watchdog.c

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/*
 * 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) "NMI watchdog: " fmt

#include <linux/mm.h>
#include <linux/cpu.h>
#include <linux/nmi.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include <linux/lockdep.h>
#include <linux/notifier.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <linux/smpboot.h>

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

int watchdog_enabled = 1;
int __read_mostly watchdog_thresh = 10;
static int __read_mostly watchdog_disabled;

static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
static DEFINE_PER_CPU(bool, softlockup_touch_sync);
static DEFINE_PER_CPU(bool, soft_watchdog_warn);
static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
#ifdef CONFIG_HARDLOCKUP_DETECTOR
static DEFINE_PER_CPU(bool, hard_watchdog_warn);
static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
#endif

/* boot commands */
/*
 * Should we panic when a soft-lockup or hard-lockup occurs:
 */
#ifdef CONFIG_HARDLOCKUP_DETECTOR
static int hardlockup_panic =
            CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;

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 = 0;
    return 1;
}
__setup("nmi_watchdog=", hardlockup_panic_setup);
#endif

unsigned int __read_mostly softlockup_panic =
            CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;

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_enabled = 0;
    return 1;
}
__setup("nowatchdog", nowatchdog_setup);

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

/*
 * 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(int this_cpu)
{
    return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
}

static u64 get_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
     */
    return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
}

/* Commands for resetting the watchdog */
static void __touch_watchdog(void)
{
    int this_cpu = smp_processor_id();

    __this_cpu_write(watchdog_touch_ts, get_timestamp(this_cpu));
}

void touch_softlockup_watchdog(void)
{
    __this_cpu_write(watchdog_touch_ts, 0);
}
EXPORT_SYMBOL(touch_softlockup_watchdog);

void touch_all_softlockup_watchdogs(void)
{
    int cpu;

    /*
     * this is done lockless
     * do we care if a 0 races with a timestamp?
     * all it means is the softlock check starts one cycle later
     */
    for_each_online_cpu(cpu)
        per_cpu(watchdog_touch_ts, cpu) = 0;
}

#ifdef CONFIG_HARDLOCKUP_DETECTOR
void touch_nmi_watchdog(void)
{
    if (watchdog_enabled) {
        unsigned cpu;

        for_each_present_cpu(cpu) {
            if (per_cpu(watchdog_nmi_touch, cpu) != true)
                per_cpu(watchdog_nmi_touch, cpu) = true;
        }
    }
    touch_softlockup_watchdog();
}
EXPORT_SYMBOL(touch_nmi_watchdog);

#endif

void touch_softlockup_watchdog_sync(void)
{
    __raw_get_cpu_var(softlockup_touch_sync) = true;
    __raw_get_cpu_var(watchdog_touch_ts) = 0;
}

#ifdef CONFIG_HARDLOCKUP_DETECTOR
/* watchdog detector functions */
static int is_hardlockup(void)
{
    unsigned long hrint = __this_cpu_read(hrtimer_interrupts);

    if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
        return 1;

    __this_cpu_write(hrtimer_interrupts_saved, hrint);
    return 0;
}
#endif

static int is_softlockup(unsigned long touch_ts)
{
    unsigned long now = get_timestamp(smp_processor_id());

    /* Warn about unreasonable delays: */
    if (time_after(now, touch_ts + get_softlockup_thresh()))
        return now - touch_ts;

    return 0;
}

#ifdef CONFIG_HARDLOCKUP_DETECTOR

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;
    }

    /* 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;

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

        __this_cpu_write(hard_watchdog_warn, true);
        return;
    }

    __this_cpu_write(hard_watchdog_warn, false);
    return;
}
#endif /* CONFIG_HARDLOCKUP_DETECTOR */

static void watchdog_interrupt_count(void)
{
    __this_cpu_inc(hrtimer_interrupts);
}

static int watchdog_nmi_enable(unsigned int cpu);
static void watchdog_nmi_disable(unsigned int cpu);

/* watchdog kicker functions */
static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
{
    unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
    struct pt_regs *regs = get_irq_regs();
    int duration;

    /* kick the hardlockup detector */
    watchdog_interrupt_count();

    /* kick the softlockup detector */
    wake_up_process(__this_cpu_read(softlockup_watchdog));

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

    if (touch_ts == 0) {
        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();
        }

        /* Clear the guest paused flag on watchdog reset */
        kvm_check_and_clear_guest_paused();
        __touch_watchdog();
        return HRTIMER_RESTART;
    }

