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
107struct epoll_filefd {
108 struct file *file;
109 int fd;
110} __packed;
111
112/* Wait structure used by the poll hooks */
113struct 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 */
136struct 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 */
177struct 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 */
232struct 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 */
241static long max_user_watches __read_mostly;
242
243/*
244 * This mutex is used to serialize ep_free() and eventpoll_release_file().
245 */
246static DEFINE_MUTEX(epmutex);
247
248static u64 loop_check_gen = 0;
249
250/* Used to check for epoll file descriptor inclusion loops */
251static struct eventpoll *inserting_into;
252
253/* Slab cache used to allocate "struct epitem" */
254static struct kmem_cache *epi_cache __read_mostly;
255
256/* Slab cache used to allocate "struct eppoll_entry" */
257static 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 */
263struct epitems_head {
264 struct hlist_head epitems;
265 struct epitems_head *next;
266};
267static struct epitems_head *tfile_check_list = EP_UNACTIVE_PTR;
268
269static struct kmem_cache *ephead_cache __read_mostly;
270
271static inline void free_ephead(struct epitems_head *head)
272{
273 if (head)
274 kmem_cache_free(ephead_cache, head);
275}
276
277static void list_file(struct file *file)
278{
279 struct epitems_head *head;
280
281 head = container_of(file->f_ep, struct epitems_head, epitems);
282 if (!head->next) {
283 head->next = tfile_check_list;
284 tfile_check_list = head;
285 }
286}
287
288static void unlist_file(struct epitems_head *head)
289{
290 struct epitems_head *to_free = head;
291 struct hlist_node *p = rcu_dereference(hlist_first_rcu(&head->epitems));
292 if (p) {
293 struct epitem *epi= container_of(p, struct epitem, fllink);
294 spin_lock(&epi->ffd.file->f_lock);
295 if (!hlist_empty(&head->epitems))
296 to_free = NULL;
297 head->next = NULL;
298 spin_unlock(&epi->ffd.file->f_lock);
299 }
300 free_ephead(to_free);
301}
302
303#ifdef CONFIG_SYSCTL
304
305#include <linux/sysctl.h>
306
307static long long_zero;
308static long long_max = LONG_MAX;
309
310static 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
323static void __init epoll_sysctls_init(void)
324{
325 register_sysctl("fs/epoll", epoll_table);
326}
327#else
328#define epoll_sysctls_init() do { } while (0)
329#endif /* CONFIG_SYSCTL */
330
331static const struct file_operations eventpoll_fops;
332
333static inline int is_file_epoll(struct file *f)
334{
335 return f->f_op == &eventpoll_fops;
336}
337
338/* Setup the structure that is used as key for the RB tree */
339static inline void ep_set_ffd(struct epoll_filefd *ffd,
340 struct file *file, int fd)
341{
342 ffd->file = file;
343 ffd->fd = fd;
344}
345
346/* Compare RB tree keys */
347static inline int ep_cmp_ffd(struct epoll_filefd *p1,
348 struct epoll_filefd *p2)
349{
350 return (p1->file > p2->file ? +1:
351 (p1->file < p2->file ? -1 : p1->fd - p2->fd));
352}
353
354/* Tells us if the item is currently linked */
355static inline int ep_is_linked(struct epitem *epi)
356{
357 return !list_empty(&epi->rdllink);
358}
359
360static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p)
361{
362 return container_of(p, struct eppoll_entry, wait);
363}
364
365/* Get the "struct epitem" from a wait queue pointer */
366static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p)
367{
368 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 */
379static inline int ep_events_available(struct eventpoll *ep)
380{
381 return !list_empty_careful(&ep->rdllist) ||
382 READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR;
383}
384
385#ifdef CONFIG_NET_RX_BUSY_POLL
386static 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 */
399static 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 */
422static 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
456static inline bool ep_busy_loop(struct eventpoll *ep, int nonblock)
