drm/modes: Fix drm_mode_vrefres() docs

[drm/drm-misc.git] / kernel / watchdog.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Detect hard and soft 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) "watchdog: " fmt

#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/irq.h>
#include <linux/irqdesc.h>
#include <linux/kernel_stat.h>
#include <linux/kvm_para.h>
#include <linux/math64.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/nmi.h>
#include <linux/stop_machine.h>
#include <linux/sysctl.h>
#include <linux/tick.h>

#include <linux/sched/clock.h>
#include <linux/sched/debug.h>
#include <linux/sched/isolation.h>

#include <asm/irq_regs.h>

static DEFINE_MUTEX(watchdog_mutex);

#if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HARDLOCKUP_DETECTOR_SPARC64)
# define WATCHDOG_HARDLOCKUP_DEFAULT    1
#else
# define WATCHDOG_HARDLOCKUP_DEFAULT    0
#endif

#define NUM_SAMPLE_PERIODS      5

unsigned long __read_mostly watchdog_enabled;
int __read_mostly watchdog_user_enabled = 1;
static int __read_mostly watchdog_hardlockup_user_enabled = WATCHDOG_HARDLOCKUP_DEFAULT;
static int __read_mostly watchdog_softlockup_user_enabled = 1;
int __read_mostly watchdog_thresh = 10;
static int __read_mostly watchdog_hardlockup_available;

struct cpumask watchdog_cpumask __read_mostly;
unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);

#ifdef CONFIG_HARDLOCKUP_DETECTOR

# ifdef CONFIG_SMP
int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
# endif /* CONFIG_SMP */

/*
 * Should we panic when a soft-lockup or hard-lockup occurs:
 */
unsigned int __read_mostly hardlockup_panic =
                        IS_ENABLED(CONFIG_BOOTPARAM_HARDLOCKUP_PANIC);
/*
 * 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 __init hardlockup_detector_disable(void)
{
        watchdog_hardlockup_user_enabled = 0;
}

static int __init hardlockup_panic_setup(char *str)
{
next:
        if (!strncmp(str, "panic", 5))
                hardlockup_panic = 1;
        else if (!strncmp(str, "nopanic", 7))
                hardlockup_panic = 0;
        else if (!strncmp(str, "0", 1))
                watchdog_hardlockup_user_enabled = 0;
        else if (!strncmp(str, "1", 1))
                watchdog_hardlockup_user_enabled = 1;
        else if (!strncmp(str, "r", 1))
                hardlockup_config_perf_event(str + 1);
        while (*(str++)) {
                if (*str == ',') {
                        str++;
                        goto next;
                }
        }
        return 1;
}
__setup("nmi_watchdog=", hardlockup_panic_setup);

#endif /* CONFIG_HARDLOCKUP_DETECTOR */

#if defined(CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER)

static DEFINE_PER_CPU(atomic_t, hrtimer_interrupts);
static DEFINE_PER_CPU(int, hrtimer_interrupts_saved);
static DEFINE_PER_CPU(bool, watchdog_hardlockup_warned);
static DEFINE_PER_CPU(bool, watchdog_hardlockup_touched);
static unsigned long hard_lockup_nmi_warn;

notrace 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_hardlockup_touched, true);
}
EXPORT_SYMBOL(arch_touch_nmi_watchdog);

void watchdog_hardlockup_touch_cpu(unsigned int cpu)
{
        per_cpu(watchdog_hardlockup_touched, cpu) = true;
}

static bool is_hardlockup(unsigned int cpu)
{
        int hrint = atomic_read(&per_cpu(hrtimer_interrupts, cpu));

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

        /*
         * NOTE: we don't need any fancy atomic_t or READ_ONCE/WRITE_ONCE
         * for hrtimer_interrupts_saved. hrtimer_interrupts_saved is
         * written/read by a single CPU.
         */
        per_cpu(hrtimer_interrupts_saved, cpu) = hrint;

        return false;
}

static void watchdog_hardlockup_kick(void)
{
        int new_interrupts;

        new_interrupts = atomic_inc_return(this_cpu_ptr(&hrtimer_interrupts));
        watchdog_buddy_check_hardlockup(new_interrupts);
}

void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
{
        if (per_cpu(watchdog_hardlockup_touched, cpu)) {
                per_cpu(watchdog_hardlockup_touched, cpu) = false;
                return;
        }

        /*
         * Check for a hardlockup by making sure the CPU's 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(cpu)) {
                unsigned int this_cpu = smp_processor_id();
                unsigned long flags;

                /* Only print hardlockups once. */
                if (per_cpu(watchdog_hardlockup_warned, cpu))
                        return;

