/*
 * Detect Soft Lockups
 *
 * started by Ingo Molnar, Copyright (C) 2005, 2006 Red Hat, Inc.
 *
 * this code detects soft lockups: incidents in where on a CPU
 * the kernel does not reschedule for 10 seconds or more.
 */
#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/notifier.h>
#include <linux/module.h>

#include <asm/irq_regs.h>

static DEFINE_SPINLOCK(print_lock);

static DEFINE_PER_CPU(unsigned long, touch_timestamp);
static DEFINE_PER_CPU(unsigned long, print_timestamp);
static DEFINE_PER_CPU(struct task_struct *, watchdog_task);

static int __read_mostly did_panic;
unsigned long __read_mostly softlockup_thresh = 60;

static int
softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
{
        did_panic = 1;

        return NOTIFY_DONE;
}

static struct notifier_block panic_block = {
        .notifier_call = softlock_panic,
};

/*
 * 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 void __touch_softlockup_watchdog(void)
{
        int this_cpu = raw_smp_processor_id();

        __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
}

void touch_softlockup_watchdog(void)
{
        __raw_get_cpu_var(touch_timestamp) = 0;
}
EXPORT_SYMBOL(touch_softlockup_watchdog);

void touch_all_softlockup_watchdogs(void)
{
        int cpu;

        /* Cause each CPU to re-update its timestamp rather than complain */
        for_each_online_cpu(cpu)
                per_cpu(touch_timestamp, cpu) = 0;
}
EXPORT_SYMBOL(touch_all_softlockup_watchdogs);

/*
 * This callback runs from the timer interrupt, and checks
 * whether the watchdog thread has hung or not:
 */
void softlockup_tick(void)
{
        int this_cpu = smp_processor_id();
        unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
        unsigned long print_timestamp;
        struct pt_regs *regs = get_irq_regs();
        unsigned long now;

        if (touch_timestamp == 0) {
                __touch_softlockup_watchdog();
                return;
        }

        print_timestamp = per_cpu(print_timestamp, this_cpu);

        /* report at most once a second */
        if ((print_timestamp >= touch_timestamp &&
                        print_timestamp < (touch_timestamp + 1)) ||
                        did_panic || !per_cpu(watchdog_task, this_cpu)) {
                return;
        }

        /* do not print during early bootup: */
        if (unlikely(system_state != SYSTEM_RUNNING)) {
                __touch_softlockup_watchdog();
                return;
        }

        now = get_timestamp(this_cpu);

        /* Wake up the high-prio watchdog task every second: */
        if (now > (touch_timestamp + 1))
                wake_up_process(per_cpu(watchdog_task, this_cpu));

        /* Warn about unreasonable delays: */
        if (now <= (touch_timestamp + softlockup_thresh))
                return;

        per_cpu(print_timestamp, this_cpu) = touch_timestamp;

        spin_lock(&print_lock);
        printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
                        this_cpu, now - touch_timestamp,
                        current->comm, task_pid_nr(current));
        print_modules();
        if (regs)
                show_regs(regs);
        else
                dump_stack();
        spin_unlock(&print_lock);
}

/*
 * Have a reasonable limit on the number of tasks checked:
 */
unsigned long __read_mostly sysctl_hung_task_check_count = 1024;

/*
 * Zero means infinite timeout - no checking done:
 */
unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;

unsigned long __read_mostly sysctl_hung_task_warnings = 10;

/*
 * Only do the hung-tasks check on one CPU:
 */
static int check_cpu __read_mostly = -1;

static void check_hung_task(struct task_struct *t, unsigned long now)
{
        unsigned long switch_count = t->nvcsw + t->nivcsw;

        if (t->flags & PF_FROZEN)
                return;

        if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
                t->last_switch_count = switch_count;
                t->last_switch_timestamp = now;
                return;
        }
        if ((long)(now - t->last_switch_timestamp) <
                                        sysctl_hung_task_timeout_secs)
                return;
        if (sysctl_hung_task_warnings < 0)
                return;
        sysctl_hung_task_warnings--;

