xref: /freebsd/lib/libc/gen/sem_new.c (revision 4f52dfbb) 
1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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  * $FreeBSD$
32  */
33 
34 #include "namespace.h"
35 #include <sys/types.h>
36 #include <sys/queue.h>
37 #include <sys/mman.h>
38 #include <sys/stat.h>
39 #include <errno.h>
40 #include <machine/atomic.h>
41 #include <sys/umtx.h>
42 #include <limits.h>
43 #include <fcntl.h>
44 #include <pthread.h>
45 #include <stdarg.h>
46 #include <stdbool.h>
47 #include <stdlib.h>
48 #include <string.h>
49 #include <time.h>
50 #include <semaphore.h>
51 #include <unistd.h>
52 #include "un-namespace.h"
53 #include "libc_private.h"
54 
55 __weak_reference(_sem_close, sem_close);
56 __weak_reference(_sem_destroy, sem_destroy);
57 __weak_reference(_sem_getvalue, sem_getvalue);
58 __weak_reference(_sem_init, sem_init);
59 __weak_reference(_sem_open, sem_open);
60 __weak_reference(_sem_post, sem_post);
61 __weak_reference(_sem_timedwait, sem_timedwait);
62 __weak_reference(_sem_clockwait_np, sem_clockwait_np);
63 __weak_reference(_sem_trywait, sem_trywait);
64 __weak_reference(_sem_unlink, sem_unlink);
65 __weak_reference(_sem_wait, sem_wait);
66 
67 #define SEM_PREFIX	"/tmp/SEMD"
68 #define SEM_MAGIC	((u_int32_t)0x73656d32)
69 
70 _Static_assert(SEM_VALUE_MAX <= USEM_MAX_COUNT, "SEM_VALUE_MAX too large");
71 
72 struct sem_nameinfo {
73 	int open_count;
74 	char *name;
75 	dev_t dev;
76 	ino_t ino;
77 	sem_t *sem;
78 	LIST_ENTRY(sem_nameinfo) next;
79 };
80 
81 static pthread_once_t once = PTHREAD_ONCE_INIT;
82 static pthread_mutex_t sem_llock;
83 static LIST_HEAD(, sem_nameinfo) sem_list = LIST_HEAD_INITIALIZER(sem_list);
84 
85 static void
86 sem_prefork(void)
87 {
88 
89 	_pthread_mutex_lock(&sem_llock);
90 }
91 
92 static void
93 sem_postfork(void)
94 {
95 
96 	_pthread_mutex_unlock(&sem_llock);
97 }
98 
99 static void
100 sem_child_postfork(void)
101 {
102 
103 	_pthread_mutex_unlock(&sem_llock);
104 }
105 
106 static void
107 sem_module_init(void)
108 {
109 
110 	_pthread_mutex_init(&sem_llock, NULL);
111 	_pthread_atfork(sem_prefork, sem_postfork, sem_child_postfork);
112 }
113 
114 static inline int
115 sem_check_validity(sem_t *sem)
116 {
117 
118 	if (sem->_magic == SEM_MAGIC)
119 		return (0);
120 	errno = EINVAL;
121 	return (-1);
122 }
123 
124 int
125 _sem_init(sem_t *sem, int pshared, unsigned int value)
126 {
127 
128 	if (value > SEM_VALUE_MAX) {
129 		errno = EINVAL;
130 		return (-1);
131 	}
132 
133 	bzero(sem, sizeof(sem_t));
134 	sem->_magic = SEM_MAGIC;
135 	sem->_kern._count = (u_int32_t)value;
136 	sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0;
137 	return (0);
138 }
139 
140 sem_t *
141 _sem_open(const char *name, int flags, ...)
142 {
143 	char path[PATH_MAX];
144 	struct stat sb;
145 	va_list ap;
146 	struct sem_nameinfo *ni;
147 	sem_t *sem, tmp;
148 	int errsave, fd, len, mode, value;
149 
150 	ni = NULL;
151 	sem = NULL;
152 	fd = -1;
153 	value = 0;
154 
155 	if (name[0] != '/') {
156 		errno = EINVAL;
157 		return (SEM_FAILED);
158 	}
159 	name++;
160 	strcpy(path, SEM_PREFIX);
161 	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
162 		errno = ENAMETOOLONG;
163 		return (SEM_FAILED);
164 	}
165 	if (flags & ~(O_CREAT|O_EXCL)) {
166 		errno = EINVAL;
167 		return (SEM_FAILED);
168 	}
169 	if ((flags & O_CREAT) != 0) {
170 		va_start(ap, flags);
171 		mode = va_arg(ap, int);
172 		value = va_arg(ap, int);
173 		va_end(ap);
174 	}
175 	fd = -1;
176 	_pthread_once(&once, sem_module_init);
177 
178 	_pthread_mutex_lock(&sem_llock);
179 	LIST_FOREACH(ni, &sem_list, next) {
180 		if (ni->name != NULL && strcmp(name, ni->name) == 0) {
181 			fd = _open(path, flags | O_RDWR | O_CLOEXEC |
182 			    O_EXLOCK, mode);
183 			if (fd == -1 || _fstat(fd, &sb) == -1) {
184 				ni = NULL;
185 				goto error;
186 			}
187 			if ((flags & (O_CREAT | O_EXCL)) == (O_CREAT |
188 			    O_EXCL) || ni->dev != sb.st_dev ||
189 			    ni->ino != sb.st_ino) {
190 				ni->name = NULL;
191 				ni = NULL;
192 				break;
193 			}
194 			ni->open_count++;
195 			sem = ni->sem;
196 			_pthread_mutex_unlock(&sem_llock);
197 			_close(fd);
198 			return (sem);
199 		}
200 	}
201 
202 	len = sizeof(*ni) + strlen(name) + 1;
203 	ni = (struct sem_nameinfo *)malloc(len);
204 	if (ni == NULL) {
205 		errno = ENOSPC;
206 		goto error;
207 	}
208 
209 	ni->name = (char *)(ni+1);
210 	strcpy(ni->name, name);
211 
212 	if (fd == -1) {
213 		fd = _open(path, flags | O_RDWR | O_CLOEXEC | O_EXLOCK, mode);
214 		if (fd == -1 || _fstat(fd, &sb) == -1)
215 			goto error;
216 	}
217 	if (sb.st_size < sizeof(sem_t)) {
218 		tmp._magic = SEM_MAGIC;
219 		tmp._kern._count = value;
220 		tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
221 		if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp))
222 			goto error;
223 	}
224 	flock(fd, LOCK_UN);
225 	sem = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE,
226 	    MAP_SHARED | MAP_NOSYNC, fd, 0);
227 	if (sem == MAP_FAILED) {
228 		sem = NULL;
229 		if (errno == ENOMEM)
230 			errno = ENOSPC;
231 		goto error;
232 	}
233 	if (sem->_magic != SEM_MAGIC) {
234 		errno = EINVAL;
235 		goto error;
236 	}
237 	ni->open_count = 1;
238 	ni->sem = sem;
239 	ni->dev = sb.st_dev;
240 	ni->ino = sb.st_ino;
241 	LIST_INSERT_HEAD(&sem_list, ni, next);
242 	_close(fd);
243 	_pthread_mutex_unlock(&sem_llock);
244 	return (sem);
245 
246 error:
247 	errsave = errno;
248 	if (fd != -1)
249 		_close(fd);
250 	if (sem != NULL)
251 		munmap(sem, sizeof(sem_t));
252 	free(ni);
253 	_pthread_mutex_unlock(&sem_llock);
254 	errno = errsave;
255 	return (SEM_FAILED);
256 }
257 
258 int
259 _sem_close(sem_t *sem)
260 {
261 	struct sem_nameinfo *ni;
262 	bool last;
263 
264 	if (sem_check_validity(sem) != 0)
265 		return (-1);
266 
267 	if (!(sem->_kern._flags & SEM_NAMED)) {
268 		errno = EINVAL;
269 		return (-1);
270 	}
271 
272 	_pthread_once(&once, sem_module_init);
273 
274 	_pthread_mutex_lock(&sem_llock);
275 	LIST_FOREACH(ni, &sem_list, next) {
276 		if (sem == ni->sem) {
277 			last = --ni->open_count == 0;
278 			if (last)
279 				LIST_REMOVE(ni, next);
280 			_pthread_mutex_unlock(&sem_llock);
281 			if (last) {
282 				munmap(sem, sizeof(*sem));
283 				free(ni);
284 			}
285 			return (0);
286 		}
287 	}
288 	_pthread_mutex_unlock(&sem_llock);
289 	errno = EINVAL;
290 	return (-1);
291 }
292 
293 int
294 _sem_unlink(const char *name)
295 {
296 	char path[PATH_MAX];
297 
298 	if (name[0] != '/') {
299 		errno = ENOENT;
300 		return -1;
301 	}
302 	name++;
303 	strcpy(path, SEM_PREFIX);
304 	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
305 		errno = ENAMETOOLONG;
306 		return (-1);
307 	}
308 
309 	return (unlink(path));
310 }
311 
312 int
313 _sem_destroy(sem_t *sem)
314 {
315 
316 	if (sem_check_validity(sem) != 0)
317 		return (-1);
318 
319 	if (sem->_kern._flags & SEM_NAMED) {
320 		errno = EINVAL;
321 		return (-1);
322 	}
323 	sem->_magic = 0;
324 	return (0);
325 }
326 
327 int
328 _sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
329 {
330 
331 	if (sem_check_validity(sem) != 0)
332 		return (-1);
333 
334 	*sval = (int)USEM_COUNT(sem->_kern._count);
335 	return (0);
336 }
337 
338 static __inline int
339 usem_wake(struct _usem2 *sem)
340 {
341 
342 	return (_umtx_op(sem, UMTX_OP_SEM2_WAKE, 0, NULL, NULL));
343 }
344 
345 static __inline int
346 usem_wait(struct _usem2 *sem, clockid_t clock_id, int flags,
347     const struct timespec *rqtp, struct timespec *rmtp)
348 {
349 	struct {
350 		struct _umtx_time timeout;
351 		struct timespec remain;
352 	} tms;
353 	void *tm_p;
354 	size_t tm_size;
355 	int retval;
356 
357 	if (rqtp == NULL) {
358 		tm_p = NULL;
359 		tm_size = 0;
360 	} else {
361 		tms.timeout._clockid = clock_id;
362 		tms.timeout._flags = (flags & TIMER_ABSTIME) ? UMTX_ABSTIME : 0;
363 		tms.timeout._timeout = *rqtp;
364 		tm_p = &tms;
365 		tm_size = sizeof(tms);
366 	}
367 	retval = _umtx_op(sem, UMTX_OP_SEM2_WAIT, 0, (void *)tm_size, tm_p);
368 	if (retval == -1 && errno == EINTR && (flags & TIMER_ABSTIME) == 0 &&
369 	    rqtp != NULL && rmtp != NULL) {
370 		*rmtp = tms.remain;
371 	}
372 
373 	return (retval);
374 }
375 
376 int
377 _sem_trywait(sem_t *sem)
378 {
379 	int val;
380 
381 	if (sem_check_validity(sem) != 0)
382 		return (-1);
383 
384 	while (USEM_COUNT(val = sem->_kern._count) > 0) {
385 		if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
386 			return (0);
387 	}
388 	errno = EAGAIN;
389 	return (-1);
390 }
391 
392 int
393 _sem_clockwait_np(sem_t * __restrict sem, clockid_t clock_id, int flags,
394 	const struct timespec *rqtp, struct timespec *rmtp)
395 {
396 	int val, retval;
397 
398 	if (sem_check_validity(sem) != 0)
399 		return (-1);
400 
401 	retval = 0;
402 	_pthread_testcancel();
403 	for (;;) {
404 		while (USEM_COUNT(val = sem->_kern._count) > 0) {
405 			if (atomic_cmpset_acq_int(&sem->_kern._count, val,
406 			    val - 1))
407 				return (0);
408 		}
409 
410 		if (retval) {
411 			_pthread_testcancel();
412 			break;
413 		}
414 
415 		/*
416 		 * The timeout argument is only supposed to
417 		 * be checked if the thread would have blocked.
418 		 */
419 		if (rqtp != NULL) {
420 			if (rqtp->tv_nsec >= 1000000000 || rqtp->tv_nsec < 0) {
421 				errno = EINVAL;
422 				return (-1);
423 			}
424 		}
425 		_pthread_cancel_enter(1);
426 		retval = usem_wait(&sem->_kern, clock_id, flags, rqtp, rmtp);
427 		_pthread_cancel_leave(0);
428 	}
429 	return (retval);
430 }
431 
432 int
433 _sem_timedwait(sem_t * __restrict sem,
434 	const struct timespec * __restrict abstime)
435 {
436 
437 	return (_sem_clockwait_np(sem, CLOCK_REALTIME, TIMER_ABSTIME, abstime,
438 	    NULL));
439 };
440 
441 int
442 _sem_wait(sem_t *sem)
443 {
444 
445 	return (_sem_timedwait(sem, NULL));
446 }
447 
448 /*
449  * POSIX:
450  * The sem_post() interface is reentrant with respect to signals and may be
451  * invoked from a signal-catching function.
452  * The implementation does not use lock, so it should be safe.
453  */
454 int
455 _sem_post(sem_t *sem)
456 {
457 	unsigned int count;
458 
459 	if (sem_check_validity(sem) != 0)
460 		return (-1);
461 
462 	do {
463 		count = sem->_kern._count;
464 		if (USEM_COUNT(count) + 1 > SEM_VALUE_MAX) {
465 			errno = EOVERFLOW;
466 			return (-1);
467 		}
468 	} while (!atomic_cmpset_rel_int(&sem->_kern._count, count, count + 1));
469 	if (count & USEM_HAS_WAITERS)
470 		usem_wake(&sem->_kern);
471 	return (0);
472 }
473