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

int watchdog_enabled = 1;
int __read_mostly watchdog_thresh = 10;

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);
#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);
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 unsigned long 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() * (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;
}
static void watchdog_interrupt_count(void)
{
        __this_cpu_inc(hrtimer_interrupts);
}
#else
static inline void watchdog_interrupt_count(void) { return; }
#endif /* CONFIG_HARDLOCKUP_DETECTOR */

/* 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();
                }
                __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)) {
                /* 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;
}


/*
 * The watchdog thread - touches the timestamp.
 */
static int watchdog(void *unused)
{
        struct sched_param param = { .sched_priority = 0 };
        struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);

        /* initialize timestamp */
        __touch_watchdog();

        /* kick off the timer for the hardlockup detector */
        /* 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);

        set_current_state(TASK_INTERRUPTIBLE);
        /*
         * Run briefly (kicked by the hrtimer callback function) 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().
         */
        while (!kthread_should_stop()) {
                __touch_watchdog();
                schedule();

                if (kthread_should_stop())
                        break;

                set_current_state(TASK_INTERRUPTIBLE);
        }
        /*
         * Drop the policy/priority elevation during thread exit to avoid a
         * scheduling latency spike.
         */
        __set_current_state(TASK_RUNNING);
        sched_setscheduler(current, SCHED_NORMAL, &param);
        return 0;
}


#ifdef CONFIG_HARDLOCKUP_DETECTOR
static int watchdog_nmi_enable(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);
        if (!IS_ERR(event)) {
                pr_info("enabled, takes one hw-pmu counter.\n");
                goto out_save;
        }


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

/* prepare/enable/disable routines */
static void watchdog_prepare_cpu(int cpu)
{
        struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);

        WARN_ON(per_cpu(softlockup_watchdog, cpu));
        hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        hrtimer->function = watchdog_timer_fn;
}

static int watchdog_enable(int cpu)
{
        struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
        int err = 0;

        /* enable the perf event */
        err = watchdog_nmi_enable(cpu);

        /* Regardless of err above, fall through and start softlockup */

        /* create the watchdog thread */
        if (!p) {
                struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
                p = kthread_create_on_node(watchdog, NULL, cpu_to_node(cpu), "watchdog/%d", cpu);
                if (IS_ERR(p)) {
                        pr_err("softlockup watchdog for %i failed\n", cpu);
                        if (!err) {
                                /* if hardlockup hasn't already set this */
                                err = PTR_ERR(p);
                                /* and disable the perf event */
                                watchdog_nmi_disable(cpu);
                        }
                        goto out;
                }
                sched_setscheduler(p, SCHED_FIFO, &param);
                kthread_bind(p, cpu);
                per_cpu(watchdog_touch_ts, cpu) = 0;
                per_cpu(softlockup_watchdog, cpu) = p;
                wake_up_process(p);
        }

out:
        return err;
}

static void watchdog_disable(int cpu)
{
        struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
        struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);

        /*
         * cancel the timer first to stop incrementing the stats
         * and waking up the kthread
         */
        hrtimer_cancel(hrtimer);

        /* disable the perf event */
        watchdog_nmi_disable(cpu);

        /* stop the watchdog thread */
        if (p) {
                per_cpu(softlockup_watchdog, cpu) = NULL;
                kthread_stop(p);
        }
}

/* sysctl functions */
#ifdef CONFIG_SYSCTL
static void watchdog_enable_all_cpus(void)
{
        int cpu;

        watchdog_enabled = 0;

        for_each_online_cpu(cpu)
                if (!watchdog_enable(cpu))
                        /* if any cpu succeeds, watchdog is considered
                           enabled for the system */
                        watchdog_enabled = 1;

        if (!watchdog_enabled)
                pr_err("failed to be enabled on some cpus\n");

}

static void watchdog_disable_all_cpus(void)
{
        int cpu;

        for_each_online_cpu(cpu)
                watchdog_disable(cpu);

        /* if all watchdogs are disabled, then they are disabled for the system */
        watchdog_enabled = 0;
}


/*
 * 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;

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

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

out:
        return ret;
}
#endif /* CONFIG_SYSCTL */


/*
 * Create/destroy watchdog threads as CPUs come and go:
 */
static int __cpuinit
cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
{
        int hotcpu = (unsigned long)hcpu;

        switch (action) {
        case CPU_UP_PREPARE:
        case CPU_UP_PREPARE_FROZEN:
                watchdog_prepare_cpu(hotcpu);
                break;
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
                if (watchdog_enabled)
                        watchdog_enable(hotcpu);
                break;
#ifdef CONFIG_HOTPLUG_CPU
        case CPU_UP_CANCELED:
        case CPU_UP_CANCELED_FROZEN:
                watchdog_disable(hotcpu);
                break;
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                watchdog_disable(hotcpu);
                break;
#endif /* CONFIG_HOTPLUG_CPU */
        }

        /*
         * hardlockup and softlockup are not important enough
         * to block cpu bring up.  Just always succeed and
         * rely on printk output to flag problems.
         */
        return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata cpu_nfb = {
        .notifier_call = cpu_callback
};

void __init lockup_detector_init(void)
{
        void *cpu = (void *)(long)smp_processor_id();
        int err;

        err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
        WARN_ON(notifier_to_errno(err));

        cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
        register_cpu_notifier(&cpu_nfb);

        return;
}