// SPDX-License-Identifier: GPL-2.0-only
/*
 * Common SMP CPU bringup/teardown functions
 */
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/smp.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/kthread.h>
#include <linux/smpboot.h>

#include "smpboot.h"

#ifdef CONFIG_SMP

#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
/*
 * For the hotplug case we keep the task structs around and reuse
 * them.
 */
static DEFINE_PER_CPU(struct task_struct *, idle_threads);

struct task_struct *idle_thread_get(unsigned int cpu)
{
        struct task_struct *tsk = per_cpu(idle_threads, cpu);

        if (!tsk)
                return ERR_PTR(-ENOMEM);
        return tsk;
}

void __init idle_thread_set_boot_cpu(void)
{
        per_cpu(idle_threads, smp_processor_id()) = current;
}

/**
 * idle_init - Initialize the idle thread for a cpu
 * @cpu:        The cpu for which the idle thread should be initialized
 *
 * Creates the thread if it does not exist.
 */
static __always_inline void idle_init(unsigned int cpu)
{
        struct task_struct *tsk = per_cpu(idle_threads, cpu);

        if (!tsk) {
                tsk = fork_idle(cpu);
                if (IS_ERR(tsk))
                        pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
                else
                        per_cpu(idle_threads, cpu) = tsk;
        }
}

/**
 * idle_threads_init - Initialize idle threads for all cpus
 */
void __init idle_threads_init(void)
{
        unsigned int cpu, boot_cpu;

        boot_cpu = smp_processor_id();

        for_each_possible_cpu(cpu) {
                if (cpu != boot_cpu)
                        idle_init(cpu);
        }
}
#endif

#endif /* #ifdef CONFIG_SMP */

static LIST_HEAD(hotplug_threads);
static DEFINE_MUTEX(smpboot_threads_lock);

struct smpboot_thread_data {
        unsigned int                    cpu;
        unsigned int                    status;
        struct smp_hotplug_thread       *ht;
};

enum {
        HP_THREAD_NONE = 0,
        HP_THREAD_ACTIVE,
        HP_THREAD_PARKED,
};

/**
 * smpboot_thread_fn - percpu hotplug thread loop function
 * @data:       thread data pointer
 *
 * Checks for thread stop and park conditions. Calls the necessary
 * setup, cleanup, park and unpark functions for the registered
 * thread.
 *
 * Returns 1 when the thread should exit, 0 otherwise.
 */
static int smpboot_thread_fn(void *data)
{
        struct smpboot_thread_data *td = data;
        struct smp_hotplug_thread *ht = td->ht;

        while (1) {
                set_current_state(TASK_INTERRUPTIBLE);
                preempt_disable();
                if (kthread_should_stop()) {
                        __set_current_state(TASK_RUNNING);
                        preempt_enable();
                        /* cleanup must mirror setup */
                        if (ht->cleanup && td->status != HP_THREAD_NONE)
                                ht->cleanup(td->cpu, cpu_online(td->cpu));
                        kfree(td);
                        return 0;
                }

                if (kthread_should_park()) {
                        __set_current_state(TASK_RUNNING);
                        preempt_enable();
                        if (ht->park && td->status == HP_THREAD_ACTIVE) {
                                BUG_ON(td->cpu != smp_processor_id());
                                ht->park(td->cpu);
                                td->status = HP_THREAD_PARKED;
                        }
                        kthread_parkme();
                        /* We might have been woken for stop */
                        continue;
                }

                BUG_ON(td->cpu != smp_processor_id());