                /*
                 * Prevent multiple hard-lockup reports if one cpu is already
                 * engaged in dumping all cpu back traces.
                 */
                if (sysctl_hardlockup_all_cpu_backtrace) {
                        if (test_and_set_bit_lock(0, &hard_lockup_nmi_warn))
                                return;
                }

                /*
                 * NOTE: we call printk_cpu_sync_get_irqsave() after printing
                 * the lockup message. While it would be nice to serialize
                 * that printout, we really want to make sure that if some
                 * other CPU somehow locked up while holding the lock associated
                 * with printk_cpu_sync_get_irqsave() that we can still at least
                 * get the message about the lockup out.
                 */
                pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n", cpu);
                printk_cpu_sync_get_irqsave(flags);

                print_modules();
                print_irqtrace_events(current);
                if (cpu == this_cpu) {
                        if (regs)
                                show_regs(regs);
                        else
                                dump_stack();
                        printk_cpu_sync_put_irqrestore(flags);
                } else {
                        printk_cpu_sync_put_irqrestore(flags);
                        trigger_single_cpu_backtrace(cpu);
                }

                if (sysctl_hardlockup_all_cpu_backtrace) {
                        trigger_allbutcpu_cpu_backtrace(cpu);
                        if (!hardlockup_panic)
                                clear_bit_unlock(0, &hard_lockup_nmi_warn);
                }

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

                per_cpu(watchdog_hardlockup_warned, cpu) = true;
        } else {
                per_cpu(watchdog_hardlockup_warned, cpu) = false;
        }
}

#else /* CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER */

static inline void watchdog_hardlockup_kick(void) { }

#endif /* !CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER */

/*
 * These functions can be overridden based on the configured hardlockdup detector.
 *
 * watchdog_hardlockup_enable/disable can be implemented to start and stop when
 * softlockup watchdog start and stop. The detector must select the
 * SOFTLOCKUP_DETECTOR Kconfig.
 */
void __weak watchdog_hardlockup_enable(unsigned int cpu) { }

void __weak watchdog_hardlockup_disable(unsigned int cpu) { }

/*
 * Watchdog-detector specific API.
 *
 * Return 0 when hardlockup watchdog is available, negative value otherwise.
 * Note that the negative value means that a delayed probe might
 * succeed later.
 */
int __weak __init watchdog_hardlockup_probe(void)
{
        return -ENODEV;
}

/**
 * watchdog_hardlockup_stop - Stop the watchdog for reconfiguration
 *
 * The reconfiguration steps are:
 * watchdog_hardlockup_stop();
 * update_variables();
 * watchdog_hardlockup_start();
 */
void __weak watchdog_hardlockup_stop(void) { }

/**
 * watchdog_hardlockup_start - Start the watchdog after reconfiguration
 *
 * Counterpart to watchdog_hardlockup_stop().
 *
 * The following variables have been updated in update_variables() and
 * contain the currently valid configuration:
 * - watchdog_enabled
 * - watchdog_thresh
 * - watchdog_cpumask
 */
void __weak watchdog_hardlockup_start(void) { }

/**
 * lockup_detector_update_enable - Update the sysctl enable bit
 *
 * Caller needs to make sure that the hard watchdogs are off, so this
 * can't race with watchdog_hardlockup_disable().
 */
static void lockup_detector_update_enable(void)
{
        watchdog_enabled = 0;
        if (!watchdog_user_enabled)
                return;
        if (watchdog_hardlockup_available && watchdog_hardlockup_user_enabled)
                watchdog_enabled |= WATCHDOG_HARDLOCKUP_ENABLED;
        if (watchdog_softlockup_user_enabled)
                watchdog_enabled |= WATCHDOG_SOFTOCKUP_ENABLED;
}

#ifdef CONFIG_SOFTLOCKUP_DETECTOR

/*
 * Delay the soflockup report when running a known slow code.
 * It does _not_ affect the timestamp of the last successdul reschedule.
 */
#define SOFTLOCKUP_DELAY_REPORT ULONG_MAX

#ifdef CONFIG_SMP
int __read_mostly sysctl_softlockup_all_cpu_backtrace;
#endif

static struct cpumask watchdog_allowed_mask __read_mostly;

/* Global variables, exported for sysctl */
unsigned int __read_mostly softlockup_panic =
                        IS_ENABLED(CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC);

static bool softlockup_initialized __read_mostly;
static u64 __read_mostly sample_period;

