1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (C) 2010 David Xu <[email protected]>.
5 * Copyright (C) 2000 Jason Evans <[email protected]>.
6 * All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice(s), this list of conditions and the following disclaimer as
13 * the first lines of this file unmodified other than the possible
14 * addition of one or more copyright notices.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice(s), this list of conditions and the following disclaimer in
17 * the documentation and/or other materials provided with the
18 * distribution.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
21 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
24 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
25 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
26 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
27 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
28 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
29 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
30 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
31 *
32 * $FreeBSD$
33 */
34
35 /*
36 * Some notes about this implementation.
37 *
38 * This is mostly a simple implementation of POSIX semaphores that
39 * does not need threading. Any semaphore created is a kernel-based
40 * semaphore regardless of the pshared attribute. This is necessary
41 * because libc's stub for pthread_cond_wait() doesn't really wait,
42 * and it is not worth the effort impose this behavior on libc.
43 *
44 * All functions here are designed to be thread-safe so that a
45 * threads library need not provide wrappers except to make
46 * sem_wait() and sem_timedwait() cancellation points or to
47 * provide a faster userland implementation for non-pshared
48 * semaphores.
49 *
50 * Also, this implementation of semaphores cannot really support
51 * real pshared semaphores. The sem_t is an allocated object
52 * and can't be seen by other processes when placed in shared
53 * memory. It should work across forks as long as the semaphore
54 * is created before any forks.
55 *
56 * The function sem_init() should be overridden by a threads
57 * library if it wants to provide a different userland version
58 * of semaphores. The functions sem_wait() and sem_timedwait()
59 * need to be wrapped to provide cancellation points. The function
60 * sem_post() may need to be wrapped to be signal-safe.
61 */
62 #include "namespace.h"
63 #include <sys/types.h>
64 #include <sys/queue.h>
65 #include <machine/atomic.h>
66 #include <errno.h>
67 #include <sys/umtx.h>
68 #include <sys/_semaphore.h>
69 #include <limits.h>
70 #include <fcntl.h>
71 #include <pthread.h>
72 #include <stdarg.h>
73 #include <stdlib.h>
74 #include <time.h>
75 #include "un-namespace.h"
76 #include "libc_private.h"
77
78 /*
79 * Old semaphore definitions.
80 */
81 struct sem {
82 #define SEM_MAGIC ((u_int32_t) 0x09fa4012)
83 u_int32_t magic;
84 pthread_mutex_t lock;
85 pthread_cond_t gtzero;
86 u_int32_t count;
87 u_int32_t nwaiters;
88 #define SEM_USER (NULL)
89 semid_t semid; /* semaphore id if kernel (shared) semaphore */
90 int syssem; /* 1 if kernel (shared) semaphore */
91 LIST_ENTRY(sem) entry;
92 struct sem **backpointer;
93 };
94
95 typedef struct sem* sem_t;
96
97 #define SEM_FAILED ((sem_t *)0)
98 #define SEM_VALUE_MAX __INT_MAX
99
