1 /****************************************************************************** 2 * 3 * Module Name: utlock - Reader/Writer lock interfaces 4 * 5 *****************************************************************************/ 6 7 /* 8 * Copyright (C) 2000 - 2014, Intel Corp. 9 * All rights reserved. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions, and the following disclaimer, 16 * without modification. 17 * 2. Redistributions in binary form must reproduce at minimum a disclaimer 18 * substantially similar to the "NO WARRANTY" disclaimer below 19 * ("Disclaimer") and any redistribution must be conditioned upon 20 * including a substantially similar Disclaimer requirement for further 21 * binary redistribution. 22 * 3. Neither the names of the above-listed copyright holders nor the names 23 * of any contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * Alternatively, this software may be distributed under the terms of the 27 * GNU General Public License ("GPL") version 2 as published by the Free 28 * Software Foundation. 29 * 30 * NO WARRANTY 31 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 32 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 33 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR 34 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 35 * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 36 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 37 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 38 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 40 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 41 * POSSIBILITY OF SUCH DAMAGES. 42 */ 43 44 #include <acpi/acpi.h> 45 #include "accommon.h" 46 47 #define _COMPONENT ACPI_UTILITIES 48 ACPI_MODULE_NAME("utlock") 49 50 /******************************************************************************* 51 * 52 * FUNCTION: acpi_ut_create_rw_lock 53 * acpi_ut_delete_rw_lock 54 * 55 * PARAMETERS: lock - Pointer to a valid RW lock 56 * 57 * RETURN: Status 58 * 59 * DESCRIPTION: Reader/writer lock creation and deletion interfaces. 60 * 61 ******************************************************************************/ 62 acpi_status acpi_ut_create_rw_lock(struct acpi_rw_lock *lock) 63 { 64 acpi_status status; 65 66 lock->num_readers = 0; 67 status = acpi_os_create_mutex(&lock->reader_mutex); 68 if (ACPI_FAILURE(status)) { 69 return (status); 70 } 71 72 status = acpi_os_create_mutex(&lock->writer_mutex); 73 return (status); 74 } 75 76 void acpi_ut_delete_rw_lock(struct acpi_rw_lock *lock) 77 { 78 79 acpi_os_delete_mutex(lock->reader_mutex); 80 acpi_os_delete_mutex(lock->writer_mutex); 81 82 lock->num_readers = 0; 83 lock->reader_mutex = NULL; 84 lock->writer_mutex = NULL; 85 } 86 87 /******************************************************************************* 88 * 89 * FUNCTION: acpi_ut_acquire_read_lock 90 * acpi_ut_release_read_lock 91 * 92 * PARAMETERS: lock - Pointer to a valid RW lock 93 * 94 * RETURN: Status 95 * 96 * DESCRIPTION: Reader interfaces for reader/writer locks. On acquisition, 97 * only the first reader acquires the write mutex. On release, 98 * only the last reader releases the write mutex. Although this 99 * algorithm can in theory starve writers, this should not be a 100 * problem with ACPICA since the subsystem is infrequently used 101 * in comparison to (for example) an I/O system. 102 * 103 ******************************************************************************/ 104 105 acpi_status acpi_ut_acquire_read_lock(struct acpi_rw_lock *lock) 106 { 107 acpi_status status; 108 109 status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER); 110 if (ACPI_FAILURE(status)) { 111 return (status); 112 } 113 114 /* Acquire the write lock only for the first reader */ 115 116 lock->num_readers++; 117 if (lock->num_readers == 1) { 118 status = 119 acpi_os_acquire_mutex(lock->writer_mutex, 120 ACPI_WAIT_FOREVER); 121 } 122 123 acpi_os_release_mutex(lock->reader_mutex); 124 return (status); 125 } 126 127 acpi_status acpi_ut_release_read_lock(struct acpi_rw_lock *lock) 128 { 129 acpi_status status; 130 131 status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER); 132 if (ACPI_FAILURE(status)) { 133 return (status); 134 } 135 136 /* Release the write lock only for the very last reader */ 137 138 lock->num_readers--; 139 if (lock->num_readers == 0) { 140 acpi_os_release_mutex(lock->writer_mutex); 141 } 142 143 acpi_os_release_mutex(lock->reader_mutex); 144 return (status); 145 } 146 147 /******************************************************************************* 148 * 149 * FUNCTION: acpi_ut_acquire_write_lock 150 * acpi_ut_release_write_lock 151 * 152 * PARAMETERS: lock - Pointer to a valid RW lock 153 * 154 * RETURN: Status 155 * 156 * DESCRIPTION: Writer interfaces for reader/writer locks. Simply acquire or 157 * release the writer mutex associated with the lock. Acquisition 158 * of the lock is fully exclusive and will block all readers and 159 * writers until it is released. 160 * 161 ******************************************************************************/ 162 163 acpi_status acpi_ut_acquire_write_lock(struct acpi_rw_lock *lock) 164 { 165 acpi_status status; 166 167 status = acpi_os_acquire_mutex(lock->writer_mutex, ACPI_WAIT_FOREVER); 168 return (status); 169 } 170 171 void acpi_ut_release_write_lock(struct acpi_rw_lock *lock) 172 { 173 174 acpi_os_release_mutex(lock->writer_mutex); 175 } 176