/* Timestamp taken after the last successful reschedule. */
static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
/* Timestamp of the last softlockup report. */
static DEFINE_PER_CPU(unsigned long, watchdog_report_ts);
static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
static DEFINE_PER_CPU(bool, softlockup_touch_sync);
static unsigned long soft_lockup_nmi_warn;

static int __init softlockup_panic_setup(char *str)
{
        softlockup_panic = simple_strtoul(str, NULL, 0);
        return 1;
}
__setup("softlockup_panic=", softlockup_panic_setup);

static int __init nowatchdog_setup(char *str)
{
        watchdog_user_enabled = 0;
        return 1;
}
__setup("nowatchdog", nowatchdog_setup);

static int __init nosoftlockup_setup(char *str)
{
        watchdog_softlockup_user_enabled = 0;
        return 1;
}
__setup("nosoftlockup", nosoftlockup_setup);

static int __init watchdog_thresh_setup(char *str)
{
        get_option(&str, &watchdog_thresh);
        return 1;
}
__setup("watchdog_thresh=", watchdog_thresh_setup);

static void __lockup_detector_cleanup(void);

#ifdef CONFIG_SOFTLOCKUP_DETECTOR_INTR_STORM
enum stats_per_group {
        STATS_SYSTEM,
        STATS_SOFTIRQ,
        STATS_HARDIRQ,
        STATS_IDLE,
        NUM_STATS_PER_GROUP,
};

static const enum cpu_usage_stat tracked_stats[NUM_STATS_PER_GROUP] = {
        CPUTIME_SYSTEM,
        CPUTIME_SOFTIRQ,
        CPUTIME_IRQ,
        CPUTIME_IDLE,
};

static DEFINE_PER_CPU(u16, cpustat_old[NUM_STATS_PER_GROUP]);
static DEFINE_PER_CPU(u8, cpustat_util[NUM_SAMPLE_PERIODS][NUM_STATS_PER_GROUP]);
static DEFINE_PER_CPU(u8, cpustat_tail);

/*
 * We don't need nanosecond resolution. A granularity of 16ms is
 * sufficient for our precision, allowing us to use u16 to store
 * cpustats, which will roll over roughly every ~1000 seconds.
 * 2^24 ~= 16 * 10^6
 */
static u16 get_16bit_precision(u64 data_ns)
{
        return data_ns >> 24LL; /* 2^24ns ~= 16.8ms */
}

static void update_cpustat(void)
{
        int i;
        u8 util;
        u16 old_stat, new_stat;
        struct kernel_cpustat kcpustat;
        u64 *cpustat = kcpustat.cpustat;
        u8 tail = __this_cpu_read(cpustat_tail);
        u16 sample_period_16 = get_16bit_precision(sample_period);

        kcpustat_cpu_fetch(&kcpustat, smp_processor_id());

        for (i = 0; i < NUM_STATS_PER_GROUP; i++) {
                old_stat = __this_cpu_read(cpustat_old[i]);
                new_stat = get_16bit_precision(cpustat[tracked_stats[i]]);
                util = DIV_ROUND_UP(100 * (new_stat - old_stat), sample_period_16);
                __this_cpu_write(cpustat_util[tail][i], util);
                __this_cpu_write(cpustat_old[i], new_stat);
        }

        __this_cpu_write(cpustat_tail, (tail + 1) % NUM_SAMPLE_PERIODS);
}

static void print_cpustat(void)
{
        int i, group;
        u8 tail = __this_cpu_read(cpustat_tail);
        u64 sample_period_second = sample_period;

        do_div(sample_period_second, NSEC_PER_SEC);

        /*
         * Outputting the "watchdog" prefix on every line is redundant and not
         * concise, and the original alarm information is sufficient for
         * positioning in logs, hence here printk() is used instead of pr_crit().
         */
        printk(KERN_CRIT "CPU#%d Utilization every %llus during lockup:\n",
               smp_processor_id(), sample_period_second);

        for (i = 0; i < NUM_SAMPLE_PERIODS; i++) {
                group = (tail + i) % NUM_SAMPLE_PERIODS;
                printk(KERN_CRIT "\t#%d: %3u%% system,\t%3u%% softirq,\t"
                        "%3u%% hardirq,\t%3u%% idle\n", i + 1,
                        __this_cpu_read(cpustat_util[group][STATS_SYSTEM]),
                        __this_cpu_read(cpustat_util[group][STATS_SOFTIRQ]),
                        __this_cpu_read(cpustat_util[group][STATS_HARDIRQ]),
                        __this_cpu_read(cpustat_util[group][STATS_IDLE]));
        }
}

#define HARDIRQ_PERCENT_THRESH          50
#define NUM_HARDIRQ_REPORT              5
struct irq_counts {
        int irq;
        u32 counts;
};

static DEFINE_PER_CPU(bool, snapshot_taken);

/* Tabulate the most frequent interrupts. */
static void tabulate_irq_count(struct irq_counts *irq_counts, int irq, u32 counts, int rank)
{
        int i;
        struct irq_counts new_count = {irq, counts};

        for (i = 0; i < rank; i++) {
                if (counts > irq_counts[i].counts)
                        swap(new_count, irq_counts[i]);
        }
}

