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/* 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/unistd.h>

#include <linux/file.h>

#include <linux/module.h>

#include <linux/mutex.h>

#include <asm/semaphore.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;

        struct completion started;

        /* Result passed back to kthread_create() from kthreadd. */

        struct task_struct *result;

        struct completion done;

        struct list_head list;

};

struct kthread_stop_info

{

        struct task_struct *k;

        int err;

        struct completion done;

};

/* Thread stopping is done by setthing this var: lock serializes

 * multiple kthread_stop calls. */

static DEFINE_MUTEX(kthread_stop_lock);

static struct kthread_stop_info kthread_stop_info;

/**

 * 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 (kthread_stop_info.k == current);

}

EXPORT_SYMBOL(kthread_should_stop);

static int kthread(void *_create)

{

        struct kthread_create_info *create = _create;

        int (*threadfn)(void *data);

        void *data;

        int ret = -EINTR;

        /* Copy data: it's on kthread's stack */

        threadfn = create->threadfn;

        data = create->data;

        /* OK, tell user we're spawned, wait for stop or wakeup */

        __set_current_state(TASK_UNINTERRUPTIBLE);

        complete(&create->started);

        schedule();

        if (!kthread_should_stop())

                ret = threadfn(data);

        /* It might have exited on its own, w/o kthread_stop.  Check. */

        if (kthread_should_stop()) {

                kthread_stop_info.err = ret;

                complete(&kthread_stop_info.done);

        }

        return 0;

}

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);

        } else {

                wait_for_completion(&create->started);

                read_lock(&tasklist_lock);

                create->result = find_task_by_pid(pid);

                read_unlock(&tasklist_lock);

        }

        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.started);

        init_completion(&create.done);

        spin_lock(&kthread_create_lock);

        list_add_tail(&create.list, &kthread_create_list);

        wake_up_process(kthreadd_task);

        spin_unlock(&kthread_create_lock);

        wait_for_completion(&create.done);

        if (!IS_ERR(create.result)) {

                va_list args;

                va_start(args, namefmt);

                vsnprintf(create.result->comm, sizeof(create.result->comm),

                          namefmt, args);

                va_end(args);

        }

        return create.result;

}

EXPORT_SYMBOL(kthread_create);

/**

 * kthread_bind - bind a just-created kthread to a cpu.

 * @k: thread created by kthread_create().

 * @cpu: cpu (might not be online, must be possible) for @k to run on.

 *

 * Description: This function is equivalent to set_cpus_allowed(),

 * except that @cpu doesn't need to be online, and the thread must be

 * stopped (i.e., just returned from kthread_create()).

 */

void kthread_bind(struct task_struct *k, unsigned int cpu)

{

        if (k->state != TASK_UNINTERRUPTIBLE) {

                WARN_ON(1);

                return;

        }

        /* Must have done schedule() in kthread() before we set_task_cpu */

        wait_task_inactive(k);

        set_task_cpu(k, cpu);

        k->cpus_allowed = cpumask_of_cpu(cpu);

}

EXPORT_SYMBOL(kthread_bind);

/**

 * 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.  Your threadfn() must not call do_exit()

 * itself if you use this function!  This can also be called after

 * kthread_create() instead of calling wake_up_process(): the thread

 * will exit without calling threadfn().

 *

 * Returns the result of threadfn(), or %-EINTR if wake_up_process()

 * was never called.

 */

int kthread_stop(struct task_struct *k)

{

        int ret;

        mutex_lock(&kthread_stop_lock);

        /* It could exit after stop_info.k set, but before wake_up_process. */

        get_task_struct(k);

        /* Must init completion *before* thread sees kthread_stop_info.k */

        init_completion(&kthread_stop_info.done);

        smp_wmb();

        /* Now set kthread_should_stop() to true, and wake it up. */

        kthread_stop_info.k = k;

        wake_up_process(k);

        put_task_struct(k);

        /* Once it dies, reset stop ptr, gather result and we're done. */

        wait_for_completion(&kthread_stop_info.done);

        kthread_stop_info.k = NULL;

        ret = kthread_stop_info.err;

        mutex_unlock(&kthread_stop_lock);

        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_user_nice(tsk, -5);

        set_cpus_allowed(tsk, CPU_MASK_ALL);

        current->flags |= PF_NOFREEZE;

        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;

}