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
44 struct kref {
45 unsigned int kr_count;
46 };
47
48 static inline void
kref_init(struct kref * kref)49 kref_init(struct kref *kref)
50 {
51 atomic_store_relaxed(&kref->kr_count, 1);
52 }
53
54 static inline void
kref_get(struct kref * kref)55 kref_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
63 static inline bool
kref_get_unless_zero(struct kref * kref)64 kref_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
78 static inline int
kref_sub(struct kref * kref,unsigned int count,void (* release)(struct kref *))79 kref_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
101 static inline int
kref_put_lock(struct kref * kref,void (* release)(struct kref *),spinlock_t * interlock)102 kref_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
128 static inline int
kref_put(struct kref * kref,void (* release)(struct kref *))129 kref_put(struct kref *kref, void (*release)(struct kref *))
130 {
131
132 return kref_sub(kref, 1, release);
133 }
134
135 static inline int
kref_put_mutex(struct kref * kref,void (* release)(struct kref *),struct mutex * interlock)136 kref_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
162 static inline unsigned
kref_read(const struct kref * kref)163 kref_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
173 static inline bool
kref_referenced_p(struct kref * kref)174 kref_referenced_p(struct kref *kref)
175 {
176
177 return (0 < kref->kr_count);
178 }
179
180 static inline bool
kref_exclusive_p(struct kref * kref)181 kref_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