457{
458 return false;
459}
460
461static 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
494static 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
532static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
533{
534 wake_up_poll(&ep->poll_wait, EPOLLIN);
535}
536
537#endif
538
539static 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 whead = smp_load_acquire(&pwq->whead);
551 if (whead)
552 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 */
561static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
562{
563 struct eppoll_entry **p = &epi->pwqlist;
564 struct eppoll_entry *pwq;
565
566 while ((pwq = *p) != NULL) {
567 *p = pwq->next;
568 ep_remove_wait_queue(pwq);
569 kmem_cache_free(pwq_cache, pwq);
570 }
571}
572
573/* call only when ep->mtx is held */
574static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
575{
576 return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
577}
578
579/* call only when ep->mtx is held */
580static inline void ep_pm_stay_awake(struct epitem *epi)
581{
582 struct wakeup_source *ws = ep_wakeup_source(epi);
583
584 if (ws)
585 __pm_stay_awake(ws);
586}
587
588static inline bool ep_has_wakeup_source(struct epitem *epi)
589{
590 return rcu_access_pointer(epi->ws) ? true : false;
591}
592
593/* call when ep->mtx cannot be held (ep_poll_callback) */
594static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
595{
596 struct wakeup_source *ws;
597
598 rcu_read_lock();
599 ws = rcu_dereference(epi->ws);
600 if (ws)
601 __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 */
610static 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 write_lock_irq(&ep->lock);
622 list_splice_init(&ep->rdllist, txlist);
623 WRITE_ONCE(ep->ovflist, NULL);
624 write_unlock_irq(&ep->lock);
625}
626
627static void ep_done_scan(struct eventpoll *ep,
628 struct list_head *txlist)
629{
630 struct epitem *epi, *nepi;
631
632 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 for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
639 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 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 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 WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR);
661
662 /*
663 * Quickly re-inject items left on "txlist".
664 */
665 list_splice(txlist, &ep->rdllist);
666 __pm_relax(ep->ws);
667
668 if (!list_empty(&ep->rdllist)) {
669 if (waitqueue_active(&ep->wq))
670 wake_up(&ep->wq);
671 }
672
673 write_unlock_irq(&ep->lock);
674}
675
676static void epi_rcu_free(struct rcu_head *head)
677{
678 struct epitem *epi = container_of(head, struct epitem, rcu);
679 kmem_cache_free(epi_cache, epi);
680}
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 */
686static int ep_remove(struct eventpoll *ep, struct epitem *epi)
687{
688 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 ep_unregister_pollwait(ep, epi);
698
699 /* Remove the current item from the list of epoll hooks */
700 spin_lock(&file->f_lock);
701 to_free = NULL;
702 head = file->f_ep;
703 if (head->first == &epi->fllink && !epi->fllink.next) {
704 file->f_ep = NULL;
705 if (!is_file_epoll(file)) {
706 struct epitems_head *v;
707 v = container_of(head, struct epitems_head, epitems);
708 if (!smp_load_acquire(&v->next))
709 to_free = v;
710 }
711 }
712 hlist_del_rcu(&epi->fllink);
713 spin_unlock(&file->f_lock);
714 free_ephead(to_free);
715
716 rb_erase_cached(&epi->rbn, &ep->rbr);
717
718 write_lock_irq(&ep->lock);
719 if (ep_is_linked(epi))
720 list_del_init(&epi->rdllink);
721 write_unlock_irq(&ep->lock);
722
723 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 call_rcu(&epi->rcu, epi_rcu_free);
732
733 percpu_counter_dec(&ep->user->epoll_watches);
734
735 return 0;
736}
737
738static 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 if (waitqueue_active(&ep->poll_wait))
745 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 mutex_lock(&epmutex);
756
757 /*
758 * Walks through the whole tree by unregistering poll callbacks.
