| Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 1 | // SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0 |
| 2 | /****************************************************************************** |
| 3 | * |
| 4 | * Module Name: utlock - Reader/Writer lock interfaces |
| 5 | * |
| 6 | * Copyright (C) 2000 - 2018, Intel Corp. |
| 7 | * |
| 8 | *****************************************************************************/ |
| 9 | |
| 10 | #include <acpi/acpi.h> |
| 11 | #include "accommon.h" |
| 12 | |
| 13 | #define _COMPONENT ACPI_UTILITIES |
| 14 | ACPI_MODULE_NAME("utlock") |
| 15 | |
| 16 | /******************************************************************************* |
| 17 | * |
| 18 | * FUNCTION: acpi_ut_create_rw_lock |
| 19 | * acpi_ut_delete_rw_lock |
| 20 | * |
| 21 | * PARAMETERS: lock - Pointer to a valid RW lock |
| 22 | * |
| 23 | * RETURN: Status |
| 24 | * |
| 25 | * DESCRIPTION: Reader/writer lock creation and deletion interfaces. |
| 26 | * |
| 27 | ******************************************************************************/ |
| 28 | acpi_status acpi_ut_create_rw_lock(struct acpi_rw_lock *lock) |
| 29 | { |
| 30 | acpi_status status; |
| 31 | |
| 32 | lock->num_readers = 0; |
| 33 | status = acpi_os_create_mutex(&lock->reader_mutex); |
| 34 | if (ACPI_FAILURE(status)) { |
| 35 | return (status); |
| 36 | } |
| 37 | |
| 38 | status = acpi_os_create_mutex(&lock->writer_mutex); |
| 39 | return (status); |
| 40 | } |
| 41 | |
| 42 | void acpi_ut_delete_rw_lock(struct acpi_rw_lock *lock) |
| 43 | { |
| 44 | |
| 45 | acpi_os_delete_mutex(lock->reader_mutex); |
| 46 | acpi_os_delete_mutex(lock->writer_mutex); |
| 47 | |
| 48 | lock->num_readers = 0; |
| 49 | lock->reader_mutex = NULL; |
| 50 | lock->writer_mutex = NULL; |
| 51 | } |
| 52 | |
| 53 | /******************************************************************************* |
| 54 | * |
| 55 | * FUNCTION: acpi_ut_acquire_read_lock |
| 56 | * acpi_ut_release_read_lock |
| 57 | * |
| 58 | * PARAMETERS: lock - Pointer to a valid RW lock |
| 59 | * |
| 60 | * RETURN: Status |
| 61 | * |
| 62 | * DESCRIPTION: Reader interfaces for reader/writer locks. On acquisition, |
| 63 | * only the first reader acquires the write mutex. On release, |
| 64 | * only the last reader releases the write mutex. Although this |
| 65 | * algorithm can in theory starve writers, this should not be a |
| 66 | * problem with ACPICA since the subsystem is infrequently used |
| 67 | * in comparison to (for example) an I/O system. |
| 68 | * |
| 69 | ******************************************************************************/ |
| 70 | |
| 71 | acpi_status acpi_ut_acquire_read_lock(struct acpi_rw_lock *lock) |
| 72 | { |
| 73 | acpi_status status; |
| 74 | |
| 75 | status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER); |
| 76 | if (ACPI_FAILURE(status)) { |
| 77 | return (status); |
| 78 | } |
| 79 | |
| 80 | /* Acquire the write lock only for the first reader */ |
| 81 | |
| 82 | lock->num_readers++; |
| 83 | if (lock->num_readers == 1) { |
| 84 | status = |
| 85 | acpi_os_acquire_mutex(lock->writer_mutex, |
| 86 | ACPI_WAIT_FOREVER); |
| 87 | } |
| 88 | |
| 89 | acpi_os_release_mutex(lock->reader_mutex); |
| 90 | return (status); |
| 91 | } |
| 92 | |
| 93 | acpi_status acpi_ut_release_read_lock(struct acpi_rw_lock *lock) |
| 94 | { |
| 95 | acpi_status status; |
| 96 | |
| 97 | status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER); |
| 98 | if (ACPI_FAILURE(status)) { |
| 99 | return (status); |
| 100 | } |
| 101 | |
| 102 | /* Release the write lock only for the very last reader */ |
| 103 | |
| 104 | lock->num_readers--; |
| 105 | if (lock->num_readers == 0) { |
| 106 | acpi_os_release_mutex(lock->writer_mutex); |
| 107 | } |
| 108 | |
| 109 | acpi_os_release_mutex(lock->reader_mutex); |
| 110 | return (status); |
| 111 | } |
| 112 | |
| 113 | /******************************************************************************* |
| 114 | * |
| 115 | * FUNCTION: acpi_ut_acquire_write_lock |
| 116 | * acpi_ut_release_write_lock |
| 117 | * |
| 118 | * PARAMETERS: lock - Pointer to a valid RW lock |
| 119 | * |
| 120 | * RETURN: Status |
| 121 | * |
| 122 | * DESCRIPTION: Writer interfaces for reader/writer locks. Simply acquire or |
| 123 | * release the writer mutex associated with the lock. Acquisition |
| 124 | * of the lock is fully exclusive and will block all readers and |
| 125 | * writers until it is released. |
| 126 | * |
| 127 | ******************************************************************************/ |
| 128 | |
| 129 | acpi_status acpi_ut_acquire_write_lock(struct acpi_rw_lock *lock) |
| 130 | { |
| 131 | acpi_status status; |
| 132 | |
| 133 | status = acpi_os_acquire_mutex(lock->writer_mutex, ACPI_WAIT_FOREVER); |
| 134 | return (status); |
| 135 | } |
| 136 | |
| 137 | void acpi_ut_release_write_lock(struct acpi_rw_lock *lock) |
| 138 | { |
| 139 | |
| 140 | acpi_os_release_mutex(lock->writer_mutex); |
| 141 | } |