Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0-or-later
2 : /*
3 : * fs/eventpoll.c (Efficient event retrieval implementation)
4 : * Copyright (C) 2001,...,2009 Davide Libenzi
5 : *
6 : * Davide Libenzi <davidel@xmailserver.org>
7 : */
8 :
9 : #include <linux/init.h>
10 : #include <linux/kernel.h>
11 : #include <linux/sched/signal.h>
12 : #include <linux/fs.h>
13 : #include <linux/file.h>
14 : #include <linux/signal.h>
15 : #include <linux/errno.h>
16 : #include <linux/mm.h>
17 : #include <linux/slab.h>
18 : #include <linux/poll.h>
19 : #include <linux/string.h>
20 : #include <linux/list.h>
21 : #include <linux/hash.h>
22 : #include <linux/spinlock.h>
23 : #include <linux/syscalls.h>
24 : #include <linux/rbtree.h>
25 : #include <linux/wait.h>
26 : #include <linux/eventpoll.h>
27 : #include <linux/mount.h>
28 : #include <linux/bitops.h>
29 : #include <linux/mutex.h>
30 : #include <linux/anon_inodes.h>
31 : #include <linux/device.h>
32 : #include <linux/uaccess.h>
33 : #include <asm/io.h>
34 : #include <asm/mman.h>
35 : #include <linux/atomic.h>
36 : #include <linux/proc_fs.h>
37 : #include <linux/seq_file.h>
38 : #include <linux/compat.h>
39 : #include <linux/rculist.h>
40 : #include <net/busy_poll.h>
41 :
42 : /*
43 : * LOCKING:
44 : * There are three level of locking required by epoll :
45 : *
46 : * 1) epmutex (mutex)
47 : * 2) ep->mtx (mutex)
48 : * 3) ep->lock (rwlock)
49 : *
50 : * The acquire order is the one listed above, from 1 to 3.
51 : * We need a rwlock (ep->lock) because we manipulate objects
52 : * from inside the poll callback, that might be triggered from
53 : * a wake_up() that in turn might be called from IRQ context.
54 : * So we can't sleep inside the poll callback and hence we need
55 : * a spinlock. During the event transfer loop (from kernel to
56 : * user space) we could end up sleeping due a copy_to_user(), so
57 : * we need a lock that will allow us to sleep. This lock is a
58 : * mutex (ep->mtx). It is acquired during the event transfer loop,
59 : * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
60 : * Then we also need a global mutex to serialize eventpoll_release_file()
61 : * and ep_free().
62 : * This mutex is acquired by ep_free() during the epoll file
63 : * cleanup path and it is also acquired by eventpoll_release_file()
64 : * if a file has been pushed inside an epoll set and it is then
65 : * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
66 : * It is also acquired when inserting an epoll fd onto another epoll
67 : * fd. We do this so that we walk the epoll tree and ensure that this
68 : * insertion does not create a cycle of epoll file descriptors, which
69 : * could lead to deadlock. We need a global mutex to prevent two
70 : * simultaneous inserts (A into B and B into A) from racing and
71 : * constructing a cycle without either insert observing that it is
72 : * going to.
73 : * It is necessary to acquire multiple "ep->mtx"es at once in the
74 : * case when one epoll fd is added to another. In this case, we
75 : * always acquire the locks in the order of nesting (i.e. after
76 : * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
77 : * before e2->mtx). Since we disallow cycles of epoll file
78 : * descriptors, this ensures that the mutexes are well-ordered. In
79 : * order to communicate this nesting to lockdep, when walking a tree
80 : * of epoll file descriptors, we use the current recursion depth as
81 : * the lockdep subkey.
82 : * It is possible to drop the "ep->mtx" and to use the global
83 : * mutex "epmutex" (together with "ep->lock") to have it working,
84 : * but having "ep->mtx" will make the interface more scalable.
85 : * Events that require holding "epmutex" are very rare, while for
86 : * normal operations the epoll private "ep->mtx" will guarantee
87 : * a better scalability.
88 : */
89 :
90 : /* Epoll private bits inside the event mask */
91 : #define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE)
92 :
93 : #define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT)
94 :
95 : #define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \
96 : EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE)
97 :
98 : /* Maximum number of nesting allowed inside epoll sets */
99 : #define EP_MAX_NESTS 4
100 :
101 : #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
102 :
103 : #define EP_UNACTIVE_PTR ((void *) -1L)
104 :
105 : #define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
106 :
107 : struct epoll_filefd {
108 : struct file *file;
109 : int fd;
110 : } __packed;
111 :
112 : /* Wait structure used by the poll hooks */
113 : struct eppoll_entry {
114 : /* List header used to link this structure to the "struct epitem" */
115 : struct eppoll_entry *next;
116 :
117 : /* The "base" pointer is set to the container "struct epitem" */
118 : struct epitem *base;
119 :
120 : /*
121 : * Wait queue item that will be linked to the target file wait
122 : * queue head.
123 : */
124 : wait_queue_entry_t wait;
125 :
126 : /* The wait queue head that linked the "wait" wait queue item */
127 : wait_queue_head_t *whead;
128 : };
129 :
130 : /*
131 : * Each file descriptor added to the eventpoll interface will
132 : * have an entry of this type linked to the "rbr" RB tree.
133 : * Avoid increasing the size of this struct, there can be many thousands
134 : * of these on a server and we do not want this to take another cache line.
135 : */
136 : struct epitem {
137 : union {
138 : /* RB tree node links this structure to the eventpoll RB tree */
139 : struct rb_node rbn;
140 : /* Used to free the struct epitem */
141 : struct rcu_head rcu;
142 : };
143 :
144 : /* List header used to link this structure to the eventpoll ready list */
145 : struct list_head rdllink;
146 :
147 : /*
148 : * Works together "struct eventpoll"->ovflist in keeping the
149 : * single linked chain of items.
150 : */
151 : struct epitem *next;
152 :
153 : /* The file descriptor information this item refers to */
154 : struct epoll_filefd ffd;
155 :
156 : /* List containing poll wait queues */
157 : struct eppoll_entry *pwqlist;
158 :
159 : /* The "container" of this item */
160 : struct eventpoll *ep;
161 :
162 : /* List header used to link this item to the "struct file" items list */
163 : struct hlist_node fllink;
164 :
165 : /* wakeup_source used when EPOLLWAKEUP is set */
166 : struct wakeup_source __rcu *ws;
167 :
168 : /* The structure that describe the interested events and the source fd */
169 : struct epoll_event event;
170 : };
171 :
172 : /*
173 : * This structure is stored inside the "private_data" member of the file
174 : * structure and represents the main data structure for the eventpoll
175 : * interface.
176 : */
177 : struct eventpoll {
178 : /*
179 : * This mutex is used to ensure that files are not removed
180 : * while epoll is using them. This is held during the event
181 : * collection loop, the file cleanup path, the epoll file exit
182 : * code and the ctl operations.
183 : */
184 : struct mutex mtx;
185 :
186 : /* Wait queue used by sys_epoll_wait() */
187 : wait_queue_head_t wq;
188 :
189 : /* Wait queue used by file->poll() */
190 : wait_queue_head_t poll_wait;
191 :
192 : /* List of ready file descriptors */
193 : struct list_head rdllist;
194 :
195 : /* Lock which protects rdllist and ovflist */
196 : rwlock_t lock;
197 :
198 : /* RB tree root used to store monitored fd structs */
199 : struct rb_root_cached rbr;
200 :
201 : /*
202 : * This is a single linked list that chains all the "struct epitem" that
203 : * happened while transferring ready events to userspace w/out
204 : * holding ->lock.
205 : */
206 : struct epitem *ovflist;
207 :
208 : /* wakeup_source used when ep_scan_ready_list is running */
209 : struct wakeup_source *ws;
210 :
211 : /* The user that created the eventpoll descriptor */
212 : struct user_struct *user;
213 :
214 : struct file *file;
215 :
216 : /* used to optimize loop detection check */
217 : u64 gen;
218 : struct hlist_head refs;
219 :
220 : #ifdef CONFIG_NET_RX_BUSY_POLL
221 : /* used to track busy poll napi_id */
222 : unsigned int napi_id;
223 : #endif
224 :
225 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
226 : /* tracks wakeup nests for lockdep validation */
227 : u8 nests;
228 : #endif
229 : };
230 :
231 : /* Wrapper struct used by poll queueing */
232 : struct ep_pqueue {
233 : poll_table pt;
234 : struct epitem *epi;
235 : };
236 :
237 : /*
238 : * Configuration options available inside /proc/sys/fs/epoll/
239 : */
240 : /* Maximum number of epoll watched descriptors, per user */
241 : static long max_user_watches __read_mostly;
242 :
243 : /*
244 : * This mutex is used to serialize ep_free() and eventpoll_release_file().
245 : */
246 : static DEFINE_MUTEX(epmutex);
247 :
248 : static u64 loop_check_gen = 0;
249 :
250 : /* Used to check for epoll file descriptor inclusion loops */
251 : static struct eventpoll *inserting_into;
252 :
253 : /* Slab cache used to allocate "struct epitem" */
254 : static struct kmem_cache *epi_cache __read_mostly;
255 :
256 : /* Slab cache used to allocate "struct eppoll_entry" */
257 : static struct kmem_cache *pwq_cache __read_mostly;
258 :
259 : /*
260 : * List of files with newly added links, where we may need to limit the number
261 : * of emanating paths. Protected by the epmutex.
