/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#ifndef __SYS_REFCOUNT_H__
#define __SYS_REFCOUNT_H__
#include <machine/atomic.h>
#if defined(_KERNEL) || defined(_STANDALONE)
#include <sys/systm.h>
#else
#include <stdbool.h>
#define KASSERT(exp, msg) /* */
#endif
#define REFCOUNT_SATURATED(val) (((val) & (1U << 31)) != 0)
#define REFCOUNT_SATURATION_VALUE (3U << 30)
/*
* Attempt to handle reference count overflow and underflow. Force the counter
* to stay at the saturation value so that a counter overflow cannot trigger
* destruction of the containing object and instead leads to a less harmful
* memory leak.
*/
static __inline void
_refcount_update_saturated(volatile u_int *count)
{
#ifdef INVARIANTS
panic("refcount %p wraparound", count);
#else
atomic_store_int(count, REFCOUNT_SATURATION_VALUE);
#endif
}
static __inline void
refcount_init(volatile u_int *count, u_int value)
{
KASSERT(!REFCOUNT_SATURATED(value),
("invalid initial refcount value %u", value));
atomic_store_int(count, value);
}
static __inline u_int
refcount_load(volatile u_int *count)
{
return (atomic_load_int(count));
}
static __inline u_int
refcount_acquire(volatile u_int *count)
{
u_int old;
old = atomic_fetchadd_int(count, 1);
if (__predict_false(REFCOUNT_SATURATED(old)))
_refcount_update_saturated(count);
return (old);
}
static __inline u_int
refcount_acquiren(volatile u_int *count, u_int n)
{
u_int old;
KASSERT(n < REFCOUNT_SATURATION_VALUE / 2,
("refcount_acquiren: n=%u too large", n));
old = atomic_fetchadd_int(count, n);
if (__predict_false(REFCOUNT_SATURATED(old)))
_refcount_update_saturated(count);
return (old);
}
static __inline __result_use_check bool
refcount_acquire_checked(volatile u_int *count)
{
u_int old;
old = atomic_load_int(count);
for (;;) {
if (__predict_false(REFCOUNT_SATURATED(old + 1)))
return (false);
if (__predict_true(atomic_fcmpset_int(count, &old,
old + 1) == 1))
return (true);
}
}
/*
* This functions returns non-zero if the refcount was
* incremented. Else zero is returned.
*/
static __inline __result_use_check bool
refcount_acquire_if_gt(volatile u_int *count, u_int n)
{
u_int old;
old = atomic_load_int(count);
for (;;) {
if (old <= n)
return (false);
if (__predict_false(REFCOUNT_SATURATED(old)))
return (true);
if (atomic_fcmpset_int(count, &old, old + 1))
return (true);
}
}
static __inline __result_use_check bool
refcount_acquire_if_not_zero(volatile u_int *count)
{
return (refcount_acquire_if_gt(count, 0));
}
static __inline bool
refcount_releasen(volatile u_int *count, u_int n)
{
u_int old;
KASSERT(n < REFCOUNT_SATURATION_VALUE / 2,
("refcount_releasen: n=%u too large", n));
atomic_thread_fence_rel();
old = atomic_fetchadd_int(count, -n);
if (__predict_false(old < n || REFCOUNT_SATURATED(old))) {
_refcount_update_saturated(count);
return (false);
}
if (old > n)
return (false);
/*
* Last reference. Signal the user to call the destructor.
*
* Ensure that the destructor sees all updates. This synchronizes with
* release fences from all routines which drop the count.
*/
atomic_thread_fence_acq();
return (true);
}
static __inline bool
refcount_release(volatile u_int *count)
{
return (refcount_releasen(count, 1));
}
#define _refcount_release_if_cond(cond, name) \
static __inline __result_use_check bool \
_refcount_release_if_##name(volatile u_int *count, u_int n) \
{ \
u_int old; \
\
KASSERT(n > 0, ("%s: zero increment", __func__)); \
old = atomic_load_int(count); \
for (;;) { \
if (!(cond)) \
return (false); \
if (__predict_false(REFCOUNT_SATURATED(old))) \
return (false); \
if (atomic_fcmpset_rel_int(count, &old, old - 1)) \
return (true); \
} \
}
_refcount_release_if_cond(old > n, gt)
_refcount_release_if_cond(old == n, eq)
static __inline __result_use_check bool
refcount_release_if_gt(volatile u_int *count, u_int n)
{
return (_refcount_release_if_gt(count, n));
}
static __inline __result_use_check bool
refcount_release_if_last(volatile u_int *count)
{
if (_refcount_release_if_eq(count, 1)) {
/* See the comment in refcount_releasen(). */
atomic_thread_fence_acq();
return (true);
}
return (false);
}
static __inline __result_use_check bool
refcount_release_if_not_last(volatile u_int *count)
{
return (_refcount_release_if_gt(count, 1));
}
#endif /* !__SYS_REFCOUNT_H__ */