759 */
760 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
761 epi = rb_entry(rbp, struct epitem, rbn);
762
763 ep_unregister_pollwait(ep, epi);
764 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 mutex_lock(&ep->mtx);
776 while ((rbp = rb_first_cached(&ep->rbr)) != NULL) {
777 epi = rb_entry(rbp, struct epitem, rbn);
778 ep_remove(ep, epi);
779 cond_resched();
780 }
781 mutex_unlock(&ep->mtx);
782
783 mutex_unlock(&epmutex);
784 mutex_destroy(&ep->mtx);
785 free_uid(ep->user);
786 wakeup_source_unregister(ep->ws);
787 kfree(ep);
788}
789
790static int ep_eventpoll_release(struct inode *inode, struct file *file)
791{
792 struct eventpoll *ep = file->private_data;
793
794 if (ep)
795 ep_free(ep);
796
797 return 0;
798}
799
800static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, int depth);
801
802static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int depth)
803{
804 struct eventpoll *ep = file->private_data;
805 LIST_HEAD(txlist);
806 struct epitem *epi, *tmp;
807 poll_table pt;
808 __poll_t res = 0;
809
810 init_poll_funcptr(&pt, NULL);
811
812 /* Insert inside our poll wait queue */
813 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 mutex_lock_nested(&ep->mtx, depth);
820 ep_start_scan(ep, &txlist);
821 list_for_each_entry_safe(epi, tmp, &txlist, rdllink) {
822 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 __pm_relax(ep_wakeup_source(epi));
832 list_del_init(&epi->rdllink);
833 }
834 }
835 ep_done_scan(ep, &txlist);
836 mutex_unlock(&ep->mtx);
837 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 */
845static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt,
846 int depth)
847{
848 struct file *file = epi->ffd.file;
849 __poll_t res;
850
851 pt->_key = epi->event.events;
852 if (!is_file_epoll(file))
853 res = vfs_poll(file, pt);
854 else
855 res = __ep_eventpoll_poll(file, pt, depth);
856 return res & epi->event.events;
857}
858
859static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait)
860{
861 return __ep_eventpoll_poll(file, wait, 0);
862}
863
864#ifdef CONFIG_PROC_FS
865static void ep_show_fdinfo(struct seq_file *m, struct file *f)
866{
867 struct eventpoll *ep = f->private_data;
868 struct rb_node *rbp;
869
870 mutex_lock(&ep->mtx);
871 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
872 struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
873 struct inode *inode = file_inode(epi->ffd.file);
874
875 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 (long long)epi->event.data,
879 (long long)epi->ffd.file->f_pos,
880 inode->i_ino, inode->i_sb->s_dev);
881 if (seq_has_overflowed(m))
882 break;
883 }
884 mutex_unlock(&ep->mtx);
885}
886#endif
887
888/* File callbacks that implement the eventpoll file behaviour */
889static 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 */
903void 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 mutex_lock(&epmutex);
923 if (unlikely(!file->f_ep)) {
924 mutex_unlock(&epmutex);
925 return;
926 }
927 hlist_for_each_entry_safe(epi, next, file->f_ep, fllink) {
928 ep = epi->ep;
929 mutex_lock_nested(&ep->mtx, 0);
930 ep_remove(ep, epi);
931 mutex_unlock(&ep->mtx);
932 }
933 mutex_unlock(&epmutex);
934}
935
936static int ep_alloc(struct eventpoll **pep)
937{
938 int error;
939 struct user_struct *user;
940 struct eventpoll *ep;
941
942 user = get_current_user();
943 error = -ENOMEM;
944 ep = kzalloc(sizeof(*ep), GFP_KERNEL);
945 if (unlikely(!ep))
946 goto free_uid;
947
948 mutex_init(&ep->mtx);
949 rwlock_init(&ep->lock);
950 init_waitqueue_head(&ep->wq);
951 init_waitqueue_head(&ep->poll_wait);
952 INIT_LIST_HEAD(&ep->rdllist);
953 ep->rbr = RB_ROOT_CACHED;
954 ep->ovflist = EP_UNACTIVE_PTR;
955 ep->user = user;
956
957 *pep = ep;
958
959 return 0;
960
961free_uid:
962 free_uid(user);
963 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 */
971static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
972{
973 int kcmp;
974 struct rb_node *rbp;