                /* Check for state change setup */
                switch (td->status) {
                case HP_THREAD_NONE:
                        __set_current_state(TASK_RUNNING);
                        preempt_enable();
                        if (ht->setup)
                                ht->setup(td->cpu);
                        td->status = HP_THREAD_ACTIVE;
                        continue;

                case HP_THREAD_PARKED:
                        __set_current_state(TASK_RUNNING);
                        preempt_enable();
                        if (ht->unpark)
                                ht->unpark(td->cpu);
                        td->status = HP_THREAD_ACTIVE;
                        continue;
                }

                if (!ht->thread_should_run(td->cpu)) {
                        preempt_enable_no_resched();
                        schedule();
                } else {
                        __set_current_state(TASK_RUNNING);
                        preempt_enable();
                        ht->thread_fn(td->cpu);
                }
        }
}

static int
__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
{
        struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
        struct smpboot_thread_data *td;

        if (tsk)
                return 0;

        td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
        if (!td)
                return -ENOMEM;
        td->cpu = cpu;
        td->ht = ht;

        tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
                                    ht->thread_comm);
        if (IS_ERR(tsk)) {
                kfree(td);
                return PTR_ERR(tsk);
        }
        kthread_set_per_cpu(tsk, cpu);
        /*
         * Park the thread so that it could start right on the CPU
         * when it is available.
         */
        kthread_park(tsk);
        get_task_struct(tsk);
        *per_cpu_ptr(ht->store, cpu) = tsk;
        if (ht->create) {
                /*
                 * Make sure that the task has actually scheduled out
                 * into park position, before calling the create
                 * callback. At least the migration thread callback
                 * requires that the task is off the runqueue.
                 */
                if (!wait_task_inactive(tsk, TASK_PARKED))
                        WARN_ON(1);
                else
                        ht->create(cpu);
        }
        return 0;
}

int smpboot_create_threads(unsigned int cpu)
{
        struct smp_hotplug_thread *cur;
        int ret = 0;

        mutex_lock(&smpboot_threads_lock);
        list_for_each_entry(cur, &hotplug_threads, list) {
                ret = __smpboot_create_thread(cur, cpu);
                if (ret)
                        break;
        }
        mutex_unlock(&smpboot_threads_lock);
        return ret;
}

static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
{
        struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);

        if (!ht->selfparking)
                kthread_unpark(tsk);
}

int smpboot_unpark_threads(unsigned int cpu)
{
        struct smp_hotplug_thread *cur;

        mutex_lock(&smpboot_threads_lock);
        list_for_each_entry(cur, &hotplug_threads, list)
                smpboot_unpark_thread(cur, cpu);
        mutex_unlock(&smpboot_threads_lock);
        return 0;
}

static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
{
        struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);

        if (tsk && !ht->selfparking)
                kthread_park(tsk);
}

int smpboot_park_threads(unsigned int cpu)
{
        struct smp_hotplug_thread *cur;

        mutex_lock(&smpboot_threads_lock);
        list_for_each_entry_reverse(cur, &hotplug_threads, list)
                smpboot_park_thread(cur, cpu);
        mutex_unlock(&smpboot_threads_lock);
        return 0;
}

static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
{
        unsigned int cpu;

        /* We need to destroy also the parked threads of offline cpus */
        for_each_possible_cpu(cpu) {
                struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);

                if (tsk) {
                        kthread_stop(tsk);
                        put_task_struct(tsk);
                        *per_cpu_ptr(ht->store, cpu) = NULL;
                }
        }
}

/**
 * smpboot_register_percpu_thread - Register a per_cpu thread related
 *                                          to hotplug
 * @plug_thread:        Hotplug thread descriptor
 *
 * Creates and starts the threads on all online cpus.
 */
int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
{
        unsigned int cpu;
        int ret = 0;

        get_online_cpus();
        mutex_lock(&smpboot_threads_lock);
        for_each_online_cpu(cpu) {
                ret = __smpboot_create_thread(plug_thread, cpu);
                if (ret) {
                        smpboot_destroy_threads(plug_thread);
                        goto out;
                }
                smpboot_unpark_thread(plug_thread, cpu);
        }
        list_add(&plug_thread->list, &hotplug_threads);
out:
        mutex_unlock(&smpboot_threads_lock);
        put_online_cpus();
        return ret;
}
EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);

/**
 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
 * @plug_thread:        Hotplug thread descriptor
 *
 * Stops all threads on all possible cpus.
 */
void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
{
        get_online_cpus();
        mutex_lock(&smpboot_threads_lock);
        list_del(&plug_thread->list);
        smpboot_destroy_threads(plug_thread);
        mutex_unlock(&smpboot_threads_lock);
        put_online_cpus();
}
EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);

static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);

