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 - 2019, 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 } 142