Fix: waiter: futex wait: handle spurious futex wakeups
[lttng-tools.git] / src / common / fd-tracker / fd-tracker.cpp
1 /*
2 * Copyright (C) 2018-2020 Jérémie Galarneau <jeremie.galarneau@efficios.com>
3 *
4 * SPDX-License-Identifier: GPL-2.0-only
5 *
6 */
7
8 #include <urcu.h>
9 #include <urcu/list.h>
10 #include <urcu/rculfhash.h>
11
12 #include <fcntl.h>
13 #include <inttypes.h>
14 #include <pthread.h>
15 #include <stdbool.h>
16 #include <sys/stat.h>
17 #include <sys/types.h>
18
19 #include <common/defaults.hpp>
20 #include <common/error.hpp>
21 #include <common/fs-handle-internal.hpp>
22 #include <common/hashtable/hashtable.hpp>
23 #include <common/hashtable/utils.hpp>
24 #include <common/macros.hpp>
25 #include <common/optional.hpp>
26
27 #include "fd-tracker.hpp"
28 #include "inode.hpp"
29
30 /* Tracker lock must be taken by the user. */
31 #define TRACKED_COUNT(tracker) \
32 (tracker->count.suspendable.active + \
33 tracker->count.suspendable.suspended + \
34 tracker->count.unsuspendable)
35
36 /* Tracker lock must be taken by the user. */
37 #define ACTIVE_COUNT(tracker) \
38 (tracker->count.suspendable.active + tracker->count.unsuspendable)
39
40 /* Tracker lock must be taken by the user. */
41 #define SUSPENDED_COUNT(tracker) (tracker->count.suspendable.suspended)
42
43 /* Tracker lock must be taken by the user. */
44 #define SUSPENDABLE_COUNT(tracker) \
45 (tracker->count.suspendable.active + \
46 tracker->count.suspendable.suspended)
47
48 /* Tracker lock must be taken by the user. */
49 #define UNSUSPENDABLE_COUNT(tracker) (tracker->count.unsuspendable)
50
51 struct fd_tracker {
52 pthread_mutex_t lock;
53 struct {
54 struct {
55 unsigned int active;
56 unsigned int suspended;
57 } suspendable;
58 unsigned int unsuspendable;
59 } count;
60 unsigned int capacity;
61 struct {
62 uint64_t uses;
63 uint64_t misses;
64 /* Failures to suspend or restore fs handles. */
65 uint64_t errors;
66 } stats;
67 /*
68 * The head of the active_handles list is always the least recently
69 * used active handle. When an handle is used, it is removed from the
70 * list and added to the end. When a file has to be suspended, the
71 * first element in the list is "popped", suspended, and added to the
72 * list of suspended handles.
73 */
74 struct cds_list_head active_handles;
75 struct cds_list_head suspended_handles;
76 struct cds_lfht *unsuspendable_fds;
77 struct lttng_inode_registry *inode_registry;
78 /* Unlinked files are moved in this directory under a unique name. */
79 struct lttng_directory_handle *unlink_directory_handle;
80 struct lttng_unlinked_file_pool *unlinked_file_pool;
81 };
82
83 namespace {
84 struct open_properties {
85 int flags;
86 LTTNG_OPTIONAL(mode_t) mode;
87 };
88
89 /*
90 * A fs_handle_tracked is not ref-counted. Therefore, it is assumed that a
91 * handle is never in-use while it is being reclaimed. It can be
92 * shared by multiple threads, but external synchronization is required
93 * to ensure it is not still being used when it is reclaimed (close method).
94 * In this respect, it is not different from a regular file descriptor.
95 *
96 * The fs_handle lock always nests _within_ the tracker's lock.
97 */
98 struct fs_handle_tracked {
99 struct fs_handle parent;
100 pthread_mutex_t lock;
101 /*
102 * Weak reference to the tracker. All fs_handles are assumed to have
103 * been closed at the moment of the destruction of the fd_tracker.
104 */
105 struct fd_tracker *tracker;
106 struct open_properties properties;
107 struct lttng_inode *inode;
108 int fd;
109 /* inode number of the file at the time of the handle's creation. */
110 uint64_t ino;
111 bool in_use;
112 /* Offset to which the file should be restored. */
113 off_t offset;
114 struct cds_list_head handles_list_node;
115 };
116
117 struct unsuspendable_fd {
118 /*
119 * Accesses are only performed through the tracker, which is protected
120 * by its own lock.