262 : */
263 : struct epitems_head {
264 : struct hlist_head epitems;
265 : struct epitems_head *next;
266 : };
267 : static struct epitems_head *tfile_check_list = EP_UNACTIVE_PTR;
268 :
269 : static struct kmem_cache *ephead_cache __read_mostly;
270 :
271 : static inline void free_ephead(struct epitems_head *head)
272 : {
273 0 : if (head)
274 0 : kmem_cache_free(ephead_cache, head);
275 : }
276 :
277 : static void list_file(struct file *file)
278 : {
279 : struct epitems_head *head;
280 :
281 0 : head = container_of(file->f_ep, struct epitems_head, epitems);
282 0 : if (!head->next) {
283 0 : head->next = tfile_check_list;
284 0 : tfile_check_list = head;
285 : }
286 : }
287 :
288 0 : static void unlist_file(struct epitems_head *head)
289 : {
290 0 : struct epitems_head *to_free = head;
291 0 : struct hlist_node *p = rcu_dereference(hlist_first_rcu(&head->epitems));
292 0 : if (p) {
293 0 : struct epitem *epi= container_of(p, struct epitem, fllink);
294 0 : spin_lock(&epi->ffd.file->f_lock);
295 0 : if (!hlist_empty(&head->epitems))
296 0 : to_free = NULL;
297 0 : head->next = NULL;
298 0 : spin_unlock(&epi->ffd.file->f_lock);
299 : }
300 0 : free_ephead(to_free);
301 0 : }
302 :
303 : #ifdef CONFIG_SYSCTL
304 :
305 : #include <linux/sysctl.h>
306 :
307 : static long long_zero;
308 : static long long_max = LONG_MAX;
309 :
310 : static struct ctl_table epoll_table[] = {
311 : {
312 : .procname = "max_user_watches",
313 : .data = &max_user_watches,
314 : .maxlen = sizeof(max_user_watches),
315 : .mode = 0644,
316 : .proc_handler = proc_doulongvec_minmax,
317 : .extra1 = &long_zero,
318 : .extra2 = &long_max,
319 : },
320 : { }
321 : };
322 :
323 1 : static void __init epoll_sysctls_init(void)
324 : {
325 1 : register_sysctl("fs/epoll", epoll_table);
326 1 : }
327 : #else
328 : #define epoll_sysctls_init() do { } while (0)
329 : #endif /* CONFIG_SYSCTL */
330 :
331 : static const struct file_operations eventpoll_fops;
332 :
333 : static inline int is_file_epoll(struct file *f)
334 : {
335 0 : return f->f_op == &eventpoll_fops;
336 : }
337 :
338 : /* Setup the structure that is used as key for the RB tree */
339 : static inline void ep_set_ffd(struct epoll_filefd *ffd,
340 : struct file *file, int fd)
341 : {
342 0 : ffd->file = file;
343 0 : ffd->fd = fd;
344 : }
345 :
346 : /* Compare RB tree keys */
347 : static inline int ep_cmp_ffd(struct epoll_filefd *p1,
348 : struct epoll_filefd *p2)
349 : {
350 0 : return (p1->file > p2->file ? +1:
351 0 : (p1->file < p2->file ? -1 : p1->fd - p2->fd));
352 : }
353 :
354 : /* Tells us if the item is currently linked */
355 : static inline int ep_is_linked(struct epitem *epi)
356 : {
357 0 : return !list_empty(&epi->rdllink);
358 : }
359 :
360 : static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p)
361 : {
362 0 : return container_of(p, struct eppoll_entry, wait);
363 : }
364 :
365 : /* Get the "struct epitem" from a wait queue pointer */
366 : static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p)
367 : {
368 0 : return container_of(p, struct eppoll_entry, wait)->base;
369 : }
370 :
371 : /**
372 : * ep_events_available - Checks if ready events might be available.
373 : *
374 : * @ep: Pointer to the eventpoll context.
375 : *
376 : * Return: a value different than %zero if ready events are available,
377 : * or %zero otherwise.
378 : */
379 : static inline int ep_events_available(struct eventpoll *ep)
380 : {
381 0 : return !list_empty_careful(&ep->rdllist) ||
382 0 : READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR;
383 : }
384 :
385 : #ifdef CONFIG_NET_RX_BUSY_POLL
386 : static bool ep_busy_loop_end(void *p, unsigned long start_time)
387 : {
388 : struct eventpoll *ep = p;
389 :
390 : return ep_events_available(ep) || busy_loop_timeout(start_time);
391 : }
392 :
393 : /*
394 : * Busy poll if globally on and supporting sockets found && no events,
395 : * busy loop will return if need_resched or ep_events_available.
396 : *
397 : * we must do our busy polling with irqs enabled
398 : */
399 : static bool ep_busy_loop(struct eventpoll *ep, int nonblock)
400 : {
401 : unsigned int napi_id = READ_ONCE(ep->napi_id);
402 :
403 : if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on()) {
404 : napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false,
405 : BUSY_POLL_BUDGET);
406 : if (ep_events_available(ep))
407 : return true;
408 : /*
409 : * Busy poll timed out. Drop NAPI ID for now, we can add
410 : * it back in when we have moved a socket with a valid NAPI
411 : * ID onto the ready list.
412 : */
413 : ep->napi_id = 0;
414 : return false;
415 : }
416 : return false;
417 : }
418 :
419 : /*
420 : * Set epoll busy poll NAPI ID from sk.
421 : */
422 : static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
423 : {
424 : struct eventpoll *ep;
425 : unsigned int napi_id;
426 : struct socket *sock;
427 : struct sock *sk;
428 :
429 : if (!net_busy_loop_on())
430 : return;
431 :
432 : sock = sock_from_file(epi->ffd.file);
433 : if (!sock)
434 : return;
435 :
436 : sk = sock->sk;
437 : if (!sk)
438 : return;
439 :
440 : napi_id = READ_ONCE(sk->sk_napi_id);
441 : ep = epi->ep;
442 :
443 : /* Non-NAPI IDs can be rejected
444 : * or
445 : * Nothing to do if we already have this ID
446 : */
447 : if (napi_id < MIN_NAPI_ID || napi_id == ep->napi_id)
448 : return;
449 :
450 : /* record NAPI ID for use in next busy poll */
451 : ep->napi_id = napi_id;
452 : }
453 :
454 : #else
455 :
456 : static inline bool ep_busy_loop(struct eventpoll *ep, int nonblock)
457 : {
458 : return false;
459 : }
460 :
461 : static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
462 : {
463 : }
464 :
465 : #endif /* CONFIG_NET_RX_BUSY_POLL */
466 :
467 : /*
468 : * As described in commit 0ccf831cb lockdep: annotate epoll
469 : * the use of wait queues used by epoll is done in a very controlled
470 : * manner. Wake ups can nest inside each other, but are never done
471 : * with the same locking. For example:
472 : *
473 : * dfd = socket(...);
474 : * efd1 = epoll_create();
475 : * efd2 = epoll_create();
476 : * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
477 : * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
478 : *
479 : * When a packet arrives to the device underneath "dfd", the net code will
480 : * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
481 : * callback wakeup entry on that queue, and the wake_up() performed by the
482 : * "dfd" net code will end up in ep_poll_callback(). At this point epoll
483 : * (efd1) notices that it may have some event ready, so it needs to wake up
484 : * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
485 : * that ends up in another wake_up(), after having checked about the
486 : * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
487 : * avoid stack blasting.
488 : *
489 : * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
490 : * this special case of epoll.
491 : */
492 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
493 :
494 : static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
495 : {
496 : struct eventpoll *ep_src;
497 : unsigned long flags;
498 : u8 nests = 0;
499 :
500 : /*
501 : * To set the subclass or nesting level for spin_lock_irqsave_nested()
502 : * it might be natural to create a per-cpu nest count. However, since
503 : * we can recurse on ep->poll_wait.lock, and a non-raw spinlock can
504 : * schedule() in the -rt kernel, the per-cpu variable are no longer
505 : * protected. Thus, we are introducing a per eventpoll nest field.
506 : * If we are not being call from ep_poll_callback(), epi is NULL and
507 : * we are at the first level of nesting, 0. Otherwise, we are being
508 : * called from ep_poll_callback() and if a previous wakeup source is
509 : * not an epoll file itself, we are at depth 1 since the wakeup source
510 : * is depth 0. If the wakeup source is a previous epoll file in the
511 : * wakeup chain then we use its nests value and record ours as
512 : * nests + 1. The previous epoll file nests value is stable since its
513 : * already holding its own poll_wait.lock.
514 : */
515 : if (epi) {
516 : if ((is_file_epoll(epi->ffd.file))) {
517 : ep_src = epi->ffd.file->private_data;
518 : nests = ep_src->nests;
519 : } else {
520 : nests = 1;
521 : }
522 : }
523 : spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests);
524 : ep->nests = nests + 1;
525 : wake_up_locked_poll(&ep->poll_wait, EPOLLIN);
526 : ep->nests = 0;
527 : spin_unlock_irqrestore(&ep->poll_wait.lock, flags);
528 : }
529 :
530 : #else
531 :
532 : static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
533 : {
534 0 : wake_up_poll(&ep->poll_wait, EPOLLIN);
535 : }
536 :
537 : #endif
538 :
539 : static void ep_remove_wait_queue(struct eppoll_entry *pwq)
540 : {
541 : wait_queue_head_t *whead;
542 :
543 : rcu_read_lock();
544 : /*
545 : * If it is cleared by POLLFREE, it should be rcu-safe.
546 : * If we read NULL we need a barrier paired with
547 : * smp_store_release() in ep_poll_callback(), otherwise
548 : * we rely on whead->lock.
549 : */
550 0 : whead = smp_load_acquire(&pwq->whead);
551 0 : if (whead)
552 0 : remove_wait_queue(whead, &pwq->wait);
553 : rcu_read_unlock();
554 : }
555 :
556 : /*
557 : * This function unregisters poll callbacks from the associated file
558 : * descriptor. Must be called with "mtx" held (or "epmutex" if called from
559 : * ep_free).
560 : */
561 0 : static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
562 : {
563 0 : struct eppoll_entry **p = &epi->pwqlist;
564 : struct eppoll_entry *pwq;
565 :
566 0 : while ((pwq = *p) != NULL) {
567 0 : *p = pwq->next;
568 0 : ep_remove_wait_queue(pwq);
569 0 : kmem_cache_free(pwq_cache, pwq);
570 : }
571 0 : }
572 :
573 : /* call only when ep->mtx is held */
574 : static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
575 : {
576 0 : return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
577 : }
578 :
579 : /* call only when ep->mtx is held */
580 : static inline void ep_pm_stay_awake(struct epitem *epi)
581 : {
582 0 : struct wakeup_source *ws = ep_wakeup_source(epi);
583 :
584 0 : if (ws)
585 0 : __pm_stay_awake(ws);
586 : }
587 :
588 : static inline bool ep_has_wakeup_source(struct epitem *epi)
589 : {
590 0 : return rcu_access_pointer(epi->ws) ? true : false;
591 : }
592 :
593 : /* call when ep->mtx cannot be held (ep_poll_callback) */
594 : static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
595 : {
596 : struct wakeup_source *ws;
597 :
598 : rcu_read_lock();
599 0 : ws = rcu_dereference(epi->ws);
600 0 : if (ws)
601 0 : __pm_stay_awake(ws);
602 : rcu_read_unlock();
603 : }
604 :
605 :
606 : /*
607 : * ep->mutex needs to be held because we could be hit by
608 : * eventpoll_release_file() and epoll_ctl().
609 : */
610 0 : static void ep_start_scan(struct eventpoll *ep, struct list_head *txlist)
611 : {
612 : /*
613 : * Steal the ready list, and re-init the original one to the
614 : * empty list. Also, set ep->ovflist to NULL so that events
615 : * happening while looping w/out locks, are not lost. We cannot
616 : * have the poll callback to queue directly on ep->rdllist,
617 : * because we want the "sproc" callback to be able to do it
618 : * in a lockless way.
619 : */
620 : lockdep_assert_irqs_enabled();
621 0 : write_lock_irq(&ep->lock);
622 0 : list_splice_init(&ep->rdllist, txlist);
623 0 : WRITE_ONCE(ep->ovflist, NULL);
624 0 : write_unlock_irq(&ep->lock);
625 0 : }
626 :
627 0 : static void ep_done_scan(struct eventpoll *ep,
628 : struct list_head *txlist)
629 : {
630 : struct epitem *epi, *nepi;
631 :
632 0 : write_lock_irq(&ep->lock);
633 : /*
634 : * During the time we spent inside the "sproc" callback, some
635 : * other events might have been queued by the poll callback.
636 : * We re-insert them inside the main ready-list here.
