xref: /freebsd/lib/libc/gen/sem_new.c (revision 7fdf597e96a02165cfe22ff357b857d5fa15ed8a) 
1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause
3  *
4  * Copyright (C) 2010 David Xu <davidxu@freebsd.org>.
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice(s), this list of conditions and the following disclaimer as
12  *    the first lines of this file unmodified other than the possible
13  *    addition of one or more copyright notices.
14  * 2. Redistributions in binary form must reproduce the above copyright
15  *    notice(s), this list of conditions and the following disclaimer in
16  *    the documentation and/or other materials provided with the
17  *    distribution.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
20  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
23  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
26  * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
27  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
28  * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
29  * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30  */
31 
32 #include "namespace.h"
33 #include <sys/types.h>
34 #include <sys/queue.h>
35 #include <sys/mman.h>
36 #include <sys/stat.h>
37 #include <errno.h>
38 #include <machine/atomic.h>
39 #include <sys/umtx.h>
40 #include <limits.h>
41 #include <fcntl.h>
42 #include <pthread.h>
43 #include <stdarg.h>
44 #include <stdbool.h>
45 #include <stdlib.h>
46 #include <string.h>
47 #include <time.h>
48 #include <semaphore.h>
49 #include <unistd.h>
50 #include "un-namespace.h"
51 #include "libc_private.h"
52 
53 __weak_reference(_sem_close, sem_close);
54 __weak_reference(_sem_destroy, sem_destroy);
55 __weak_reference(_sem_getvalue, sem_getvalue);
56 __weak_reference(_sem_init, sem_init);
57 __weak_reference(_sem_open, sem_open);
58 __weak_reference(_sem_post, sem_post);
59 __weak_reference(_sem_timedwait, sem_timedwait);
60 __weak_reference(_sem_clockwait_np, sem_clockwait_np);
61 __weak_reference(_sem_trywait, sem_trywait);
62 __weak_reference(_sem_unlink, sem_unlink);
63 __weak_reference(_sem_wait, sem_wait);
64 
65 #define SEM_PREFIX	"/tmp/SEMD"
66 #define SEM_MAGIC	((u_int32_t)0x73656d32)
67 
68 _Static_assert(SEM_VALUE_MAX <= USEM_MAX_COUNT, "SEM_VALUE_MAX too large");
69 
70 struct sem_nameinfo {
71 	int open_count;
72 	char *name;
73 	dev_t dev;
74 	ino_t ino;
75 	sem_t *sem;
76 	LIST_ENTRY(sem_nameinfo) next;
77 };
78 
79 static pthread_once_t once = PTHREAD_ONCE_INIT;
80 static pthread_mutex_t sem_llock;
81 static LIST_HEAD(, sem_nameinfo) sem_list = LIST_HEAD_INITIALIZER(sem_list);
82 
83 static void
84 sem_prefork(void)
85 {
86 
87 	_pthread_mutex_lock(&sem_llock);
88 }
89 
90 static void
91 sem_postfork(void)
92 {
93 
94 	_pthread_mutex_unlock(&sem_llock);
95 }
96 
97 static void
98 sem_child_postfork(void)
99 {
100 
101 	_pthread_mutex_unlock(&sem_llock);
102 }
103 
104 static void
105 sem_module_init(void)
106 {
107 
108 	_pthread_mutex_init(&sem_llock, NULL);
109 	_pthread_atfork(sem_prefork, sem_postfork, sem_child_postfork);
110 }
111 
112 static inline int
113 sem_check_validity(sem_t *sem)
114 {
115 
116 	if (sem->_magic == SEM_MAGIC)
117 		return (0);
118 	errno = EINVAL;
119 	return (-1);
120 }
121 
122 int
123 _sem_init(sem_t *sem, int pshared, unsigned int value)
124 {
125 
126 	if (value > SEM_VALUE_MAX) {
127 		errno = EINVAL;
128 		return (-1);
129 	}
130 
131 	bzero(sem, sizeof(sem_t));
132 	sem->_magic = SEM_MAGIC;
133 	sem->_kern._count = (u_int32_t)value;
134 	sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0;
135 	return (0);
136 }
137 
138 sem_t *
139 _sem_open(const char *name, int flags, ...)