100 #define SYM_FB10(sym) __CONCAT(sym, _fb10)
101 #define WEAK_REF(sym, alias) __weak_reference(sym, alias)
102 #define SYM_COMPAT(sym, impl, ver) __sym_compat(sym, impl, ver)
103
104 #define FB10_COMPAT(func, sym) \
105 WEAK_REF(func, SYM_FB10(sym)); \
106 SYM_COMPAT(sym, SYM_FB10(sym), FBSD_1.0)
107
108 static sem_t sem_alloc(unsigned int value, semid_t semid, int system_sem);
109 static void sem_free(sem_t sem);
110
111 static LIST_HEAD(, sem) named_sems = LIST_HEAD_INITIALIZER(named_sems);
112 static pthread_mutex_t named_sems_mtx = PTHREAD_MUTEX_INITIALIZER;
113
114 FB10_COMPAT(_libc_sem_init_compat, sem_init);
115 FB10_COMPAT(_libc_sem_destroy_compat, sem_destroy);
116 FB10_COMPAT(_libc_sem_open_compat, sem_open);
117 FB10_COMPAT(_libc_sem_close_compat, sem_close);
118 FB10_COMPAT(_libc_sem_unlink_compat, sem_unlink);
119 FB10_COMPAT(_libc_sem_wait_compat, sem_wait);
120 FB10_COMPAT(_libc_sem_trywait_compat, sem_trywait);
121 FB10_COMPAT(_libc_sem_timedwait_compat, sem_timedwait);
122 FB10_COMPAT(_libc_sem_post_compat, sem_post);
123 FB10_COMPAT(_libc_sem_getvalue_compat, sem_getvalue);
124
125 static inline int
sem_check_validity(sem_t * sem)126 sem_check_validity(sem_t *sem)
127 {
128
129 if ((sem != NULL) && ((*sem)->magic == SEM_MAGIC))
130 return (0);
131 else {
132 errno = EINVAL;
133 return (-1);
134 }
135 }
136
137 static void
sem_free(sem_t sem)138 sem_free(sem_t sem)
139 {
140
141 sem->magic = 0;
142 free(sem);
143 }
144
145 static sem_t
sem_alloc(unsigned int value,semid_t semid,int system_sem)146 sem_alloc(unsigned int value, semid_t semid, int system_sem)
147 {
148 sem_t sem;
149
150 if (value > SEM_VALUE_MAX) {
151 errno = EINVAL;
152 return (NULL);
153 }
154
155 sem = (sem_t)malloc(sizeof(struct sem));
156 if (sem == NULL) {
157 errno = ENOSPC;
158 return (NULL);
159 }
160
161 sem->count = (u_int32_t)value;
162 sem->nwaiters = 0;
163 sem->magic = SEM_MAGIC;
164 sem->semid = semid;
165 sem->syssem = system_sem;
166 return (sem);
167 }
168
169 int
_libc_sem_init_compat(sem_t * sem,int pshared,unsigned int value)170 _libc_sem_init_compat(sem_t *sem, int pshared, unsigned int value)
171 {
172 semid_t semid;
173
174 /*
175 * We always have to create the kernel semaphore if the
176 * threads library isn't present since libc's version of
177 * pthread_cond_wait() is just a stub that doesn't really
178 * wait.
179 */
180 semid = (semid_t)SEM_USER;
181 if ((pshared != 0) && ksem_init(&semid, value) != 0)
182 return (-1);
183
184 *sem = sem_alloc(value, semid, pshared);
185 if ((*sem) == NULL) {
186 if (pshared != 0)
187 ksem_destroy(semid);
188 return (-1);
189 }
190 return (0);
191 }
192
193 int
_libc_sem_destroy_compat(sem_t * sem)194 _libc_sem_destroy_compat(sem_t *sem)
195 {
196 int retval;
197
198 if (sem_check_validity(sem) != 0)
199 return (-1);
200
201 /*
202 * If this is a system semaphore let the kernel track it otherwise
203 * make sure there are no waiters.
204 */
205 if ((*sem)->syssem != 0)
206 retval = ksem_destroy((*sem)->semid);
207 else if ((*sem)->nwaiters > 0) {
208 errno = EBUSY;
209 retval = -1;
210 }
211 else {
212 retval = 0;
213 (*sem)->magic = 0;
214 }
215
216 if (retval == 0)
217 sem_free(*sem);
218 return (retval);
219 }
220
221 sem_t *
_libc_sem_open_compat(const char * name,int oflag,...)222 _libc_sem_open_compat(const char *name, int oflag, ...)
