1 /* $NetBSD: kern_mutex_obj.c,v 1.11 2023/02/24 11:02:27 riastradh Exp $ */ 2 3 /*- 4 * Copyright (c) 2008, 2019 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Andrew Doran. 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 #include <sys/cdefs.h> 33 __KERNEL_RCSID(0, "$NetBSD: kern_mutex_obj.c,v 1.11 2023/02/24 11:02:27 riastradh Exp $"); 34 35 #include <sys/param.h> 36 #include <sys/atomic.h> 37 #include <sys/mutex.h> 38 #include <sys/pool.h> 39 40 /* Mutex cache */ 41 #define MUTEX_OBJ_MAGIC 0x5aa3c85d 42 struct kmutexobj { 43 kmutex_t mo_lock; 44 u_int mo_magic; 45 u_int mo_refcnt; 46 }; 47 48 static int mutex_obj_ctor(void *, void *, int); 49 50 static pool_cache_t mutex_obj_cache __read_mostly; 51 52 /* 53 * mutex_obj_init: 54 * 55 * Initialize the mutex object store. 56 */ 57 void 58 mutex_obj_init(void) 59 { 60 61 mutex_obj_cache = pool_cache_init(sizeof(struct kmutexobj), 62 coherency_unit, 0, 0, "mutex", NULL, IPL_NONE, mutex_obj_ctor, 63 NULL, NULL); 64 } 65 66 /* 67 * mutex_obj_ctor: 68 * 69 * Initialize a new lock for the cache. 70 */ 71 static int 72 mutex_obj_ctor(void *arg, void *obj, int flags) 73 { 74 struct kmutexobj * mo = obj; 75 76 mo->mo_magic = MUTEX_OBJ_MAGIC; 77 78 return 0; 79 } 80 81 /* 82 * mutex_obj_alloc: 83 * 84 * Allocate a single lock object, waiting for memory if needed. 85 */ 86 kmutex_t * 87 mutex_obj_alloc(kmutex_type_t type, int ipl) 88 { 89 struct kmutexobj *mo; 90 91 mo = pool_cache_get(mutex_obj_cache, PR_WAITOK); 92 _mutex_init(&mo->mo_lock, type, ipl, 93 (uintptr_t)__builtin_return_address(0)); 94 mo->mo_refcnt = 1; 95 96 return (kmutex_t *)mo; 97 } 98 99 /* 100 * mutex_obj_alloc: 101 * 102 * Allocate a single lock object, failing if no memory available. 103 */ 104 kmutex_t * 105 mutex_obj_tryalloc(kmutex_type_t type, int ipl) 106 { 107 struct kmutexobj *mo; 108 109 mo = pool_cache_get(mutex_obj_cache, PR_NOWAIT); 110 if (__predict_true(mo != NULL)) { 111 _mutex_init(&mo->mo_lock, type, ipl, 112 (uintptr_t)__builtin_return_address(0)); 113 mo->mo_refcnt = 1; 114 } 115 116 return (kmutex_t *)mo; 117 } 118 119 /* 120 * mutex_obj_hold: 121 * 122 * Add a single reference to a lock object. A reference to the object 123 * must already be held, and must be held across this call. 124 */ 125 void 126 mutex_obj_hold(kmutex_t *lock) 127 { 128 struct kmutexobj *mo = (struct kmutexobj *)lock; 129 130 KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC, 131 "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)", 132 __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC); 133 KASSERTMSG(mo->mo_refcnt > 0, 134 "%s: lock %p: mo->mo_refcnt (%#x) == 0", 135 __func__, mo, mo->mo_refcnt); 136 137 atomic_inc_uint(&mo->mo_refcnt); 138 } 139 140 /* 141 * mutex_obj_free: 142 * 143 * Drop a reference from a lock object. If the last reference is being 144 * dropped, free the object and return true. Otherwise, return false. 145 */ 146 bool 147 mutex_obj_free(kmutex_t *lock) 148 { 149 struct kmutexobj *mo = (struct kmutexobj *)lock; 150 151 KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC, 152 "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)", 153 __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC); 154 KASSERTMSG(mo->mo_refcnt > 0, 155 "%s: lock %p: mo->mo_refcnt (%#x) == 0", 156 __func__, mo, mo->mo_refcnt); 157 158 membar_release(); 159 if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) { 160 return false; 161 } 162 membar_acquire(); 163 mutex_destroy(&mo->mo_lock); 164 pool_cache_put(mutex_obj_cache, mo); 165 return true; 166 } 167 168 /* 169 * mutex_obj_refcnt: 170 * 171 * Return the reference count on a lock object. 172 */ 173 u_int 174 mutex_obj_refcnt(kmutex_t *lock) 175 { 176 struct kmutexobj *mo = (struct kmutexobj *)lock; 177 178 return mo->mo_refcnt; 179 } 180