/* Kernel thread helper functions.
 *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
 *
 * Creation is done via kthreadd, so that we get a clean environment
 * even if we're invoked from userspace (think modprobe, hotplug cpu,
 * etc.).
 */
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/cpuset.h>
#include <linux/unistd.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <trace/events/sched.h>

static DEFINE_SPINLOCK(kthread_create_lock);
static LIST_HEAD(kthread_create_list);
struct task_struct *kthreadd_task;

struct kthread_create_info
{
        /* Information passed to kthread() from kthreadd. */
        int (*threadfn)(void *data);
        void *data;

        /* Result passed back to kthread_create() from kthreadd. */
        struct task_struct *result;
        struct completion done;

        struct list_head list;
};

struct kthread {
        int should_stop;
        struct completion exited;
};

#define to_kthread(tsk) \
        container_of((tsk)->vfork_done, struct kthread, exited)

/**
 * kthread_should_stop - should this kthread return now?
 *
 * When someone calls kthread_stop() on your kthread, it will be woken
 * and this will return true.  You should then return, and your return
 * value will be passed through to kthread_stop().
 */
int kthread_should_stop(void)
{
        return to_kthread(current)->should_stop;
}
EXPORT_SYMBOL(kthread_should_stop);

static int kthread(void *_create)
{
        /* Copy data: it's on kthread's stack */
        struct kthread_create_info *create = _create;
        int (*threadfn)(void *data) = create->threadfn;
        void *data = create->data;
        struct kthread self;
        int ret;

        self.should_stop = 0;
        init_completion(&self.exited);
        current->vfork_done = &self.exited;

        /* OK, tell user we're spawned, wait for stop or wakeup */
        __set_current_state(TASK_UNINTERRUPTIBLE);
        create->result = current;
        complete(&create->done);
        schedule();

        ret = -EINTR;
        if (!self.should_stop)
                ret = threadfn(data);

        /* we can't just return, we must preserve "self" on stack */
        do_exit(ret);
}

static void create_kthread(struct kthread_create_info *create)
{
        int pid;

        /* We want our own signal handler (we take no signals by default). */
        pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
        if (pid < 0) {
                create->result = ERR_PTR(pid);
                complete(&create->done);
        }
}

/**
 * kthread_create - create a kthread.
 * @threadfn: the function to run until signal_pending(current).
 * @data: data ptr for @threadfn.
 * @namefmt: printf-style name for the thread.
 *
 * Description: This helper function creates and names a kernel
 * thread.  The thread will be stopped: use wake_up_process() to start
 * it.  See also kthread_run(), kthread_create_on_cpu().
 *
 * When woken, the thread will run @threadfn() with @data as its
 * argument. @threadfn() can either call do_exit() directly if it is a
 * standalone thread for which noone will call kthread_stop(), or
 * return when 'kthread_should_stop()' is true (which means
 * kthread_stop() has been called).  The return value should be zero
 * or a negative error number; it will be passed to kthread_stop().
 *
 * Returns a task_struct or ERR_PTR(-ENOMEM).
 */
struct task_struct *kthread_create(int (*threadfn)(void *data),
                                   void *data,
                                   const char namefmt[],
                                   ...)
{
        struct kthread_create_info create;

        create.threadfn = threadfn;
        create.data = data;
        init_completion(&create.done);

        spin_lock(&kthread_create_lock);
        list_add_tail(&create.list, &kthread_create_list);
        spin_unlock(&kthread_create_lock);

        wake_up_process(kthreadd_task);
        wait_for_completion(&create.done);

        if (!IS_ERR(create.result)) {
                struct sched_param param = { .sched_priority = 0 };
                va_list args;

                va_start(args, namefmt);
                vsnprintf(create.result->comm, sizeof(create.result->comm),
                          namefmt, args);
                va_end(args);
                /*
                 * root may have changed our (kthreadd's) priority or CPU mask.
                 * The kernel thread should not inherit these properties.
                 */
                sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
                set_cpus_allowed_ptr(create.result, cpu_all_mask);
        }
        return create.result;
}
EXPORT_SYMBOL(kthread_create);

/**
 * kthread_stop - stop a thread created by kthread_create().
 * @k: thread created by kthread_create().
 *
 * Sets kthread_should_stop() for @k to return true, wakes it, and
 * waits for it to exit. This can also be called after kthread_create()
 * instead of calling wake_up_process(): the thread will exit without
 * calling threadfn().
 *
 * If threadfn() may call do_exit() itself, the caller must ensure
 * task_struct can't go away.
 *
 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 * was never called.
 */
int kthread_stop(struct task_struct *k)
{
        struct kthread *kthread;
        int ret;

        trace_sched_kthread_stop(k);
        get_task_struct(k);

        kthread = to_kthread(k);
        barrier(); /* it might have exited */
        if (k->vfork_done != NULL) {
                kthread->should_stop = 1;
                wake_up_process(k);
                wait_for_completion(&kthread->exited);
        }
        ret = k->exit_code;

        put_task_struct(k);
        trace_sched_kthread_stop_ret(ret);

        return ret;
}
EXPORT_SYMBOL(kthread_stop);

int kthreadd(void *unused)
{
        struct task_struct *tsk = current;

        /* Setup a clean context for our children to inherit. */
        set_task_comm(tsk, "kthreadd");
        ignore_signals(tsk);
        set_cpus_allowed_ptr(tsk, cpu_all_mask);
        set_mems_allowed(node_possible_map);

        current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;

        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);
                if (list_empty(&kthread_create_list))
                        schedule();
                __set_current_state(TASK_RUNNING);

                spin_lock(&kthread_create_lock);
                while (!list_empty(&kthread_create_list)) {
                        struct kthread_create_info *create;

                        create = list_entry(kthread_create_list.next,
                                            struct kthread_create_info, list);
                        list_del_init(&create->list);
                        spin_unlock(&kthread_create_lock);

                        create_kthread(create);

                        spin_lock(&kthread_create_lock);
                }
                spin_unlock(&kthread_create_lock);
        }

        return 0;
}