/*
 * If the hardirq time exceeds HARDIRQ_PERCENT_THRESH% of the sample_period,
 * then the cause of softlockup might be interrupt storm. In this case, it
 * would be useful to start interrupt counting.
 */
static bool need_counting_irqs(void)
{
        u8 util;
        int tail = __this_cpu_read(cpustat_tail);

        tail = (tail + NUM_HARDIRQ_REPORT - 1) % NUM_HARDIRQ_REPORT;
        util = __this_cpu_read(cpustat_util[tail][STATS_HARDIRQ]);
        return util > HARDIRQ_PERCENT_THRESH;
}

static void start_counting_irqs(void)
{
        if (!__this_cpu_read(snapshot_taken)) {
                kstat_snapshot_irqs();
                __this_cpu_write(snapshot_taken, true);
        }
}

static void stop_counting_irqs(void)
{
        __this_cpu_write(snapshot_taken, false);
}

static void print_irq_counts(void)
{
        unsigned int i, count;
        struct irq_counts irq_counts_sorted[NUM_HARDIRQ_REPORT] = {
                {-1, 0}, {-1, 0}, {-1, 0}, {-1, 0}, {-1, 0}
        };

        if (__this_cpu_read(snapshot_taken)) {
                for_each_active_irq(i) {
                        count = kstat_get_irq_since_snapshot(i);
                        tabulate_irq_count(irq_counts_sorted, i, count, NUM_HARDIRQ_REPORT);
                }

                /*
                 * Outputting the "watchdog" prefix on every line is redundant and not
                 * concise, and the original alarm information is sufficient for
                 * positioning in logs, hence here printk() is used instead of pr_crit().
                 */
                printk(KERN_CRIT "CPU#%d Detect HardIRQ Time exceeds %d%%. Most frequent HardIRQs:\n",
                       smp_processor_id(), HARDIRQ_PERCENT_THRESH);

                for (i = 0; i < NUM_HARDIRQ_REPORT; i++) {
                        if (irq_counts_sorted[i].irq == -1)
                                break;

                        printk(KERN_CRIT "\t#%u: %-10u\tirq#%d\n",
                               i + 1, irq_counts_sorted[i].counts,
                               irq_counts_sorted[i].irq);
                }

                /*
                 * If the hardirq time is less than HARDIRQ_PERCENT_THRESH% in the last
                 * sample_period, then we suspect the interrupt storm might be subsiding.
                 */
                if (!need_counting_irqs())
                        stop_counting_irqs();
        }
}

static void report_cpu_status(void)
{
        print_cpustat();
        print_irq_counts();
}
#else
static inline void update_cpustat(void) { }
static inline void report_cpu_status(void) { }
static inline bool need_counting_irqs(void) { return false; }
static inline void start_counting_irqs(void) { }
static inline void stop_counting_irqs(void) { }
#endif

/*
 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 * lockups can have false positives under extreme conditions. So we generally
 * want a higher threshold for soft lockups than for hard lockups. So we couple
 * the thresholds with a factor: we make the soft threshold twice the amount of
 * time the hard threshold is.
 */
static int get_softlockup_thresh(void)
{
        return watchdog_thresh * 2;
}

/*
 * Returns seconds, approximately.  We don't need nanosecond
 * resolution, and we don't need to waste time with a big divide when
 * 2^30ns == 1.074s.
 */
static unsigned long get_timestamp(void)
{
        return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
}

static void set_sample_period(void)
{
        /*
         * convert watchdog_thresh from seconds to ns
         * the divide by 5 is to give hrtimer several chances (two
         * or three with the current relation between the soft
         * and hard thresholds) to increment before the
         * hardlockup detector generates a warning
         */
        sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / NUM_SAMPLE_PERIODS);
        watchdog_update_hrtimer_threshold(sample_period);
}

static void update_report_ts(void)
{
        __this_cpu_write(watchdog_report_ts, get_timestamp());
}

/* Commands for resetting the watchdog */
static void update_touch_ts(void)
{
        __this_cpu_write(watchdog_touch_ts, get_timestamp());
        update_report_ts();
}

/**
 * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 *
 * Call when the scheduler may have stalled for legitimate reasons
 * preventing the watchdog task from executing - e.g. the scheduler
 * entering idle state.  This should only be used for scheduler events.
 * Use touch_softlockup_watchdog() for everything else.
 */
notrace void touch_softlockup_watchdog_sched(void)
{
        /*
         * Preemption can be enabled.  It doesn't matter which CPU's watchdog
         * report period gets restarted here, so use the raw_ operation.
         */
        raw_cpu_write(watchdog_report_ts, SOFTLOCKUP_DELAY_REPORT);
}

notrace void touch_softlockup_watchdog(void)
{
        touch_softlockup_watchdog_sched();
        wq_watchdog_touch(raw_smp_processor_id());
}
EXPORT_SYMBOL(touch_softlockup_watchdog);

void touch_all_softlockup_watchdogs(void)
{
        int cpu;