121 */
122 int fd;
123 char *name;
124 struct cds_lfht_node tracker_node;
125 struct rcu_head rcu_head;
126 };
127
128 struct {
129 pthread_mutex_t lock;
130 bool initialized;
131 unsigned long value;
132 } seed = {
133 .lock = PTHREAD_MUTEX_INITIALIZER,
134 .initialized = false,
135 .value = 0,
136 };
137 } /* namespace */
138
139 static int match_fd(struct cds_lfht_node *node, const void *key);
140 static void unsuspendable_fd_destroy(struct unsuspendable_fd *entry);
141 static struct unsuspendable_fd *unsuspendable_fd_create(
142 const char *name, int fd);
143 static int open_from_properties(const struct lttng_directory_handle *dir_handle,
144 const char *path, struct open_properties *properties);
145
146 static void fs_handle_tracked_log(struct fs_handle_tracked *handle);
147 static int fs_handle_tracked_suspend(struct fs_handle_tracked *handle);
148 static int fs_handle_tracked_restore(struct fs_handle_tracked *handle);
149 static int fs_handle_tracked_get_fd(struct fs_handle *_handle);
150 static void fs_handle_tracked_put_fd(struct fs_handle *_handle);
151 static int fs_handle_tracked_unlink(struct fs_handle *_handle);
152 static int fs_handle_tracked_close(struct fs_handle *_handle);
153
154 static void fd_tracker_track(
155 struct fd_tracker *tracker, struct fs_handle_tracked *handle);
156 static void fd_tracker_untrack(
157 struct fd_tracker *tracker, struct fs_handle_tracked *handle);
158 static int fd_tracker_suspend_handles(
159 struct fd_tracker *tracker, unsigned int count);
160 static int fd_tracker_restore_handle(
161 struct fd_tracker *tracker, struct fs_handle_tracked *handle);
162
163 /* Match function of the tracker's unsuspendable_fds hash table. */
164 static int match_fd(struct cds_lfht_node *node, const void *key)
165 {
166 struct unsuspendable_fd *entry = lttng::utils::container_of(
167 node, &unsuspendable_fd::tracker_node);
168
169 return hash_match_key_ulong(
170 (void *) (unsigned long) entry->fd, (void *) key);
171 }
172
173 static void delete_unsuspendable_fd(struct rcu_head *head)
174 {
175 struct unsuspendable_fd *fd = caa_container_of(
176 head, struct unsuspendable_fd, rcu_head);
177
178 free(fd->name);
179 free(fd);
180 }
181
182 static void unsuspendable_fd_destroy(struct unsuspendable_fd *entry)
183 {
184 if (!entry) {
185 return;
186 }
187 call_rcu(&entry->rcu_head, delete_unsuspendable_fd);
188 }
189
190 static struct unsuspendable_fd *unsuspendable_fd_create(
191 const char *name, int fd)
192 {
193 struct unsuspendable_fd *entry = zmalloc<unsuspendable_fd>();
194
195 if (!entry) {
196 goto error;
197 }
198 if (name) {
199 entry->name = strdup(name);
200 if (!entry->name) {
201 goto error;
202 }
203 }
204 cds_lfht_node_init(&entry->tracker_node);
205 entry->fd = fd;
206 return entry;
207 error:
208 unsuspendable_fd_destroy(entry);
209 return NULL;
210 }
211
212 static void fs_handle_tracked_log(struct fs_handle_tracked *handle)
213 {
214 const char *path;
215
216 pthread_mutex_lock(&handle->lock);
217 lttng_inode_borrow_location(handle->inode, NULL, &path);
218
219 if (handle->fd >= 0) {
220 DBG_NO_LOC(" %s [active, fd %d%s]", path, handle->fd,
221 handle->in_use ? ", in use" : "");
222 } else {
223 DBG_NO_LOC(" %s [suspended]", path);
224 }
225 pthread_mutex_unlock(&handle->lock);
226 }
227
228 /* Tracker lock must be held by the caller. */
229 static int fs_handle_tracked_suspend(struct fs_handle_tracked *handle)
230 {
231 int ret = 0;
232 struct stat fs_stat;
233 const char *path;
234 const struct lttng_directory_handle *node_directory_handle;
235
236 pthread_mutex_lock(&handle->lock);