637 : */
638 0 : for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
639 0 : nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
640 : /*
641 : * We need to check if the item is already in the list.
642 : * During the "sproc" callback execution time, items are
643 : * queued into ->ovflist but the "txlist" might already
644 : * contain them, and the list_splice() below takes care of them.
645 : */
646 0 : if (!ep_is_linked(epi)) {
647 : /*
648 : * ->ovflist is LIFO, so we have to reverse it in order
649 : * to keep in FIFO.
650 : */
651 0 : list_add(&epi->rdllink, &ep->rdllist);
652 : ep_pm_stay_awake(epi);
653 : }
654 : }
655 : /*
656 : * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
657 : * releasing the lock, events will be queued in the normal way inside
658 : * ep->rdllist.
659 : */
660 0 : WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR);
661 :
662 : /*
663 : * Quickly re-inject items left on "txlist".
664 : */
665 0 : list_splice(txlist, &ep->rdllist);
666 0 : __pm_relax(ep->ws);
667 :
668 0 : if (!list_empty(&ep->rdllist)) {
669 0 : if (waitqueue_active(&ep->wq))
670 0 : wake_up(&ep->wq);
671 : }
672 :
673 0 : write_unlock_irq(&ep->lock);
674 0 : }
675 :
676 0 : static void epi_rcu_free(struct rcu_head *head)
677 : {
678 0 : struct epitem *epi = container_of(head, struct epitem, rcu);
679 0 : kmem_cache_free(epi_cache, epi);
680 0 : }
681 :
682 : /*
683 : * Removes a "struct epitem" from the eventpoll RB tree and deallocates
684 : * all the associated resources. Must be called with "mtx" held.
685 : */
686 0 : static int ep_remove(struct eventpoll *ep, struct epitem *epi)
687 : {
688 0 : struct file *file = epi->ffd.file;
689 : struct epitems_head *to_free;
690 : struct hlist_head *head;
691 :
692 : lockdep_assert_irqs_enabled();
693 :
694 : /*
695 : * Removes poll wait queue hooks.
696 : */
697 0 : ep_unregister_pollwait(ep, epi);
698 :
699 : /* Remove the current item from the list of epoll hooks */
700 0 : spin_lock(&file->f_lock);
701 0 : to_free = NULL;
702 0 : head = file->f_ep;
703 0 : if (head->first == &epi->fllink && !epi->fllink.next) {
704 0 : file->f_ep = NULL;
705 0 : if (!is_file_epoll(file)) {
706 : struct epitems_head *v;
707 0 : v = container_of(head, struct epitems_head, epitems);
708 0 : if (!smp_load_acquire(&v->next))
709 0 : to_free = v;
710 : }
711 : }
712 0 : hlist_del_rcu(&epi->fllink);
713 0 : spin_unlock(&file->f_lock);
714 0 : free_ephead(to_free);
715 :
716 0 : rb_erase_cached(&epi->rbn, &ep->rbr);
717 :
718 0 : write_lock_irq(&ep->lock);
719 0 : if (ep_is_linked(epi))
720 0 : list_del_init(&epi->rdllink);
721 0 : write_unlock_irq(&ep->lock);
722 :
723 0 : wakeup_source_unregister(ep_wakeup_source(epi));
724 : /*
725 : * At this point it is safe to free the eventpoll item. Use the union
726 : * field epi->rcu, since we are trying to minimize the size of
727 : * 'struct epitem'. The 'rbn' field is no longer in use. Protected by
728 : * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
729 : * use of the rbn field.
730 : */
731 0 : call_rcu(&epi->rcu, epi_rcu_free);
732 :
733 0 : percpu_counter_dec(&ep->user->epoll_watches);
734 :
735 0 : return 0;
736 : }
737 :
738 0 : static void ep_free(struct eventpoll *ep)
739 : {
740 : struct rb_node *rbp;
741 : struct epitem *epi;
742 :
743 : /* We need to release all tasks waiting for these file */
744 0 : if (waitqueue_active(&ep->poll_wait))
745 0 : ep_poll_safewake(ep, NULL);
746 :
747 : /*
748 : * We need to lock this because we could be hit by
749 : * eventpoll_release_file() while we're freeing the "struct eventpoll".
750 : * We do not need to hold "ep->mtx" here because the epoll file
751 : * is on the way to be removed and no one has references to it
752 : * anymore. The only hit might come from eventpoll_release_file() but
753 : * holding "epmutex" is sufficient here.
754 : */
755 0 : mutex_lock(&epmutex);
756 :
757 : /*
758 : * Walks through the whole tree by unregistering poll callbacks.
759 : */
760 0 : for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
761 0 : epi = rb_entry(rbp, struct epitem, rbn);
762 :
763 0 : ep_unregister_pollwait(ep, epi);
764 0 : cond_resched();
765 : }
766 :
767 : /*
768 : * Walks through the whole tree by freeing each "struct epitem". At this
769 : * point we are sure no poll callbacks will be lingering around, and also by
770 : * holding "epmutex" we can be sure that no file cleanup code will hit
771 : * us during this operation. So we can avoid the lock on "ep->lock".
772 : * We do not need to lock ep->mtx, either, we only do it to prevent
773 : * a lockdep warning.
774 : */
775 0 : mutex_lock(&ep->mtx);
776 0 : while ((rbp = rb_first_cached(&ep->rbr)) != NULL) {
777 0 : epi = rb_entry(rbp, struct epitem, rbn);
778 0 : ep_remove(ep, epi);
779 0 : cond_resched();
780 : }
781 0 : mutex_unlock(&ep->mtx);
782 :
783 0 : mutex_unlock(&epmutex);
784 0 : mutex_destroy(&ep->mtx);
785 0 : free_uid(ep->user);
786 0 : wakeup_source_unregister(ep->ws);
787 0 : kfree(ep);
788 0 : }
789 :
790 0 : static int ep_eventpoll_release(struct inode *inode, struct file *file)
791 : {
792 0 : struct eventpoll *ep = file->private_data;
793 :
794 0 : if (ep)
795 0 : ep_free(ep);
796 :
797 0 : return 0;
798 : }
799 :
800 : static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, int depth);
801 :
802 0 : static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int depth)
803 : {
804 0 : struct eventpoll *ep = file->private_data;
805 0 : LIST_HEAD(txlist);
806 : struct epitem *epi, *tmp;
807 : poll_table pt;
808 0 : __poll_t res = 0;
809 :
810 0 : init_poll_funcptr(&pt, NULL);
811 :
812 : /* Insert inside our poll wait queue */
813 0 : poll_wait(file, &ep->poll_wait, wait);
814 :
815 : /*
816 : * Proceed to find out if wanted events are really available inside
817 : * the ready list.
818 : */
819 0 : mutex_lock_nested(&ep->mtx, depth);
820 0 : ep_start_scan(ep, &txlist);
821 0 : list_for_each_entry_safe(epi, tmp, &txlist, rdllink) {
822 0 : if (ep_item_poll(epi, &pt, depth + 1)) {
823 : res = EPOLLIN | EPOLLRDNORM;
824 : break;
825 : } else {
826 : /*
827 : * Item has been dropped into the ready list by the poll
828 : * callback, but it's not actually ready, as far as
829 : * caller requested events goes. We can remove it here.
830 : */
831 0 : __pm_relax(ep_wakeup_source(epi));
832 0 : list_del_init(&epi->rdllink);
833 : }
834 : }
835 0 : ep_done_scan(ep, &txlist);
836 0 : mutex_unlock(&ep->mtx);
837 0 : return res;
838 : }
839 :
840 : /*
841 : * Differs from ep_eventpoll_poll() in that internal callers already have
842 : * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested()
843 : * is correctly annotated.
844 : */
845 0 : static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt,
846 : int depth)
847 : {
848 0 : struct file *file = epi->ffd.file;
849 : __poll_t res;
850 :
851 0 : pt->_key = epi->event.events;
852 0 : if (!is_file_epoll(file))
853 : res = vfs_poll(file, pt);
854 : else
855 0 : res = __ep_eventpoll_poll(file, pt, depth);
856 0 : return res & epi->event.events;
857 : }
858 :
859 0 : static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait)
860 : {
861 0 : return __ep_eventpoll_poll(file, wait, 0);
862 : }
863 :
864 : #ifdef CONFIG_PROC_FS
865 0 : static void ep_show_fdinfo(struct seq_file *m, struct file *f)
866 : {
867 0 : struct eventpoll *ep = f->private_data;
868 : struct rb_node *rbp;
869 :
870 0 : mutex_lock(&ep->mtx);
871 0 : for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
872 0 : struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
873 0 : struct inode *inode = file_inode(epi->ffd.file);
874 :
875 0 : seq_printf(m, "tfd: %8d events: %8x data: %16llx "
876 : " pos:%lli ino:%lx sdev:%x\n",
877 : epi->ffd.fd, epi->event.events,
878 0 : (long long)epi->event.data,
879 0 : (long long)epi->ffd.file->f_pos,
880 0 : inode->i_ino, inode->i_sb->s_dev);
881 0 : if (seq_has_overflowed(m))
882 : break;
883 : }
884 0 : mutex_unlock(&ep->mtx);
885 0 : }
886 : #endif
887 :
888 : /* File callbacks that implement the eventpoll file behaviour */
889 : static const struct file_operations eventpoll_fops = {
890 : #ifdef CONFIG_PROC_FS
891 : .show_fdinfo = ep_show_fdinfo,
892 : #endif
893 : .release = ep_eventpoll_release,
894 : .poll = ep_eventpoll_poll,
895 : .llseek = noop_llseek,
896 : };
897 :
898 : /*
899 : * This is called from eventpoll_release() to unlink files from the eventpoll
900 : * interface. We need to have this facility to cleanup correctly files that are
901 : * closed without being removed from the eventpoll interface.
902 : */
903 0 : void eventpoll_release_file(struct file *file)
904 : {
905 : struct eventpoll *ep;
906 : struct epitem *epi;
907 : struct hlist_node *next;
908 :
909 : /*
910 : * We don't want to get "file->f_lock" because it is not
911 : * necessary. It is not necessary because we're in the "struct file"
912 : * cleanup path, and this means that no one is using this file anymore.
913 : * So, for example, epoll_ctl() cannot hit here since if we reach this
914 : * point, the file counter already went to zero and fget() would fail.
915 : * The only hit might come from ep_free() but by holding the mutex
916 : * will correctly serialize the operation. We do need to acquire
917 : * "ep->mtx" after "epmutex" because ep_remove() requires it when called
918 : * from anywhere but ep_free().
919 : *
920 : * Besides, ep_remove() acquires the lock, so we can't hold it here.
