// SPDX-License-Identifier: GPL-2.0-only
/*
 * Detect Hung Task
 *
 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
 *
 */

#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/export.h>
#include <linux/panic_notifier.h>
#include <linux/sysctl.h>
#include <linux/suspend.h>
#include <linux/utsname.h>
#include <linux/sched/signal.h>
#include <linux/sched/debug.h>
#include <linux/sched/sysctl.h>
#include <linux/hung_task.h>
#include <linux/rwsem.h>
#include <linux/sys_info.h>

#include <trace/events/sched.h>

/*
 * The number of tasks checked:
 */
static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;

/*
 * Total number of tasks detected as hung since boot:
 */
static unsigned long __read_mostly sysctl_hung_task_detect_count;

/*
 * Limit number of tasks checked in a batch.
 *
 * This value controls the preemptibility of khungtaskd since preemption
 * is disabled during the critical section. It also controls the size of
 * the RCU grace period. So it needs to be upper-bound.
 */
#define HUNG_TASK_LOCK_BREAK (HZ / 10)

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

/*
 * Zero (default value) means use sysctl_hung_task_timeout_secs:
 */
static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;

static int __read_mostly sysctl_hung_task_warnings = 10;

static int __read_mostly did_panic;
static bool hung_task_call_panic;

static struct task_struct *watchdog_task;

/*
 * A bitmask to control what kinds of system info to be printed when
 * a hung task is detected, it could be task, memory, lock etc. Refer
 * include/linux/sys_info.h for detailed bit definition.
 */
static unsigned long hung_task_si_mask;

#ifdef CONFIG_SMP
/*
 * Should we dump all CPUs backtraces in a hung task event?
 * Defaults to 0, can be changed via sysctl.
 */
static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
#else
#define sysctl_hung_task_all_cpu_backtrace 0
#endif /* CONFIG_SMP */

/*
 * Should we panic (and reboot, if panic_timeout= is set) when a
 * hung task is detected:
 */
static unsigned int __read_mostly sysctl_hung_task_panic =
        CONFIG_BOOTPARAM_HUNG_TASK_PANIC;

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

        return NOTIFY_DONE;
}

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

static bool task_is_hung(struct task_struct *t, unsigned long timeout)
{
        unsigned long switch_count = t->nvcsw + t->nivcsw;
        unsigned int state = READ_ONCE(t->__state);

        /*
         * skip the TASK_KILLABLE tasks -- these can be killed
         * skip the TASK_IDLE tasks -- those are genuinely idle
         * skip the TASK_FROZEN task -- it reasonably stops scheduling by freezer
         */
        if (!(state & TASK_UNINTERRUPTIBLE) ||
            (state & (TASK_WAKEKILL | TASK_NOLOAD | TASK_FROZEN)))
                return false;

        /*
         * When a freshly created task is scheduled once, changes its state to
         * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
         * musn't be checked.
         */
        if (unlikely(!switch_count))
                return false;

        if (switch_count != t->last_switch_count) {
                t->last_switch_count = switch_count;
                t->last_switch_time = jiffies;
                return false;
        }
        if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
                return false;

        return true;
}

#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER
static void debug_show_blocker(struct task_struct *task, unsigned long timeout)
{
        struct task_struct *g, *t;
        unsigned long owner, blocker, blocker_type;
        const char *rwsem_blocked_by, *rwsem_blocked_as;

        RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "No rcu lock held");

        blocker = READ_ONCE(task->blocker);
        if (!blocker)
                return;

        blocker_type = hung_task_get_blocker_type(blocker);

        switch (blocker_type) {
        case BLOCKER_TYPE_MUTEX:
                owner = mutex_get_owner(hung_task_blocker_to_lock(blocker));
                break;
        case BLOCKER_TYPE_SEM:
                owner = sem_last_holder(hung_task_blocker_to_lock(blocker));
                break;
        case BLOCKER_TYPE_RWSEM_READER:
        case BLOCKER_TYPE_RWSEM_WRITER:
                owner = (unsigned long)rwsem_owner(
                                        hung_task_blocker_to_lock(blocker));
                rwsem_blocked_as = (blocker_type == BLOCKER_TYPE_RWSEM_READER) ?
                                        "reader" : "writer";
                rwsem_blocked_by = is_rwsem_reader_owned(
                                        hung_task_blocker_to_lock(blocker)) ?
                                        "reader" : "writer";
                break;
        default:
                WARN_ON_ONCE(1);
                return;
        }


        if (unlikely(!owner)) {
                switch (blocker_type) {
                case BLOCKER_TYPE_MUTEX:
                        pr_err("INFO: task %s:%d is blocked on a mutex, but the owner is not found.\n",
                               task->comm, task->pid);
                        break;
                case BLOCKER_TYPE_SEM:
                        pr_err("INFO: task %s:%d is blocked on a semaphore, but the last holder is not found.\n",
                               task->comm, task->pid);
                        break;
                case BLOCKER_TYPE_RWSEM_READER:
                case BLOCKER_TYPE_RWSEM_WRITER:
                        pr_err("INFO: task %s:%d is blocked on an rw-semaphore, but the owner is not found.\n",
                               task->comm, task->pid);
                        break;
                }
                return;
        }