237 lttng_inode_borrow_location(
238 handle->inode, &node_directory_handle, &path);
239 LTTNG_ASSERT(handle->fd >= 0);
240 if (handle->in_use) {
241 /* This handle can't be suspended as it is currently in use. */
242 ret = -EAGAIN;
243 goto end;
244 }
245
246 ret = lttng_directory_handle_stat(
247 node_directory_handle, path, &fs_stat);
248 if (ret) {
249 PERROR("Filesystem handle to %s cannot be suspended as stat() failed",
250 path);
251 ret = -errno;
252 goto end;
253 }
254
255 if (fs_stat.st_ino != handle->ino) {
256 /* Don't suspend as the handle would not be restorable. */
257 WARN("Filesystem handle to %s cannot be suspended as its inode changed",
258 path);
259 ret = -ENOENT;
260 goto end;
261 }
262
263 handle->offset = lseek(handle->fd, 0, SEEK_CUR);
264 if (handle->offset == -1) {
265 WARN("Filesystem handle to %s cannot be suspended as lseek() failed to sample its current position",
266 path);
267 ret = -errno;
268 goto end;
269 }
270
271 ret = close(handle->fd);
272 if (ret) {
273 PERROR("Filesystem handle to %s cannot be suspended as close() failed",
274 path);
275 ret = -errno;
276 goto end;
277 }
278 DBG("Suspended filesystem handle to %s (fd %i) at position %" PRId64,
279 path, handle->fd, handle->offset);
280 handle->fd = -1;
281 end:
282 if (ret) {
283 handle->tracker->stats.errors++;
284 }
285 pthread_mutex_unlock(&handle->lock);
286 return ret;
287 }
288
289 /* Caller must hold the tracker and handle's locks. */
290 static int fs_handle_tracked_restore(struct fs_handle_tracked *handle)
291 {
292 int ret, fd = -1;
293 const char *path;
294 const struct lttng_directory_handle *node_directory_handle;
295
296 lttng_inode_borrow_location(
297 handle->inode, &node_directory_handle, &path);
298
299 LTTNG_ASSERT(handle->fd == -1);
300 LTTNG_ASSERT(path);
301 ret = open_from_properties(
302 node_directory_handle, path, &handle->properties);
303 if (ret < 0) {
304 PERROR("Failed to restore filesystem handle to %s, open() failed",
305 path);
306 ret = -errno;
307 goto end;
308 }
309 fd = ret;
310
311 ret = lseek(fd, handle->offset, SEEK_SET);
312 if (ret < 0) {
313 PERROR("Failed to restore filesystem handle to %s, lseek() failed",
314 path);
315 ret = -errno;
316 goto end;
317 }
318 DBG("Restored filesystem handle to %s (fd %i) at position %" PRId64,
319 path, fd, handle->offset);
320 ret = 0;
321 handle->fd = fd;
322 fd = -1;
323 end:
324 if (fd >= 0) {
325 (void) close(fd);
326 }
327 return ret;
328 }
329
330 static int open_from_properties(const struct lttng_directory_handle *dir_handle,
331 const char *path, struct open_properties *properties)
332 {
333 int ret;
334
335 /*
336 * open() ignores the 'flags' parameter unless the O_CREAT or O_TMPFILE
337 * flags are set. O_TMPFILE would not make sense in the context of a
338 * suspendable fs_handle as it would not be restorable (see OPEN(2)),
339 * thus it is ignored here.
340 */
341 if ((properties->flags & O_CREAT) && properties->mode.is_set) {
342 ret = lttng_directory_handle_open_file(dir_handle, path,
343 properties->flags, properties->mode.value);
344 } else {
345 ret = lttng_directory_handle_open_file(dir_handle, path,
346 properties->flags, 0);
347 }
348 /*
349 * Some flags should not be used beyond the initial open() of a
350 * restorable file system handle. O_CREAT and O_TRUNC must
351 * be cleared since it would be unexpected to re-use them
352 * when the handle is retored:
353 * - O_CREAT should not be needed as the file has been created
354 * on the initial call to open(),
355 * - O_TRUNC would destroy the file's contents by truncating it
356 * to length 0.
357 */
358 properties->flags &= ~(O_CREAT | O_TRUNC);
359 if (ret < 0) {
360 ret = -errno;
361 goto end;
362 }
363 end:
364 return ret;
365 }
366
367 struct fd_tracker *fd_tracker_create(const char *unlinked_file_path,
368 unsigned int capacity)
369 {
370 struct fd_tracker *tracker = zmalloc<fd_tracker>();
371
372 if (!tracker) {
373 goto end;
374 }
375
376 pthread_mutex_lock(&seed.lock);
377 if (!seed.initialized) {
378 seed.value = (unsigned long) time(NULL);
379 seed.initialized = true;
380 }
381 pthread_mutex_unlock(&seed.lock);
382
383 CDS_INIT_LIST_HEAD(&tracker->active_handles);
384 CDS_INIT_LIST_HEAD(&tracker->suspended_handles);
385 tracker->capacity = capacity;
386 tracker->unsuspendable_fds = cds_lfht_new(DEFAULT_HT_SIZE, 1, 0,
387 CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING, NULL);
388 if (!tracker->unsuspendable_fds) {
389 ERR("Failed to create fd-tracker's unsuspendable_fds hash table");
390 goto error;
391 }
392 tracker->inode_registry = lttng_inode_registry_create();
393 if (!tracker->inode_registry) {
394 ERR("Failed to create fd-tracker's inode registry");
395 goto error;
396 }
397
398 tracker->unlinked_file_pool =
399 lttng_unlinked_file_pool_create(unlinked_file_path);
400 if (!tracker->unlinked_file_pool) {
401 goto error;
402 }
403 DBG("File descriptor tracker created with a limit of %u simultaneously-opened FDs",
404 capacity);
405 end:
406 return tracker;
407 error:
408 fd_tracker_destroy(tracker);
409 return NULL;
410 }
411
412 void fd_tracker_log(struct fd_tracker *tracker)
413 {
414 struct fs_handle_tracked *handle;
415 struct unsuspendable_fd *unsuspendable_fd;
416 struct cds_lfht_iter iter;
417
418 pthread_mutex_lock(&tracker->lock);
419 DBG_NO_LOC("File descriptor tracker");
420 DBG_NO_LOC(" Stats:");
421 DBG_NO_LOC(" uses: %" PRIu64, tracker->stats.uses);
422 DBG_NO_LOC(" misses: %" PRIu64, tracker->stats.misses);
423 DBG_NO_LOC(" errors: %" PRIu64, tracker->stats.errors);
424 DBG_NO_LOC(" Tracked: %u", TRACKED_COUNT(tracker));
425 DBG_NO_LOC(" active: %u", ACTIVE_COUNT(tracker));
426 DBG_NO_LOC(" suspendable: %u", SUSPENDABLE_COUNT(tracker));
427 DBG_NO_LOC(" unsuspendable: %u", UNSUSPENDABLE_COUNT(tracker));
428 DBG_NO_LOC(" suspended: %u", SUSPENDED_COUNT(tracker));
429 DBG_NO_LOC(" capacity: %u", tracker->capacity);
430
431 DBG_NO_LOC(" Tracked suspendable file descriptors");
432 cds_list_for_each_entry(
433 handle, &tracker->active_handles, handles_list_node) {
434 fs_handle_tracked_log(handle);
435 }
436 cds_list_for_each_entry(handle, &tracker->suspended_handles,
437 handles_list_node) {
438 fs_handle_tracked_log(handle);
439 }
440 if (!SUSPENDABLE_COUNT(tracker)) {
441 DBG_NO_LOC(" None");
442 }
443
444 DBG_NO_LOC(" Tracked unsuspendable file descriptors");
445 rcu_read_lock();
446 cds_lfht_for_each_entry(tracker->unsuspendable_fds, &iter,
447 unsuspendable_fd, tracker_node) {
448 DBG_NO_LOC(" %s [active, fd %d]",
449 unsuspendable_fd->name ?: "Unnamed",
450 unsuspendable_fd->fd);
451 }
452 rcu_read_unlock();
453 if (!UNSUSPENDABLE_COUNT(tracker)) {
454 DBG_NO_LOC(" None");
455 }
456
457 pthread_mutex_unlock(&tracker->lock);
458 }
459
460 int fd_tracker_destroy(struct fd_tracker *tracker)
461 {
462 int ret = 0;
463
464 if (!tracker) {
465 goto end;
466 }
467 /*
468 * Refuse to destroy the tracker as fs_handles may still old
469 * weak references to the tracker.