921 : */
922 0 : mutex_lock(&epmutex);
923 0 : if (unlikely(!file->f_ep)) {
924 0 : mutex_unlock(&epmutex);
925 0 : return;
926 : }
927 0 : hlist_for_each_entry_safe(epi, next, file->f_ep, fllink) {
928 0 : ep = epi->ep;
929 0 : mutex_lock_nested(&ep->mtx, 0);
930 0 : ep_remove(ep, epi);
931 0 : mutex_unlock(&ep->mtx);
932 : }
933 0 : mutex_unlock(&epmutex);
934 : }
935 :
936 0 : static int ep_alloc(struct eventpoll **pep)
937 : {
938 : int error;
939 : struct user_struct *user;
940 : struct eventpoll *ep;
941 :
942 0 : user = get_current_user();
943 0 : error = -ENOMEM;
944 0 : ep = kzalloc(sizeof(*ep), GFP_KERNEL);
945 0 : if (unlikely(!ep))
946 : goto free_uid;
947 :
948 0 : mutex_init(&ep->mtx);
949 : rwlock_init(&ep->lock);
950 0 : init_waitqueue_head(&ep->wq);
951 0 : init_waitqueue_head(&ep->poll_wait);
952 0 : INIT_LIST_HEAD(&ep->rdllist);
953 0 : ep->rbr = RB_ROOT_CACHED;
954 0 : ep->ovflist = EP_UNACTIVE_PTR;
955 0 : ep->user = user;
956 :
957 0 : *pep = ep;
958 :
959 0 : return 0;
960 :
961 : free_uid:
962 0 : free_uid(user);
963 0 : return error;
964 : }
965 :
966 : /*
967 : * Search the file inside the eventpoll tree. The RB tree operations
968 : * are protected by the "mtx" mutex, and ep_find() must be called with
969 : * "mtx" held.
970 : */
971 : static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
972 : {
973 : int kcmp;
974 : struct rb_node *rbp;
975 0 : struct epitem *epi, *epir = NULL;
976 : struct epoll_filefd ffd;
977 :
978 0 : ep_set_ffd(&ffd, file, fd);
979 0 : for (rbp = ep->rbr.rb_root.rb_node; rbp; ) {
980 0 : epi = rb_entry(rbp, struct epitem, rbn);
981 0 : kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
982 0 : if (kcmp > 0)
983 0 : rbp = rbp->rb_right;
984 0 : else if (kcmp < 0)
985 0 : rbp = rbp->rb_left;
986 : else {
987 : epir = epi;
988 : break;
989 : }
990 : }
991 :
992 : return epir;
993 : }
994 :
995 : #ifdef CONFIG_KCMP
996 0 : static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff)
997 : {
998 : struct rb_node *rbp;
999 : struct epitem *epi;
1000 :
1001 0 : for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1002 0 : epi = rb_entry(rbp, struct epitem, rbn);
1003 0 : if (epi->ffd.fd == tfd) {
1004 0 : if (toff == 0)
1005 : return epi;
1006 : else
1007 0 : toff--;
1008 : }
1009 0 : cond_resched();
1010 : }
1011 :
1012 : return NULL;
1013 : }
1014 :
1015 0 : struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
1016 : unsigned long toff)
1017 : {
1018 : struct file *file_raw;
1019 : struct eventpoll *ep;
1020 : struct epitem *epi;
1021 :
1022 0 : if (!is_file_epoll(file))
1023 : return ERR_PTR(-EINVAL);
1024 :
1025 0 : ep = file->private_data;
1026 :
1027 0 : mutex_lock(&ep->mtx);
1028 0 : epi = ep_find_tfd(ep, tfd, toff);
1029 0 : if (epi)
1030 0 : file_raw = epi->ffd.file;
1031 : else
1032 : file_raw = ERR_PTR(-ENOENT);
1033 0 : mutex_unlock(&ep->mtx);
1034 :
1035 0 : return file_raw;
1036 : }
1037 : #endif /* CONFIG_KCMP */
1038 :
1039 : /*
1040 : * Adds a new entry to the tail of the list in a lockless way, i.e.
1041 : * multiple CPUs are allowed to call this function concurrently.
1042 : *
1043 : * Beware: it is necessary to prevent any other modifications of the
1044 : * existing list until all changes are completed, in other words
1045 : * concurrent list_add_tail_lockless() calls should be protected
1046 : * with a read lock, where write lock acts as a barrier which
1047 : * makes sure all list_add_tail_lockless() calls are fully
1048 : * completed.
1049 : *
1050 : * Also an element can be locklessly added to the list only in one
1051 : * direction i.e. either to the tail or to the head, otherwise
1052 : * concurrent access will corrupt the list.
1053 : *
1054 : * Return: %false if element has been already added to the list, %true
1055 : * otherwise.
1056 : */
1057 : static inline bool list_add_tail_lockless(struct list_head *new,
1058 : struct list_head *head)
1059 : {
1060 : struct list_head *prev;
1061 :
1062 : /*
1063 : * This is simple 'new->next = head' operation, but cmpxchg()
1064 : * is used in order to detect that same element has been just
1065 : * added to the list from another CPU: the winner observes
1066 : * new->next == new.
1067 : */
1068 0 : if (cmpxchg(&new->next, new, head) != new)
1069 : return false;
1070 :
1071 : /*
1072 : * Initially ->next of a new element must be updated with the head
1073 : * (we are inserting to the tail) and only then pointers are atomically
1074 : * exchanged. XCHG guarantees memory ordering, thus ->next should be
1075 : * updated before pointers are actually swapped and pointers are
1076 : * swapped before prev->next is updated.
1077 : */
1078 :
1079 0 : prev = xchg(&head->prev, new);
1080 :
1081 : /*
1082 : * It is safe to modify prev->next and new->prev, because a new element
1083 : * is added only to the tail and new->next is updated before XCHG.
1084 : */
1085 :
1086 0 : prev->next = new;
1087 0 : new->prev = prev;
1088 :
1089 : return true;
1090 : }
1091 :
1092 : /*
1093 : * Chains a new epi entry to the tail of the ep->ovflist in a lockless way,
1094 : * i.e. multiple CPUs are allowed to call this function concurrently.
1095 : *
1096 : * Return: %false if epi element has been already chained, %true otherwise.
1097 : */
1098 : static inline bool chain_epi_lockless(struct epitem *epi)
1099 : {
1100 0 : struct eventpoll *ep = epi->ep;
1101 :
1102 : /* Fast preliminary check */
1103 0 : if (epi->next != EP_UNACTIVE_PTR)
1104 : return false;
1105 :
1106 : /* Check that the same epi has not been just chained from another CPU */
1107 0 : if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR)
1108 : return false;
1109 :
1110 : /* Atomically exchange tail */
1111 0 : epi->next = xchg(&ep->ovflist, epi);
1112 :
1113 : return true;
1114 : }
1115 :
1116 : /*
1117 : * This is the callback that is passed to the wait queue wakeup
1118 : * mechanism. It is called by the stored file descriptors when they
1119 : * have events to report.
1120 : *
1121 : * This callback takes a read lock in order not to contend with concurrent
1122 : * events from another file descriptor, thus all modifications to ->rdllist
1123 : * or ->ovflist are lockless. Read lock is paired with the write lock from
1124 : * ep_scan_ready_list(), which stops all list modifications and guarantees
1125 : * that lists state is seen correctly.
1126 : *
1127 : * Another thing worth to mention is that ep_poll_callback() can be called
1128 : * concurrently for the same @epi from different CPUs if poll table was inited
1129 : * with several wait queues entries. Plural wakeup from different CPUs of a
1130 : * single wait queue is serialized by wq.lock, but the case when multiple wait
1131 : * queues are used should be detected accordingly. This is detected using
1132 : * cmpxchg() operation.
1133 : */
1134 0 : static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
1135 : {
1136 0 : int pwake = 0;
1137 0 : struct epitem *epi = ep_item_from_wait(wait);
1138 0 : struct eventpoll *ep = epi->ep;
1139 0 : __poll_t pollflags = key_to_poll(key);
1140 : unsigned long flags;
1141 0 : int ewake = 0;
1142 :
1143 0 : read_lock_irqsave(&ep->lock, flags);
1144 :
1145 : ep_set_busy_poll_napi_id(epi);
1146 :
1147 : /*
1148 : * If the event mask does not contain any poll(2) event, we consider the
1149 : * descriptor to be disabled. This condition is likely the effect of the
1150 : * EPOLLONESHOT bit that disables the descriptor when an event is received,
1151 : * until the next EPOLL_CTL_MOD will be issued.
1152 : */
1153 0 : if (!(epi->event.events & ~EP_PRIVATE_BITS))
1154 : goto out_unlock;
1155 :
1156 : /*
1157 : * Check the events coming with the callback. At this stage, not
1158 : * every device reports the events in the "key" parameter of the
1159 : * callback. We need to be able to handle both cases here, hence the
1160 : * test for "key" != NULL before the event match test.
1161 : */
1162 0 : if (pollflags && !(pollflags & epi->event.events))
1163 : goto out_unlock;
1164 :
1165 : /*
1166 : * If we are transferring events to userspace, we can hold no locks
1167 : * (because we're accessing user memory, and because of linux f_op->poll()
1168 : * semantics). All the events that happen during that period of time are
1169 : * chained in ep->ovflist and requeued later on.
1170 : */
1171 0 : if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) {
1172 0 : if (chain_epi_lockless(epi))
1173 : ep_pm_stay_awake_rcu(epi);
1174 0 : } else if (!ep_is_linked(epi)) {
1175 : /* In the usual case, add event to ready list. */
1176 0 : if (list_add_tail_lockless(&epi->rdllink, &ep->rdllist))
1177 : ep_pm_stay_awake_rcu(epi);
1178 : }
1179 :
1180 : /*
1181 : * Wake up ( if active ) both the eventpoll wait list and the ->poll()
1182 : * wait list.
1183 : */
1184 0 : if (waitqueue_active(&ep->wq)) {
1185 0 : if ((epi->event.events & EPOLLEXCLUSIVE) &&
1186 0 : !(pollflags & POLLFREE)) {
1187 0 : switch (pollflags & EPOLLINOUT_BITS) {
1188 : case EPOLLIN:
1189 0 : if (epi->event.events & EPOLLIN)
1190 0 : ewake = 1;
1191 : break;
1192 : case EPOLLOUT:
1193 0 : if (epi->event.events & EPOLLOUT)
1194 0 : ewake = 1;
1195 : break;
1196 : case 0:
1197 0 : ewake = 1;
1198 0 : break;
1199 : }
1200 : }
1201 0 : wake_up(&ep->wq);
1202 : }
1203 0 : if (waitqueue_active(&ep->poll_wait))
1204 0 : pwake++;
1205 :
1206 : out_unlock:
1207 0 : read_unlock_irqrestore(&ep->lock, flags);
1208 :
1209 : /* We have to call this outside the lock */
1210 0 : if (pwake)
1211 0 : ep_poll_safewake(ep, epi);
1212 :
1213 0 : if (!(epi->event.events & EPOLLEXCLUSIVE))
1214 0 : ewake = 1;
1215 :
1216 0 : if (pollflags & POLLFREE) {
1217 : /*
1218 : * If we race with ep_remove_wait_queue() it can miss
1219 : * ->whead = NULL and do another remove_wait_queue() after
1220 : * us, so we can't use __remove_wait_queue().