        /*
         * watchdog_mutex cannpt be taken here, as this might be called
         * from (soft)interrupt context, so the access to
         * watchdog_allowed_cpumask might race with a concurrent update.
         *
         * The watchdog time stamp can race against a concurrent real
         * update as well, the only side effect might be a cycle delay for
         * the softlockup check.
         */
        for_each_cpu(cpu, &watchdog_allowed_mask) {
                per_cpu(watchdog_report_ts, cpu) = SOFTLOCKUP_DELAY_REPORT;
                wq_watchdog_touch(cpu);
        }
}

void touch_softlockup_watchdog_sync(void)
{
        __this_cpu_write(softlockup_touch_sync, true);
        __this_cpu_write(watchdog_report_ts, SOFTLOCKUP_DELAY_REPORT);
}

static int is_softlockup(unsigned long touch_ts,
                         unsigned long period_ts,
                         unsigned long now)
{
        if ((watchdog_enabled & WATCHDOG_SOFTOCKUP_ENABLED) && watchdog_thresh) {
                /*
                 * If period_ts has not been updated during a sample_period, then
                 * in the subsequent few sample_periods, period_ts might also not
                 * be updated, which could indicate a potential softlockup. In
                 * this case, if we suspect the cause of the potential softlockup
                 * might be interrupt storm, then we need to count the interrupts
                 * to find which interrupt is storming.
                 */
                if (time_after_eq(now, period_ts + get_softlockup_thresh() / NUM_SAMPLE_PERIODS) &&
                    need_counting_irqs())
                        start_counting_irqs();

                /*
                 * A poorly behaving BPF scheduler can live-lock the system into
                 * soft lockups. Tell sched_ext to try ejecting the BPF
                 * scheduler when close to a soft lockup.
                 */
                if (time_after_eq(now, period_ts + get_softlockup_thresh() * 3 / 4))
                        scx_softlockup(now - touch_ts);

                /* Warn about unreasonable delays. */
                if (time_after(now, period_ts + get_softlockup_thresh()))
                        return now - touch_ts;
        }
        return 0;
}

/* watchdog detector functions */
static DEFINE_PER_CPU(struct completion, softlockup_completion);
static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);

/*
 * The watchdog feed function - touches the timestamp.
 *
 * It only runs once every sample_period seconds (4 seconds by
 * default) to reset the softlockup timestamp. If this gets delayed
 * for more than 2*watchdog_thresh seconds then the debug-printout
 * triggers in watchdog_timer_fn().
 */
static int softlockup_fn(void *data)
{
        update_touch_ts();
        stop_counting_irqs();
        complete(this_cpu_ptr(&softlockup_completion));

        return 0;
}

/* watchdog kicker functions */
static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
{
        unsigned long touch_ts, period_ts, now;
        struct pt_regs *regs = get_irq_regs();
        int duration;
        int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
        unsigned long flags;

        if (!watchdog_enabled)
                return HRTIMER_NORESTART;

        watchdog_hardlockup_kick();

        /* kick the softlockup detector */
        if (completion_done(this_cpu_ptr(&softlockup_completion))) {
                reinit_completion(this_cpu_ptr(&softlockup_completion));
                stop_one_cpu_nowait(smp_processor_id(),
                                softlockup_fn, NULL,
                                this_cpu_ptr(&softlockup_stop_work));
        }

        /* .. and repeat */
        hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));

        /*
         * Read the current timestamp first. It might become invalid anytime
         * when a virtual machine is stopped by the host or when the watchog
         * is touched from NMI.
         */
        now = get_timestamp();
        /*
         * If a virtual machine is stopped by the host it can look to
         * the watchdog like a soft lockup. This function touches the watchdog.
         */
        kvm_check_and_clear_guest_paused();
        /*
         * The stored timestamp is comparable with @now only when not touched.
         * It might get touched anytime from NMI. Make sure that is_softlockup()
         * uses the same (valid) value.
         */
        period_ts = READ_ONCE(*this_cpu_ptr(&watchdog_report_ts));

        update_cpustat();

        /* Reset the interval when touched by known problematic code. */
        if (period_ts == SOFTLOCKUP_DELAY_REPORT) {
                if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
                        /*
                         * If the time stamp was touched atomically
                         * make sure the scheduler tick is up to date.
                         */
                        __this_cpu_write(softlockup_touch_sync, false);
                        sched_clock_tick();
                }

                update_report_ts();
                return HRTIMER_RESTART;
        }

        /* Check for a softlockup. */
        touch_ts = __this_cpu_read(watchdog_touch_ts);
        duration = is_softlockup(touch_ts, period_ts, now);
        if (unlikely(duration)) {
                /*
                 * Prevent multiple soft-lockup reports if one cpu is already
                 * engaged in dumping all cpu back traces.
                 */
                if (softlockup_all_cpu_backtrace) {
                        if (test_and_set_bit_lock(0, &soft_lockup_nmi_warn))
                                return HRTIMER_RESTART;
                }