470 */
471 pthread_mutex_lock(&tracker->lock);
472 if (TRACKED_COUNT(tracker)) {
473 ERR("A file descriptor leak has been detected: %u tracked file descriptors are still being tracked",
474 TRACKED_COUNT(tracker));
475 pthread_mutex_unlock(&tracker->lock);
476 fd_tracker_log(tracker);
477 ret = -1;
478 goto end;
479 }
480 pthread_mutex_unlock(&tracker->lock);
481
482 if (tracker->unsuspendable_fds) {
483 ret = cds_lfht_destroy(tracker->unsuspendable_fds, NULL);
484 LTTNG_ASSERT(!ret);
485 }
486
487 lttng_inode_registry_destroy(tracker->inode_registry);
488 lttng_unlinked_file_pool_destroy(tracker->unlinked_file_pool);
489 pthread_mutex_destroy(&tracker->lock);
490 free(tracker);
491 end:
492 return ret;
493 }
494
495 struct fs_handle *fd_tracker_open_fs_handle(struct fd_tracker *tracker,
496 struct lttng_directory_handle *directory,
497 const char *path,
498 int flags,
499 mode_t *mode)
500 {
501 int ret;
502 struct fs_handle_tracked *handle = NULL;
503 struct stat fd_stat;
504 struct open_properties properties = {
505 .flags = flags,
506 .mode = {
507 .is_set = !!mode,
508 .value = static_cast<mode_t>(mode ? *mode : 0),
509 }
510 };
511
512 pthread_mutex_lock(&tracker->lock);
513 if (ACTIVE_COUNT(tracker) == tracker->capacity) {
514 if (tracker->count.suspendable.active > 0) {
515 ret = fd_tracker_suspend_handles(tracker, 1);
516 if (ret) {
517 goto end;
518 }
519 } else {
520 /*
521 * There are not enough active suspendable file
522 * descriptors to open a new fd and still accommodate
523 * the tracker's capacity.
524 */
525 WARN("Cannot open file system handle, too many unsuspendable file descriptors are opened (%u)",
526 tracker->count.unsuspendable);
527 goto end;
528 }
529 }
530
531 handle = zmalloc<fs_handle_tracked>();
532 if (!handle) {
533 goto end;
534 }
535 handle->parent = (typeof(handle->parent)) {
536 .get_fd = fs_handle_tracked_get_fd,
537 .put_fd = fs_handle_tracked_put_fd,
538 .unlink = fs_handle_tracked_unlink,
539 .close = fs_handle_tracked_close,
540 };
541
542 handle->tracker = tracker;
543
544 ret = pthread_mutex_init(&handle->lock, NULL);
545 if (ret) {
546 PERROR("Failed to initialize handle mutex while creating fs handle");
547 goto error_mutex_init;
548 }
549
550 handle->fd = open_from_properties(directory, path, &properties);
551 if (handle->fd < 0) {
552 PERROR("Failed to open fs handle to %s, open() returned", path);
553 goto error;
554 }
555
556 handle->properties = properties;
557
558 handle->inode = lttng_inode_registry_get_inode(tracker->inode_registry,
559 directory, path, handle->fd,
560 tracker->unlinked_file_pool);
561 if (!handle->inode) {
562 ERR("Failed to get lttng_inode corresponding to file %s", path);
563 goto error;
564 }
565
566 if (fstat(handle->fd, &fd_stat)) {
567 PERROR("Failed to retrieve file descriptor inode while creating fs handle, fstat() returned");
568 goto error;
569 }
570 handle->ino = fd_stat.st_ino;
571
572 fd_tracker_track(tracker, handle);
573 end:
574 pthread_mutex_unlock(&tracker->lock);
575 return handle ? &handle->parent : NULL;
576 error:
577 if (handle->inode) {
578 lttng_inode_put(handle->inode);
579 }
580 pthread_mutex_destroy(&handle->lock);
581 error_mutex_init:
582 free(handle);
583 handle = NULL;
584 goto end;
585 }
586
587 /* Caller must hold the tracker's lock. */
588 static int fd_tracker_suspend_handles(
589 struct fd_tracker *tracker, unsigned int count)
