 #include <linux/perf_event.h>

 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);

 static unsigned long hardlockup_allcpu_dumped;

 void arch_touch_nmi_watchdog(void)
 {
 	/*
 	 * Using __raw here because some code paths have
 	 * preemption enabled.  If preemption is enabled
 	 * then interrupts should be enabled too, in which
 	 * case we shouldn't have to worry about the watchdog
 	 * going off.
 	 */
 	raw_cpu_write(watchdog_nmi_touch, true);
 }
 EXPORT_SYMBOL(arch_touch_nmi_watchdog);

 #ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
 static DEFINE_PER_CPU(ktime_t, last_timestamp);
 static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
 static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;

 void watchdog_update_hrtimer_threshold(u64 period)
 {
 	/*
 	 * The hrtimer runs with a period of (watchdog_threshold * 2) / 5
 	 *
 	 * So it runs effectively with 2.5 times the rate of the NMI
 	 * watchdog. That means the hrtimer should fire 2-3 times before
 	 * the NMI watchdog expires. The NMI watchdog on x86 is based on
 	 * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
 	 * might run way faster than expected and the NMI fires in a
 	 * smaller period than the one deduced from the nominal CPU
 	 * frequency. Depending on the Turbo-Mode factor this might be fast
 	 * enough to get the NMI period smaller than the hrtimer watchdog
 	 * period and trigger false positives.
 	 *
 	 * The sample threshold is used to check in the NMI handler whether
 	 * the minimum time between two NMI samples has elapsed. That
 	 * prevents false positives.
 	 *
 	 * Set this to 4/5 of the actual watchdog threshold period so the
 	 * hrtimer is guaranteed to fire at least once within the real
 	 * watchdog threshold.
 	 */
 	watchdog_hrtimer_sample_threshold = period * 2;
 }

 static bool watchdog_check_timestamp(void)
 {
 	ktime_t delta, now = ktime_get_mono_fast_ns();

 	delta = now - __this_cpu_read(last_timestamp);
 	if (delta < watchdog_hrtimer_sample_threshold) {
 		/*
 		 * If ktime is jiffies based, a stalled timer would prevent
 		 * jiffies from being incremented and the filter would look
 		 * at a stale timestamp and never trigger.
 		 */
 		if (__this_cpu_inc_return(nmi_rearmed) < 10)
 			return false;
 	}
 	__this_cpu_write(nmi_rearmed, 0);
 	__this_cpu_write(last_timestamp, now);
 	return true;
 }
 #else
 static inline bool watchdog_check_timestamp(void)
 {
 	return true;
 }
 #endif

 static struct perf_event_attr wd_hw_attr = {
 	.type		= PERF_TYPE_HARDWARE,
 	.config		= PERF_COUNT_HW_CPU_CYCLES,
 	.size		= sizeof(struct perf_event_attr),
 	.pinned		= 1,
 	.disabled	= 1,
 };

 /* Callback function for perf event subsystem */
 static void watchdog_overflow_callback(struct perf_event *event,
 		 struct perf_sample_data *data,
 		 struct pt_regs *regs)
 {
 	/* Ensure the watchdog never gets throttled */
 	event->hw.interrupts = 0;

 	if (atomic_read(&watchdog_park_in_progress) != 0)
 		return;

 	if (__this_cpu_read(watchdog_nmi_touch) == true) {
 		__this_cpu_write(watchdog_nmi_touch, false);
 		return;
 	}

 	if (!watchdog_check_timestamp())
 		return;

 	/* check for a hardlockup
 	 * This is done by making sure our timer interrupt
 	 * is incrementing.  The timer interrupt should have
 	 * fired multiple times before we overflow'd.  If it hasn't
 	 * then this is a good indication the cpu is stuck
 	 */
 	if (is_hardlockup()) {
 		int this_cpu = smp_processor_id();

 		/* only print hardlockups once */
 		if (__this_cpu_read(hard_watchdog_warn) == true)
 			return;

 		pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
 		print_modules();
 		print_irqtrace_events(current);
 		if (regs)
 			show_regs(regs);
 		else
 			dump_stack();

 		/*
 		 * Perform all-CPU dump only once to avoid multiple hardlockups
 		 * generating interleaving traces
 		 */
 		if (sysctl_hardlockup_all_cpu_backtrace &&
 				!test_and_set_bit(0, &hardlockup_allcpu_dumped))
 			trigger_allbutself_cpu_backtrace();

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

 		__this_cpu_write(hard_watchdog_warn, true);
 		return;
 	}

 	__this_cpu_write(hard_watchdog_warn, false);
 	return;
 }

 /*
  * People like the simple clean cpu node info on boot.
  * Reduce the watchdog noise by only printing messages
  * that are different from what cpu0 displayed.
  */
 static unsigned long firstcpu_err;
 static atomic_t watchdog_cpus;

 int watchdog_nmi_enable(unsigned int cpu)
 {
 	struct perf_event_attr *wd_attr;
 	struct perf_event *event = per_cpu(watchdog_ev, cpu);
 	int firstcpu = 0;

 	/* nothing to do if the hard lockup detector is disabled */
 	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 		goto out;

 	/* is it already setup and enabled? */
 	if (event && event->state > PERF_EVENT_STATE_OFF)
 		goto out;

 	/* it is setup but not enabled */
 	if (event != NULL)
 		goto out_enable;

 	if (atomic_inc_return(&watchdog_cpus) == 1)
 		firstcpu = 1;

 	wd_attr = &wd_hw_attr;
 	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);

 	/* Try to register using hardware perf events */
 	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);

 	/* save the first cpu's error for future comparision */
 	if (firstcpu && IS_ERR(event))
 		firstcpu_err = PTR_ERR(event);

 	if (!IS_ERR(event)) {
 		/* only print for the first cpu initialized */
 		if (firstcpu || firstcpu_err)
 			pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
 		goto out_save;
 	}

 	/*
 	 * Disable the hard lockup detector if _any_ CPU fails to set up
 	 * set up the hardware perf event. The watchdog() function checks
 	 * the NMI_WATCHDOG_ENABLED bit periodically.
 	 *
 	 * The barriers are for syncing up watchdog_enabled across all the
 	 * cpus, as clear_bit() does not use barriers.
 	 */
 	smp_mb__before_atomic();
 	clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
 	smp_mb__after_atomic();

 	/* skip displaying the same error again */
 	if (!firstcpu && (PTR_ERR(event) == firstcpu_err))
 		return PTR_ERR(event);

 	/* vary the KERN level based on the returned errno */
 	if (PTR_ERR(event) == -EOPNOTSUPP)
 		pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
 	else if (PTR_ERR(event) == -ENOENT)
 		pr_warn("disabled (cpu%i): hardware events not enabled\n",
 			 cpu);
 	else
 		pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
 			cpu, PTR_ERR(event));

 	pr_info("Shutting down hard lockup detector on all cpus\n");

 	return PTR_ERR(event);

 	/* success path */
 out_save:
 	per_cpu(watchdog_ev, cpu) = event;
 out_enable:
 	perf_event_enable(per_cpu(watchdog_ev, cpu));
 out:
 	return 0;
 }

 void watchdog_nmi_disable(unsigned int cpu)
 {
 	struct perf_event *event = per_cpu(watchdog_ev, cpu);

 	if (event) {
 		perf_event_disable(event);
 		per_cpu(watchdog_ev, cpu) = NULL;

 		/* should be in cleanup, but blocks oprofile */
 		perf_event_release_kernel(event);

 		/* watchdog_nmi_enable() expects this to be zero initially. */
 		if (atomic_dec_and_test(&watchdog_cpus))
 			firstcpu_err = 0;
 	}
 }
	/*
	* Detect hard lockups on a system
	*
	* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
	*
	* Note: Most of this code is borrowed heavily from the original softlockup
	* detector, so thanks to Ingo for the initial implementation.
	* Some chunks also taken from the old x86-specific nmi watchdog code, thanks
	* to those contributors as well.
	*/

	#define pr_fmt(fmt) "NMI watchdog: " fmt

	#include <linux/nmi.h>
	#include <linux/module.h>
	#include <linux/sched/debug.h>

	#include <asm/irq_regs.h>
	#include <linux/perf_event.h>

	static DEFINE_PER_CPU(bool, hard_watchdog_warn);
	static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
	static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);

	static unsigned long hardlockup_allcpu_dumped;

	void arch_touch_nmi_watchdog(void)
	{
	/*
	* Using __raw here because some code paths have
	* preemption enabled. If preemption is enabled
	* then interrupts should be enabled too, in which
	* case we shouldn't have to worry about the watchdog
	* going off.
	*/
	raw_cpu_write(watchdog_nmi_touch, true);
	}
	EXPORT_SYMBOL(arch_touch_nmi_watchdog);

	#ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
	static DEFINE_PER_CPU(ktime_t, last_timestamp);
	static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
	static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;

	void watchdog_update_hrtimer_threshold(u64 period)
	{
	/*
	* The hrtimer runs with a period of (watchdog_threshold * 2) / 5
	*
	* So it runs effectively with 2.5 times the rate of the NMI
	* watchdog. That means the hrtimer should fire 2-3 times before
	* the NMI watchdog expires. The NMI watchdog on x86 is based on
	* unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
	* might run way faster than expected and the NMI fires in a
	* smaller period than the one deduced from the nominal CPU
	* frequency. Depending on the Turbo-Mode factor this might be fast
	* enough to get the NMI period smaller than the hrtimer watchdog
	* period and trigger false positives.
	*
	* The sample threshold is used to check in the NMI handler whether
	* the minimum time between two NMI samples has elapsed. That
	* prevents false positives.
	*
	* Set this to 4/5 of the actual watchdog threshold period so the
	* hrtimer is guaranteed to fire at least once within the real
	* watchdog threshold.
	*/
	watchdog_hrtimer_sample_threshold = period * 2;
	}

	static bool watchdog_check_timestamp(void)
	{
	ktime_t delta, now = ktime_get_mono_fast_ns();

	delta = now - __this_cpu_read(last_timestamp);
	if (delta < watchdog_hrtimer_sample_threshold) {
	/*
	* If ktime is jiffies based, a stalled timer would prevent
	* jiffies from being incremented and the filter would look
	* at a stale timestamp and never trigger.
	*/
	if (__this_cpu_inc_return(nmi_rearmed) < 10)
	return false;
	}
	__this_cpu_write(nmi_rearmed, 0);
	__this_cpu_write(last_timestamp, now);
	return true;
	}
	#else
	static inline bool watchdog_check_timestamp(void)
	{
	return true;
	}
	#endif

	static struct perf_event_attr wd_hw_attr = {
	.type = PERF_TYPE_HARDWARE,
	.config = PERF_COUNT_HW_CPU_CYCLES,
	.size = sizeof(struct perf_event_attr),
	.pinned = 1,
	.disabled = 1,
	};

	/* Callback function for perf event subsystem */
	static void watchdog_overflow_callback(struct perf_event *event,
	struct perf_sample_data *data,
	struct pt_regs *regs)
	{
	/* Ensure the watchdog never gets throttled */
	event->hw.interrupts = 0;

	if (atomic_read(&watchdog_park_in_progress) != 0)
	return;

	if (__this_cpu_read(watchdog_nmi_touch) == true) {
	__this_cpu_write(watchdog_nmi_touch, false);
	return;
	}

	if (!watchdog_check_timestamp())
	return;

	/* check for a hardlockup
	* This is done by making sure our timer interrupt
	* is incrementing. The timer interrupt should have
	* fired multiple times before we overflow'd. If it hasn't
	* then this is a good indication the cpu is stuck
	*/
	if (is_hardlockup()) {
	int this_cpu = smp_processor_id();

	/* only print hardlockups once */
	if (__this_cpu_read(hard_watchdog_warn) == true)
	return;

	pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
	print_modules();
	print_irqtrace_events(current);
	if (regs)
	show_regs(regs);
	else
	dump_stack();

	/*
	* Perform all-CPU dump only once to avoid multiple hardlockups
	* generating interleaving traces
	*/
	if (sysctl_hardlockup_all_cpu_backtrace &&
	!test_and_set_bit(0, &hardlockup_allcpu_dumped))
	trigger_allbutself_cpu_backtrace();

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

	__this_cpu_write(hard_watchdog_warn, true);
	return;
	}

	__this_cpu_write(hard_watchdog_warn, false);
	return;
	}

	/*
	* People like the simple clean cpu node info on boot.
	* Reduce the watchdog noise by only printing messages
	* that are different from what cpu0 displayed.
	*/
	static unsigned long firstcpu_err;
	static atomic_t watchdog_cpus;

	int watchdog_nmi_enable(unsigned int cpu)
	{
	struct perf_event_attr *wd_attr;
	struct perf_event *event = per_cpu(watchdog_ev, cpu);
	int firstcpu = 0;

	/* nothing to do if the hard lockup detector is disabled */
	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
	goto out;

	/* is it already setup and enabled? */
	if (event && event->state > PERF_EVENT_STATE_OFF)
	goto out;

	/* it is setup but not enabled */
	if (event != NULL)
	goto out_enable;

	if (atomic_inc_return(&watchdog_cpus) == 1)
	firstcpu = 1;

	wd_attr = &wd_hw_attr;
	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);

	/* Try to register using hardware perf events */
	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);

	/* save the first cpu's error for future comparision */
	if (firstcpu && IS_ERR(event))
	firstcpu_err = PTR_ERR(event);

	if (!IS_ERR(event)) {
	/* only print for the first cpu initialized */
	if (firstcpu \|\| firstcpu_err)
	pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
	goto out_save;
	}

	/*
	* Disable the hard lockup detector if _any_ CPU fails to set up
	* set up the hardware perf event. The watchdog() function checks
	* the NMI_WATCHDOG_ENABLED bit periodically.
	*
	* The barriers are for syncing up watchdog_enabled across all the
	* cpus, as clear_bit() does not use barriers.
	*/
	smp_mb__before_atomic();
	clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
	smp_mb__after_atomic();

	/* skip displaying the same error again */
	if (!firstcpu && (PTR_ERR(event) == firstcpu_err))
	return PTR_ERR(event);

	/* vary the KERN level based on the returned errno */
	if (PTR_ERR(event) == -EOPNOTSUPP)
	pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
	else if (PTR_ERR(event) == -ENOENT)
	pr_warn("disabled (cpu%i): hardware events not enabled\n",
	cpu);
	else
	pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
	cpu, PTR_ERR(event));

	pr_info("Shutting down hard lockup detector on all cpus\n");

	return PTR_ERR(event);

	/* success path */
	out_save:
	per_cpu(watchdog_ev, cpu) = event;
	out_enable:
	perf_event_enable(per_cpu(watchdog_ev, cpu));
	out:
	return 0;
	}

	void watchdog_nmi_disable(unsigned int cpu)
	{
	struct perf_event *event = per_cpu(watchdog_ev, cpu);

	if (event) {
	perf_event_disable(event);
	per_cpu(watchdog_ev, cpu) = NULL;

	/* should be in cleanup, but blocks oprofile */
	perf_event_release_kernel(event);

	/* watchdog_nmi_enable() expects this to be zero initially. */
	if (atomic_dec_and_test(&watchdog_cpus))
	firstcpu_err = 0;
	}
	}