1221 : */
1222 0 : list_del_init(&wait->entry);
1223 : /*
1224 : * ->whead != NULL protects us from the race with ep_free()
1225 : * or ep_remove(), ep_remove_wait_queue() takes whead->lock
1226 : * held by the caller. Once we nullify it, nothing protects
1227 : * ep/epi or even wait.
1228 : */
1229 0 : smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL);
1230 : }
1231 :
1232 0 : return ewake;
1233 : }
1234 :
1235 : /*
1236 : * This is the callback that is used to add our wait queue to the
1237 : * target file wakeup lists.
1238 : */
1239 0 : static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
1240 : poll_table *pt)
1241 : {
1242 0 : struct ep_pqueue *epq = container_of(pt, struct ep_pqueue, pt);
1243 0 : struct epitem *epi = epq->epi;
1244 : struct eppoll_entry *pwq;
1245 :
1246 0 : if (unlikely(!epi)) // an earlier allocation has failed
1247 : return;
1248 :
1249 0 : pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL);
1250 0 : if (unlikely(!pwq)) {
1251 0 : epq->epi = NULL;
1252 0 : return;
1253 : }
1254 :
1255 0 : init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
1256 0 : pwq->whead = whead;
1257 0 : pwq->base = epi;
1258 0 : if (epi->event.events & EPOLLEXCLUSIVE)
1259 0 : add_wait_queue_exclusive(whead, &pwq->wait);
1260 : else
1261 0 : add_wait_queue(whead, &pwq->wait);
1262 0 : pwq->next = epi->pwqlist;
1263 0 : epi->pwqlist = pwq;
1264 : }
1265 :
1266 0 : static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
1267 : {
1268 : int kcmp;
1269 0 : struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL;
1270 : struct epitem *epic;
1271 0 : bool leftmost = true;
1272 :
1273 0 : while (*p) {
1274 0 : parent = *p;
1275 0 : epic = rb_entry(parent, struct epitem, rbn);
1276 0 : kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
1277 0 : if (kcmp > 0) {
1278 0 : p = &parent->rb_right;
1279 0 : leftmost = false;
1280 : } else
1281 0 : p = &parent->rb_left;
1282 : }
1283 0 : rb_link_node(&epi->rbn, parent, p);
1284 0 : rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost);
1285 0 : }
1286 :
1287 :
1288 :
1289 : #define PATH_ARR_SIZE 5
1290 : /*
1291 : * These are the number paths of length 1 to 5, that we are allowing to emanate
1292 : * from a single file of interest. For example, we allow 1000 paths of length
1293 : * 1, to emanate from each file of interest. This essentially represents the
1294 : * potential wakeup paths, which need to be limited in order to avoid massive
1295 : * uncontrolled wakeup storms. The common use case should be a single ep which
1296 : * is connected to n file sources. In this case each file source has 1 path
1297 : * of length 1. Thus, the numbers below should be more than sufficient. These
1298 : * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
1299 : * and delete can't add additional paths. Protected by the epmutex.
1300 : */
1301 : static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
1302 : static int path_count[PATH_ARR_SIZE];
1303 :
1304 : static int path_count_inc(int nests)
1305 : {
1306 : /* Allow an arbitrary number of depth 1 paths */
1307 0 : if (nests == 0)
1308 : return 0;
1309 :
1310 0 : if (++path_count[nests] > path_limits[nests])
1311 : return -1;
1312 : return 0;
1313 : }
1314 :
1315 : static void path_count_init(void)
1316 : {
1317 : int i;
1318 :
1319 0 : for (i = 0; i < PATH_ARR_SIZE; i++)
1320 0 : path_count[i] = 0;
1321 : }
1322 :
1323 0 : static int reverse_path_check_proc(struct hlist_head *refs, int depth)
1324 : {
1325 0 : int error = 0;
1326 : struct epitem *epi;
1327 :
1328 0 : if (depth > EP_MAX_NESTS) /* too deep nesting */
1329 : return -1;
1330 :
1331 : /* CTL_DEL can remove links here, but that can't increase our count */
1332 0 : hlist_for_each_entry_rcu(epi, refs, fllink) {
1333 0 : struct hlist_head *refs = &epi->ep->refs;
1334 0 : if (hlist_empty(refs))
1335 : error = path_count_inc(depth);
1336 : else
1337 0 : error = reverse_path_check_proc(refs, depth + 1);
1338 0 : if (error != 0)
1339 : break;
1340 : }
1341 : return error;
1342 : }
1343 :
1344 : /**
1345 : * reverse_path_check - The tfile_check_list is list of epitem_head, which have
1346 : * links that are proposed to be newly added. We need to
1347 : * make sure that those added links don't add too many
1348 : * paths such that we will spend all our time waking up
1349 : * eventpoll objects.
1350 : *
1351 : * Return: %zero if the proposed links don't create too many paths,
1352 : * %-1 otherwise.
1353 : */
1354 0 : static int reverse_path_check(void)
1355 : {
1356 : struct epitems_head *p;
1357 :
1358 0 : for (p = tfile_check_list; p != EP_UNACTIVE_PTR; p = p->next) {
1359 : int error;
1360 0 : path_count_init();
1361 : rcu_read_lock();
1362 0 : error = reverse_path_check_proc(&p->epitems, 0);
1363 : rcu_read_unlock();
1364 0 : if (error)
1365 : return error;
1366 : }
1367 : return 0;
1368 : }
1369 :
1370 0 : static int ep_create_wakeup_source(struct epitem *epi)
1371 : {
1372 : struct name_snapshot n;
1373 : struct wakeup_source *ws;
1374 :
1375 0 : if (!epi->ep->ws) {
1376 0 : epi->ep->ws = wakeup_source_register(NULL, "eventpoll");
1377 0 : if (!epi->ep->ws)
1378 : return -ENOMEM;
1379 : }
1380 :
1381 0 : take_dentry_name_snapshot(&n, epi->ffd.file->f_path.dentry);
1382 0 : ws = wakeup_source_register(NULL, n.name.name);
1383 0 : release_dentry_name_snapshot(&n);
1384 :
1385 0 : if (!ws)
1386 : return -ENOMEM;
1387 0 : rcu_assign_pointer(epi->ws, ws);
1388 :
1389 0 : return 0;
1390 : }
1391 :
1392 : /* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
1393 0 : static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1394 : {
1395 0 : struct wakeup_source *ws = ep_wakeup_source(epi);
1396 :
1397 0 : RCU_INIT_POINTER(epi->ws, NULL);
1398 :
1399 : /*
1400 : * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
1401 : * used internally by wakeup_source_remove, too (called by
1402 : * wakeup_source_unregister), so we cannot use call_rcu
1403 : */
1404 0 : synchronize_rcu();
1405 0 : wakeup_source_unregister(ws);
1406 0 : }
1407 :
1408 0 : static int attach_epitem(struct file *file, struct epitem *epi)
1409 : {
1410 0 : struct epitems_head *to_free = NULL;
1411 0 : struct hlist_head *head = NULL;
1412 0 : struct eventpoll *ep = NULL;
1413 :
1414 0 : if (is_file_epoll(file))
1415 0 : ep = file->private_data;
1416 :
1417 0 : if (ep) {
1418 0 : head = &ep->refs;
1419 0 : } else if (!READ_ONCE(file->f_ep)) {
1420 : allocate:
1421 0 : to_free = kmem_cache_zalloc(ephead_cache, GFP_KERNEL);
1422 0 : if (!to_free)
1423 : return -ENOMEM;
1424 0 : head = &to_free->epitems;
1425 : }
1426 0 : spin_lock(&file->f_lock);
1427 0 : if (!file->f_ep) {
1428 0 : if (unlikely(!head)) {
1429 0 : spin_unlock(&file->f_lock);
1430 : goto allocate;
1431 : }
1432 0 : file->f_ep = head;
1433 0 : to_free = NULL;
1434 : }
1435 0 : hlist_add_head_rcu(&epi->fllink, file->f_ep);
1436 0 : spin_unlock(&file->f_lock);
1437 : free_ephead(to_free);
1438 : return 0;
1439 : }
1440 :
1441 : /*
1442 : * Must be called with "mtx" held.
1443 : */
1444 0 : static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
1445 : struct file *tfile, int fd, int full_check)
1446 : {
1447 0 : int error, pwake = 0;
1448 : __poll_t revents;
1449 : struct epitem *epi;
1450 : struct ep_pqueue epq;
1451 0 : struct eventpoll *tep = NULL;
1452 :
1453 0 : if (is_file_epoll(tfile))
1454 0 : tep = tfile->private_data;
1455 :
1456 : lockdep_assert_irqs_enabled();
1457 :
1458 0 : if (unlikely(percpu_counter_compare(&ep->user->epoll_watches,
1459 : max_user_watches) >= 0))
1460 : return -ENOSPC;
1461 0 : percpu_counter_inc(&ep->user->epoll_watches);
1462 :
1463 0 : if (!(epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL))) {
1464 0 : percpu_counter_dec(&ep->user->epoll_watches);
1465 0 : return -ENOMEM;
1466 : }
1467 :
1468 : /* Item initialization follow here ... */
1469 0 : INIT_LIST_HEAD(&epi->rdllink);
1470 0 : epi->ep = ep;
1471 0 : ep_set_ffd(&epi->ffd, tfile, fd);
1472 0 : epi->event = *event;
1473 0 : epi->next = EP_UNACTIVE_PTR;
1474 :
1475 0 : if (tep)
1476 0 : mutex_lock_nested(&tep->mtx, 1);
1477 : /* Add the current item to the list of active epoll hook for this file */
1478 0 : if (unlikely(attach_epitem(tfile, epi) < 0)) {
1479 0 : if (tep)
1480 0 : mutex_unlock(&tep->mtx);
1481 0 : kmem_cache_free(epi_cache, epi);
1482 0 : percpu_counter_dec(&ep->user->epoll_watches);
1483 0 : return -ENOMEM;
1484 : }
1485 :
1486 0 : if (full_check && !tep)
1487 0 : list_file(tfile);
1488 :
1489 : /*
1490 : * Add the current item to the RB tree. All RB tree operations are
1491 : * protected by "mtx", and ep_insert() is called with "mtx" held.
1492 : */
1493 0 : ep_rbtree_insert(ep, epi);
1494 0 : if (tep)
1495 0 : mutex_unlock(&tep->mtx);
1496 :
1497 : /* now check if we've created too many backpaths */
1498 0 : if (unlikely(full_check && reverse_path_check())) {
1499 0 : ep_remove(ep, epi);
1500 0 : return -EINVAL;
1501 : }
1502 :
1503 0 : if (epi->event.events & EPOLLWAKEUP) {
1504 0 : error = ep_create_wakeup_source(epi);
1505 0 : if (error) {
1506 0 : ep_remove(ep, epi);
1507 0 : return error;
1508 : }
1509 : }
1510 :
1511 : /* Initialize the poll table using the queue callback */
1512 0 : epq.epi = epi;
1513 0 : init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
1514 :
1515 : /*
1516 : * Attach the item to the poll hooks and get current event bits.
1517 : * We can safely use the file* here because its usage count has
1518 : * been increased by the caller of this function. Note that after
1519 : * this operation completes, the poll callback can start hitting
1520 : * the new item.