975 struct epitem *epi, *epir = NULL;
976 struct epoll_filefd ffd;
977
978 ep_set_ffd(&ffd, file, fd);
979 for (rbp = ep->rbr.rb_root.rb_node; rbp; ) {
980 epi = rb_entry(rbp, struct epitem, rbn);
981 kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
982 if (kcmp > 0)
983 rbp = rbp->rb_right;
984 else if (kcmp < 0)
985 rbp = rbp->rb_left;
986 else {
987 epir = epi;
988 break;
989 }
990 }
991
992 return epir;
993}
994
995#ifdef CONFIG_KCMP
996static 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 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1002 epi = rb_entry(rbp, struct epitem, rbn);
1003 if (epi->ffd.fd == tfd) {
1004 if (toff == 0)
1005 return epi;
1006 else
1007 toff--;
1008 }
1009 cond_resched();
1010 }
1011
1012 return NULL;
1013}
1014
1015struct 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 if (!is_file_epoll(file))
1023 return ERR_PTR(-EINVAL);
1024
1025 ep = file->private_data;
1026
1027 mutex_lock(&ep->mtx);
1028 epi = ep_find_tfd(ep, tfd, toff);
1029 if (epi)
1030 file_raw = epi->ffd.file;
1031 else
1032 file_raw = ERR_PTR(-ENOENT);
1033 mutex_unlock(&ep->mtx);
1034
1035 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 */
1057static 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 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 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 prev->next = new;
1087 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 */
1098static inline bool chain_epi_lockless(struct epitem *epi)
1099{
1100 struct eventpoll *ep = epi->ep;
1101
1102 /* Fast preliminary check */
1103 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 if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR)
1108 return false;
1109
1110 /* Atomically exchange tail */
1111 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 */
1134static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
1135{
1136 int pwake = 0;
1137 struct epitem *epi = ep_item_from_wait(wait);
1138 struct eventpoll *ep = epi->ep;
1139 __poll_t pollflags = key_to_poll(key);
1140 unsigned long flags;
1141 int ewake = 0;
1142
1143 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 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 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 if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) {
1172 if (chain_epi_lockless(epi))
1173 ep_pm_stay_awake_rcu(epi);
1174 } else if (!ep_is_linked(epi)) {
1175 /* In the usual case, add event to ready list. */
1176 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 if (waitqueue_active(&ep->wq)) {
1185 if ((epi->event.events & EPOLLEXCLUSIVE) &&
1186 !(pollflags & POLLFREE)) {
1187 switch (pollflags & EPOLLINOUT_BITS) {
1188 case EPOLLIN:
1189 if (epi->event.events & EPOLLIN)
1190 ewake = 1;
1191 break;
1192 case EPOLLOUT:
1193 if (epi->event.events & EPOLLOUT)
1194 ewake = 1;
1195 break;
1196 case 0:
1197 ewake = 1;
1198 break;
1199 }
1200 }
1201 wake_up(&ep->wq);
1202 }
1203 if (waitqueue_active(&ep->poll_wait))
1204 pwake++;
1205
1206out_unlock:
1207 read_unlock_irqrestore(&ep->lock, flags);
1208
1209 /* We have to call this outside the lock */
1210 if (pwake)
1211 ep_poll_safewake(ep, epi);
1212
1213 if (!(epi->event.events & EPOLLEXCLUSIVE))
1214 ewake = 1;
1215
1216 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 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 smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL);
1230 }
1231
1232 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 */
1239static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
1240 poll_table *pt)
1241{
1242 struct ep_pqueue *epq = container_of(pt, struct ep_pqueue, pt);
1243 struct epitem *epi = epq->epi;
1244 struct eppoll_entry *pwq;
1245
1246 if (unlikely(!epi)) // an earlier allocation has failed
1247 return;
1248
1249 pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL);
1250 if (unlikely(!pwq)) {
1251 epq->epi = NULL;
1252 return;
1253 }
1254
1255 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