    /* check for a softlockup
     * This is done by making sure a high priority task is
     * being scheduled.  The task touches the watchdog to
     * indicate it is getting cpu time.  If it hasn't then
     * this is a good indication some task is hogging the cpu
     */
    duration = is_softlockup(touch_ts);
    if (unlikely(duration)) {
        /*
         * If a virtual machine is stopped by the host it can look to
         * the watchdog like a soft lockup, check to see if the host
         * stopped the vm before we issue the warning
         */
        if (kvm_check_and_clear_guest_paused())
            return HRTIMER_RESTART;

        /* only warn once */
        if (__this_cpu_read(soft_watchdog_warn) == true)
            return HRTIMER_RESTART;

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

        if (softlockup_panic)
            panic("softlockup: hung tasks");
        __this_cpu_write(soft_watchdog_warn, true);
    } else
        __this_cpu_write(soft_watchdog_warn, false);

    return HRTIMER_RESTART;
}

static void watchdog_set_prio(unsigned int policy, unsigned int prio)
{
    struct sched_param param = { .sched_priority = prio };

    sched_setscheduler(current, policy, &param);
}

static void watchdog_enable(unsigned int cpu)
{
    struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);

    if (!watchdog_enabled) {
        kthread_park(current);
        return;
    }

    /* Enable the perf event */
    watchdog_nmi_enable(cpu);

    /* kick off the timer for the hardlockup detector */
    hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
    hrtimer->function = watchdog_timer_fn;

    /* done here because hrtimer_start can only pin to smp_processor_id() */
    hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
              HRTIMER_MODE_REL_PINNED);

    /* initialize timestamp */
    watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
    __touch_watchdog();
}

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

    if (!watchdog_enabled)
        return;

    watchdog_set_prio(SCHED_NORMAL, 0);
    hrtimer_cancel(hrtimer);
    /* disable the perf event */
    watchdog_nmi_disable(cpu);
}

static int watchdog_should_run(unsigned int cpu)
{
    return __this_cpu_read(hrtimer_interrupts) !=
        __this_cpu_read(soft_lockup_hrtimer_cnt);
}

/*
 * The watchdog thread function - touches the timestamp.
 *
 * It only runs once every get_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 void watchdog(unsigned int cpu)
{
    __this_cpu_write(soft_lockup_hrtimer_cnt,
             __this_cpu_read(hrtimer_interrupts));
    __touch_watchdog();
}

#ifdef CONFIG_HARDLOCKUP_DETECTOR
/*
 * 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;

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

    /* 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;
    }

    /* 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_warning("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));
    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;
}

static 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);
    }
    return;
}
#else
static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
static void watchdog_nmi_disable(unsigned int cpu) { return; }
#endif /* CONFIG_HARDLOCKUP_DETECTOR */

/* prepare/enable/disable routines */
/* sysctl functions */
#ifdef CONFIG_SYSCTL
static void watchdog_enable_all_cpus(void)
{
    unsigned int cpu;

    if (watchdog_disabled) {
        watchdog_disabled = 0;
        for_each_online_cpu(cpu)
            kthread_unpark(per_cpu(softlockup_watchdog, cpu));
    }
}

static void watchdog_disable_all_cpus(void)
{
    unsigned int cpu;

    if (!watchdog_disabled) {
        watchdog_disabled = 1;
        for_each_online_cpu(cpu)
            kthread_park(per_cpu(softlockup_watchdog, cpu));
    }
}

/*
 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
 */

int proc_dowatchdog(struct ctl_table *table, int write,
            void __user *buffer, size_t *lenp, loff_t *ppos)
{
    int ret;

    if (watchdog_disabled < 0)
        return -ENODEV;

    ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
    if (ret || !write)
        return ret;

    if (watchdog_enabled && watchdog_thresh)
        watchdog_enable_all_cpus();
    else
        watchdog_disable_all_cpus();

    return ret;
}
#endif /* CONFIG_SYSCTL */

static struct smp_hotplug_thread watchdog_threads = {
    .store          = &softlockup_watchdog,
    .thread_should_run  = watchdog_should_run,
    .thread_fn      = watchdog,
    .thread_comm        = "watchdog/%u",
    .setup          = watchdog_enable,
    .park           = watchdog_disable,
    .unpark         = watchdog_enable,
};

void __init lockup_detector_init(void)
{
    if (smpboot_register_percpu_thread(&watchdog_threads)) {
        pr_err("Failed to create watchdog threads, disabled\n");
        watchdog_disabled = -ENODEV;
    }
}