// SPDX-License-Identifier: GPL-2.0

  /*

   * Out-of-line refcount functions.

   */

  #include <linux/mutex.h>

  #include <linux/refcount.h>

  #include <linux/spinlock.h>

  #include <linux/bug.h>

  #define REFCOUNT_WARN(str)	WARN_ONCE(1, "refcount_t: " str ".
  ")
  
  void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
  {
  	refcount_set(r, REFCOUNT_SATURATED);
  
  	switch (t) {
  	case REFCOUNT_ADD_NOT_ZERO_OVF:
  		REFCOUNT_WARN("saturated; leaking memory");
  		break;
  	case REFCOUNT_ADD_OVF:
  		REFCOUNT_WARN("saturated; leaking memory");
  		break;
  	case REFCOUNT_ADD_UAF:
  		REFCOUNT_WARN("addition on 0; use-after-free");
  		break;
  	case REFCOUNT_SUB_UAF:
  		REFCOUNT_WARN("underflow; use-after-free");
  		break;
  	case REFCOUNT_DEC_LEAK:
  		REFCOUNT_WARN("decrement hit 0; leaking memory");
  		break;
  	default:
  		REFCOUNT_WARN("unknown saturation event!?");
  	}
  }
  EXPORT_SYMBOL(refcount_warn_saturate);

  /**
   * refcount_dec_if_one - decrement a refcount if it is 1
   * @r: the refcount
   *

   * No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
   * success thereof.
   *
   * Like all decrement operations, it provides release memory order and provides
   * a control dependency.
   *
   * It can be used like a try-delete operator; this explicit case is provided
   * and not cmpxchg in generic, because that would allow implementing unsafe
   * operations.

   *
   * Return: true if the resulting refcount is 0, false otherwise

   */
  bool refcount_dec_if_one(refcount_t *r)
  {

  	int val = 1;
  
  	return atomic_try_cmpxchg_release(&r->refs, &val, 0);

  }

  EXPORT_SYMBOL(refcount_dec_if_one);

  /**
   * refcount_dec_not_one - decrement a refcount if it is not 1
   * @r: the refcount
   *

   * No atomic_t counterpart, it decrements unless the value is 1, in which case
   * it will return false.
   *
   * Was often done like: atomic_add_unless(&var, -1, 1)

   *
   * Return: true if the decrement operation was successful, false otherwise

   */
  bool refcount_dec_not_one(refcount_t *r)
  {

  	unsigned int new, val = atomic_read(&r->refs);

  	do {

  		if (unlikely(val == REFCOUNT_SATURATED))

  			return true;
  
  		if (val == 1)
  			return false;
  
  		new = val - 1;
  		if (new > val) {

  			WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.
  ");

  			return true;
  		}

  	} while (!atomic_try_cmpxchg_release(&r->refs, &val, new));

  
  	return true;
  }

  EXPORT_SYMBOL(refcount_dec_not_one);

  /**
   * refcount_dec_and_mutex_lock - return holding mutex if able to decrement
   *                               refcount to 0
   * @r: the refcount
   * @lock: the mutex to be locked
   *

   * Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail

   * to decrement when saturated at REFCOUNT_SATURATED.

   *
   * Provides release memory ordering, such that prior loads and stores are done
   * before, and provides a control dependency such that free() must come after.
   * See the comment on top.

   *
   * Return: true and hold mutex if able to decrement refcount to 0, false
   *         otherwise

   */
  bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
  {
  	if (refcount_dec_not_one(r))
  		return false;
  
  	mutex_lock(lock);
  	if (!refcount_dec_and_test(r)) {
  		mutex_unlock(lock);
  		return false;
  	}
  
  	return true;
  }

  EXPORT_SYMBOL(refcount_dec_and_mutex_lock);

  /**
   * refcount_dec_and_lock - return holding spinlock if able to decrement
   *                         refcount to 0
   * @r: the refcount
   * @lock: the spinlock to be locked
   *

   * Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to

   * decrement when saturated at REFCOUNT_SATURATED.

   *
   * Provides release memory ordering, such that prior loads and stores are done
   * before, and provides a control dependency such that free() must come after.
   * See the comment on top.

   *
   * Return: true and hold spinlock if able to decrement refcount to 0, false
   *         otherwise

   */
  bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
  {
  	if (refcount_dec_not_one(r))
  		return false;
  
  	spin_lock(lock);
  	if (!refcount_dec_and_test(r)) {
  		spin_unlock(lock);
  		return false;
  	}
  
  	return true;
  }

  EXPORT_SYMBOL(refcount_dec_and_lock);

  /**
   * refcount_dec_and_lock_irqsave - return holding spinlock with disabled
   *                                 interrupts if able to decrement refcount to 0
   * @r: the refcount
   * @lock: the spinlock to be locked
   * @flags: saved IRQ-flags if the is acquired
   *
   * Same as refcount_dec_and_lock() above except that the spinlock is acquired
   * with disabled interupts.
   *
   * Return: true and hold spinlock if able to decrement refcount to 0, false
   *         otherwise
   */
  bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,
  				   unsigned long *flags)
  {
  	if (refcount_dec_not_one(r))
  		return false;
  
  	spin_lock_irqsave(lock, *flags);
  	if (!refcount_dec_and_test(r)) {
  		spin_unlock_irqrestore(lock, *flags);
  		return false;
  	}
  
  	return true;
  }
  EXPORT_SYMBOL(refcount_dec_and_lock_irqsave);