/*
 * Called to poll specified CPU's state, for example, when waiting for
 * a CPU to come online.
 */
int cpu_report_state(int cpu)
{
        return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
}

/*
 * If CPU has died properly, set its state to CPU_UP_PREPARE and
 * return success.  Otherwise, return -EBUSY if the CPU died after
 * cpu_wait_death() timed out.  And yet otherwise again, return -EAGAIN
 * if cpu_wait_death() timed out and the CPU still hasn't gotten around
 * to dying.  In the latter two cases, the CPU might not be set up
 * properly, but it is up to the arch-specific code to decide.
 * Finally, -EIO indicates an unanticipated problem.
 *
 * Note that it is permissible to omit this call entirely, as is
 * done in architectures that do no CPU-hotplug error checking.
 */
int cpu_check_up_prepare(int cpu)
{
        if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
                atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
                return 0;
        }

        switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {

        case CPU_POST_DEAD:

                /* The CPU died properly, so just start it up again. */
                atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
                return 0;

        case CPU_DEAD_FROZEN:

                /*
                 * Timeout during CPU death, so let caller know.
                 * The outgoing CPU completed its processing, but after
                 * cpu_wait_death() timed out and reported the error. The
                 * caller is free to proceed, in which case the state
                 * will be reset properly by cpu_set_state_online().
                 * Proceeding despite this -EBUSY return makes sense
                 * for systems where the outgoing CPUs take themselves
                 * offline, with no post-death manipulation required from
                 * a surviving CPU.
                 */
                return -EBUSY;

        case CPU_BROKEN:

                /*
                 * The most likely reason we got here is that there was
                 * a timeout during CPU death, and the outgoing CPU never
                 * did complete its processing.  This could happen on
                 * a virtualized system if the outgoing VCPU gets preempted
                 * for more than five seconds, and the user attempts to
                 * immediately online that same CPU.  Trying again later
                 * might return -EBUSY above, hence -EAGAIN.
                 */
                return -EAGAIN;

        default:

                /* Should not happen.  Famous last words. */
                return -EIO;
        }
}

/*
 * Mark the specified CPU online.
 *
 * Note that it is permissible to omit this call entirely, as is
 * done in architectures that do no CPU-hotplug error checking.
 */
void cpu_set_state_online(int cpu)
{
        (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
}

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Wait for the specified CPU to exit the idle loop and die.
 */
bool cpu_wait_death(unsigned int cpu, int seconds)
{
        int jf_left = seconds * HZ;
        int oldstate;
        bool ret = true;
        int sleep_jf = 1;

        might_sleep();

        /* The outgoing CPU will normally get done quite quickly. */
        if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
                goto update_state;
        udelay(5);

        /* But if the outgoing CPU dawdles, wait increasingly long times. */
        while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
                schedule_timeout_uninterruptible(sleep_jf);
                jf_left -= sleep_jf;
                if (jf_left <= 0)
                        break;
                sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
        }
update_state:
        oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
        if (oldstate == CPU_DEAD) {
                /* Outgoing CPU died normally, update state. */
                smp_mb(); /* atomic_read() before update. */
                atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
        } else {
                /* Outgoing CPU still hasn't died, set state accordingly. */
                if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
                                   oldstate, CPU_BROKEN) != oldstate)
                        goto update_state;
                ret = false;
        }
        return ret;
}

/*
 * Called by the outgoing CPU to report its successful death.  Return
 * false if this report follows the surviving CPU's timing out.
 *
 * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
 * timed out.  This approach allows architectures to omit calls to
 * cpu_check_up_prepare() and cpu_set_state_online() without defeating
 * the next cpu_wait_death()'s polling loop.
 */
bool cpu_report_death(void)
{
        int oldstate;
        int newstate;
        int cpu = smp_processor_id();

        do {
                oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
                if (oldstate != CPU_BROKEN)
                        newstate = CPU_DEAD;
                else
                        newstate = CPU_DEAD_FROZEN;
        } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
                                oldstate, newstate) != oldstate);
        return newstate == CPU_DEAD;
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */