source: mainline/kernel/generic/src/synch/mutex.c

Last change on this file was 9f2f5ee, checked in by Jiří Zárevúcky <zarevucky.jiri@…>, 3 months ago

Rewrite kernel mutex implementation a little

Removes MUTEX_ACTIVE, the use of which has been removed in favor of
irq_spinlock_t, and fixes some issues with the old implementation.

  • A race in mtx→owner access is unavoidable, so make it explicitly atomic.
  • The THREAD==NULL case happens when there are no other threads yet, so we factor it out as a special case. Also ensures recursive mutex works before threads are initialized, just as normal mutex does.
  • More and better asserts.
  • Property mode set to 100644
File size: 4.4 KB
Line 
1/*
2 * Copyright (c) 2001-2004 Jakub Jermar
3 * Copyright (c) 2025 Jiří Zárevúcky
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 *
10 * - Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * - Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * - The name of the author may not be used to endorse or promote products
16 * derived from this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
22 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
23 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
27 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 */
29
30/** @addtogroup kernel_sync
31 * @{
32 */
33
34/**
35 * @file
36 * @brief Mutexes.
37 */
38
39#include <assert.h>
40#include <errno.h>
41#include <proc/thread.h>
42#include <stdatomic.h>
43#include <synch/mutex.h>
44#include <synch/semaphore.h>
45
46/** Initialize mutex.
47 *
48 * @param mtx Mutex.
49 * @param type Type of the mutex.
50 */
51void mutex_initialize(mutex_t *mtx, mutex_type_t type)
52{
53 *mtx = MUTEX_INITIALIZER(*mtx, type);
54}
55
56/** A race in mtx->owner access is unavoidable, so we have to make
57 * access to it formally atomic. These are convenience functions to
58 * read/write the variable without memory barriers, since we don't need
59 * them and C11 atomics default to the strongest possible memory ordering
60 * by default, which is utterly ridiculous.
61 */
62static inline thread_t *_get_owner(mutex_t *mtx)
63{
64 return atomic_load_explicit(&mtx->owner, memory_order_relaxed);
65}
66
67/** Counterpart to _get_owner(). */
68static inline void _set_owner(mutex_t *mtx, thread_t *owner)
69{
70 atomic_store_explicit(&mtx->owner, owner, memory_order_relaxed);
71}
72
73/** Find out whether the mutex is currently locked.
74 *
75 * @param mtx Mutex.
76 *
77 * @return True if the mutex is locked, false otherwise.
78 */
79bool mutex_locked(mutex_t *mtx)
80{
81 if (!THREAD)
82 return mtx->nesting > 0;
83
84 return _get_owner(mtx) == THREAD;
85}
86
87/** Acquire mutex.
88 *
89 * This operation is uninterruptible and cannot fail.
90 */
91void mutex_lock(mutex_t *mtx)
92{
93 if (!THREAD) {
94 assert(mtx->type == MUTEX_RECURSIVE || mtx->nesting == 0);
95 mtx->nesting++;
96 return;
97 }
98
99 if (_get_owner(mtx) == THREAD) {
100 /* This will also detect nested locks on a non-recursive mutex. */
101 assert(mtx->type == MUTEX_RECURSIVE);
102 assert(mtx->nesting > 0);
103 mtx->nesting++;
104 return;
105 }
106
107 semaphore_down(&mtx->sem);
108
109 _set_owner(mtx, THREAD);
110 assert(mtx->nesting == 0);
111 mtx->nesting = 1;
112}
113
114/** Acquire mutex with timeout.
115 *
116 * @param mtx Mutex.
117 * @param usec Timeout in microseconds.
118 *
119 * @return EOK if lock was successfully acquired, something else otherwise.
120 */
121errno_t mutex_lock_timeout(mutex_t *mtx, uint32_t usec)
122{
123 if (!THREAD) {
124 assert(mtx->type == MUTEX_RECURSIVE || mtx->nesting == 0);
125 mtx->nesting++;
126 return EOK;
127 }
128
129 if (_get_owner(mtx) == THREAD) {
130 assert(mtx->type == MUTEX_RECURSIVE);
131 assert(mtx->nesting > 0);
132 mtx->nesting++;
133 return EOK;
134 }
135
136 errno_t rc = semaphore_down_timeout(&mtx->sem, usec);
137 if (rc != EOK)
138 return rc;
139
140 _set_owner(mtx, THREAD);
141 assert(mtx->nesting == 0);
142 mtx->nesting = 1;
143 return EOK;
144}
145
146/** Attempt to acquire mutex without blocking.
147 *
148 * @return EOK if lock was successfully acquired, something else otherwise.
149 */
150errno_t mutex_trylock(mutex_t *mtx)
151{
152 return mutex_lock_timeout(mtx, 0);
153}
154
155/** Release mutex.
156 *
157 * @param mtx Mutex.
158 */
159void mutex_unlock(mutex_t *mtx)
160{
161 if (--mtx->nesting > 0) {
162 assert(mtx->type == MUTEX_RECURSIVE);
163 return;
164 }
165
166 assert(mtx->nesting == 0);
167
168 if (!THREAD)
169 return;
170
171 assert(_get_owner(mtx) == THREAD);
172 _set_owner(mtx, NULL);
173
174 semaphore_up(&mtx->sem);
175}
176
177/** @}
178 */
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