        /* Ensure the owner information is correct. */
        for_each_process_thread(g, t) {
                if ((unsigned long)t != owner)
                        continue;

                switch (blocker_type) {
                case BLOCKER_TYPE_MUTEX:
                        pr_err("INFO: task %s:%d is blocked on a mutex likely owned by task %s:%d.\n",
                               task->comm, task->pid, t->comm, t->pid);
                        break;
                case BLOCKER_TYPE_SEM:
                        pr_err("INFO: task %s:%d blocked on a semaphore likely last held by task %s:%d\n",
                               task->comm, task->pid, t->comm, t->pid);
                        break;
                case BLOCKER_TYPE_RWSEM_READER:
                case BLOCKER_TYPE_RWSEM_WRITER:
                        pr_err("INFO: task %s:%d <%s> blocked on an rw-semaphore likely owned by task %s:%d <%s>\n",
                               task->comm, task->pid, rwsem_blocked_as, t->comm,
                               t->pid, rwsem_blocked_by);
                        break;
                }
                /* Avoid duplicated task dump, skip if the task is also hung. */
                if (!task_is_hung(t, timeout))
                        sched_show_task(t);
                return;
        }
}
#else
static inline void debug_show_blocker(struct task_struct *task, unsigned long timeout)
{
}
#endif

static void check_hung_task(struct task_struct *t, unsigned long timeout,
                unsigned long prev_detect_count)
{
        unsigned long total_hung_task;

        if (!task_is_hung(t, timeout))
                return;

        /*
         * This counter tracks the total number of tasks detected as hung
         * since boot.
         */
        sysctl_hung_task_detect_count++;

        total_hung_task = sysctl_hung_task_detect_count - prev_detect_count;
        trace_sched_process_hang(t);

        if (sysctl_hung_task_panic && total_hung_task >= sysctl_hung_task_panic) {
                console_verbose();
                hung_task_call_panic = true;
        }

        /*
         * Ok, the task did not get scheduled for more than 2 minutes,
         * complain:
         */
        if (sysctl_hung_task_warnings || hung_task_call_panic) {
                if (sysctl_hung_task_warnings > 0)
                        sysctl_hung_task_warnings--;
                pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
                       t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
                pr_err("      %s %s %.*s\n",
                        print_tainted(), init_utsname()->release,
                        (int)strcspn(init_utsname()->version, " "),
                        init_utsname()->version);
                if (t->flags & PF_POSTCOREDUMP)
                        pr_err("      Blocked by coredump.\n");
                pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
                        " disables this message.\n");
                sched_show_task(t);
                debug_show_blocker(t, timeout);

                if (!sysctl_hung_task_warnings)
                        pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
        }

        touch_nmi_watchdog();
}

/*
 * To avoid extending the RCU grace period for an unbounded amount of time,
 * periodically exit the critical section and enter a new one.
 *
 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
 * to exit the grace period. For classic RCU, a reschedule is required.
 */
static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
{
        bool can_cont;

        get_task_struct(g);
        get_task_struct(t);
        rcu_read_unlock();
        cond_resched();
        rcu_read_lock();
        can_cont = pid_alive(g) && pid_alive(t);
        put_task_struct(t);
        put_task_struct(g);

        return can_cont;
}

/*
 * 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(unsigned long timeout)
{
        int max_count = sysctl_hung_task_check_count;
        unsigned long last_break = jiffies;
        struct task_struct *g, *t;
        unsigned long prev_detect_count = sysctl_hung_task_detect_count;
        int need_warning = sysctl_hung_task_warnings;
        unsigned long si_mask = hung_task_si_mask;