590 {
591 unsigned int left_to_close = count;
592 unsigned int attempts_left = tracker->count.suspendable.active;
593 struct fs_handle_tracked *handle, *tmp;
594
595 cds_list_for_each_entry_safe(handle, tmp, &tracker->active_handles,
596 handles_list_node) {
597 int ret;
598
599 fd_tracker_untrack(tracker, handle);
600 ret = fs_handle_tracked_suspend(handle);
601 fd_tracker_track(tracker, handle);
602 if (!ret) {
603 left_to_close--;
604 }
605 attempts_left--;
606
607 if (left_to_close == 0 || attempts_left == 0) {
608 break;
609 }
610 }
611 return left_to_close ? -EMFILE : 0;
612 }
613
614 int fd_tracker_open_unsuspendable_fd(struct fd_tracker *tracker,
615 int *out_fds,
616 const char **names,
617 unsigned int fd_count,
618 fd_open_cb open,
619 void *user_data)
620 {
621 int ret, user_ret, i, fds_to_suspend;
622 unsigned int active_fds;
623 struct unsuspendable_fd **entries;
624
625 entries = calloc<unsuspendable_fd *>(fd_count);
626 if (!entries) {
627 ret = -1;
628 goto end;
629 }
630
631 pthread_mutex_lock(&tracker->lock);
632
633 active_fds = ACTIVE_COUNT(tracker);
634 fds_to_suspend = (int) active_fds + (int) fd_count -
635 (int) tracker->capacity;
636 if (fds_to_suspend > 0) {
637 if (fds_to_suspend <= tracker->count.suspendable.active) {
638 ret = fd_tracker_suspend_handles(
639 tracker, fds_to_suspend);
640 if (ret) {
641 goto end_unlock;
642 }
643 } else {
644 /*
645 * There are not enough active suspendable file
646 * descriptors to open a new fd and still accommodates the
647 * tracker's capacity.
648 */
649 WARN("Cannot open unsuspendable fd, too many unsuspendable file descriptors are opened (%u)",
650 tracker->count.unsuspendable);
651 ret = -EMFILE;
652 goto end_unlock;
653 }
654 }
655
656 user_ret = open(user_data, out_fds);
657 if (user_ret) {
658 ret = user_ret;
659 goto end_unlock;
660 }
661
662 /*
663 * Add the fds returned by the user's callback to the hashtable
664 * of unsuspendable fds.
665 */
666 for (i = 0; i < fd_count; i++) {
667 struct unsuspendable_fd *entry = unsuspendable_fd_create(
668 names ? names[i] : NULL, out_fds[i]);
669
670 if (!entry) {
671 ret = -1;
672 goto end_free_entries;
673 }
674 entries[i] = entry;
675 }
676
677 rcu_read_lock();
678 for (i = 0; i < fd_count; i++) {
679 struct cds_lfht_node *node;
680 struct unsuspendable_fd *entry = entries[i];
681
682 node = cds_lfht_add_unique(tracker->unsuspendable_fds,
683 hash_key_ulong((void *) (unsigned long)
684 out_fds[i],
685 seed.value),
686 match_fd, (void *) (unsigned long) out_fds[i],
687 &entry->tracker_node);
688
689 if (node != &entry->tracker_node) {
690 ret = -EEXIST;
691 rcu_read_unlock();
692 goto end_free_entries;
693 }
694 entries[i] = NULL;
695 }
696 tracker->count.unsuspendable += fd_count;
697 rcu_read_unlock();
698 ret = user_ret;
699 end_unlock:
700 pthread_mutex_unlock(&tracker->lock);
701 end:
702 free(entries);
703 return ret;
704 end_free_entries:
705 for (i = 0; i < fd_count; i++) {
706 unsuspendable_fd_destroy(entries[i]);
707 }
708 goto end_unlock;
709 }
710
711 int fd_tracker_close_unsuspendable_fd(struct fd_tracker *tracker,
712 int *fds_in,
713 unsigned int fd_count,
714 fd_close_cb close,
715 void *user_data)
716 {
717 int i, ret, user_ret;
718 int *fds = NULL;
719
720 /*
721 * Maintain a local copy of fds_in as the user's callback may modify its
722 * contents (e.g. setting the fd(s) to -1 after close).
