/*
   * kernel/freezer.c - Function to freeze a process
   *
   * Originally from kernel/power/process.c
   */
  
  #include <linux/interrupt.h>
  #include <linux/suspend.h>

  #include <linux/export.h>

  #include <linux/syscalls.h>
  #include <linux/freezer.h>

  #include <linux/kthread.h>

  /* total number of freezing conditions in effect */
  atomic_t system_freezing_cnt = ATOMIC_INIT(0);
  EXPORT_SYMBOL(system_freezing_cnt);

  /* indicate whether PM freezing is in effect, protected by
   * system_transition_mutex
   */

  bool pm_freezing;
  bool pm_nosig_freezing;

  /*
   * Temporary export for the deadlock workaround in ata_scsi_hotplug().
   * Remove once the hack becomes unnecessary.
   */
  EXPORT_SYMBOL_GPL(pm_freezing);

  /* protects freezing and frozen transitions */
  static DEFINE_SPINLOCK(freezer_lock);

  /**
   * freezing_slow_path - slow path for testing whether a task needs to be frozen
   * @p: task to be tested
   *
   * This function is called by freezing() if system_freezing_cnt isn't zero
   * and tests whether @p needs to enter and stay in frozen state.  Can be
   * called under any context.  The freezers are responsible for ensuring the
   * target tasks see the updated state.
   */
  bool freezing_slow_path(struct task_struct *p)
  {

  	if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))

  		return false;

  	if (test_tsk_thread_flag(p, TIF_MEMDIE))

  		return false;

  	if (pm_nosig_freezing || cgroup_freezing(p))
  		return true;

  	if (pm_freezing && !(p->flags & PF_KTHREAD))

  		return true;
  
  	return false;
  }
  EXPORT_SYMBOL(freezing_slow_path);

  /* Refrigerator is place where frozen processes are stored :-). */

  bool __refrigerator(bool check_kthr_stop)

  {
  	/* Hmm, should we be allowed to suspend when there are realtime
  	   processes around? */

  	bool was_frozen = false;

  	long save = current->state;

  	pr_debug("%s entered refrigerator
  ", current->comm);

  	for (;;) {
  		set_current_state(TASK_UNINTERRUPTIBLE);

  
  		spin_lock_irq(&freezer_lock);
  		current->flags |= PF_FROZEN;

  		if (!freezing(current) ||

  		    (check_kthr_stop && kthread_should_stop()))

  			current->flags &= ~PF_FROZEN;
  		spin_unlock_irq(&freezer_lock);
  
  		if (!(current->flags & PF_FROZEN))

  			break;

  		was_frozen = true;

  		schedule();
  	}

  	pr_debug("%s left refrigerator
  ", current->comm);

  
  	/*
  	 * Restore saved task state before returning.  The mb'd version
  	 * needs to be used; otherwise, it might silently break
  	 * synchronization which depends on ordered task state change.
  	 */
  	set_current_state(save);

  
  	return was_frozen;

  }

  EXPORT_SYMBOL(__refrigerator);

  
  static void fake_signal_wake_up(struct task_struct *p)
  {
  	unsigned long flags;

  	if (lock_task_sighand(p, &flags)) {
  		signal_wake_up(p, 0);
  		unlock_task_sighand(p, &flags);
  	}

  }
  
  /**

   * freeze_task - send a freeze request to given task
   * @p: task to send the request to

   *

   * If @p is freezing, the freeze request is sent either by sending a fake
   * signal (if it's not a kernel thread) or waking it up (if it's a kernel
   * thread).

   *
   * RETURNS:
   * %false, if @p is not freezing or already frozen; %true, otherwise

   */

  bool freeze_task(struct task_struct *p)

  {

  	unsigned long flags;

  	/*
  	 * This check can race with freezer_do_not_count, but worst case that
  	 * will result in an extra wakeup being sent to the task.  It does not
  	 * race with freezer_count(), the barriers in freezer_count() and
  	 * freezer_should_skip() ensure that either freezer_count() sees
  	 * freezing == true in try_to_freeze() and freezes, or
  	 * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
  	 * normally.
  	 */
  	if (freezer_should_skip(p))
  		return false;

  	spin_lock_irqsave(&freezer_lock, flags);

  	if (!freezing(p) || frozen(p)) {
  		spin_unlock_irqrestore(&freezer_lock, flags);
  		return false;
  	}

  	if (!(p->flags & PF_KTHREAD))

  		fake_signal_wake_up(p);

  	else

  		wake_up_state(p, TASK_INTERRUPTIBLE);

  	spin_unlock_irqrestore(&freezer_lock, flags);

  	return true;

  }

  void __thaw_task(struct task_struct *p)

  {

  	unsigned long flags;

  	spin_lock_irqsave(&freezer_lock, flags);

  	if (frozen(p))

  		wake_up_process(p);

  	spin_unlock_irqrestore(&freezer_lock, flags);

  }

  
  /**

   * set_freezable - make %current freezable

   *
   * Mark %current freezable and enter refrigerator if necessary.
   */

  bool set_freezable(void)

  {
  	might_sleep();
  
  	/*
  	 * Modify flags while holding freezer_lock.  This ensures the
  	 * freezer notices that we aren't frozen yet or the freezing
  	 * condition is visible to try_to_freeze() below.
  	 */
  	spin_lock_irq(&freezer_lock);
  	current->flags &= ~PF_NOFREEZE;

  	spin_unlock_irq(&freezer_lock);
  
  	return try_to_freeze();
  }

  EXPORT_SYMBOL(set_freezable);