1 /******************************************************************************
2  *
3  * Module Name: utlock - Reader/Writer lock interfaces
4  *
5  *****************************************************************************/
6 
7 /*
8  * Copyright (C) 2000 - 2012, 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