1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 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 28 #ifndef __SYS_REFCOUNT_H__ 29 #define __SYS_REFCOUNT_H__ 30 31 #include <sys/types.h> 32 #include <sys/kassert.h> 33 #if !defined(_KERNEL) && !defined(_STANDALONE) 34 #include <stdbool.h> 35 #endif 36 37 #include <machine/atomic.h> 38 39 #define REFCOUNT_SATURATED(val) (((val) & (1U << 31)) != 0) 40 #define REFCOUNT_SATURATION_VALUE (3U << 30) 41 42 /* 43 * Attempt to handle reference count overflow and underflow. Force the counter 44 * to stay at the saturation value so that a counter overflow cannot trigger 45 * destruction of the containing object and instead leads to a less harmful 46 * memory leak. 47 */ 48 static __inline void 49 _refcount_update_saturated(volatile u_int *count) 50 { 51 #ifdef INVARIANTS 52 panic("refcount %p wraparound", count); 53 #else 54 atomic_store_int(count, REFCOUNT_SATURATION_VALUE); 55 #endif 56 } 57 58 static __inline void 59 refcount_init(volatile u_int *count, u_int value) 60 { 61 KASSERT(!REFCOUNT_SATURATED(value), 62 ("invalid initial refcount value %u", value)); 63 atomic_store_int(count, value); 64 } 65 66 static __inline u_int 67 refcount_load(volatile const u_int *count) 68 { 69 return (atomic_load_int(count)); 70 } 71 72 static __inline u_int 73 refcount_acquire(volatile u_int *count) 74 { 75 u_int old; 76 77 old = atomic_fetchadd_int(count, 1); 78 if (__predict_false(REFCOUNT_SATURATED(old))) 79 _refcount_update_saturated(count); 80 81 return (old); 82 } 83 84 static __inline u_int 85 refcount_acquiren(volatile u_int *count, u_int n) 86 { 87 u_int old; 88 89 KASSERT(n < REFCOUNT_SATURATION_VALUE / 2, 90 ("refcount_acquiren: n=%u too large", n)); 91 old = atomic_fetchadd_int(count, n); 92 if (__predict_false(REFCOUNT_SATURATED(old))) 93 _refcount_update_saturated(count); 94 95 return (old); 96 } 97 98 static __inline __result_use_check bool 99 refcount_acquire_checked(volatile u_int *count) 100 { 101 u_int old; 102 103 old = atomic_load_int(count); 104 for (;;) { 105 if (__predict_false(REFCOUNT_SATURATED(old + 1))) 106 return (false); 107 if (__predict_true(atomic_fcmpset_int(count, &old, 108 old + 1) == 1)) 109 return (true); 110 } 111 } 112 113 /* 114 * This functions returns non-zero if the refcount was 115 * incremented. Else zero is returned. 116 */ 117 static __inline __result_use_check bool 118 refcount_acquire_if_gt(volatile u_int *count, u_int n) 119 { 120 u_int old; 121 122 old = atomic_load_int(count); 123 for (;;) { 124 if (old <= n) 125 return (false); 126 if (__predict_false(REFCOUNT_SATURATED(old))) 127 return (true); 128 if (atomic_fcmpset_int(count, &old, old + 1)) 129 return (true); 130 } 131 } 132 133 static __inline __result_use_check bool 134 refcount_acquire_if_not_zero(volatile u_int *count) 135 { 136 137 return (refcount_acquire_if_gt(count, 0)); 138 } 139 140 static __inline bool 141 refcount_releasen(volatile u_int *count, u_int n) 142 { 143 u_int old; 144 145 KASSERT(n < REFCOUNT_SATURATION_VALUE / 2, 146 ("refcount_releasen: n=%u too large", n)); 147 148 atomic_thread_fence_rel(); 149 old = atomic_fetchadd_int(count, -n); 150 if (__predict_false(old < n || REFCOUNT_SATURATED(old))) { 151 _refcount_update_saturated(count); 152 return (false); 153 } 154 if (old > n) 155 return (false); 156 157 /* 158 * Last reference. Signal the user to call the destructor. 159 * 160 * Ensure that the destructor sees all updates. This synchronizes with 161 * release fences from all routines which drop the count. 162 */ 163 atomic_thread_fence_acq(); 164 return (true); 165 } 166 167 static __inline bool 168 refcount_release(volatile u_int *count) 169 { 170 171 return (refcount_releasen(count, 1)); 172 } 173 174 #define _refcount_release_if_cond(cond, name) \ 175 static __inline __result_use_check bool \ 176 _refcount_release_if_##name(volatile u_int *count, u_int n) \ 177 { \ 178 u_int old; \ 179 \ 180 KASSERT(n > 0, ("%s: zero increment", __func__)); \ 181 old = atomic_load_int(count); \ 182 for (;;) { \ 183 if (!(cond)) \ 184 return (false); \ 185 if (__predict_false(REFCOUNT_SATURATED(old))) \ 186 return (false); \ 187 if (atomic_fcmpset_rel_int(count, &old, old - 1)) \ 188 return (true); \ 189 } \ 190 } 191 _refcount_release_if_cond(old > n, gt) 192 _refcount_release_if_cond(old == n, eq) 193 194 static __inline __result_use_check bool 195 refcount_release_if_gt(volatile u_int *count, u_int n) 196 { 197 198 return (_refcount_release_if_gt(count, n)); 199 } 200 201 static __inline __result_use_check bool 202 refcount_release_if_last(volatile u_int *count) 203 { 204 205 if (_refcount_release_if_eq(count, 1)) { 206 /* See the comment in refcount_releasen(). */ 207 atomic_thread_fence_acq(); 208 return (true); 209 } 210 return (false); 211 } 212 213 static __inline __result_use_check bool 214 refcount_release_if_not_last(volatile u_int *count) 215 { 216 217 return (_refcount_release_if_gt(count, 1)); 218 } 219 220 #endif /* !__SYS_REFCOUNT_H__ */ 221