1256 pwq->whead = whead;
1257 pwq->base = epi;
1258 if (epi->event.events & EPOLLEXCLUSIVE)
1259 add_wait_queue_exclusive(whead, &pwq->wait);
1260 else
1261 add_wait_queue(whead, &pwq->wait);
1262 pwq->next = epi->pwqlist;
1263 epi->pwqlist = pwq;
1264}
1265
1266static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
1267{
1268 int kcmp;
1269 struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL;
1270 struct epitem *epic;
1271 bool leftmost = true;
1272
1273 while (*p) {
1274 parent = *p;
1275 epic = rb_entry(parent, struct epitem, rbn);
1276 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
1277 if (kcmp > 0) {
1278 p = &parent->rb_right;
1279 leftmost = false;
1280 } else
1281 p = &parent->rb_left;
1282 }
1283 rb_link_node(&epi->rbn, parent, p);
1284 rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost);
1285}
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 */
1301static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
1302static int path_count[PATH_ARR_SIZE];
1303
1304static int path_count_inc(int nests)
1305{
1306 /* Allow an arbitrary number of depth 1 paths */
1307 if (nests == 0)
1308 return 0;
1309
1310 if (++path_count[nests] > path_limits[nests])
1311 return -1;
1312 return 0;
1313}
1314
1315static void path_count_init(void)
1316{
1317 int i;
1318
1319 for (i = 0; i < PATH_ARR_SIZE; i++)
1320 path_count[i] = 0;
1321}
1322
1323static int reverse_path_check_proc(struct hlist_head *refs, int depth)
1324{
1325 int error = 0;
1326 struct epitem *epi;
1327
1328 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 hlist_for_each_entry_rcu(epi, refs, fllink) {
1333 struct hlist_head *refs = &epi->ep->refs;
1334 if (hlist_empty(refs))
1335 error = path_count_inc(depth);
1336 else
1337 error = reverse_path_check_proc(refs, depth + 1);
1338 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 */
1354static int reverse_path_check(void)
1355{
1356 struct epitems_head *p;
1357
1358 for (p = tfile_check_list; p != EP_UNACTIVE_PTR; p = p->next) {
1359 int error;
1360 path_count_init();
1361 rcu_read_lock();
1362 error = reverse_path_check_proc(&p->epitems, 0);
1363 rcu_read_unlock();
1364 if (error)
1365 return error;
1366 }
1367 return 0;
1368}
1369
1370static int ep_create_wakeup_source(struct epitem *epi)
1371{
1372 struct name_snapshot n;
1373 struct wakeup_source *ws;
1374
1375 if (!epi->ep->ws) {
1376 epi->ep->ws = wakeup_source_register(NULL, "eventpoll");
1377 if (!epi->ep->ws)
1378 return -ENOMEM;
1379 }
1380
1381 take_dentry_name_snapshot(&n, epi->ffd.file->f_path.dentry);
1382 ws = wakeup_source_register(NULL, n.name.name);
1383 release_dentry_name_snapshot(&n);
1384
1385 if (!ws)
1386 return -ENOMEM;
1387 rcu_assign_pointer(epi->ws, ws);
1388
1389 return 0;
1390}
1391
1392/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
1393static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1394{
1395 struct wakeup_source *ws = ep_wakeup_source(epi);
1396
1397 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 synchronize_rcu();
1405 wakeup_source_unregister(ws);
1406}
1407
1408static int attach_epitem(struct file *file, struct epitem *epi)
1409{
1410 struct epitems_head *to_free = NULL;
1411 struct hlist_head *head = NULL;
1412 struct eventpoll *ep = NULL;
1413
1414 if (is_file_epoll(file))
1415 ep = file->private_data;
1416
1417 if (ep) {
1418 head = &ep->refs;
1419 } else if (!READ_ONCE(file->f_ep)) {
1420allocate:
1421 to_free = kmem_cache_zalloc(ephead_cache, GFP_KERNEL);
1422 if (!to_free)
1423 return -ENOMEM;
1424 head = &to_free->epitems;
1425 }
1426 spin_lock(&file->f_lock);
1427 if (!file->f_ep) {
1428 if (unlikely(!head)) {
1429 spin_unlock(&file->f_lock);
1430 goto allocate;
1431 }
1432 file->f_ep = head;
1433 to_free = NULL;
1434 }
1435 hlist_add_head_rcu(&epi->fllink, file->f_ep);
1436 spin_unlock(&file->f_lock);
1437 free_ephead(to_free);
1438 return 0;
1439}
1440
1441/*
1442 * Must be called with "mtx" held.