1521 : */
1522 0 : revents = ep_item_poll(epi, &epq.pt, 1);
1523 :
1524 : /*
1525 : * We have to check if something went wrong during the poll wait queue
1526 : * install process. Namely an allocation for a wait queue failed due
1527 : * high memory pressure.
1528 : */
1529 0 : if (unlikely(!epq.epi)) {
1530 0 : ep_remove(ep, epi);
1531 0 : return -ENOMEM;
1532 : }
1533 :
1534 : /* We have to drop the new item inside our item list to keep track of it */
1535 0 : write_lock_irq(&ep->lock);
1536 :
1537 : /* record NAPI ID of new item if present */
1538 : ep_set_busy_poll_napi_id(epi);
1539 :
1540 : /* If the file is already "ready" we drop it inside the ready list */
1541 0 : if (revents && !ep_is_linked(epi)) {
1542 0 : list_add_tail(&epi->rdllink, &ep->rdllist);
1543 0 : ep_pm_stay_awake(epi);
1544 :
1545 : /* Notify waiting tasks that events are available */
1546 0 : if (waitqueue_active(&ep->wq))
1547 0 : wake_up(&ep->wq);
1548 0 : if (waitqueue_active(&ep->poll_wait))
1549 0 : pwake++;
1550 : }
1551 :
1552 0 : write_unlock_irq(&ep->lock);
1553 :
1554 : /* We have to call this outside the lock */
1555 0 : if (pwake)
1556 0 : ep_poll_safewake(ep, NULL);
1557 :
1558 : return 0;
1559 : }
1560 :
1561 : /*
1562 : * Modify the interest event mask by dropping an event if the new mask
1563 : * has a match in the current file status. Must be called with "mtx" held.
1564 : */
1565 0 : static int ep_modify(struct eventpoll *ep, struct epitem *epi,
1566 : const struct epoll_event *event)
1567 : {
1568 0 : int pwake = 0;
1569 : poll_table pt;
1570 :
1571 : lockdep_assert_irqs_enabled();
1572 :
1573 0 : init_poll_funcptr(&pt, NULL);
1574 :
1575 : /*
1576 : * Set the new event interest mask before calling f_op->poll();
1577 : * otherwise we might miss an event that happens between the
1578 : * f_op->poll() call and the new event set registering.
1579 : */
1580 0 : epi->event.events = event->events; /* need barrier below */
1581 0 : epi->event.data = event->data; /* protected by mtx */
1582 0 : if (epi->event.events & EPOLLWAKEUP) {
1583 0 : if (!ep_has_wakeup_source(epi))
1584 0 : ep_create_wakeup_source(epi);
1585 0 : } else if (ep_has_wakeup_source(epi)) {
1586 0 : ep_destroy_wakeup_source(epi);
1587 : }
1588 :
1589 : /*
1590 : * The following barrier has two effects:
1591 : *
1592 : * 1) Flush epi changes above to other CPUs. This ensures
1593 : * we do not miss events from ep_poll_callback if an
1594 : * event occurs immediately after we call f_op->poll().
1595 : * We need this because we did not take ep->lock while
1596 : * changing epi above (but ep_poll_callback does take
1597 : * ep->lock).
1598 : *
1599 : * 2) We also need to ensure we do not miss _past_ events
1600 : * when calling f_op->poll(). This barrier also
1601 : * pairs with the barrier in wq_has_sleeper (see
1602 : * comments for wq_has_sleeper).
1603 : *
1604 : * This barrier will now guarantee ep_poll_callback or f_op->poll
1605 : * (or both) will notice the readiness of an item.
1606 : */
1607 0 : smp_mb();
1608 :
1609 : /*
1610 : * Get current event bits. We can safely use the file* here because
1611 : * its usage count has been increased by the caller of this function.
1612 : * If the item is "hot" and it is not registered inside the ready
1613 : * list, push it inside.
1614 : */
1615 0 : if (ep_item_poll(epi, &pt, 1)) {
1616 0 : write_lock_irq(&ep->lock);
1617 0 : if (!ep_is_linked(epi)) {
1618 0 : list_add_tail(&epi->rdllink, &ep->rdllist);
1619 0 : ep_pm_stay_awake(epi);
1620 :
1621 : /* Notify waiting tasks that events are available */
1622 0 : if (waitqueue_active(&ep->wq))
1623 0 : wake_up(&ep->wq);
1624 0 : if (waitqueue_active(&ep->poll_wait))
1625 0 : pwake++;
1626 : }
1627 0 : write_unlock_irq(&ep->lock);
1628 : }
1629 :
1630 : /* We have to call this outside the lock */
1631 0 : if (pwake)
1632 0 : ep_poll_safewake(ep, NULL);
1633 :
1634 0 : return 0;
1635 : }
1636 :
1637 0 : static int ep_send_events(struct eventpoll *ep,
1638 : struct epoll_event __user *events, int maxevents)
1639 : {
1640 : struct epitem *epi, *tmp;
1641 0 : LIST_HEAD(txlist);
1642 : poll_table pt;
1643 0 : int res = 0;
1644 :
1645 : /*
1646 : * Always short-circuit for fatal signals to allow threads to make a
1647 : * timely exit without the chance of finding more events available and
1648 : * fetching repeatedly.
1649 : */
1650 0 : if (fatal_signal_pending(current))
1651 : return -EINTR;
1652 :
1653 0 : init_poll_funcptr(&pt, NULL);
1654 :
1655 0 : mutex_lock(&ep->mtx);
1656 0 : ep_start_scan(ep, &txlist);
1657 :
1658 : /*
1659 : * We can loop without lock because we are passed a task private list.
1660 : * Items cannot vanish during the loop we are holding ep->mtx.
1661 : */
1662 0 : list_for_each_entry_safe(epi, tmp, &txlist, rdllink) {
1663 : struct wakeup_source *ws;
1664 : __poll_t revents;
1665 :
1666 0 : if (res >= maxevents)
1667 : break;
1668 :
1669 : /*
1670 : * Activate ep->ws before deactivating epi->ws to prevent
1671 : * triggering auto-suspend here (in case we reactive epi->ws
1672 : * below).
1673 : *
1674 : * This could be rearranged to delay the deactivation of epi->ws
1675 : * instead, but then epi->ws would temporarily be out of sync
1676 : * with ep_is_linked().
1677 : */
1678 0 : ws = ep_wakeup_source(epi);
1679 0 : if (ws) {
1680 0 : if (ws->active)
1681 0 : __pm_stay_awake(ep->ws);
1682 0 : __pm_relax(ws);
1683 : }
1684 :
1685 0 : list_del_init(&epi->rdllink);
1686 :
1687 : /*
1688 : * If the event mask intersect the caller-requested one,
1689 : * deliver the event to userspace. Again, we are holding ep->mtx,
1690 : * so no operations coming from userspace can change the item.
1691 : */
1692 0 : revents = ep_item_poll(epi, &pt, 1);
1693 0 : if (!revents)
1694 0 : continue;
1695 :
1696 0 : events = epoll_put_uevent(revents, epi->event.data, events);
1697 0 : if (!events) {
1698 0 : list_add(&epi->rdllink, &txlist);
1699 0 : ep_pm_stay_awake(epi);
1700 0 : if (!res)
1701 0 : res = -EFAULT;
1702 : break;
1703 : }
1704 0 : res++;
1705 0 : if (epi->event.events & EPOLLONESHOT)
1706 0 : epi->event.events &= EP_PRIVATE_BITS;
1707 0 : else if (!(epi->event.events & EPOLLET)) {
1708 : /*
1709 : * If this file has been added with Level
1710 : * Trigger mode, we need to insert back inside
1711 : * the ready list, so that the next call to
1712 : * epoll_wait() will check again the events
1713 : * availability. At this point, no one can insert
1714 : * into ep->rdllist besides us. The epoll_ctl()
1715 : * callers are locked out by
1716 : * ep_scan_ready_list() holding "mtx" and the
1717 : * poll callback will queue them in ep->ovflist.
1718 : */
1719 0 : list_add_tail(&epi->rdllink, &ep->rdllist);
1720 : ep_pm_stay_awake(epi);
1721 : }
1722 : }
1723 0 : ep_done_scan(ep, &txlist);
1724 0 : mutex_unlock(&ep->mtx);
1725 :
1726 0 : return res;
1727 : }
1728 :
1729 0 : static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms)
1730 : {
1731 : struct timespec64 now;
1732 :
1733 0 : if (ms < 0)
1734 : return NULL;
1735 :
1736 0 : if (!ms) {
1737 0 : to->tv_sec = 0;
1738 0 : to->tv_nsec = 0;
1739 0 : return to;
1740 : }
1741 :
1742 0 : to->tv_sec = ms / MSEC_PER_SEC;
1743 0 : to->tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC);
1744 :
1745 0 : ktime_get_ts64(&now);
1746 0 : *to = timespec64_add_safe(now, *to);
1747 0 : return to;
1748 : }
1749 :
1750 : /**
1751 : * ep_poll - Retrieves ready events, and delivers them to the caller-supplied
1752 : * event buffer.
1753 : *
1754 : * @ep: Pointer to the eventpoll context.
1755 : * @events: Pointer to the userspace buffer where the ready events should be
1756 : * stored.
1757 : * @maxevents: Size (in terms of number of events) of the caller event buffer.
1758 : * @timeout: Maximum timeout for the ready events fetch operation, in
1759 : * timespec. If the timeout is zero, the function will not block,
1760 : * while if the @timeout ptr is NULL, the function will block
1761 : * until at least one event has been retrieved (or an error
1762 : * occurred).
1763 : *
1764 : * Return: the number of ready events which have been fetched, or an
1765 : * error code, in case of error.
1766 : */
1767 0 : static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1768 : int maxevents, struct timespec64 *timeout)
1769 : {
1770 0 : int res, eavail, timed_out = 0;
1771 0 : u64 slack = 0;
1772 : wait_queue_entry_t wait;
1773 0 : ktime_t expires, *to = NULL;
1774 :
1775 : lockdep_assert_irqs_enabled();
1776 :
1777 0 : if (timeout && (timeout->tv_sec | timeout->tv_nsec)) {
1778 0 : slack = select_estimate_accuracy(timeout);
1779 0 : to = &expires;
1780 0 : *to = timespec64_to_ktime(*timeout);
1781 0 : } else if (timeout) {
1782 : /*
1783 : * Avoid the unnecessary trip to the wait queue loop, if the
1784 : * caller specified a non blocking operation.
1785 : */
1786 0 : timed_out = 1;
1787 : }
1788 :
1789 : /*
1790 : * This call is racy: We may or may not see events that are being added
1791 : * to the ready list under the lock (e.g., in IRQ callbacks). For cases
1792 : * with a non-zero timeout, this thread will check the ready list under
1793 : * lock and will add to the wait queue. For cases with a zero
1794 : * timeout, the user by definition should not care and will have to
1795 : * recheck again.
1796 : */
1797 : eavail = ep_events_available(ep);
1798 :
1799 : while (1) {
1800 0 : if (eavail) {
1801 : /*
1802 : * Try to transfer events to user space. In case we get
1803 : * 0 events and there's still timeout left over, we go
1804 : * trying again in search of more luck.
