// SPDX-License-Identifier: GPL-2.0
/*
 * 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/atomic.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 DEFINE_PER_CPU(struct perf_event *, dead_event);
static struct cpumask dead_events_mask;

static unsigned long hardlockup_allcpu_dumped;
static atomic_t watchdog_cpus = ATOMIC_INIT(0);

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 (__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;
}

static int hardlockup_detector_event_create(void)
{
        unsigned int cpu = smp_processor_id();
        struct perf_event_attr *wd_attr;
        struct perf_event *evt;

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

        /* Try to register using hardware perf events */
        evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
                                               watchdog_overflow_callback, NULL);
        if (IS_ERR(evt)) {
                pr_info("Perf event create on CPU %d failed with %ld\n", cpu,
                        PTR_ERR(evt));
                return PTR_ERR(evt);
        }
        this_cpu_write(watchdog_ev, evt);
        return 0;
}

/**
 * hardlockup_detector_perf_enable - Enable the local event
 */
void hardlockup_detector_perf_enable(void)
{
        if (hardlockup_detector_event_create())
                return;

        /* use original value for check */
        if (!atomic_fetch_inc(&watchdog_cpus))
                pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");

        perf_event_enable(this_cpu_read(watchdog_ev));
}

/**
 * hardlockup_detector_perf_disable - Disable the local event
 */
void hardlockup_detector_perf_disable(void)
{
        struct perf_event *event = this_cpu_read(watchdog_ev);

        if (event) {
                perf_event_disable(event);
                this_cpu_write(watchdog_ev, NULL);
                this_cpu_write(dead_event, event);
                cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
                atomic_dec(&watchdog_cpus);
        }
}

/**
 * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
 *
 * Called from lockup_detector_cleanup(). Serialized by the caller.
 */
void hardlockup_detector_perf_cleanup(void)
{
        int cpu;

        for_each_cpu(cpu, &dead_events_mask) {
                struct perf_event *event = per_cpu(dead_event, cpu);

                /*
                 * Required because for_each_cpu() reports  unconditionally
                 * CPU0 as set on UP kernels. Sigh.
                 */
                if (event)
                        perf_event_release_kernel(event);
                per_cpu(dead_event, cpu) = NULL;
        }
        cpumask_clear(&dead_events_mask);
}

/**
 * hardlockup_detector_perf_stop - Globally stop watchdog events
 *
 * Special interface for x86 to handle the perf HT bug.
 */
void __init hardlockup_detector_perf_stop(void)
{
        int cpu;

        lockdep_assert_cpus_held();

        for_each_online_cpu(cpu) {
                struct perf_event *event = per_cpu(watchdog_ev, cpu);

                if (event)
                        perf_event_disable(event);
        }
}

/**
 * hardlockup_detector_perf_restart - Globally restart watchdog events
 *
 * Special interface for x86 to handle the perf HT bug.
 */
void __init hardlockup_detector_perf_restart(void)
{
        int cpu;

        lockdep_assert_cpus_held();

        if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
                return;

        for_each_online_cpu(cpu) {
                struct perf_event *event = per_cpu(watchdog_ev, cpu);

                if (event)
                        perf_event_enable(event);
        }
}

/**
 * hardlockup_detector_perf_init - Probe whether NMI event is available at all
 */
int __init hardlockup_detector_perf_init(void)
{
        int ret = hardlockup_detector_event_create();

        if (ret) {
                pr_info("Perf NMI watchdog permanently disabled\n");
        } else {
                perf_event_release_kernel(this_cpu_read(watchdog_ev));
                this_cpu_write(watchdog_ev, NULL);
        }
        return ret;
}