kref.h revision 1.14 
1/*	$NetBSD: kref.h,v 1.14 2023/02/24 11:02:06 riastradh Exp $	*/
2
3/*-
4 * Copyright (c) 2013 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Taylor R. Campbell.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32#ifndef _LINUX_KREF_H_
33#define _LINUX_KREF_H_
34
35#include <sys/types.h>
36#include <sys/atomic.h>
37#include <sys/systm.h>
38
39#include <linux/atomic.h>
40#include <linux/refcount.h>
41#include <linux/mutex.h>
42#include <linux/spinlock.h>
43
44struct kref {
45	unsigned int kr_count;
46};
47
48static inline void
49kref_init(struct kref *kref)
50{
51	atomic_store_relaxed(&kref->kr_count, 1);
52}
53
54static inline void
55kref_get(struct kref *kref)
56{
57	const unsigned int count __unused =
58	    atomic_inc_uint_nv(&kref->kr_count);
59
60	KASSERTMSG((count > 1), "getting released kref");
61}
62
63static inline bool
64kref_get_unless_zero(struct kref *kref)
65{
66	unsigned count;
67
68	do {
69		count = atomic_load_relaxed(&kref->kr_count);
70		if ((count == 0) || (count == UINT_MAX))
71			return false;
72	} while (atomic_cas_uint(&kref->kr_count, count, (count + 1)) !=
73	    count);
74
75	return true;
76}
77
78static inline int
79kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *))
80{
81	unsigned int old, new;
82
83	membar_release();
84
85	do {
86		old = atomic_load_relaxed(&kref->kr_count);
87		KASSERTMSG((count <= old), "overreleasing kref: %u - %u",
88		    old, count);
89		new = (old - count);
90	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
91
92	if (new == 0) {
93		membar_acquire();
94		(*release)(kref);
95		return 1;
96	}
97
98	return 0;
99}
100
101static inline int
102kref_put_lock(struct kref *kref, void (*release)(struct kref *),
103    spinlock_t *interlock)
104{
105	unsigned int old, new;
106
107	membar_release();
108
109	do {
110		old = atomic_load_relaxed(&kref->kr_count);
111		KASSERT(old > 0);
112		if (old == 1) {
113			spin_lock(interlock);
114			if (atomic_add_int_nv(&kref->kr_count, -1) == 0) {
115				membar_acquire();
116				(*release)(kref);
117				return 1;
118			}
119			spin_unlock(interlock);
120			return 0;
121		}
122		new = (old - 1);
123	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
124
125	return 0;
126}
127
128static inline int
129kref_put(struct kref *kref, void (*release)(struct kref *))
130{
131
132	return kref_sub(kref, 1, release);
133}
134
135static inline int
136kref_put_mutex(struct kref *kref, void (*release)(struct kref *),
137    struct mutex *interlock)
138{
139	unsigned int old, new;
140
141	membar_release();
142
143	do {
144		old = atomic_load_relaxed(&kref->kr_count);
145		KASSERT(old > 0);
146		if (old == 1) {
147			mutex_lock(interlock);
148			if (atomic_add_int_nv(&kref->kr_count, -1) == 0) {
149				membar_acquire();
150				(*release)(kref);
151				return 1;
152			}
153			mutex_unlock(interlock);
154			return 0;
155		}
156		new = (old - 1);
157	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
158
159	return 0;
160}
161
162static inline unsigned
163kref_read(const struct kref *kref)
164{
165
166	return atomic_load_relaxed(&kref->kr_count);
167}
168
169/*
170 * Not native to Linux.  Mostly used for assertions...
171 */
172
173static inline bool
174kref_referenced_p(struct kref *kref)
175{
176
177	return (0 < kref->kr_count);
178}
179
180static inline bool
181kref_exclusive_p(struct kref *kref)
182{
183
184	KASSERT(0 < kref->kr_count);
185	return (kref->kr_count == 1);
186}
187
188#endif  /* _LINUX_KREF_H_ */
189