1 /* $NetBSD: kern_rwlock_obj.c,v 1.13 2023/10/02 21:03:55 ad Exp $ */ 2 3 /*- 4 * Copyright (c) 2008, 2009, 2019, 2023 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_rwlock_obj.c,v 1.13 2023/10/02 21:03:55 ad Exp $"); 34 35 #include <sys/param.h> 36 #include <sys/atomic.h> 37 #include <sys/kmem.h> 38 #include <sys/rwlock.h> 39 40 /* Mutex cache */ 41 #define RW_OBJ_MAGIC 0x85d3c85d 42 struct krwobj { 43 krwlock_t ro_lock; 44 u_int ro_magic; 45 u_int ro_refcnt; 46 uint8_t mo_pad[COHERENCY_UNIT - sizeof(krwlock_t) - 47 sizeof(u_int) * 2]; 48 }; 49 50 /* 51 * rw_obj_alloc: 52 * 53 * Allocate a single lock object, waiting for memory if needed. 54 */ 55 krwlock_t * 56 rw_obj_alloc(void) 57 { 58 struct krwobj *ro; 59 60 ro = kmem_intr_alloc(sizeof(*ro), KM_SLEEP); 61 KASSERT(ALIGNED_POINTER(ro, coherency_unit)); 62 _rw_init(&ro->ro_lock, (uintptr_t)__builtin_return_address(0)); 63 ro->ro_magic = RW_OBJ_MAGIC; 64 ro->ro_refcnt = 1; 65 66 return (krwlock_t *)ro; 67 } 68 69 /* 70 * rw_obj_tryalloc: 71 * 72 * Allocate a single lock object, but fail if no memory is available. 73 */ 74 krwlock_t * 75 rw_obj_tryalloc(void) 76 { 77 struct krwobj *ro; 78 79 ro = kmem_intr_alloc(sizeof(*ro), KM_NOSLEEP); 80 KASSERT(ALIGNED_POINTER(ro, coherency_unit)); 81 if (__predict_true(ro != NULL)) { 82 _rw_init(&ro->ro_lock, (uintptr_t)__builtin_return_address(0)); 83 ro->ro_magic = RW_OBJ_MAGIC; 84 ro->ro_refcnt = 1; 85 } 86 87 return (krwlock_t *)ro; 88 } 89 90 /* 91 * rw_obj_hold: 92 * 93 * Add a single reference to a lock object. A reference to the object 94 * must already be held, and must be held across this call. 95 */ 96 void 97 rw_obj_hold(krwlock_t *lock) 98 { 99 struct krwobj *ro = (struct krwobj *)lock; 100 101 KASSERT(ro->ro_magic == RW_OBJ_MAGIC); 102 KASSERT(ro->ro_refcnt > 0); 103 104 atomic_inc_uint(&ro->ro_refcnt); 105 } 106 107 /* 108 * rw_obj_free: 109 * 110 * Drop a reference from a lock object. If the last reference is being 111 * dropped, free the object and return true. Otherwise, return false. 112 */ 113 bool 114 rw_obj_free(krwlock_t *lock) 115 { 116 struct krwobj *ro = (struct krwobj *)lock; 117 118 KASSERT(ro->ro_magic == RW_OBJ_MAGIC); 119 KASSERT(ro->ro_refcnt > 0); 120 121 membar_release(); 122 if (atomic_dec_uint_nv(&ro->ro_refcnt) > 0) { 123 return false; 124 } 125 membar_acquire(); 126 rw_destroy(&ro->ro_lock); 127 kmem_intr_free(ro, sizeof(*ro)); 128 return true; 129 } 130 131 /* 132 * rw_obj_refcnt: 133 * 134 * Return the reference count for a lock object. 135 */ 136 u_int 137 rw_obj_refcnt(krwlock_t *lock) 138 { 139 struct krwobj *ro = (struct krwobj *)lock; 140 141 return ro->ro_refcnt; 142 } 143