723 */
724 fds = malloc<int>(sizeof(*fds) * fd_count);
725 if (!fds) {
726 ret = -1;
727 goto end;
728 }
729 memcpy(fds, fds_in, sizeof(*fds) * fd_count);
730
731 pthread_mutex_lock(&tracker->lock);
732 rcu_read_lock();
733
734 /* Let the user close the file descriptors. */
735 user_ret = close(user_data, fds_in);
736 if (user_ret) {
737 ret = user_ret;
738 goto end_unlock;
739 }
740
741 /* Untrack the fds that were just closed by the user's callback. */
742 for (i = 0; i < fd_count; i++) {
743 struct cds_lfht_node *node;
744 struct cds_lfht_iter iter;
745 struct unsuspendable_fd *entry;
746
747 cds_lfht_lookup(tracker->unsuspendable_fds,
748 hash_key_ulong((void *) (unsigned long) fds[i],
749 seed.value),
750 match_fd, (void *) (unsigned long) fds[i],
751 &iter);
752 node = cds_lfht_iter_get_node(&iter);
753 if (!node) {
754 /* Unknown file descriptor. */
755 WARN("Untracked file descriptor %d passed to fd_tracker_close_unsuspendable_fd()",
756 fds[i]);
757 ret = -EINVAL;
758 goto end_unlock;
759 }
760 entry = lttng::utils::container_of(
761 node, &unsuspendable_fd::tracker_node);
762
763 cds_lfht_del(tracker->unsuspendable_fds, node);
764 unsuspendable_fd_destroy(entry);
765 fds[i] = -1;
766 }
767
768 tracker->count.unsuspendable -= fd_count;
769 ret = 0;
770 end_unlock:
771 rcu_read_unlock();
772 pthread_mutex_unlock(&tracker->lock);
773 free(fds);
774 end:
775 return ret;
776 }
777
778 /* Caller must have taken the tracker's and handle's locks. */
779 static void fd_tracker_track(
780 struct fd_tracker *tracker, struct fs_handle_tracked *handle)
781 {
782 if (handle->fd >= 0) {
783 tracker->count.suspendable.active++;
784 cds_list_add_tail(&handle->handles_list_node,
785 &tracker->active_handles);
786 } else {
787 tracker->count.suspendable.suspended++;
788 cds_list_add_tail(&handle->handles_list_node,
789 &tracker->suspended_handles);
790 }
791 }
792
793 /* Caller must have taken the tracker's and handle's locks. */
794 static void fd_tracker_untrack(
795 struct fd_tracker *tracker, struct fs_handle_tracked *handle)
796 {
797 if (handle->fd >= 0) {
798 tracker->count.suspendable.active--;
799 } else {
800 tracker->count.suspendable.suspended--;
801 }
802 cds_list_del(&handle->handles_list_node);
803 }
804
805 /* Caller must have taken the tracker's and handle's locks. */
806 static int fd_tracker_restore_handle(
807 struct fd_tracker *tracker, struct fs_handle_tracked *handle)
808 {
809 int ret;
810
811 fd_tracker_untrack(tracker, handle);
812 if (ACTIVE_COUNT(tracker) >= tracker->capacity) {
813 ret = fd_tracker_suspend_handles(tracker, 1);
814 if (ret) {
815 goto end;
816 }
817 }
818 ret = fs_handle_tracked_restore(handle);
819 end:
820 fd_tracker_track(tracker, handle);
821 return ret ? ret : handle->fd;
822 }
823
824 static int fs_handle_tracked_get_fd(struct fs_handle *_handle)
825 {
826 int ret;
827 struct fs_handle_tracked *handle =
828 lttng::utils::container_of(_handle, &fs_handle_tracked::parent);
829
830 /*
831 * TODO This should be optimized as it is a fairly hot path.
832 * The fd-tracker's lock should only be taken when a fs_handle is
833 * restored (slow path). On the fast path (fs_handle is active),
834 * the only effect on the fd_tracker is marking the handle as the
835 * most recently used. Currently, it is done by a call to the
836 * track/untrack helpers, but it should be done atomically.