1805 : */
1806 0 : res = ep_send_events(ep, events, maxevents);
1807 0 : if (res)
1808 : return res;
1809 : }
1810 :
1811 0 : if (timed_out)
1812 : return 0;
1813 :
1814 0 : eavail = ep_busy_loop(ep, timed_out);
1815 : if (eavail)
1816 : continue;
1817 :
1818 0 : if (signal_pending(current))
1819 : return -EINTR;
1820 :
1821 : /*
1822 : * Internally init_wait() uses autoremove_wake_function(),
1823 : * thus wait entry is removed from the wait queue on each
1824 : * wakeup. Why it is important? In case of several waiters
1825 : * each new wakeup will hit the next waiter, giving it the
1826 : * chance to harvest new event. Otherwise wakeup can be
1827 : * lost. This is also good performance-wise, because on
1828 : * normal wakeup path no need to call __remove_wait_queue()
1829 : * explicitly, thus ep->lock is not taken, which halts the
1830 : * event delivery.
1831 : */
1832 0 : init_wait(&wait);
1833 :
1834 0 : write_lock_irq(&ep->lock);
1835 : /*
1836 : * Barrierless variant, waitqueue_active() is called under
1837 : * the same lock on wakeup ep_poll_callback() side, so it
1838 : * is safe to avoid an explicit barrier.
1839 : */
1840 0 : __set_current_state(TASK_INTERRUPTIBLE);
1841 :
1842 : /*
1843 : * Do the final check under the lock. ep_scan_ready_list()
1844 : * plays with two lists (->rdllist and ->ovflist) and there
1845 : * is always a race when both lists are empty for short
1846 : * period of time although events are pending, so lock is
1847 : * important.
1848 : */
1849 0 : eavail = ep_events_available(ep);
1850 0 : if (!eavail)
1851 0 : __add_wait_queue_exclusive(&ep->wq, &wait);
1852 :
1853 0 : write_unlock_irq(&ep->lock);
1854 :
1855 0 : if (!eavail)
1856 0 : timed_out = !schedule_hrtimeout_range(to, slack,
1857 : HRTIMER_MODE_ABS);
1858 0 : __set_current_state(TASK_RUNNING);
1859 :
1860 : /*
1861 : * We were woken up, thus go and try to harvest some events.
1862 : * If timed out and still on the wait queue, recheck eavail
1863 : * carefully under lock, below.
1864 : */
1865 0 : eavail = 1;
1866 :
1867 0 : if (!list_empty_careful(&wait.entry)) {
1868 0 : write_lock_irq(&ep->lock);
1869 : /*
1870 : * If the thread timed out and is not on the wait queue,
1871 : * it means that the thread was woken up after its
1872 : * timeout expired before it could reacquire the lock.
1873 : * Thus, when wait.entry is empty, it needs to harvest
1874 : * events.
1875 : */
1876 0 : if (timed_out)
1877 0 : eavail = list_empty(&wait.entry);
1878 0 : __remove_wait_queue(&ep->wq, &wait);
1879 0 : write_unlock_irq(&ep->lock);
1880 : }
1881 : }
1882 : }
1883 :
1884 : /**
1885 : * ep_loop_check_proc - verify that adding an epoll file inside another
1886 : * epoll structure does not violate the constraints, in
1887 : * terms of closed loops, or too deep chains (which can
1888 : * result in excessive stack usage).
1889 : *
1890 : * @ep: the &struct eventpoll to be currently checked.
1891 : * @depth: Current depth of the path being checked.
1892 : *
1893 : * Return: %zero if adding the epoll @file inside current epoll
1894 : * structure @ep does not violate the constraints, or %-1 otherwise.
1895 : */
1896 0 : static int ep_loop_check_proc(struct eventpoll *ep, int depth)
1897 : {
1898 0 : int error = 0;
1899 : struct rb_node *rbp;
1900 : struct epitem *epi;
1901 :
1902 0 : mutex_lock_nested(&ep->mtx, depth + 1);
1903 0 : ep->gen = loop_check_gen;
1904 0 : for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1905 0 : epi = rb_entry(rbp, struct epitem, rbn);
1906 0 : if (unlikely(is_file_epoll(epi->ffd.file))) {
1907 : struct eventpoll *ep_tovisit;
1908 0 : ep_tovisit = epi->ffd.file->private_data;
1909 0 : if (ep_tovisit->gen == loop_check_gen)
1910 0 : continue;
1911 0 : if (ep_tovisit == inserting_into || depth > EP_MAX_NESTS)
1912 : error = -1;
1913 : else
1914 0 : error = ep_loop_check_proc(ep_tovisit, depth + 1);
1915 0 : if (error != 0)
1916 : break;
1917 : } else {
1918 : /*
1919 : * If we've reached a file that is not associated with
1920 : * an ep, then we need to check if the newly added
1921 : * links are going to add too many wakeup paths. We do
1922 : * this by adding it to the tfile_check_list, if it's
1923 : * not already there, and calling reverse_path_check()
1924 : * during ep_insert().
1925 : */
1926 0 : list_file(epi->ffd.file);
1927 : }
1928 : }
1929 0 : mutex_unlock(&ep->mtx);
1930 :
1931 0 : return error;
1932 : }
1933 :
1934 : /**
1935 : * ep_loop_check - Performs a check to verify that adding an epoll file (@to)
1936 : * into another epoll file (represented by @ep) does not create
1937 : * closed loops or too deep chains.
1938 : *
1939 : * @ep: Pointer to the epoll we are inserting into.
1940 : * @to: Pointer to the epoll to be inserted.
1941 : *
1942 : * Return: %zero if adding the epoll @to inside the epoll @from
1943 : * does not violate the constraints, or %-1 otherwise.
1944 : */
1945 : static int ep_loop_check(struct eventpoll *ep, struct eventpoll *to)
1946 : {
1947 0 : inserting_into = ep;
1948 0 : return ep_loop_check_proc(to, 0);
1949 : }
1950 :
1951 : static void clear_tfile_check_list(void)
1952 : {
1953 : rcu_read_lock();
1954 0 : while (tfile_check_list != EP_UNACTIVE_PTR) {
1955 0 : struct epitems_head *head = tfile_check_list;
1956 0 : tfile_check_list = head->next;
1957 0 : unlist_file(head);
1958 : }
1959 : rcu_read_unlock();
1960 : }
1961 :
1962 : /*
1963 : * Open an eventpoll file descriptor.
1964 : */
1965 0 : static int do_epoll_create(int flags)
1966 : {
1967 : int error, fd;
1968 0 : struct eventpoll *ep = NULL;
1969 : struct file *file;
1970 :
1971 : /* Check the EPOLL_* constant for consistency. */
1972 : BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
1973 :
1974 0 : if (flags & ~EPOLL_CLOEXEC)
1975 : return -EINVAL;
1976 : /*
1977 : * Create the internal data structure ("struct eventpoll").
1978 : */
1979 0 : error = ep_alloc(&ep);
1980 0 : if (error < 0)
1981 : return error;
1982 : /*
1983 : * Creates all the items needed to setup an eventpoll file. That is,
1984 : * a file structure and a free file descriptor.
1985 : */
1986 0 : fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
1987 0 : if (fd < 0) {
1988 : error = fd;
1989 : goto out_free_ep;
1990 : }
1991 0 : file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
1992 : O_RDWR | (flags & O_CLOEXEC));
1993 0 : if (IS_ERR(file)) {
1994 0 : error = PTR_ERR(file);
1995 : goto out_free_fd;
1996 : }
1997 0 : ep->file = file;
1998 0 : fd_install(fd, file);
1999 0 : return fd;
2000 :
2001 : out_free_fd:
2002 0 : put_unused_fd(fd);
2003 : out_free_ep:
2004 0 : ep_free(ep);
2005 0 : return error;
2006 : }
2007 :
2008 0 : SYSCALL_DEFINE1(epoll_create1, int, flags)
2009 : {
2010 0 : return do_epoll_create(flags);
2011 : }
2012 :
2013 0 : SYSCALL_DEFINE1(epoll_create, int, size)
2014 : {
2015 0 : if (size <= 0)
2016 : return -EINVAL;
2017 :
2018 0 : return do_epoll_create(0);
2019 : }
2020 :
2021 : static inline int epoll_mutex_lock(struct mutex *mutex, int depth,
2022 : bool nonblock)
2023 : {
2024 0 : if (!nonblock) {
2025 0 : mutex_lock_nested(mutex, depth);
2026 : return 0;
2027 : }
2028 0 : if (mutex_trylock(mutex))
2029 : return 0;
2030 : return -EAGAIN;
2031 : }
2032 :
2033 0 : int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
2034 : bool nonblock)
2035 : {
2036 : int error;
2037 0 : int full_check = 0;
2038 : struct fd f, tf;
2039 : struct eventpoll *ep;
2040 : struct epitem *epi;
2041 0 : struct eventpoll *tep = NULL;
2042 :
2043 0 : error = -EBADF;
2044 0 : f = fdget(epfd);
2045 0 : if (!f.file)
2046 : goto error_return;
2047 :
2048 : /* Get the "struct file *" for the target file */
2049 0 : tf = fdget(fd);
2050 0 : if (!tf.file)
2051 : goto error_fput;
2052 :
2053 : /* The target file descriptor must support poll */
2054 0 : error = -EPERM;
2055 0 : if (!file_can_poll(tf.file))
2056 : goto error_tgt_fput;
2057 :
2058 : /* Check if EPOLLWAKEUP is allowed */
2059 0 : if (ep_op_has_event(op))
2060 0 : ep_take_care_of_epollwakeup(epds);
2061 :
2062 : /*
2063 : * We have to check that the file structure underneath the file descriptor
2064 : * the user passed to us _is_ an eventpoll file. And also we do not permit
2065 : * adding an epoll file descriptor inside itself.
2066 : */
2067 0 : error = -EINVAL;
2068 0 : if (f.file == tf.file || !is_file_epoll(f.file))
2069 : goto error_tgt_fput;
2070 :
2071 : /*
2072 : * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only,
2073 : * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
2074 : * Also, we do not currently supported nested exclusive wakeups.
2075 : */
2076 0 : if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) {
2077 0 : if (op == EPOLL_CTL_MOD)
2078 : goto error_tgt_fput;
2079 0 : if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
2080 0 : (epds->events & ~EPOLLEXCLUSIVE_OK_BITS)))
2081 : goto error_tgt_fput;
2082 : }
2083 :
2084 : /*
2085 : * At this point it is safe to assume that the "private_data" contains
2086 : * our own data structure.
2087 : */
2088 0 : ep = f.file->private_data;
2089 :
2090 : /*
2091 : * When we insert an epoll file descriptor inside another epoll file
2092 : * descriptor, there is the chance of creating closed loops, which are
2093 : * better be handled here, than in more critical paths. While we are
2094 : * checking for loops we also determine the list of files reachable
2095 : * and hang them on the tfile_check_list, so we can check that we
2096 : * haven't created too many possible wakeup paths.
