1/******************************************************************************
2 *
3 * Module Name: utlock - Reader/Writer lock interfaces
4 *
5 *****************************************************************************/
6
7/*
8 * Copyright (C) 2000 - 2015, 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
48ACPI_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 ******************************************************************************/
62acpi_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
76void 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
105acpi_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
127acpi_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
163acpi_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
171void acpi_ut_release_write_lock(struct acpi_rw_lock *lock)
172{
173
174	acpi_os_release_mutex(lock->writer_mutex);
175}
176