1443 */
1444static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
1445 struct file *tfile, int fd, int full_check)
1446{
1447 int error, pwake = 0;
1448 __poll_t revents;
1449 struct epitem *epi;
1450 struct ep_pqueue epq;
1451 struct eventpoll *tep = NULL;
1452
1453 if (is_file_epoll(tfile))
1454 tep = tfile->private_data;
1455
1456 lockdep_assert_irqs_enabled();
1457
1458 if (unlikely(percpu_counter_compare(&ep->user->epoll_watches,
1459 max_user_watches) >= 0))
1460 return -ENOSPC;
1461 percpu_counter_inc(&ep->user->epoll_watches);
1462
1463 if (!(epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL))) {
1464 percpu_counter_dec(&ep->user->epoll_watches);
1465 return -ENOMEM;
1466 }
1467
1468 /* Item initialization follow here ... */
1469 INIT_LIST_HEAD(&epi->rdllink);
1470 epi->ep = ep;
1471 ep_set_ffd(&epi->ffd, tfile, fd);
1472 epi->event = *event;
1473 epi->next = EP_UNACTIVE_PTR;
1474
1475 if (tep)
1476 mutex_lock_nested(&tep->mtx, 1);
1477 /* Add the current item to the list of active epoll hook for this file */
1478 if (unlikely(attach_epitem(tfile, epi) < 0)) {
1479 if (tep)
1480 mutex_unlock(&tep->mtx);
1481 kmem_cache_free(epi_cache, epi);
1482 percpu_counter_dec(&ep->user->epoll_watches);
1483 return -ENOMEM;
1484 }
1485
1486 if (full_check && !tep)
1487 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 ep_rbtree_insert(ep, epi);
1494 if (tep)
1495 mutex_unlock(&tep->mtx);
1496
1497 /* now check if we've created too many backpaths */
1498 if (unlikely(full_check && reverse_path_check())) {
1499 ep_remove(ep, epi);
1500 return -EINVAL;
1501 }
1502
1503 if (epi->event.events & EPOLLWAKEUP) {
1504 error = ep_create_wakeup_source(epi);
1505 if (error) {
1506 ep_remove(ep, epi);
1507 return error;
1508 }
1509 }
1510
1511 /* Initialize the poll table using the queue callback */
1512 epq.epi = epi;
1513 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 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 if (unlikely(!epq.epi)) {
1530 ep_remove(ep, epi);
1531 return -ENOMEM;
1532 }
1533
1534 /* We have to drop the new item inside our item list to keep track of it */
1535 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 if (revents && !ep_is_linked(epi)) {
1542 list_add_tail(&epi->rdllink, &ep->rdllist);
1543 ep_pm_stay_awake(epi);
1544
1545 /* Notify waiting tasks that events are available */
1546 if (waitqueue_active(&ep->wq))
1547 wake_up(&ep->wq);
1548 if (waitqueue_active(&ep->poll_wait))
1549 pwake++;
1550 }
1551
1552 write_unlock_irq(&ep->lock);
1553
1554 /* We have to call this outside the lock */
1555 if (pwake)
1556 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 */
1565static int ep_modify(struct eventpoll *ep, struct epitem *epi,
1566 const struct epoll_event *event)
1567{
1568 int pwake = 0;
1569 poll_table pt;
1570
1571 lockdep_assert_irqs_enabled();
1572
1573 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 epi->event.events = event->events; /* need barrier below */