223 {
224 sem_t *sem;
225 sem_t s;
226 semid_t semid;
227 mode_t mode;
228 unsigned int value;
229
230 mode = 0;
231 value = 0;
232
233 if ((oflag & O_CREAT) != 0) {
234 va_list ap;
235
236 va_start(ap, oflag);
237 mode = va_arg(ap, int);
238 value = va_arg(ap, unsigned int);
239 va_end(ap);
240 }
241 /*
242 * we can be lazy and let the kernel handle the "oflag",
243 * we'll just merge duplicate IDs into our list.
244 */
245 if (ksem_open(&semid, name, oflag, mode, value) == -1)
246 return (SEM_FAILED);
247 /*
248 * search for a duplicate ID, we must return the same sem_t *
249 * if we locate one.
250 */
251 _pthread_mutex_lock(&named_sems_mtx);
252 LIST_FOREACH(s, &named_sems, entry) {
253 if (s->semid == semid) {
254 sem = s->backpointer;
255 _pthread_mutex_unlock(&named_sems_mtx);
256 return (sem);
257 }
258 }
259 sem = (sem_t *)malloc(sizeof(*sem));
260 if (sem == NULL)
261 goto err;
262 *sem = sem_alloc(value, semid, 1);
263 if ((*sem) == NULL)
264 goto err;
265 LIST_INSERT_HEAD(&named_sems, *sem, entry);
266 (*sem)->backpointer = sem;
267 _pthread_mutex_unlock(&named_sems_mtx);
268 return (sem);
269 err:
270 _pthread_mutex_unlock(&named_sems_mtx);
271 ksem_close(semid);
272 if (sem != NULL) {
273 if (*sem != NULL)
274 sem_free(*sem);
275 else
276 errno = ENOSPC;
277 free(sem);
278 } else {
279 errno = ENOSPC;
280 }
281 return (SEM_FAILED);
282 }
283
284 int
_libc_sem_close_compat(sem_t * sem)285 _libc_sem_close_compat(sem_t *sem)
286 {
287
288 if (sem_check_validity(sem) != 0)
289 return (-1);
290
291 if ((*sem)->syssem == 0) {
292 errno = EINVAL;
293 return (-1);
294 }
295
296 _pthread_mutex_lock(&named_sems_mtx);
297 if (ksem_close((*sem)->semid) != 0) {
298 _pthread_mutex_unlock(&named_sems_mtx);
299 return (-1);
300 }
301 LIST_REMOVE((*sem), entry);
302 _pthread_mutex_unlock(&named_sems_mtx);
303 sem_free(*sem);
304 *sem = NULL;
305 free(sem);
306 return (0);
307 }
308
309 int
_libc_sem_unlink_compat(const char * name)310 _libc_sem_unlink_compat(const char *name)
311 {
312
313 return (ksem_unlink(name));
314 }
315
316 static int
_umtx_wait_uint(volatile unsigned * mtx,unsigned id,const struct timespec * abstime)317 _umtx_wait_uint(volatile unsigned *mtx, unsigned id, const struct timespec *abstime)
318 {
319 struct _umtx_time *tm_p, timeout;
320 size_t tm_size;
321
322 if (abstime == NULL) {
323 tm_p = NULL;
324 tm_size = 0;
325 } else {
326 timeout._clockid = CLOCK_REALTIME;
327 timeout._flags = UMTX_ABSTIME;
328 timeout._timeout = *abstime;
329 tm_p = &timeout;
330 tm_size = sizeof(timeout);
331 }
332 return _umtx_op(__DEVOLATILE(void *, mtx),
333 UMTX_OP_WAIT_UINT_PRIVATE, id,
334 (void *)tm_size, __DECONST(void*, tm_p));
335 }
336
337 static int
_umtx_wake(volatile void * mtx)338 _umtx_wake(volatile void *mtx)
339 {
340 return _umtx_op(__DEVOLATILE(void *, mtx), UMTX_OP_WAKE_PRIVATE,
341 1, NULL, NULL);
342 }
343
344 #define TIMESPEC_SUB(dst, src, val) \
345 do { \
346 (dst)->tv_sec = (src)->tv_sec - (val)->tv_sec; \