                /* Start period for the next softlockup warning. */
                update_report_ts();

                printk_cpu_sync_get_irqsave(flags);
                pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
                        smp_processor_id(), duration,
                        current->comm, task_pid_nr(current));
                report_cpu_status();
                print_modules();
                print_irqtrace_events(current);
                if (regs)
                        show_regs(regs);
                else
                        dump_stack();
                printk_cpu_sync_put_irqrestore(flags);

                if (softlockup_all_cpu_backtrace) {
                        trigger_allbutcpu_cpu_backtrace(smp_processor_id());
                        if (!softlockup_panic)
                                clear_bit_unlock(0, &soft_lockup_nmi_warn);
                }

                add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
                if (softlockup_panic)
                        panic("softlockup: hung tasks");
        }

        return HRTIMER_RESTART;
}

static void watchdog_enable(unsigned int cpu)
{
        struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
        struct completion *done = this_cpu_ptr(&softlockup_completion);

        WARN_ON_ONCE(cpu != smp_processor_id());

        init_completion(done);
        complete(done);

        /*
         * Start the timer first to prevent the hardlockup watchdog triggering
         * before the timer has a chance to fire.
         */
        hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
        hrtimer->function = watchdog_timer_fn;
        hrtimer_start(hrtimer, ns_to_ktime(sample_period),
                      HRTIMER_MODE_REL_PINNED_HARD);

        /* Initialize timestamp */
        update_touch_ts();
        /* Enable the hardlockup detector */
        if (watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED)
                watchdog_hardlockup_enable(cpu);
}

static void watchdog_disable(unsigned int cpu)
{
        struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);

        WARN_ON_ONCE(cpu != smp_processor_id());

        /*
         * Disable the hardlockup detector first. That prevents that a large
         * delay between disabling the timer and disabling the hardlockup
         * detector causes a false positive.
         */
        watchdog_hardlockup_disable(cpu);
        hrtimer_cancel(hrtimer);
        wait_for_completion(this_cpu_ptr(&softlockup_completion));
}

static int softlockup_stop_fn(void *data)
{
        watchdog_disable(smp_processor_id());
        return 0;
}

static void softlockup_stop_all(void)
{
        int cpu;

        if (!softlockup_initialized)
                return;

        for_each_cpu(cpu, &watchdog_allowed_mask)
                smp_call_on_cpu(cpu, softlockup_stop_fn, NULL, false);

        cpumask_clear(&watchdog_allowed_mask);
}

static int softlockup_start_fn(void *data)
{
        watchdog_enable(smp_processor_id());
        return 0;
}

static void softlockup_start_all(void)
{
        int cpu;

        cpumask_copy(&watchdog_allowed_mask, &watchdog_cpumask);
        for_each_cpu(cpu, &watchdog_allowed_mask)
                smp_call_on_cpu(cpu, softlockup_start_fn, NULL, false);
}

int lockup_detector_online_cpu(unsigned int cpu)
{
        if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
                watchdog_enable(cpu);
        return 0;
}

int lockup_detector_offline_cpu(unsigned int cpu)
{
        if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
                watchdog_disable(cpu);
        return 0;
}

static void __lockup_detector_reconfigure(void)
{
        cpus_read_lock();
        watchdog_hardlockup_stop();

        softlockup_stop_all();
        set_sample_period();
        lockup_detector_update_enable();
        if (watchdog_enabled && watchdog_thresh)
                softlockup_start_all();

        watchdog_hardlockup_start();
        cpus_read_unlock();
        /*
         * Must be called outside the cpus locked section to prevent
         * recursive locking in the perf code.
         */
        __lockup_detector_cleanup();
}

void lockup_detector_reconfigure(void)
{
        mutex_lock(&watchdog_mutex);
        __lockup_detector_reconfigure();
        mutex_unlock(&watchdog_mutex);
}

/*
 * Create the watchdog infrastructure and configure the detector(s).
 */
static __init void lockup_detector_setup(void)
{
        /*
         * If sysctl is off and watchdog got disabled on the command line,
         * nothing to do here.
         */
        lockup_detector_update_enable();

        if (!IS_ENABLED(CONFIG_SYSCTL) &&
            !(watchdog_enabled && watchdog_thresh))
                return;

        mutex_lock(&watchdog_mutex);
        __lockup_detector_reconfigure();
        softlockup_initialized = true;
        mutex_unlock(&watchdog_mutex);
}