1581 epi->event.data = event->data; /* protected by mtx */
1582 if (epi->event.events & EPOLLWAKEUP) {
1583 if (!ep_has_wakeup_source(epi))
1584 ep_create_wakeup_source(epi);
1585 } else if (ep_has_wakeup_source(epi)) {
1586 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 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 if (ep_item_poll(epi, &pt, 1)) {
1616 write_lock_irq(&ep->lock);
1617 if (!ep_is_linked(epi)) {
1618 list_add_tail(&epi->rdllink, &ep->rdllist);
1619 ep_pm_stay_awake(epi);
1620
1621 /* Notify waiting tasks that events are available */
1622 if (waitqueue_active(&ep->wq))
1623 wake_up(&ep->wq);
1624 if (waitqueue_active(&ep->poll_wait))
1625 pwake++;
1626 }
1627 write_unlock_irq(&ep->lock);
1628 }
1629
1630 /* We have to call this outside the lock */
1631 if (pwake)
1632 ep_poll_safewake(ep, NULL);
1633
1634 return 0;
1635}
1636
1637static int ep_send_events(struct eventpoll *ep,
1638 struct epoll_event __user *events, int maxevents)
1639{
1640 struct epitem *epi, *tmp;
1641 LIST_HEAD(txlist);
1642 poll_table pt;
1643 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 if (fatal_signal_pending(current))
1651 return -EINTR;
1652
1653 init_poll_funcptr(&pt, NULL);
1654
1655 mutex_lock(&ep->mtx);
1656 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 list_for_each_entry_safe(epi, tmp, &txlist, rdllink) {
1663 struct wakeup_source *ws;
1664 __poll_t revents;
1665
1666 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 ws = ep_wakeup_source(epi);
1679 if (ws) {
1680 if (ws->active)
1681 __pm_stay_awake(ep->ws);
1682 __pm_relax(ws);
1683 }
1684
1685 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 revents = ep_item_poll(epi, &pt, 1);
1693 if (!revents)
1694 continue;
1695
1696 events = epoll_put_uevent(revents, epi->event.data, events);
1697 if (!events) {
1698 list_add(&epi->rdllink, &txlist);
1699 ep_pm_stay_awake(epi);
1700 if (!res)
1701 res = -EFAULT;
1702 break;
1703 }
1704 res++;
1705 if (epi->event.events & EPOLLONESHOT)
1706 epi->event.events &= EP_PRIVATE_BITS;
1707 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 list_add_tail(&epi->rdllink, &ep->rdllist);
1720 ep_pm_stay_awake(epi);
1721 }
1722 }
1723 ep_done_scan(ep, &txlist);
1724 mutex_unlock(&ep->mtx);
1725
1726 return res;
1727}
1728
1729static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms)
1730{
1731 struct timespec64 now;
1732
1733 if (ms < 0)
1734 return NULL;
1735
1736 if (!ms) {
1737 to->tv_sec = 0;
1738 to->tv_nsec = 0;
1739 return to;
1740 }
1741
1742 to->tv_sec = ms / MSEC_PER_SEC;
1743 to->tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC);
1744
1745 ktime_get_ts64(&now);
1746 *to = timespec64_add_safe(now, *to);
1747 return to;
1748}
1749
1750/*
1751 * autoremove_wake_function, but remove even on failure to wake up, because we
1752 * know that default_wake_function/ttwu will only fail if the thread is already
1753 * woken, and in that case the ep_poll loop will remove the entry anyways, not
1754 * try to reuse it.
