FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_umtx.c
1 /*
2 * Copyright (c) 2002, Jeffrey Roberson <jeff@freebsd.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice unmodified, this list of conditions, and the following
10 * disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 *
26 * $FreeBSD: releng/5.1/sys/kern/kern_umtx.c 115784 2003-06-03 20:43:18Z jeff $
27 *
28 */
29
30 #include <sys/param.h>
31 #include <sys/kernel.h>
32 #include <sys/lock.h>
33 #include <sys/malloc.h>
34 #include <sys/mutex.h>
35 #include <sys/proc.h>
36 #include <sys/signalvar.h>
37 #include <sys/sysent.h>
38 #include <sys/systm.h>
39 #include <sys/sysproto.h>
40 #include <sys/sx.h>
41 #include <sys/thr.h>
42 #include <sys/umtx.h>
43
44 struct umtx_q {
45 LIST_ENTRY(umtx_q) uq_next; /* Linked list for the hash. */
46 TAILQ_HEAD(, thread) uq_tdq; /* List of threads blocked here. */
47 struct umtx *uq_umtx; /* Pointer key component. */
48 pid_t uq_pid; /* Pid key component. */
49 };
50
51 #define UMTX_QUEUES 128
52 #define UMTX_HASH(pid, umtx) \
53 (((uintptr_t)pid + ((uintptr_t)umtx & ~65535)) % UMTX_QUEUES)
54
55 LIST_HEAD(umtx_head, umtx_q);
56 static struct umtx_head queues[UMTX_QUEUES];
57 static MALLOC_DEFINE(M_UMTX, "umtx", "UMTX queue memory");
58
59 static struct mtx umtx_lock;
60 MTX_SYSINIT(umtx, &umtx_lock, "umtx", MTX_DEF);
61
62 #define UMTX_LOCK() mtx_lock(&umtx_lock);
63 #define UMTX_UNLOCK() mtx_unlock(&umtx_lock);
64
65
66 static struct umtx_q *umtx_lookup(struct thread *, struct umtx *umtx);
67 static struct umtx_q *umtx_insert(struct thread *, struct umtx *umtx);
68
69 static struct umtx_q *
70 umtx_lookup(struct thread *td, struct umtx *umtx)
71 {
72 struct umtx_head *head;
73 struct umtx_q *uq;
74 pid_t pid;
75
76 pid = td->td_proc->p_pid;
77
78 head = &queues[UMTX_HASH(td->td_proc->p_pid, umtx)];
79
80 LIST_FOREACH(uq, head, uq_next) {
81 if (uq->uq_pid == pid && uq->uq_umtx == umtx)
82 return (uq);
83 }
84
85 return (NULL);
86 }
87
88 /*
89 * Insert a thread onto the umtx queue.
90 */
91 static struct umtx_q *
92 umtx_insert(struct thread *td, struct umtx *umtx)
93 {
94 struct umtx_head *head;
95 struct umtx_q *uq;
96 pid_t pid;
97
98 pid = td->td_proc->p_pid;
99
100 if ((uq = umtx_lookup(td, umtx)) == NULL) {
101 struct umtx_q *ins;
102
103 UMTX_UNLOCK();
104 ins = malloc(sizeof(*uq), M_UMTX, M_ZERO | M_WAITOK);
105 UMTX_LOCK();
106
107 /*
108 * Some one else could have succeeded while we were blocked
109 * waiting on memory.
110 */
111 if ((uq = umtx_lookup(td, umtx)) == NULL) {
112 head = &queues[UMTX_HASH(pid, umtx)];
113 uq = ins;
114 uq->uq_pid = pid;
115 uq->uq_umtx = umtx;
116 LIST_INSERT_HEAD(head, uq, uq_next);
117 TAILQ_INIT(&uq->uq_tdq);
118 } else
119 free(ins, M_UMTX);
120 }
121
122 /*
123 * Insert us onto the end of the TAILQ.
124 */
125 TAILQ_INSERT_TAIL(&uq->uq_tdq, td, td_umtx);
126
127 return (uq);
128 }
129
130 static void
131 umtx_remove(struct umtx_q *uq, struct thread *td)
132 {
133 TAILQ_REMOVE(&uq->uq_tdq, td, td_umtx);
134
135 if (TAILQ_EMPTY(&uq->uq_tdq)) {
136 LIST_REMOVE(uq, uq_next);
137 free(uq, M_UMTX);
138 }
139 }
140
141 int
142 _umtx_lock(struct thread *td, struct _umtx_lock_args *uap)
143 /* struct umtx *umtx */
144 {
145 struct umtx_q *uq;
146 struct umtx *umtx;
147 intptr_t owner;
148 intptr_t old;
149 int error;
150
151 uq = NULL;
152
153 /*
154 * Care must be exercised when dealing with this structure. It
155 * can fault on any access.