140 {
141 	char path[PATH_MAX];
142 	struct stat sb;
143 	va_list ap;
144 	struct sem_nameinfo *ni;
145 	sem_t *sem, tmp;
146 	int errsave, fd, len, mode, value;
147 
148 	ni = NULL;
149 	sem = NULL;
150 	fd = -1;
151 	value = 0;
152 
153 	if (name[0] != '/') {
154 		errno = EINVAL;
155 		return (SEM_FAILED);
156 	}
157 	name++;
158 	strcpy(path, SEM_PREFIX);
159 	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
160 		errno = ENAMETOOLONG;
161 		return (SEM_FAILED);
162 	}
163 	if (flags & ~(O_CREAT|O_EXCL)) {
164 		errno = EINVAL;
165 		return (SEM_FAILED);
166 	}
167 	if ((flags & O_CREAT) != 0) {
168 		va_start(ap, flags);
169 		mode = va_arg(ap, int);
170 		value = va_arg(ap, int);
171 		va_end(ap);
172 	}
173 	fd = -1;
174 	_pthread_once(&once, sem_module_init);
175 
176 	_pthread_mutex_lock(&sem_llock);
177 	LIST_FOREACH(ni, &sem_list, next) {
178 		if (ni->name != NULL && strcmp(name, ni->name) == 0) {
179 			fd = _open(path, flags | O_RDWR | O_CLOEXEC |
180 			    O_EXLOCK, mode);
181 			if (fd == -1 || _fstat(fd, &sb) == -1) {
182 				ni = NULL;
183 				goto error;
184 			}
185 			if ((flags & (O_CREAT | O_EXCL)) == (O_CREAT |
186 			    O_EXCL) || ni->dev != sb.st_dev ||
187 			    ni->ino != sb.st_ino) {
188 				ni->name = NULL;
189 				ni = NULL;
190 				break;
191 			}
192 			ni->open_count++;
193 			sem = ni->sem;
194 			_pthread_mutex_unlock(&sem_llock);
195 			_close(fd);
196 			return (sem);
197 		}
198 	}
199 
200 	len = sizeof(*ni) + strlen(name) + 1;
201 	ni = (struct sem_nameinfo *)malloc(len);
202 	if (ni == NULL) {
203 		errno = ENOSPC;
204 		goto error;
205 	}
206 
207 	ni->name = (char *)(ni+1);
208 	strcpy(ni->name, name);
209 
210 	if (fd == -1) {
211 		fd = _open(path, flags | O_RDWR | O_CLOEXEC | O_EXLOCK, mode);
212 		if (fd == -1 || _fstat(fd, &sb) == -1)
213 			goto error;
214 	}
215 	if (sb.st_size < sizeof(sem_t)) {
216 		tmp._magic = SEM_MAGIC;
217 		tmp._kern._count = value;
218 		tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
219 		if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp))
220 			goto error;
221 	}
222 	flock(fd, LOCK_UN);
223 	sem = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE,
224 	    MAP_SHARED | MAP_NOSYNC, fd, 0);
225 	if (sem == MAP_FAILED) {
226 		sem = NULL;
227 		if (errno == ENOMEM)
228 			errno = ENOSPC;
229 		goto error;
230 	}
231 	if (sem->_magic != SEM_MAGIC) {
232 		errno = EINVAL;
233 		goto error;
234 	}
235 	ni->open_count = 1;
236 	ni->sem = sem;
237 	ni->dev = sb.st_dev;
238 	ni->ino = sb.st_ino;
239 	LIST_INSERT_HEAD(&sem_list, ni, next);
240 	_close(fd);
241 	_pthread_mutex_unlock(&sem_llock);
242 	return (sem);
243 
244 error:
245 	errsave = errno;
246 	if (fd != -1)
247 		_close(fd);
248 	if (sem != NULL)
249 		munmap(sem, sizeof(sem_t));
250 	free(ni);
251 	_pthread_mutex_unlock(&sem_llock);
252 	errno = errsave;
253 	return (SEM_FAILED);
254 }
255 
256 int
257 _sem_close(sem_t *sem)
258 {
259 	struct sem_nameinfo *ni;
260 	bool last;
261 
262 	if (sem_check_validity(sem) != 0)
263 		return (-1);
264 
265 	if (!(sem->_kern._flags & SEM_NAMED)) {
266 		errno = EINVAL;
267 		return (-1);
268 	}
269 
270 	_pthread_once(&once, sem_module_init);
271 
272 	_pthread_mutex_lock(&sem_llock);
273 	LIST_FOREACH(ni, &sem_list, next) {
274 		if (sem == ni->sem) {
275 			last = --ni->open_count == 0;
276 			if (last)
277 				LIST_REMOVE(ni, next);
278 			_pthread_mutex_unlock(&sem_llock);
279 			if (last) {
280 				munmap(sem, sizeof(*sem));
281 				free(ni);
282 			}
283 			return (0);
284 		}
285 	}
286 	_pthread_mutex_unlock(&sem_llock);
287 	errno = EINVAL;
288 	return (-1);
289 }
290 
291 int
292 _sem_unlink(const char *name)
293 {
294 	char path[PATH_MAX];
295 
296 	if (name[0] != '/') {
297 		errno = ENOENT;
298 		return -1;
299 	}
300 	name++;
301 	strcpy(path, SEM_PREFIX);
302 	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