#else /* CONFIG_SOFTLOCKUP_DETECTOR */
static void __lockup_detector_reconfigure(void)
{
        cpus_read_lock();
        watchdog_hardlockup_stop();
        lockup_detector_update_enable();
        watchdog_hardlockup_start();
        cpus_read_unlock();
}
void lockup_detector_reconfigure(void)
{
        __lockup_detector_reconfigure();
}
static inline void lockup_detector_setup(void)
{
        __lockup_detector_reconfigure();
}
#endif /* !CONFIG_SOFTLOCKUP_DETECTOR */

static void __lockup_detector_cleanup(void)
{
        lockdep_assert_held(&watchdog_mutex);
        hardlockup_detector_perf_cleanup();
}

/**
 * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
 *
 * Caller must not hold the cpu hotplug rwsem.
 */
void lockup_detector_cleanup(void)
{
        mutex_lock(&watchdog_mutex);
        __lockup_detector_cleanup();
        mutex_unlock(&watchdog_mutex);
}

/**
 * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
 *
 * Special interface for parisc. It prevents lockup detector warnings from
 * the default pm_poweroff() function which busy loops forever.
 */
void lockup_detector_soft_poweroff(void)
{
        watchdog_enabled = 0;
}

#ifdef CONFIG_SYSCTL

/* Propagate any changes to the watchdog infrastructure */
static void proc_watchdog_update(void)
{
        /* Remove impossible cpus to keep sysctl output clean. */
        cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
        __lockup_detector_reconfigure();
}

/*
 * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 *
 * caller             | table->data points to            | 'which'
 * -------------------|----------------------------------|-------------------------------
 * proc_watchdog      | watchdog_user_enabled            | WATCHDOG_HARDLOCKUP_ENABLED |
 *                    |                                  | WATCHDOG_SOFTOCKUP_ENABLED
 * -------------------|----------------------------------|-------------------------------
 * proc_nmi_watchdog  | watchdog_hardlockup_user_enabled | WATCHDOG_HARDLOCKUP_ENABLED
 * -------------------|----------------------------------|-------------------------------
 * proc_soft_watchdog | watchdog_softlockup_user_enabled | WATCHDOG_SOFTOCKUP_ENABLED
 */
static int proc_watchdog_common(int which, const struct ctl_table *table, int write,
                                void *buffer, size_t *lenp, loff_t *ppos)
{
        int err, old, *param = table->data;

        mutex_lock(&watchdog_mutex);

        old = *param;
        if (!write) {
                /*
                 * On read synchronize the userspace interface. This is a
                 * racy snapshot.
                 */
                *param = (watchdog_enabled & which) != 0;
                err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
                *param = old;
        } else {
                err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
                if (!err && old != READ_ONCE(*param))
                        proc_watchdog_update();
        }
        mutex_unlock(&watchdog_mutex);
        return err;
}

/*
 * /proc/sys/kernel/watchdog
 */
static int proc_watchdog(const struct ctl_table *table, int write,
                         void *buffer, size_t *lenp, loff_t *ppos)
{
        return proc_watchdog_common(WATCHDOG_HARDLOCKUP_ENABLED |
                                    WATCHDOG_SOFTOCKUP_ENABLED,
                                    table, write, buffer, lenp, ppos);
}

/*
 * /proc/sys/kernel/nmi_watchdog
 */
static int proc_nmi_watchdog(const struct ctl_table *table, int write,
                             void *buffer, size_t *lenp, loff_t *ppos)
{
        if (!watchdog_hardlockup_available && write)
                return -ENOTSUPP;
        return proc_watchdog_common(WATCHDOG_HARDLOCKUP_ENABLED,
                                    table, write, buffer, lenp, ppos);
}

#ifdef CONFIG_SOFTLOCKUP_DETECTOR
/*
 * /proc/sys/kernel/soft_watchdog
 */
static int proc_soft_watchdog(const struct ctl_table *table, int write,
                              void *buffer, size_t *lenp, loff_t *ppos)
{
        return proc_watchdog_common(WATCHDOG_SOFTOCKUP_ENABLED,
                                    table, write, buffer, lenp, ppos);
}
#endif