156 */
157 umtx = uap->umtx;
158
159 for (;;) {
160 /*
161 * Try the uncontested case. This should be done in userland.
162 */
163 owner = casuptr((intptr_t *)&umtx->u_owner,
164 UMTX_UNOWNED, (intptr_t)td);
165
166 /* The address was invalid. */
167 if (owner == -1)
168 return (EFAULT);
169
170 /* The acquire succeeded. */
171 if (owner == UMTX_UNOWNED)
172 return (0);
173
174 /* If no one owns it but it is contested try to acquire it. */
175 if (owner == UMTX_CONTESTED) {
176 owner = casuptr((intptr_t *)&umtx->u_owner,
177 UMTX_CONTESTED, ((intptr_t)td | UMTX_CONTESTED));
178
179 /* The address was invalid. */
180 if (owner == -1)
181 return (EFAULT);
182
183 if (owner == MTX_CONTESTED);
184 return (0);
185
186 /* If this failed the lock has changed, restart. */
187 continue;
188 }
189
190
191 UMTX_LOCK();
192 uq = umtx_insert(td, umtx);
193 UMTX_UNLOCK();
194
195 /*
196 * Set the contested bit so that a release in user space
197 * knows to use the system call for unlock. If this fails
198 * either some one else has acquired the lock or it has been
199 * released.
200 */
201 old = casuptr((intptr_t *)&umtx->u_owner, owner,
202 owner | UMTX_CONTESTED);
203
204 /* The address was invalid. */
205 if (old == -1) {
206 UMTX_LOCK();
207 umtx_remove(uq, td);
208 UMTX_UNLOCK();
209 return (EFAULT);
210 }
211
212 /*
213 * We set the contested bit, sleep. Otherwise the lock changed
214 * and we need to retry.
215 */
216 UMTX_LOCK();
217 if (old == owner)
218 error = msleep(td, &umtx_lock,
219 td->td_priority | PCATCH, "umtx", 0);
220 else
221 error = 0;
222
223 umtx_remove(uq, td);
224 UMTX_UNLOCK();
225
226 /*
227 * If we caught a signal we might have to retry or exit
228 * immediately.
229 */
230 if (error)
231 return (error);
232 }
233
234 return (0);
235 }
236
237 int
238 _umtx_unlock(struct thread *td, struct _umtx_unlock_args *uap)
239 /* struct umtx *umtx */
240 {
241 struct thread *blocked;
242 struct umtx *umtx;
243 struct umtx_q *uq;
244 intptr_t owner;
245 intptr_t old;
246
247 umtx = uap->umtx;
248
249 /*
250 * Make sure we own this mtx.
251 *
252 * XXX Need a {fu,su}ptr this is not correct on arch where
253 * sizeof(intptr_t) != sizeof(long).
254 */
255 if ((owner = fuword(&umtx->u_owner)) == -1)
256 return (EFAULT);
257
258 if ((struct thread *)(owner & ~UMTX_CONTESTED) != td)
259 return (EPERM);
260 /*
261 * If we own it but it isn't contested then we can just release and
262 * return.
263 */
264 if ((owner & UMTX_CONTESTED) == 0) {
265 owner = casuptr((intptr_t *)&umtx->u_owner,
266 (intptr_t)td, UMTX_UNOWNED);
267
268 if (owner == -1)
269 return (EFAULT);
270 /*
271 * If this failed someone modified the memory without going
272 * through this api.
273 */
274 if (owner != (intptr_t)td)
275 return (EINVAL);
276
277 return (0);
278 }
279
280 old = casuptr((intptr_t *)&umtx->u_owner, owner, UMTX_CONTESTED);
281
282 if (old == -1)
283 return (EFAULT);
284
285 /*
286 * This will only happen if someone modifies the lock without going
287 * through this api.
288 */
289 if (old != owner)
290 return (EINVAL);
291
292 /*
293 * We have to wake up one of the blocked threads.
294 */
295 UMTX_LOCK();
296 uq = umtx_lookup(td, umtx);
297 if (uq != NULL) {
298 blocked = TAILQ_FIRST(&uq->uq_tdq);
299 wakeup(blocked);
300 }
301
302 UMTX_UNLOCK();
303
304 return (0);
305 }
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