1 /* $NetBSD: kref.h,v 1.13 2022/04/09 23:43:39 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 49 kref_init(struct kref *kref) 50 { 51 atomic_store_relaxed(&kref->kr_count, 1); 52 } 53 54 static inline void 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 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 79 kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *)) 80 { 81 unsigned int old, new; 82 83 #ifndef __HAVE_ATOMIC_AS_MEMBAR 84 membar_release(); 85 #endif 86 87 do { 88 old = atomic_load_relaxed(&kref->kr_count); 89 KASSERTMSG((count <= old), "overreleasing kref: %u - %u", 90 old, count); 91 new = (old - count); 92 } while (atomic_cas_uint(&kref->kr_count, old, new) != old); 93 94 if (new == 0) { 95 #ifndef __HAVE_ATOMIC_AS_MEMBAR 96 membar_acquire(); 97 #endif 98 (*release)(kref); 99 return 1; 100 } 101 102 return 0; 103 } 104 105 static inline int 106 kref_put_lock(struct kref *kref, void (*release)(struct kref *), 107 spinlock_t *interlock) 108 { 109 unsigned int old, new; 110 111 #ifndef __HAVE_ATOMIC_AS_MEMBAR 112 membar_release(); 113 #endif 114 115 do { 116 old = atomic_load_relaxed(&kref->kr_count); 117 KASSERT(old > 0); 118 if (old == 1) { 119 spin_lock(interlock); 120 if (atomic_add_int_nv(&kref->kr_count, -1) == 0) { 121 #ifndef __HAVE_ATOMIC_AS_MEMBAR 122 membar_acquire(); 123 #endif 124 (*release)(kref); 125 return 1; 126 } 127 spin_unlock(interlock); 128 return 0; 129 } 130 new = (old - 1); 131 } while (atomic_cas_uint(&kref->kr_count, old, new) != old); 132 133 return 0; 134 } 135 136 static inline int 137 kref_put(struct kref *kref, void (*release)(struct kref *)) 138 { 139 140 return kref_sub(kref, 1, release); 141 } 142 143 static inline int 144 kref_put_mutex(struct kref *kref, void (*release)(struct kref *), 145 struct mutex *interlock) 146 { 147 unsigned int old, new; 148 149 #ifndef __HAVE_ATOMIC_AS_MEMBAR 150 membar_release(); 151 #endif 152 153 do { 154 old = atomic_load_relaxed(&kref->kr_count); 155 KASSERT(old > 0); 156 if (old == 1) { 157 mutex_lock(interlock); 158 if (atomic_add_int_nv(&kref->kr_count, -1) == 0) { 159 #ifndef __HAVE_ATOMIC_AS_MEMBAR 160 membar_acquire(); 161 #endif 162 (*release)(kref); 163 return 1; 164 } 165 mutex_unlock(interlock); 166 return 0; 167 } 168 new = (old - 1); 169 } while (atomic_cas_uint(&kref->kr_count, old, new) != old); 170 171 return 0; 172 } 173 174 static inline unsigned 175 kref_read(const struct kref *kref) 176 { 177 178 return atomic_load_relaxed(&kref->kr_count); 179 } 180 181 /* 182 * Not native to Linux. Mostly used for assertions... 183 */ 184 185 static inline bool 186 kref_referenced_p(struct kref *kref) 187 { 188 189 return (0 < kref->kr_count); 190 } 191 192 static inline bool 193 kref_exclusive_p(struct kref *kref) 194 { 195 196 KASSERT(0 < kref->kr_count); 197 return (kref->kr_count == 1); 198 } 199 200 #endif /* _LINUX_KREF_H_ */ 201