/*
 * /proc/sys/kernel/watchdog_thresh
 */
static int proc_watchdog_thresh(const struct ctl_table *table, int write,
                                void *buffer, size_t *lenp, loff_t *ppos)
{
        int err, old;

        mutex_lock(&watchdog_mutex);

        old = READ_ONCE(watchdog_thresh);
        err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);

        if (!err && write && old != READ_ONCE(watchdog_thresh))
                proc_watchdog_update();

        mutex_unlock(&watchdog_mutex);
        return err;
}

/*
 * The cpumask is the mask of possible cpus that the watchdog can run
 * on, not the mask of cpus it is actually running on.  This allows the
 * user to specify a mask that will include cpus that have not yet
 * been brought online, if desired.
 */
static int proc_watchdog_cpumask(const struct ctl_table *table, int write,
                                 void *buffer, size_t *lenp, loff_t *ppos)
{
        int err;

        mutex_lock(&watchdog_mutex);

        err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
        if (!err && write)
                proc_watchdog_update();

        mutex_unlock(&watchdog_mutex);
        return err;
}

static const int sixty = 60;

static struct ctl_table watchdog_sysctls[] = {
        {
                .procname       = "watchdog",
                .data           = &watchdog_user_enabled,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_watchdog,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
        {
                .procname       = "watchdog_thresh",
                .data           = &watchdog_thresh,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_watchdog_thresh,
                .extra1         = SYSCTL_ZERO,
                .extra2         = (void *)&sixty,
        },
        {
                .procname       = "watchdog_cpumask",
                .data           = &watchdog_cpumask_bits,
                .maxlen         = NR_CPUS,
                .mode           = 0644,
                .proc_handler   = proc_watchdog_cpumask,
        },
#ifdef CONFIG_SOFTLOCKUP_DETECTOR
        {
                .procname       = "soft_watchdog",
                .data           = &watchdog_softlockup_user_enabled,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_soft_watchdog,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
        {
                .procname       = "softlockup_panic",
                .data           = &softlockup_panic,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
#ifdef CONFIG_SMP
        {
                .procname       = "softlockup_all_cpu_backtrace",
                .data           = &sysctl_softlockup_all_cpu_backtrace,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
#endif /* CONFIG_SMP */
#endif
#ifdef CONFIG_HARDLOCKUP_DETECTOR
        {
                .procname       = "hardlockup_panic",
                .data           = &hardlockup_panic,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
#ifdef CONFIG_SMP
        {
                .procname       = "hardlockup_all_cpu_backtrace",
                .data           = &sysctl_hardlockup_all_cpu_backtrace,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
#endif /* CONFIG_SMP */
#endif
};

static struct ctl_table watchdog_hardlockup_sysctl[] = {
        {
                .procname       = "nmi_watchdog",
                .data           = &watchdog_hardlockup_user_enabled,
                .maxlen         = sizeof(int),
                .mode           = 0444,
                .proc_handler   = proc_nmi_watchdog,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
};

static void __init watchdog_sysctl_init(void)
{
        register_sysctl_init("kernel", watchdog_sysctls);

        if (watchdog_hardlockup_available)
                watchdog_hardlockup_sysctl[0].mode = 0644;
        register_sysctl_init("kernel", watchdog_hardlockup_sysctl);
}

#else
#define watchdog_sysctl_init() do { } while (0)
#endif /* CONFIG_SYSCTL */

static void __init lockup_detector_delay_init(struct work_struct *work);
static bool allow_lockup_detector_init_retry __initdata;

static struct work_struct detector_work __initdata =
                __WORK_INITIALIZER(detector_work, lockup_detector_delay_init);

static void __init lockup_detector_delay_init(struct work_struct *work)
{
        int ret;

        ret = watchdog_hardlockup_probe();
        if (ret) {
                if (ret == -ENODEV)
                        pr_info("NMI not fully supported\n");
                else
                        pr_info("Delayed init of the lockup detector failed: %d\n", ret);
                pr_info("Hard watchdog permanently disabled\n");
                return;
        }

        allow_lockup_detector_init_retry = false;

        watchdog_hardlockup_available = true;
        lockup_detector_setup();
}

/*
 * lockup_detector_retry_init - retry init lockup detector if possible.
 *
 * Retry hardlockup detector init. It is useful when it requires some
 * functionality that has to be initialized later on a particular
 * platform.
 */
void __init lockup_detector_retry_init(void)
{
        /* Must be called before late init calls */
        if (!allow_lockup_detector_init_retry)
                return;

        schedule_work(&detector_work);
}

/*
 * Ensure that optional delayed hardlockup init is proceed before
 * the init code and memory is freed.
 */
static int __init lockup_detector_check(void)
{
        /* Prevent any later retry. */
        allow_lockup_detector_init_retry = false;

        /* Make sure no work is pending. */
        flush_work(&detector_work);

        watchdog_sysctl_init();

        return 0;

}
late_initcall_sync(lockup_detector_check);

void __init lockup_detector_init(void)
{
        if (tick_nohz_full_enabled())
                pr_info("Disabling watchdog on nohz_full cores by default\n");

        cpumask_copy(&watchdog_cpumask,
                     housekeeping_cpumask(HK_TYPE_TIMER));

        if (!watchdog_hardlockup_probe())
                watchdog_hardlockup_available = true;
        else
                allow_lockup_detector_init_retry = true;

        lockup_detector_setup();
}