// 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_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

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_put(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;

        cpus_read_lock();
        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);
        cpus_read_unlock();
        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)
{
        cpus_read_lock();
        mutex_lock(&smpboot_threads_lock);
        list_del(&plug_thread->list);
        smpboot_destroy_threads(plug_thread);
        mutex_unlock(&smpboot_threads_lock);
        cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);