/*
 * 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 <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);
#ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
static cpumask_t __read_mostly watchdog_cpus;
#else
static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
#endif

/* boot commands */
/*
 * Should we panic when a soft-lockup or hard-lockup occurs:
 */
unsigned int __read_mostly hardlockup_panic =
			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;

#ifdef CONFIG_HARDLOCKUP_DETECTOR_NMI
static unsigned long hardlockup_allcpu_dumped;
#endif
/*
 * We may not want to enable hard lockup detection by default in all cases,
 * for example when running the kernel as a guest on a hypervisor. In these
 * cases this function can be called to disable hard lockup detection. This
 * function should only be executed once by the boot processor before the
 * kernel command line parameters are parsed, because otherwise it is not
 * possible to override this in hardlockup_panic_setup().
 */
void hardlockup_detector_disable(void)
{
	watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
}

static int __init hardlockup_panic_setup(char *str)
{
	if (!strncmp(str, "panic", 5))
		hardlockup_panic = 1;
	else if (!strncmp(str, "nopanic", 7))
		hardlockup_panic = 0;
	else if (!strncmp(str, "0", 1))
		watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
	else if (!strncmp(str, "1", 1))
		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
	return 1;
}
__setup("nmi_watchdog=", hardlockup_panic_setup);

void 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);
	touch_softlockup_watchdog();
}
EXPORT_SYMBOL(touch_nmi_watchdog);

#ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU
static unsigned int watchdog_next_cpu(unsigned int cpu)
{
	cpumask_t cpus = watchdog_cpus;
	unsigned int next_cpu;

	next_cpu = cpumask_next(cpu, &cpus);
	if (next_cpu >= nr_cpu_ids)
		next_cpu = cpumask_first(&cpus);

	if (next_cpu == cpu)
		return nr_cpu_ids;

	return next_cpu;
}

static int is_hardlockup_other_cpu(unsigned int cpu)
{
	unsigned long hrint = per_cpu(hrtimer_interrupts, cpu);

	if (per_cpu(hrtimer_interrupts_saved, cpu) == hrint)
		return 1;

	per_cpu(hrtimer_interrupts_saved, cpu) = hrint;
	return 0;
}

void watchdog_check_hardlockup_other_cpu(void)
{
	unsigned int next_cpu;

	/*
	 * Test for hardlockups every 3 samples.  The sample period is
	 *  watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over
	 *  watchdog_thresh (over by 20%).
	 */
	if (__this_cpu_read(hrtimer_interrupts) % 3 != 0)
		return;

	/* check for a hardlockup on the next cpu */
	next_cpu = watchdog_next_cpu(smp_processor_id());
	if (next_cpu >= nr_cpu_ids)
		return;

	smp_rmb();

	if (per_cpu(watchdog_nmi_touch, next_cpu) == true) {
		per_cpu(watchdog_nmi_touch, next_cpu) = false;
		return;
	}

	if (is_hardlockup_other_cpu(next_cpu)) {
		/* only warn once */
		if (per_cpu(hard_watchdog_warn, next_cpu) == true)
			return;

		if (hardlockup_panic)
			panic("Watchdog detected hard LOCKUP on cpu %u",
				next_cpu);
		else
			WARN(1, "Watchdog detected hard LOCKUP on cpu %u",
				next_cpu);

		per_cpu(hard_watchdog_warn, next_cpu) = true;
	} else {
		per_cpu(hard_watchdog_warn, next_cpu) = false;
	}
}

int watchdog_nmi_enable(unsigned int cpu)
{
	/*
	 * The new cpu will be marked online before the first hrtimer interrupt
	 * runs on it.  If another cpu tests for a hardlockup on the new cpu
	 * before it has run its first hrtimer, it will get a false positive.
	 * Touch the watchdog on the new cpu to delay the first check for at
	 * least 3 sampling periods to guarantee one hrtimer has run on the new
	 * cpu.
	 */
	per_cpu(watchdog_nmi_touch, cpu) = true;
	smp_wmb();
	cpumask_set_cpu(cpu, &watchdog_cpus);
	return 0;
}

void watchdog_nmi_disable(unsigned int cpu)
{
	unsigned int next_cpu = watchdog_next_cpu(cpu);

	/*
	 * Offlining this cpu will cause the cpu before this one to start
	 * checking the one after this one.  If this cpu just finished checking
	 * the next cpu and updating hrtimer_interrupts_saved, and then the
	 * previous cpu checks it within one sample period, it will trigger a
	 * false positive.  Touch the watchdog on the next cpu to prevent it.
	 */
	if (next_cpu < nr_cpu_ids)
		per_cpu(watchdog_nmi_touch, next_cpu) = true;
	smp_wmb();
	cpumask_clear_cpu(cpu, &watchdog_cpus);
}
#else
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;
	}

	/* 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 cpu0_err;

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

	/* 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;

	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 cpu0 error for future comparision */
	if (cpu == 0 && IS_ERR(event))
		cpu0_err = PTR_ERR(event);

	if (!IS_ERR(event)) {
		/* only print for cpu0 or different than cpu0 */
		if (cpu == 0 || cpu0_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 (cpu > 0 && (PTR_ERR(event) == cpu0_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);
	}
	if (cpu == 0) {
		/* watchdog_nmi_enable() expects this to be zero initially. */
		cpu0_err = 0;
	}
}
#endif