        /*
         * Ok, the task did not get scheduled for more than 2 minutes,
         * complain:
         */
        printk(KERN_ERR "INFO: task %s:%d blocked for more than "
                        "%ld seconds.\n", t->comm, t->pid,
                        sysctl_hung_task_timeout_secs);
        printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
                        " disables this message.\n");
        sched_show_task(t);
        __debug_show_held_locks(t);

        t->last_switch_timestamp = now;
        touch_nmi_watchdog();
}

/*
 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
 * a really long time (120 seconds). If that happens, print out
 * a warning.
 */
static void check_hung_uninterruptible_tasks(int this_cpu)
{
        int max_count = sysctl_hung_task_check_count;
        unsigned long now = get_timestamp(this_cpu);
        struct task_struct *g, *t;

        /*
         * If the system crashed already then all bets are off,
         * do not report extra hung tasks:
         */
        if ((tainted & TAINT_DIE) || did_panic)
                return;

        read_lock(&tasklist_lock);
        do_each_thread(g, t) {
                if (!--max_count)
                        goto unlock;
                if (t->state & TASK_UNINTERRUPTIBLE)
                        check_hung_task(t, now);
        } while_each_thread(g, t);
 unlock:
        read_unlock(&tasklist_lock);
}

/*
 * The watchdog thread - runs every second and touches the timestamp.
 */
static int watchdog(void *__bind_cpu)
{
        struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
        int this_cpu = (long)__bind_cpu;

        sched_setscheduler(current, SCHED_FIFO, &param);

        /* initialize timestamp */
        __touch_softlockup_watchdog();

        set_current_state(TASK_INTERRUPTIBLE);
        /*
         * Run briefly once per second to reset the softlockup timestamp.
         * If this gets delayed for more than 60 seconds then the
         * debug-printout triggers in softlockup_tick().
         */
        while (!kthread_should_stop()) {
                __touch_softlockup_watchdog();
                schedule();

                if (kthread_should_stop())
                        break;

                if (this_cpu == check_cpu) {
                        if (sysctl_hung_task_timeout_secs)
                                check_hung_uninterruptible_tasks(this_cpu);
                }

                set_current_state(TASK_INTERRUPTIBLE);
        }
        __set_current_state(TASK_RUNNING);

        return 0;
}

/*
 * 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;
        struct task_struct *p;

        switch (action) {
        case CPU_UP_PREPARE:
        case CPU_UP_PREPARE_FROZEN:
                BUG_ON(per_cpu(watchdog_task, hotcpu));
                p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
                if (IS_ERR(p)) {
                        printk(KERN_ERR "watchdog for %i failed\n", hotcpu);
                        return NOTIFY_BAD;
                }
                per_cpu(touch_timestamp, hotcpu) = 0;
                per_cpu(watchdog_task, hotcpu) = p;
                kthread_bind(p, hotcpu);
                break;
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
                check_cpu = any_online_cpu(cpu_online_map);
                wake_up_process(per_cpu(watchdog_task, hotcpu));
                break;
#ifdef CONFIG_HOTPLUG_CPU
        case CPU_DOWN_PREPARE:
        case CPU_DOWN_PREPARE_FROZEN:
                if (hotcpu == check_cpu) {
                        cpumask_t temp_cpu_online_map = cpu_online_map;

                        cpu_clear(hotcpu, temp_cpu_online_map);
                        check_cpu = any_online_cpu(temp_cpu_online_map);
                }
                break;

        case CPU_UP_CANCELED:
        case CPU_UP_CANCELED_FROZEN:
                if (!per_cpu(watchdog_task, hotcpu))
                        break;
                /* Unbind so it can run.  Fall thru. */
                kthread_bind(per_cpu(watchdog_task, hotcpu),
                             any_online_cpu(cpu_online_map));
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                p = per_cpu(watchdog_task, hotcpu);
                per_cpu(watchdog_task, hotcpu) = NULL;
                kthread_stop(p);
                break;
#endif /* CONFIG_HOTPLUG_CPU */
        }
        return NOTIFY_OK;
}

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

__init void spawn_softlockup_task(void)
{
        void *cpu = (void *)(long)smp_processor_id();
        int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);

        BUG_ON(err == NOTIFY_BAD);
        cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
        register_cpu_notifier(&cpu_nfb);

        atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
}