1 /******************************************************************************
2 *
3 * Module Name: utlock - Reader/Writer lock interfaces
4 *
5 *****************************************************************************/
6
7 /*
8 * Copyright (C) 2000 - 2011, 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 ******************************************************************************/
acpi_ut_create_rw_lock(struct acpi_rw_lock * lock)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
acpi_ut_delete_rw_lock(struct acpi_rw_lock * lock)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
acpi_ut_acquire_read_lock(struct acpi_rw_lock * lock)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
acpi_ut_release_read_lock(struct acpi_rw_lock * lock)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
acpi_ut_acquire_write_lock(struct acpi_rw_lock * lock)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
acpi_ut_release_write_lock(struct acpi_rw_lock * lock)171 void acpi_ut_release_write_lock(struct acpi_rw_lock *lock)
172 {
173
174 acpi_os_release_mutex(lock->writer_mutex);
175 }
176