1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org> 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 * 27 * $FreeBSD$ 28 */ 29 30 #ifndef __SYS_REFCOUNT_H__ 31 #define __SYS_REFCOUNT_H__ 32 33 #include <machine/atomic.h> 34 35 #if defined(_KERNEL) || defined(_STANDALONE) 36 #include <sys/systm.h> 37 #else 38 #include <stdbool.h> 39 #define KASSERT(exp, msg) /* */ 40 #endif 41 42 #define REFCOUNT_SATURATED(val) (((val) & (1U << 31)) != 0) 43 #define REFCOUNT_SATURATION_VALUE (3U << 30) 44 45 /* 46 * Attempt to handle reference count overflow and underflow. Force the counter 47 * to stay at the saturation value so that a counter overflow cannot trigger 48 * destruction of the containing object and instead leads to a less harmful 49 * memory leak. 50 */ 51 static __inline void 52 _refcount_update_saturated(volatile u_int *count) 53 { 54 #ifdef INVARIANTS 55 panic("refcount %p wraparound", count); 56 #else 57 atomic_store_int(count, REFCOUNT_SATURATION_VALUE); 58 #endif 59 } 60 61 static __inline void 62 refcount_init(volatile u_int *count, u_int value) 63 { 64 KASSERT(!REFCOUNT_SATURATED(value), 65 ("invalid initial refcount value %u", value)); 66 atomic_store_int(count, value); 67 } 68 69 static __inline u_int 70 refcount_load(volatile u_int *count) 71 { 72 return (atomic_load_int(count)); 73 } 74 75 static __inline u_int 76 refcount_acquire(volatile u_int *count) 77 { 78 u_int old; 79 80 old = atomic_fetchadd_int(count, 1); 81 if (__predict_false(REFCOUNT_SATURATED(old))) 82 _refcount_update_saturated(count); 83 84 return (old); 85 } 86 87 static __inline u_int 88 refcount_acquiren(volatile u_int *count, u_int n) 89 { 90 u_int old; 91 92 KASSERT(n < REFCOUNT_SATURATION_VALUE / 2, 93 ("refcount_acquiren: n=%u too large", n)); 94 old = atomic_fetchadd_int(count, n); 95 if (__predict_false(REFCOUNT_SATURATED(old))) 96 _refcount_update_saturated(count); 97 98 return (old); 99 } 100 101 static __inline __result_use_check bool 102 refcount_acquire_checked(volatile u_int *count) 103 { 104 u_int old; 105 106 old = atomic_load_int(count); 107 for (;;) { 108 if (__predict_false(REFCOUNT_SATURATED(old + 1))) 109 return (false); 110 if (__predict_true(atomic_fcmpset_int(count, &old, 111 old + 1) == 1)) 112 return (true); 113 } 114 } 115 116 /* 117 * This functions returns non-zero if the refcount was 118 * incremented. Else zero is returned. 119 */ 120 static __inline __result_use_check bool 121 refcount_acquire_if_gt(volatile u_int *count, u_int n) 122 { 123 u_int old; 124 125 old = atomic_load_int(count); 126 for (;;) { 127 if (old <= n) 128 return (false); 129 if (__predict_false(REFCOUNT_SATURATED(old))) 130 return (true); 131 if (atomic_fcmpset_int(count, &old, old + 1)) 132 return (true); 133 } 134 } 135 136 static __inline __result_use_check bool 137 refcount_acquire_if_not_zero(volatile u_int *count) 138 { 139 140 return (refcount_acquire_if_gt(count, 0)); 141 } 142 143 static __inline bool 144 refcount_releasen(volatile u_int *count, u_int n) 145 { 146 u_int old; 147 148 KASSERT(n < REFCOUNT_SATURATION_VALUE / 2, 149 ("refcount_releasen: n=%u too large", n)); 150 151 atomic_thread_fence_rel(); 152 old = atomic_fetchadd_int(count, -n); 153 if (__predict_false(old < n || REFCOUNT_SATURATED(old))) { 154 _refcount_update_saturated(count); 155 return (false); 156 } 157 if (old > n) 158 return (false); 159 160 /* 161 * Last reference. Signal the user to call the destructor. 162 * 163 * Ensure that the destructor sees all updates. This synchronizes with 164 * release fences from all routines which drop the count. 165 */ 166 atomic_thread_fence_acq(); 167 return (true); 168 } 169 170 static __inline bool 171 refcount_release(volatile u_int *count) 172 { 173 174 return (refcount_releasen(count, 1)); 175 } 176 177 #define _refcount_release_if_cond(cond, name) \ 178 static __inline __result_use_check bool \ 179 _refcount_release_if_##name(volatile u_int *count, u_int n) \ 180 { \ 181 u_int old; \ 182 \ 183 KASSERT(n > 0, ("%s: zero increment", __func__)); \ 184 old = atomic_load_int(count); \ 185 for (;;) { \ 186 if (!(cond)) \ 187 return (false); \ 188 if (__predict_false(REFCOUNT_SATURATED(old))) \ 189 return (false); \ 190 if (atomic_fcmpset_rel_int(count, &old, old - 1)) \ 191 return (true); \ 192 } \ 193 } 194 _refcount_release_if_cond(old > n, gt) 195 _refcount_release_if_cond(old == n, eq) 196 197 static __inline __result_use_check bool 198 refcount_release_if_gt(volatile u_int *count, u_int n) 199 { 200 201 return (_refcount_release_if_gt(count, n)); 202 } 203 204 static __inline __result_use_check bool 205 refcount_release_if_last(volatile u_int *count) 206 { 207 208 if (_refcount_release_if_eq(count, 1)) { 209 /* See the comment in refcount_releasen(). */ 210 atomic_thread_fence_acq(); 211 return (true); 212 } 213 return (false); 214 } 215 216 static __inline __result_use_check bool 217 refcount_release_if_not_last(volatile u_int *count) 218 { 219 220 return (_refcount_release_if_gt(count, 1)); 221 } 222 223 #endif /* !__SYS_REFCOUNT_H__ */ 224