drm: Don't return 0 for a value used as a denominator

[linux-2.6/btrfs-unstable.git] / kernel / watchdog.c

/*
 * 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 <linux/sched/rt.h>

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

int watchdog_user_enabled = 1;
int __read_mostly watchdog_thresh = 10;
#ifdef CONFIG_SMP
int __read_mostly sysctl_softlockup_all_cpu_backtrace;
#else
#define sysctl_softlockup_all_cpu_backtrace 0
#endif

static int __read_mostly watchdog_running;
static u64 __read_mostly sample_period;

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
static unsigned long soft_lockup_nmi_warn;

/* 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_user_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_user_enabled = 0;
        return 1;
}
__setup("nowatchdog", nowatchdog_setup);

/* deprecated */
static int __init nosoftlockup_setup(char *str)
{
        watchdog_user_enabled = 0;
        return 1;
}
__setup("nosoftlockup", nosoftlockup_setup);
/*  */
#ifdef CONFIG_SMP
static int __init softlockup_all_cpu_backtrace_setup(char *str)
{
        sysctl_softlockup_all_cpu_backtrace =
                !!simple_strtol(str, NULL, 0);
        return 1;
}
__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
#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 local_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 / 5);
}

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

void touch_softlockup_watchdog(void)
{
        /*
         * Preemption can be enabled.  It doesn't matter which CPU's timestamp
         * gets zeroed here, so use the raw_ operation.
         */
        raw_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)
{
        /*
         * 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_get_cpu_var(watchdog_nmi_touch) = 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();

        /* 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;
        int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;

        /* 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(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;

                if (softlockup_all_cpu_backtrace) {
                        /* Prevent multiple soft-lockup reports if one cpu is already
                         * engaged in dumping cpu back traces
                         */
                        if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
                                /* Someone else will report us. Let's give up */
                                __this_cpu_write(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_all_cpu_backtrace) {
                        /* Avoid generating two back traces for current
                         * given that one is already made above
                         */
                        trigger_allbutself_cpu_backtrace();

                        clear_bit(0, &soft_lockup_nmi_warn);
                        /* Barrier to sync with other cpus */
                        smp_mb__after_atomic();
                }

                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);

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

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

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

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

static void watchdog_cleanup(unsigned int cpu, bool online)
{
        watchdog_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 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 */

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,
        .cleanup                = watchdog_cleanup,
        .park                   = watchdog_disable,
        .unpark                 = watchdog_enable,
};

static void restart_watchdog_hrtimer(void *info)
{
        struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
        int ret;

        /*
         * No need to cancel and restart hrtimer if it is currently executing
         * because it will reprogram itself with the new period now.
         * We should never see it unqueued here because we are running per-cpu
         * with interrupts disabled.
         */
        ret = hrtimer_try_to_cancel(hrtimer);
        if (ret == 1)
                hrtimer_start(hrtimer, ns_to_ktime(sample_period),
                                HRTIMER_MODE_REL_PINNED);
}

static void update_timers(int cpu)
{
        /*
         * Make sure that perf event counter will adopt to a new
         * sampling period. Updating the sampling period directly would
         * be much nicer but we do not have an API for that now so
         * let's use a big hammer.
         * Hrtimer will adopt the new period on the next tick but this
         * might be late already so we have to restart the timer as well.
         */
        watchdog_nmi_disable(cpu);
        smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);
        watchdog_nmi_enable(cpu);
}

static void update_timers_all_cpus(void)
{
        int cpu;

        get_online_cpus();
        for_each_online_cpu(cpu)
                update_timers(cpu);
        put_online_cpus();
}

static int watchdog_enable_all_cpus(bool sample_period_changed)
{
        int err = 0;

        if (!watchdog_running) {
                err = smpboot_register_percpu_thread(&watchdog_threads);
                if (err)
                        pr_err("Failed to create watchdog threads, disabled\n");
                else
                        watchdog_running = 1;
        } else if (sample_period_changed) {
                update_timers_all_cpus();
        }

        return err;
}

/* prepare/enable/disable routines */
/* sysctl functions */
#ifdef CONFIG_SYSCTL
static void watchdog_disable_all_cpus(void)
{
        if (watchdog_running) {
                watchdog_running = 0;
                smpboot_unregister_percpu_thread(&watchdog_threads);
        }
}

/*
 * 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 err, old_thresh, old_enabled;
        static DEFINE_MUTEX(watchdog_proc_mutex);

        mutex_lock(&watchdog_proc_mutex);
        old_thresh = ACCESS_ONCE(watchdog_thresh);
        old_enabled = ACCESS_ONCE(watchdog_user_enabled);

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

        set_sample_period();
        /*
         * Watchdog threads shouldn't be enabled if they are
         * disabled. The 'watchdog_running' variable check in
         * watchdog_*_all_cpus() function takes care of this.
         */
        if (watchdog_user_enabled && watchdog_thresh)
                err = watchdog_enable_all_cpus(old_thresh != watchdog_thresh);
        else
                watchdog_disable_all_cpus();

        /* Restore old values on failure */
        if (err) {
                watchdog_thresh = old_thresh;
                watchdog_user_enabled = old_enabled;
        }
out:
        mutex_unlock(&watchdog_proc_mutex);
        return err;
}
#endif /* CONFIG_SYSCTL */

void __init lockup_detector_init(void)
{
        set_sample_period();

        if (watchdog_user_enabled)
                watchdog_enable_all_cpus(false);
}