347 (dst)->tv_nsec = (src)->tv_nsec - (val)->tv_nsec; \
348 if ((dst)->tv_nsec < 0) { \
349 (dst)->tv_sec--; \
350 (dst)->tv_nsec += 1000000000; \
351 } \
352 } while (0)
353
354
355 static void
sem_cancel_handler(void * arg)356 sem_cancel_handler(void *arg)
357 {
358 sem_t *sem = arg;
359
360 atomic_add_int(&(*sem)->nwaiters, -1);
361 if ((*sem)->nwaiters && (*sem)->count)
362 _umtx_wake(&(*sem)->count);
363 }
364
365 int
_libc_sem_timedwait_compat(sem_t * __restrict sem,const struct timespec * __restrict abstime)366 _libc_sem_timedwait_compat(sem_t * __restrict sem,
367 const struct timespec * __restrict abstime)
368 {
369 int val, retval;
370
371 if (sem_check_validity(sem) != 0)
372 return (-1);
373
374 if ((*sem)->syssem != 0) {
375 _pthread_cancel_enter(1);
376 retval = ksem_wait((*sem)->semid); /* XXX no timeout */
377 _pthread_cancel_leave(retval == -1);
378 return (retval);
379 }
380
381 retval = 0;
382 _pthread_testcancel();
383 for (;;) {
384 while ((val = (*sem)->count) > 0) {
385 if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1))
386 return (0);
387 }
388 if (retval) {
389 _pthread_testcancel();
390 break;
391 }
392 if (abstime) {
393 if (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0) {
394 errno = EINVAL;
395 return (-1);
396 }
397 }
398 atomic_add_int(&(*sem)->nwaiters, 1);
399 pthread_cleanup_push(sem_cancel_handler, sem);
400 _pthread_cancel_enter(1);
401 retval = _umtx_wait_uint(&(*sem)->count, 0, abstime);
402 _pthread_cancel_leave(0);
403 pthread_cleanup_pop(0);
404 atomic_add_int(&(*sem)->nwaiters, -1);
405 }
406 return (retval);
407 }
408
409 int
_libc_sem_wait_compat(sem_t * sem)410 _libc_sem_wait_compat(sem_t *sem)
411 {
412 return _libc_sem_timedwait_compat(sem, NULL);
413 }
414
415 int
_libc_sem_trywait_compat(sem_t * sem)416 _libc_sem_trywait_compat(sem_t *sem)
417 {
418 int val;
419
420 if (sem_check_validity(sem) != 0)
421 return (-1);
422
423 if ((*sem)->syssem != 0)
424 return ksem_trywait((*sem)->semid);
425
426 while ((val = (*sem)->count) > 0) {
427 if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1))
428 return (0);
429 }
430 errno = EAGAIN;
431 return (-1);
432 }
433
434 int
_libc_sem_post_compat(sem_t * sem)435 _libc_sem_post_compat(sem_t *sem)
436 {
437
438 if (sem_check_validity(sem) != 0)
439 return (-1);
440
441 if ((*sem)->syssem != 0)
442 return ksem_post((*sem)->semid);
443
444 atomic_add_rel_int(&(*sem)->count, 1);
445 rmb();
446 if ((*sem)->nwaiters)
447 return _umtx_wake(&(*sem)->count);
448 return (0);
449 }
450
451 int
_libc_sem_getvalue_compat(sem_t * __restrict sem,int * __restrict sval)452 _libc_sem_getvalue_compat(sem_t * __restrict sem, int * __restrict sval)
453 {
454 int retval;
455
456 if (sem_check_validity(sem) != 0)
457 return (-1);
458
459 if ((*sem)->syssem != 0)
460 retval = ksem_getvalue((*sem)->semid, sval);
461 else {
462 *sval = (int)(*sem)->count;
463 retval = 0;
464 }
465 return (retval);
466 }
467