837 *
838 * Note that the lock's nesting order must still be respected here.
839 * The handle's lock nests inside the tracker's lock.
840 */
841 pthread_mutex_lock(&handle->tracker->lock);
842 pthread_mutex_lock(&handle->lock);
843 LTTNG_ASSERT(!handle->in_use);
844
845 handle->tracker->stats.uses++;
846 if (handle->fd >= 0) {
847 ret = handle->fd;
848 /* Mark as most recently used. */
849 fd_tracker_untrack(handle->tracker, handle);
850 fd_tracker_track(handle->tracker, handle);
851 } else {
852 handle->tracker->stats.misses++;
853 ret = fd_tracker_restore_handle(handle->tracker, handle);
854 if (ret < 0) {
855 handle->tracker->stats.errors++;
856 goto end;
857 }
858 }
859 handle->in_use = true;
860 end:
861 pthread_mutex_unlock(&handle->lock);
862 pthread_mutex_unlock(&handle->tracker->lock);
863 return ret;
864 }
865
866 static void fs_handle_tracked_put_fd(struct fs_handle *_handle)
867 {
868 struct fs_handle_tracked *handle =
869 lttng::utils::container_of(_handle, &fs_handle_tracked::parent);
870
871 pthread_mutex_lock(&handle->lock);
872 handle->in_use = false;
873 pthread_mutex_unlock(&handle->lock);
874 }
875
876 static int fs_handle_tracked_unlink(struct fs_handle *_handle)
877 {
878 int ret;
879 struct fs_handle_tracked *handle =
880 lttng::utils::container_of(_handle, &fs_handle_tracked::parent);
881
882 pthread_mutex_lock(&handle->tracker->lock);
883 pthread_mutex_lock(&handle->lock);
884 ret = lttng_inode_unlink(handle->inode);
885 pthread_mutex_unlock(&handle->lock);
886 pthread_mutex_unlock(&handle->tracker->lock);
887 return ret;
888 }
889
890 static int fs_handle_tracked_close(struct fs_handle *_handle)
891 {
892 int ret = 0;
893 const char *path = NULL;
894 struct fs_handle_tracked *handle =
895 lttng::utils::container_of(_handle, &fs_handle_tracked::parent);
896 struct lttng_directory_handle *inode_directory_handle = NULL;
897
898 if (!handle) {
899 ret = -EINVAL;
900 goto end;
901 }
902
903 pthread_mutex_lock(&handle->tracker->lock);
904 pthread_mutex_lock(&handle->lock);
905 if (handle->inode) {
906 lttng_inode_borrow_location(handle->inode, NULL, &path);
907 /*
908 * Here a reference to the inode's directory handle is acquired
909 * to prevent the last reference to it from being released while
910 * the tracker's lock is taken.
911 *
912 * If this wasn't done, the directory handle could attempt to
913 * close its underlying directory file descriptor, which would
914 * attempt to lock the tracker's lock, resulting in a deadlock.
915 *
916 * Since a new reference to the directory handle is taken within
917 * the scope of this function, it is not possible for the last
918 * reference to the inode's location directory handle to be
919 * released during the call to lttng_inode_put().
920 *
921 * We wait until the tracker's lock is released to release the
922 * reference. Hence, the call to the tracker is delayed just
923 * enough to not attempt to recursively acquire the tracker's
924 * lock twice.
925 */
926 inode_directory_handle =
927 lttng_inode_get_location_directory_handle(
928 handle->inode);
929 }
930 fd_tracker_untrack(handle->tracker, handle);
931 if (handle->fd >= 0) {
932 /*
933 * The return value of close() is not propagated as there
934 * isn't much the user can do about it.
935 */
936 if (close(handle->fd)) {
937 PERROR("Failed to close the file descriptor (%d) of fs handle to %s, close() returned",
938 handle->fd, path ? path : "Unknown");
939 }
940 handle->fd = -1;
941 }
942 if (handle->inode) {
943 lttng_inode_put(handle->inode);
944 }
945 pthread_mutex_unlock(&handle->lock);
946 pthread_mutex_destroy(&handle->lock);
947 pthread_mutex_unlock(&handle->tracker->lock);
948 free(handle);
949 lttng_directory_handle_put(inode_directory_handle);
950 end:
951 return ret;
952 }
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