// SPDX-License-Identifier: GPL-2.0

#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/kernel.h>
#include <linux/nmi.h>
#include <linux/percpu-defs.h>

static cpumask_t __read_mostly watchdog_cpus;

static unsigned int watchdog_next_cpu(unsigned int cpu)
{
        unsigned int next_cpu;

        next_cpu = cpumask_next_wrap(cpu, &watchdog_cpus);
        if (next_cpu == cpu)
                return nr_cpu_ids;

        return next_cpu;
}

int __init watchdog_hardlockup_probe(void)
{
        return 0;
}

void watchdog_hardlockup_enable(unsigned int cpu)
{
        unsigned int next_cpu;

        /*
         * The new CPU will be marked online before the hrtimer interrupt
         * gets a chance to run on it. If another CPU tests for a
         * hardlockup on the new CPU before it has run its the hrtimer
         * interrupt, it will get a false positive. Touch the watchdog on
         * the new CPU to delay the check for at least 3 sampling periods
         * to guarantee one hrtimer has run on the new CPU.
         */
        watchdog_hardlockup_touch_cpu(cpu);

        /*
         * We are going to check the next CPU. Our watchdog_hrtimer
         * need not be zero if the CPU has already been online earlier.
         * Touch the watchdog on the next CPU to avoid false positive
         * if we try to check it in less then 3 interrupts.
         */
        next_cpu = watchdog_next_cpu(cpu);
        if (next_cpu < nr_cpu_ids)
                watchdog_hardlockup_touch_cpu(next_cpu);

        /*
         * Makes sure that watchdog is touched on this CPU before
         * other CPUs could see it in watchdog_cpus. The counter
         * part is in watchdog_buddy_check_hardlockup().
         */
        smp_wmb();

        cpumask_set_cpu(cpu, &watchdog_cpus);
}

void watchdog_hardlockup_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)
                watchdog_hardlockup_touch_cpu(next_cpu);

        /*
         * Makes sure that watchdog is touched on the next CPU before
         * this CPU disappear in watchdog_cpus. The counter part is in
         * watchdog_buddy_check_hardlockup().
         */
        smp_wmb();

        cpumask_clear_cpu(cpu, &watchdog_cpus);
}

void watchdog_buddy_check_hardlockup(int hrtimer_interrupts)
{
        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 (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;

        /*
         * Make sure that the watchdog was touched on next CPU when
         * watchdog_next_cpu() returned another one because of
         * a change in watchdog_hardlockup_enable()/disable().
         */
        smp_rmb();

        watchdog_hardlockup_check(next_cpu, NULL);
}