locking/refcount: Add refcount_t API kernel-doc comments

#include <linux/mutex.h>

#include <linux/spinlock.h>

/**

 * refcount_t - variant of atomic_t specialized for reference counts

 * @refs: atomic_t counter field

 *

 * The counter saturates at UINT_MAX and will not move once

 * there. This avoids wrapping the counter and causing 'spurious'

 * use-after-free bugs.

 */

typedef struct refcount_struct {

	atomic_t refs;

} refcount_t;

#define REFCOUNT_INIT(n)	{ .refs = ATOMIC_INIT(n), }

/**

 * refcount_set - set a refcount's value

 * @r: the refcount

 * @n: value to which the refcount will be set

 */

static inline void refcount_set(refcount_t *r, unsigned int n)

{

	atomic_set(&r->refs, n);

}

/**

 * refcount_read - get a refcount's value

 * @r: the refcount

 *

 * Return: the refcount's value

 */

static inline unsigned int refcount_read(const refcount_t *r)

{

	return atomic_read(&r->refs);

#include <linux/refcount.h>

#include <linux/bug.h>

/**

 * refcount_add_not_zero - add a value to a refcount unless it is 0

 * @i: the value to add to the refcount

 * @r: the refcount

 *

 * Will saturate at UINT_MAX and WARN.

 *

 * Provides no memory ordering, it is assumed the caller has guaranteed the

 * object memory to be stable (RCU, etc.). It does provide a control dependency

 * and thereby orders future stores. See the comment on top.

 *

 * Use of this function is not recommended for the normal reference counting

 * use case in which references are taken and released one at a time.  In these

 * cases, refcount_inc(), or one of its variants, should instead be used to

 * increment a reference count.

 *

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

 */

bool refcount_add_not_zero(unsigned int i, refcount_t *r)

{

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

}

EXPORT_SYMBOL_GPL(refcount_add_not_zero);

/**

 * refcount_add - add a value to a refcount

 * @i: the value to add to the refcount

 * @r: the refcount

 *

 * Similar to atomic_add(), but will saturate at UINT_MAX and WARN.

 *

 * Provides no memory ordering, it is assumed the caller has guaranteed the

 * object memory to be stable (RCU, etc.). It does provide a control dependency

 * and thereby orders future stores. See the comment on top.

 *

 * Use of this function is not recommended for the normal reference counting

 * use case in which references are taken and released one at a time.  In these

 * cases, refcount_inc(), or one of its variants, should instead be used to

 * increment a reference count.

 */

void refcount_add(unsigned int i, refcount_t *r)

{

	WARN_ONCE(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");

}

EXPORT_SYMBOL_GPL(refcount_add);

/*

 * Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.

/**

 * refcount_inc_not_zero - increment a refcount unless it is 0

 * @r: the refcount to increment

 *

 * Similar to atomic_inc_not_zero(), but will saturate at UINT_MAX and WARN.

 *

 * Provides no memory ordering, it is assumed the caller has guaranteed the

 * object memory to be stable (RCU, etc.). It does provide a control dependency

 * and thereby orders future stores. See the comment on top.

 *

 * Return: true if the increment was successful, false otherwise

 */

bool refcount_inc_not_zero(refcount_t *r)

{

}

EXPORT_SYMBOL_GPL(refcount_inc_not_zero);

/*

 * Similar to atomic_inc(), will saturate at UINT_MAX and WARN.

/**

 * refcount_inc - increment a refcount

 * @r: the refcount to increment

 *

 * Similar to atomic_inc(), but will saturate at UINT_MAX and WARN.

 *

 * Provides no memory ordering, it is assumed the caller already has a

 * reference on the object, will WARN when this is not so.

 * reference on the object.

 *

 * Will WARN if the refcount is 0, as this represents a possible use-after-free

 * condition.

 */

void refcount_inc(refcount_t *r)

{

}

EXPORT_SYMBOL_GPL(refcount_inc);

/**

 * refcount_sub_and_test - subtract from a refcount and test if it is 0

 * @i: amount to subtract from the refcount

 * @r: the refcount

 *

 * Similar to atomic_dec_and_test(), but it will WARN, return false and

 * ultimately leak on underflow and will fail to decrement when saturated

 * at UINT_MAX.

 *

 * 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.

 *

 * Use of this function is not recommended for the normal reference counting

 * use case in which references are taken and released one at a time.  In these

 * cases, refcount_dec(), or one of its variants, should instead be used to

 * decrement a reference count.

 *

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

 */

bool refcount_sub_and_test(unsigned int i, refcount_t *r)

{

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

}

EXPORT_SYMBOL_GPL(refcount_sub_and_test);

/*

/**

 * refcount_dec_and_test - decrement a refcount and test if it is 0

 * @r: the refcount

 *

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

 * decrement when saturated at UINT_MAX.

 *

 * 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 if the resulting refcount is 0, false otherwise

 */

bool refcount_dec_and_test(refcount_t *r)

{

}

EXPORT_SYMBOL_GPL(refcount_dec_and_test);

/*

/**

 * refcount_dec - decrement a refcount

 * @r: the refcount

 *

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

 * when saturated at UINT_MAX.

 *

 * Provides release memory ordering, such that prior loads and stores are done

 * before.

 */

void refcount_dec(refcount_t *r)

{

	WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");

}

EXPORT_SYMBOL_GPL(refcount_dec);

/*

/**

 * 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.

 *

 * 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)

{

}

EXPORT_SYMBOL_GPL(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)

{

}

EXPORT_SYMBOL_GPL(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 UINT_MAX.

 *

 * 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)

{

}

EXPORT_SYMBOL_GPL(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 UINT_MAX.

 *

 * 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)

{