303 		errno = ENAMETOOLONG;
304 		return (-1);
305 	}
306 
307 	return (unlink(path));
308 }
309 
310 int
311 _sem_destroy(sem_t *sem)
312 {
313 
314 	if (sem_check_validity(sem) != 0)
315 		return (-1);
316 
317 	if (sem->_kern._flags & SEM_NAMED) {
318 		errno = EINVAL;
319 		return (-1);
320 	}
321 	sem->_magic = 0;
322 	return (0);
323 }
324 
325 int
326 _sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
327 {
328 
329 	if (sem_check_validity(sem) != 0)
330 		return (-1);
331 
332 	*sval = (int)USEM_COUNT(sem->_kern._count);
333 	return (0);
334 }
335 
336 static __inline int
337 usem_wake(struct _usem2 *sem)
338 {
339 
340 	return (_umtx_op(sem, UMTX_OP_SEM2_WAKE, 0, NULL, NULL));
341 }
342 
343 static __inline int
344 usem_wait(struct _usem2 *sem, clockid_t clock_id, int flags,
345     const struct timespec *rqtp, struct timespec *rmtp)
346 {
347 	struct {
348 		struct _umtx_time timeout;
349 		struct timespec remain;
350 	} tms;
351 	void *tm_p;
352 	size_t tm_size;
353 	int retval;
354 
355 	if (rqtp == NULL) {
356 		tm_p = NULL;
357 		tm_size = 0;
358 	} else {
359 		tms.timeout._clockid = clock_id;
360 		tms.timeout._flags = (flags & TIMER_ABSTIME) ? UMTX_ABSTIME : 0;
361 		tms.timeout._timeout = *rqtp;
362 		tm_p = &tms;
363 		tm_size = sizeof(tms);
364 	}
365 	retval = _umtx_op(sem, UMTX_OP_SEM2_WAIT, 0, (void *)tm_size, tm_p);
366 	if (retval == -1 && errno == EINTR && (flags & TIMER_ABSTIME) == 0 &&
367 	    rqtp != NULL && rmtp != NULL) {
368 		*rmtp = tms.remain;
369 	}
370 
371 	return (retval);
372 }
373 
374 int
375 _sem_trywait(sem_t *sem)
376 {
377 	int val;
378 
379 	if (sem_check_validity(sem) != 0)
380 		return (-1);
381 
382 	while (USEM_COUNT(val = sem->_kern._count) > 0) {
383 		if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
384 			return (0);
385 	}
386 	errno = EAGAIN;
387 	return (-1);
388 }
389 
390 int
391 _sem_clockwait_np(sem_t * __restrict sem, clockid_t clock_id, int flags,
392 	const struct timespec *rqtp, struct timespec *rmtp)
393 {
394 	int val, retval;
395 
396 	if (sem_check_validity(sem) != 0)
397 		return (-1);
398 
399 	retval = 0;
400 	_pthread_testcancel();
401 	for (;;) {
402 		while (USEM_COUNT(val = sem->_kern._count) > 0) {
403 			if (atomic_cmpset_acq_int(&sem->_kern._count, val,
404 			    val - 1))
405 				return (0);
406 		}
407 
408 		if (retval) {
409 			_pthread_testcancel();
410 			break;
411 		}
412 
413 		/*
414 		 * The timeout argument is only supposed to
415 		 * be checked if the thread would have blocked.
416 		 */
417 		if (rqtp != NULL) {
418 			if (rqtp->tv_nsec >= 1000000000 || rqtp->tv_nsec < 0) {
419 				errno = EINVAL;
420 				return (-1);
421 			}
422 		}
423 		_pthread_cancel_enter(1);
424 		retval = usem_wait(&sem->_kern, clock_id, flags, rqtp, rmtp);
425 		_pthread_cancel_leave(0);
426 	}
427 	return (retval);
428 }
429 
430 int
431 _sem_timedwait(sem_t * __restrict sem,
432 	const struct timespec * __restrict abstime)
433 {
434 
435 	return (_sem_clockwait_np(sem, CLOCK_REALTIME, TIMER_ABSTIME, abstime,
436 	    NULL));
437 };
438 
439 int
440 _sem_wait(sem_t *sem)
441 {
442 
443 	return (_sem_timedwait(sem, NULL));
444 }
445 
446 /*
447  * POSIX:
448  * The sem_post() interface is reentrant with respect to signals and may be
449  * invoked from a signal-catching function.
450  * The implementation does not use lock, so it should be safe.
451  */
452 int
453 _sem_post(sem_t *sem)
454 {
455 	unsigned int count;
456 
457 	if (sem_check_validity(sem) != 0)
458 		return (-1);
459 
460 	do {
461 		count = sem->_kern._count;
462 		if (USEM_COUNT(count) + 1 > SEM_VALUE_MAX) {
463 			errno = EOVERFLOW;
464 			return (-1);
465 		}
466 	} while (!atomic_cmpset_rel_int(&sem->_kern._count, count, count + 1));
467 	if (count & USEM_HAS_WAITERS)
468 		usem_wake(&sem->_kern);
469 	return (0);
470 }
471