/* 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 <linux/slab.h>
  #include <linux/freezer.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;

  	void *data;

  	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);

  /**
   * kthread_data - return data value specified on kthread creation
   * @task: kthread task in question
   *
   * Return the data value specified when kthread @task was created.
   * The caller is responsible for ensuring the validity of @task when
   * calling this function.
   */
  void *kthread_data(struct task_struct *task)
  {
  	return to_kthread(task)->data;
  }

  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;

  	self.data = data;

  	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().

   *
   * 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)) {

  		static const 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_bind - bind a just-created kthread to a cpu.
   * @p: 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 *p, unsigned int cpu)
  {
  	/* Must have done schedule() in kthread() before we set_task_cpu */
  	if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
  		WARN_ON(1);
  		return;
  	}
  
  	p->cpus_allowed = cpumask_of_cpu(cpu);
  	p->rt.nr_cpus_allowed = 1;
  	p->flags |= PF_THREAD_BOUND;
  }
  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. 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_states[N_HIGH_MEMORY]);

  	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;
  }

  void __init_kthread_worker(struct kthread_worker *worker,
  				const char *name,
  				struct lock_class_key *key)
  {
  	spin_lock_init(&worker->lock);
  	lockdep_set_class_and_name(&worker->lock, key, name);
  	INIT_LIST_HEAD(&worker->work_list);
  	worker->task = NULL;
  }
  EXPORT_SYMBOL_GPL(__init_kthread_worker);

  /**
   * kthread_worker_fn - kthread function to process kthread_worker
   * @worker_ptr: pointer to initialized kthread_worker
   *
   * This function can be used as @threadfn to kthread_create() or
   * kthread_run() with @worker_ptr argument pointing to an initialized
   * kthread_worker.  The started kthread will process work_list until
   * the it is stopped with kthread_stop().  A kthread can also call
   * this function directly after extra initialization.
   *
   * Different kthreads can be used for the same kthread_worker as long
   * as there's only one kthread attached to it at any given time.  A
   * kthread_worker without an attached kthread simply collects queued
   * kthread_works.
   */
  int kthread_worker_fn(void *worker_ptr)
  {
  	struct kthread_worker *worker = worker_ptr;
  	struct kthread_work *work;
  
  	WARN_ON(worker->task);
  	worker->task = current;
  repeat:
  	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
  
  	if (kthread_should_stop()) {
  		__set_current_state(TASK_RUNNING);
  		spin_lock_irq(&worker->lock);
  		worker->task = NULL;
  		spin_unlock_irq(&worker->lock);
  		return 0;
  	}
  
  	work = NULL;
  	spin_lock_irq(&worker->lock);
  	if (!list_empty(&worker->work_list)) {
  		work = list_first_entry(&worker->work_list,
  					struct kthread_work, node);
  		list_del_init(&work->node);
  	}
  	spin_unlock_irq(&worker->lock);
  
  	if (work) {
  		__set_current_state(TASK_RUNNING);
  		work->func(work);
  		smp_wmb();	/* wmb worker-b0 paired with flush-b1 */
  		work->done_seq = work->queue_seq;
  		smp_mb();	/* mb worker-b1 paired with flush-b0 */
  		if (atomic_read(&work->flushing))
  			wake_up_all(&work->done);
  	} else if (!freezing(current))
  		schedule();
  
  	try_to_freeze();
  	goto repeat;
  }
  EXPORT_SYMBOL_GPL(kthread_worker_fn);
  
  /**
   * queue_kthread_work - queue a kthread_work
   * @worker: target kthread_worker
   * @work: kthread_work to queue
   *
   * Queue @work to work processor @task for async execution.  @task
   * must have been created with kthread_worker_create().  Returns %true
   * if @work was successfully queued, %false if it was already pending.
   */
  bool queue_kthread_work(struct kthread_worker *worker,
  			struct kthread_work *work)
  {
  	bool ret = false;
  	unsigned long flags;
  
  	spin_lock_irqsave(&worker->lock, flags);
  	if (list_empty(&work->node)) {
  		list_add_tail(&work->node, &worker->work_list);
  		work->queue_seq++;
  		if (likely(worker->task))
  			wake_up_process(worker->task);
  		ret = true;
  	}
  	spin_unlock_irqrestore(&worker->lock, flags);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(queue_kthread_work);
  
  /**
   * flush_kthread_work - flush a kthread_work
   * @work: work to flush
   *
   * If @work is queued or executing, wait for it to finish execution.
   */
  void flush_kthread_work(struct kthread_work *work)
  {
  	int seq = work->queue_seq;
  
  	atomic_inc(&work->flushing);
  
  	/*
  	 * mb flush-b0 paired with worker-b1, to make sure either
  	 * worker sees the above increment or we see done_seq update.
  	 */
  	smp_mb__after_atomic_inc();
  
  	/* A - B <= 0 tests whether B is in front of A regardless of overflow */
  	wait_event(work->done, seq - work->done_seq <= 0);
  	atomic_dec(&work->flushing);
  
  	/*
  	 * rmb flush-b1 paired with worker-b0, to make sure our caller
  	 * sees every change made by work->func().
  	 */
  	smp_mb__after_atomic_dec();
  }
  EXPORT_SYMBOL_GPL(flush_kthread_work);
  
  struct kthread_flush_work {
  	struct kthread_work	work;
  	struct completion	done;
  };
  
  static void kthread_flush_work_fn(struct kthread_work *work)
  {
  	struct kthread_flush_work *fwork =
  		container_of(work, struct kthread_flush_work, work);
  	complete(&fwork->done);
  }
  
  /**
   * flush_kthread_worker - flush all current works on a kthread_worker
   * @worker: worker to flush
   *
   * Wait until all currently executing or pending works on @worker are
   * finished.
   */
  void flush_kthread_worker(struct kthread_worker *worker)
  {
  	struct kthread_flush_work fwork = {
  		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
  		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
  	};
  
  	queue_kthread_work(worker, &fwork.work);
  	wait_for_completion(&fwork.done);
  }
  EXPORT_SYMBOL_GPL(flush_kthread_worker);