2097 : *
2098 : * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
2099 : * the epoll file descriptor is attaching directly to a wakeup source,
2100 : * unless the epoll file descriptor is nested. The purpose of taking the
2101 : * 'epmutex' on add is to prevent complex toplogies such as loops and
2102 : * deep wakeup paths from forming in parallel through multiple
2103 : * EPOLL_CTL_ADD operations.
2104 : */
2105 0 : error = epoll_mutex_lock(&ep->mtx, 0, nonblock);
2106 0 : if (error)
2107 : goto error_tgt_fput;
2108 0 : if (op == EPOLL_CTL_ADD) {
2109 0 : if (READ_ONCE(f.file->f_ep) || ep->gen == loop_check_gen ||
2110 0 : is_file_epoll(tf.file)) {
2111 0 : mutex_unlock(&ep->mtx);
2112 0 : error = epoll_mutex_lock(&epmutex, 0, nonblock);
2113 0 : if (error)
2114 : goto error_tgt_fput;
2115 0 : loop_check_gen++;
2116 0 : full_check = 1;
2117 0 : if (is_file_epoll(tf.file)) {
2118 0 : tep = tf.file->private_data;
2119 0 : error = -ELOOP;
2120 0 : if (ep_loop_check(ep, tep) != 0)
2121 : goto error_tgt_fput;
2122 : }
2123 0 : error = epoll_mutex_lock(&ep->mtx, 0, nonblock);
2124 0 : if (error)
2125 : goto error_tgt_fput;
2126 : }
2127 : }
2128 :
2129 : /*
2130 : * Try to lookup the file inside our RB tree. Since we grabbed "mtx"
2131 : * above, we can be sure to be able to use the item looked up by
2132 : * ep_find() till we release the mutex.
2133 : */
2134 0 : epi = ep_find(ep, tf.file, fd);
2135 :
2136 0 : error = -EINVAL;
2137 0 : switch (op) {
2138 : case EPOLL_CTL_ADD:
2139 0 : if (!epi) {
2140 0 : epds->events |= EPOLLERR | EPOLLHUP;
2141 0 : error = ep_insert(ep, epds, tf.file, fd, full_check);
2142 : } else
2143 : error = -EEXIST;
2144 : break;
2145 : case EPOLL_CTL_DEL:
2146 0 : if (epi)
2147 0 : error = ep_remove(ep, epi);
2148 : else
2149 : error = -ENOENT;
2150 : break;
2151 : case EPOLL_CTL_MOD:
2152 0 : if (epi) {
2153 0 : if (!(epi->event.events & EPOLLEXCLUSIVE)) {
2154 0 : epds->events |= EPOLLERR | EPOLLHUP;
2155 0 : error = ep_modify(ep, epi, epds);
2156 : }
2157 : } else
2158 : error = -ENOENT;
2159 : break;
2160 : }
2161 0 : mutex_unlock(&ep->mtx);
2162 :
2163 : error_tgt_fput:
2164 0 : if (full_check) {
2165 : clear_tfile_check_list();
2166 0 : loop_check_gen++;
2167 0 : mutex_unlock(&epmutex);
2168 : }
2169 :
2170 0 : fdput(tf);
2171 : error_fput:
2172 0 : fdput(f);
2173 : error_return:
2174 :
2175 0 : return error;
2176 : }
2177 :
2178 : /*
2179 : * The following function implements the controller interface for
2180 : * the eventpoll file that enables the insertion/removal/change of
2181 : * file descriptors inside the interest set.
2182 : */
2183 0 : SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
2184 : struct epoll_event __user *, event)
2185 : {
2186 : struct epoll_event epds;
2187 :
2188 0 : if (ep_op_has_event(op) &&
2189 0 : copy_from_user(&epds, event, sizeof(struct epoll_event)))
2190 : return -EFAULT;
2191 :
2192 0 : return do_epoll_ctl(epfd, op, fd, &epds, false);
2193 : }
2194 :
2195 : /*
2196 : * Implement the event wait interface for the eventpoll file. It is the kernel
2197 : * part of the user space epoll_wait(2).
2198 : */
2199 0 : static int do_epoll_wait(int epfd, struct epoll_event __user *events,
2200 : int maxevents, struct timespec64 *to)
2201 : {
2202 : int error;
2203 : struct fd f;
2204 : struct eventpoll *ep;
2205 :
2206 : /* The maximum number of event must be greater than zero */
2207 0 : if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
2208 : return -EINVAL;
2209 :
2210 : /* Verify that the area passed by the user is writeable */
2211 0 : if (!access_ok(events, maxevents * sizeof(struct epoll_event)))
2212 : return -EFAULT;
2213 :
2214 : /* Get the "struct file *" for the eventpoll file */
2215 0 : f = fdget(epfd);
2216 0 : if (!f.file)
2217 : return -EBADF;
2218 :
2219 : /*
2220 : * We have to check that the file structure underneath the fd
2221 : * the user passed to us _is_ an eventpoll file.
2222 : */
2223 0 : error = -EINVAL;
2224 0 : if (!is_file_epoll(f.file))
2225 : goto error_fput;
2226 :
2227 : /*
2228 : * At this point it is safe to assume that the "private_data" contains
2229 : * our own data structure.
2230 : */
2231 0 : ep = f.file->private_data;
2232 :
2233 : /* Time to fish for events ... */
2234 0 : error = ep_poll(ep, events, maxevents, to);
2235 :
2236 : error_fput:
2237 0 : fdput(f);
2238 : return error;
2239 : }
2240 :
2241 0 : SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
2242 : int, maxevents, int, timeout)
2243 : {
2244 : struct timespec64 to;
2245 :
2246 0 : return do_epoll_wait(epfd, events, maxevents,
2247 : ep_timeout_to_timespec(&to, timeout));
2248 : }
2249 :
2250 : /*
2251 : * Implement the event wait interface for the eventpoll file. It is the kernel
2252 : * part of the user space epoll_pwait(2).
2253 : */
2254 0 : static int do_epoll_pwait(int epfd, struct epoll_event __user *events,
2255 : int maxevents, struct timespec64 *to,
2256 : const sigset_t __user *sigmask, size_t sigsetsize)
2257 : {
2258 : int error;
2259 :
2260 : /*
2261 : * If the caller wants a certain signal mask to be set during the wait,
2262 : * we apply it here.
2263 : */
2264 0 : error = set_user_sigmask(sigmask, sigsetsize);
2265 0 : if (error)
2266 : return error;
2267 :
2268 0 : error = do_epoll_wait(epfd, events, maxevents, to);
2269 :
2270 0 : restore_saved_sigmask_unless(error == -EINTR);
2271 :
2272 0 : return error;
2273 : }
2274 :
2275 0 : SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
2276 : int, maxevents, int, timeout, const sigset_t __user *, sigmask,
2277 : size_t, sigsetsize)
2278 : {
2279 : struct timespec64 to;
2280 :
2281 0 : return do_epoll_pwait(epfd, events, maxevents,
2282 : ep_timeout_to_timespec(&to, timeout),
2283 : sigmask, sigsetsize);
2284 : }
2285 :
2286 0 : SYSCALL_DEFINE6(epoll_pwait2, int, epfd, struct epoll_event __user *, events,
2287 : int, maxevents, const struct __kernel_timespec __user *, timeout,
2288 : const sigset_t __user *, sigmask, size_t, sigsetsize)
2289 : {
2290 0 : struct timespec64 ts, *to = NULL;
2291 :
2292 0 : if (timeout) {
2293 0 : if (get_timespec64(&ts, timeout))
2294 : return -EFAULT;
2295 0 : to = &ts;
2296 0 : if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
2297 : return -EINVAL;
2298 : }
2299 :
2300 0 : return do_epoll_pwait(epfd, events, maxevents, to,
2301 : sigmask, sigsetsize);
2302 : }
2303 :
2304 : #ifdef CONFIG_COMPAT
2305 : static int do_compat_epoll_pwait(int epfd, struct epoll_event __user *events,
2306 : int maxevents, struct timespec64 *timeout,
2307 : const compat_sigset_t __user *sigmask,
2308 : compat_size_t sigsetsize)
2309 : {
2310 : long err;
2311 :
2312 : /*
2313 : * If the caller wants a certain signal mask to be set during the wait,
2314 : * we apply it here.
2315 : */
2316 : err = set_compat_user_sigmask(sigmask, sigsetsize);
2317 : if (err)
2318 : return err;
2319 :
2320 : err = do_epoll_wait(epfd, events, maxevents, timeout);
2321 :
2322 : restore_saved_sigmask_unless(err == -EINTR);
2323 :
2324 : return err;
2325 : }
2326 :
2327 : COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
2328 : struct epoll_event __user *, events,
2329 : int, maxevents, int, timeout,
2330 : const compat_sigset_t __user *, sigmask,
2331 : compat_size_t, sigsetsize)
2332 : {
2333 : struct timespec64 to;
2334 :
2335 : return do_compat_epoll_pwait(epfd, events, maxevents,
2336 : ep_timeout_to_timespec(&to, timeout),
2337 : sigmask, sigsetsize);
2338 : }
2339 :
2340 : COMPAT_SYSCALL_DEFINE6(epoll_pwait2, int, epfd,
2341 : struct epoll_event __user *, events,
2342 : int, maxevents,
2343 : const struct __kernel_timespec __user *, timeout,
2344 : const compat_sigset_t __user *, sigmask,
2345 : compat_size_t, sigsetsize)
2346 : {
2347 : struct timespec64 ts, *to = NULL;
2348 :
2349 : if (timeout) {
2350 : if (get_timespec64(&ts, timeout))
2351 : return -EFAULT;
2352 : to = &ts;
2353 : if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
2354 : return -EINVAL;
2355 : }
2356 :
2357 : return do_compat_epoll_pwait(epfd, events, maxevents, to,
2358 : sigmask, sigsetsize);
2359 : }
2360 :
2361 : #endif
2362 :
2363 1 : static int __init eventpoll_init(void)
2364 : {
2365 : struct sysinfo si;
2366 :
2367 1 : si_meminfo(&si);
2368 : /*
2369 : * Allows top 4% of lomem to be allocated for epoll watches (per user).
2370 : */
2371 1 : max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2372 : EP_ITEM_COST;
2373 1 : BUG_ON(max_user_watches < 0);
2374 :
2375 : /*
2376 : * We can have many thousands of epitems, so prevent this from
2377 : * using an extra cache line on 64-bit (and smaller) CPUs
2378 : */
2379 : BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
2380 :
2381 : /* Allocates slab cache used to allocate "struct epitem" items */
2382 1 : epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
2383 : 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
2384 :
2385 : /* Allocates slab cache used to allocate "struct eppoll_entry" */
2386 1 : pwq_cache = kmem_cache_create("eventpoll_pwq",
2387 : sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
2388 1 : epoll_sysctls_init();
2389 :
2390 1 : ephead_cache = kmem_cache_create("ep_head",
2391 : sizeof(struct epitems_head), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
2392 :
2393 1 : return 0;
2394 : }
2395 : fs_initcall(eventpoll_init);
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