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


        rcu_read_lock();
        for_each_process_thread(g, t) {

                if (!max_count--)
                        goto unlock;
                if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
                        if (!rcu_lock_break(g, t))
                                goto unlock;
                        last_break = jiffies;
                }

                check_hung_task(t, timeout, prev_detect_count);
        }
 unlock:
        rcu_read_unlock();

        if (!(sysctl_hung_task_detect_count - prev_detect_count))
                return;

        if (need_warning || hung_task_call_panic) {
                si_mask |= SYS_INFO_LOCKS;

                if (sysctl_hung_task_all_cpu_backtrace)
                        si_mask |= SYS_INFO_ALL_BT;
        }

        sys_info(si_mask);

        if (hung_task_call_panic)
                panic("hung_task: blocked tasks");
}

static long hung_timeout_jiffies(unsigned long last_checked,
                                 unsigned long timeout)
{
        /* timeout of 0 will disable the watchdog */
        return timeout ? last_checked - jiffies + timeout * HZ :
                MAX_SCHEDULE_TIMEOUT;
}

#ifdef CONFIG_SYSCTL
/*
 * Process updating of timeout sysctl
 */
static int proc_dohung_task_timeout_secs(const struct ctl_table *table, int write,
                                  void *buffer,
                                  size_t *lenp, loff_t *ppos)
{
        int ret;

        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);

        if (ret || !write)
                goto out;

        wake_up_process(watchdog_task);

 out:
        return ret;
}

/*
 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
 * and hung_task_check_interval_secs
 */
static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
static const struct ctl_table hung_task_sysctls[] = {
#ifdef CONFIG_SMP
        {
                .procname       = "hung_task_all_cpu_backtrace",
                .data           = &sysctl_hung_task_all_cpu_backtrace,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
#endif /* CONFIG_SMP */
        {
                .procname       = "hung_task_panic",
                .data           = &sysctl_hung_task_panic,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_INT_MAX,
        },
        {
                .procname       = "hung_task_check_count",
                .data           = &sysctl_hung_task_check_count,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
        },
        {
                .procname       = "hung_task_timeout_secs",
                .data           = &sysctl_hung_task_timeout_secs,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_dohung_task_timeout_secs,
                .extra2         = (void *)&hung_task_timeout_max,
        },
        {
                .procname       = "hung_task_check_interval_secs",
                .data           = &sysctl_hung_task_check_interval_secs,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_dohung_task_timeout_secs,
                .extra2         = (void *)&hung_task_timeout_max,
        },
        {
                .procname       = "hung_task_warnings",
                .data           = &sysctl_hung_task_warnings,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_NEG_ONE,
        },
        {
                .procname       = "hung_task_detect_count",
                .data           = &sysctl_hung_task_detect_count,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0444,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "hung_task_sys_info",
                .data           = &hung_task_si_mask,
                .maxlen         = sizeof(hung_task_si_mask),
                .mode           = 0644,
                .proc_handler   = sysctl_sys_info_handler,
        },
};

static void __init hung_task_sysctl_init(void)
{
        register_sysctl_init("kernel", hung_task_sysctls);
}
#else
#define hung_task_sysctl_init() do { } while (0)
#endif /* CONFIG_SYSCTL */


static atomic_t reset_hung_task = ATOMIC_INIT(0);

void reset_hung_task_detector(void)
{
        atomic_set(&reset_hung_task, 1);
}
EXPORT_SYMBOL_GPL(reset_hung_task_detector);

static bool hung_detector_suspended;

static int hungtask_pm_notify(struct notifier_block *self,
                              unsigned long action, void *hcpu)
{
        switch (action) {
        case PM_SUSPEND_PREPARE:
        case PM_HIBERNATION_PREPARE:
        case PM_RESTORE_PREPARE:
                hung_detector_suspended = true;
                break;
        case PM_POST_SUSPEND:
        case PM_POST_HIBERNATION:
        case PM_POST_RESTORE:
                hung_detector_suspended = false;
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

/*
 * kthread which checks for tasks stuck in D state
 */
static int watchdog(void *dummy)
{
        unsigned long hung_last_checked = jiffies;

        set_user_nice(current, 0);

        for ( ; ; ) {
                unsigned long timeout = sysctl_hung_task_timeout_secs;
                unsigned long interval = sysctl_hung_task_check_interval_secs;
                long t;

                if (interval == 0)
                        interval = timeout;
                interval = min_t(unsigned long, interval, timeout);
                t = hung_timeout_jiffies(hung_last_checked, interval);
                if (t <= 0) {
                        if (!atomic_xchg(&reset_hung_task, 0) &&
                            !hung_detector_suspended)
                                check_hung_uninterruptible_tasks(timeout);
                        hung_last_checked = jiffies;
                        continue;
                }
                schedule_timeout_interruptible(t);
        }

        return 0;
}

static int __init hung_task_init(void)
{
        atomic_notifier_chain_register(&panic_notifier_list, &panic_block);

        /* Disable hung task detector on suspend */
        pm_notifier(hungtask_pm_notify, 0);

        watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
        hung_task_sysctl_init();

        return 0;
}
subsys_initcall(hung_task_init);