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/*

 * 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/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 did_panic;

int softlockup_thresh = 10;

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) >> 30;  /* 2^30 ~= 10^9 */

}

void touch_softlockup_watchdog(void)

{

        int this_cpu = raw_smp_processor_id();

        __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);

}

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 10+ seconds 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));

        if (regs)

                show_regs(regs);

        else

                dump_stack();

        spin_unlock(&print_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 };

        sched_setscheduler(current, SCHED_FIFO, &param);

        /* initialize timestamp */

        touch_softlockup_watchdog();

        /*

         * Run briefly once per second to reset the softlockup timestamp.

         * If this gets delayed for more than 10 seconds then the

         * debug-printout triggers in softlockup_tick().

         */

        while (!kthread_should_stop()) {

                set_current_state(TASK_INTERRUPTIBLE);

                touch_softlockup_watchdog();

                schedule();

        }

        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:

                wake_up_process(per_cpu(watchdog_task, hotcpu));

                break;

#ifdef CONFIG_HOTPLUG_CPU

        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);

}