1755 */
1756static int ep_autoremove_wake_function(struct wait_queue_entry *wq_entry,
1757 unsigned int mode, int sync, void *key)
1758{
1759 int ret = default_wake_function(wq_entry, mode, sync, key);
1760
1761 list_del_init(&wq_entry->entry);
1762 return ret;
1763}
1764
1765/**
1766 * ep_poll - Retrieves ready events, and delivers them to the caller-supplied
1767 * event buffer.
1768 *
1769 * @ep: Pointer to the eventpoll context.
1770 * @events: Pointer to the userspace buffer where the ready events should be
1771 * stored.
1772 * @maxevents: Size (in terms of number of events) of the caller event buffer.
1773 * @timeout: Maximum timeout for the ready events fetch operation, in
1774 * timespec. If the timeout is zero, the function will not block,
1775 * while if the @timeout ptr is NULL, the function will block
1776 * until at least one event has been retrieved (or an error
1777 * occurred).
1778 *
1779 * Return: the number of ready events which have been fetched, or an
1780 * error code, in case of error.
1781 */
1782static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1783 int maxevents, struct timespec64 *timeout)
1784{
1785 int res, eavail, timed_out = 0;
1786 u64 slack = 0;
1787 wait_queue_entry_t wait;
1788 ktime_t expires, *to = NULL;
1789
1790 lockdep_assert_irqs_enabled();
1791
1792 if (timeout && (timeout->tv_sec | timeout->tv_nsec)) {
1793 slack = select_estimate_accuracy(timeout);
1794 to = &expires;
1795 *to = timespec64_to_ktime(*timeout);
1796 } else if (timeout) {
1797 /*
1798 * Avoid the unnecessary trip to the wait queue loop, if the
1799 * caller specified a non blocking operation.
1800 */
1801 timed_out = 1;
1802 }
1803
1804 /*
1805 * This call is racy: We may or may not see events that are being added
1806 * to the ready list under the lock (e.g., in IRQ callbacks). For cases
1807 * with a non-zero timeout, this thread will check the ready list under
1808 * lock and will add to the wait queue. For cases with a zero
1809 * timeout, the user by definition should not care and will have to
1810 * recheck again.
1811 */
1812 eavail = ep_events_available(ep);
1813
1814 while (1) {
1815 if (eavail) {
1816 /*
1817 * Try to transfer events to user space. In case we get
1818 * 0 events and there's still timeout left over, we go
1819 * trying again in search of more luck.
1820 */
1821 res = ep_send_events(ep, events, maxevents);
1822 if (res)
1823 return res;
1824 }
1825
1826 if (timed_out)
1827 return 0;
1828
1829 eavail = ep_busy_loop(ep, timed_out);
1830 if (eavail)
1831 continue;
1832
1833 if (signal_pending(current))
1834 return -EINTR;
1835
1836 /*
1837 * Internally init_wait() uses autoremove_wake_function(),
1838 * thus wait entry is removed from the wait queue on each
1839 * wakeup. Why it is important? In case of several waiters
1840 * each new wakeup will hit the next waiter, giving it the
1841 * chance to harvest new event. Otherwise wakeup can be
1842 * lost. This is also good performance-wise, because on
1843 * normal wakeup path no need to call __remove_wait_queue()
1844 * explicitly, thus ep->lock is not taken, which halts the
1845 * event delivery.
1846 *
1847 * In fact, we now use an even more aggressive function that
1848 * unconditionally removes, because we don't reuse the wait
1849 * entry between loop iterations. This lets us also avoid the
1850 * performance issue if a process is killed, causing all of its
1851 * threads to wake up without being removed normally.
1852 */
1853 init_wait(&wait);
1854 wait.func = ep_autoremove_wake_function;
1855
1856 write_lock_irq(&ep->lock);
1857 /*
1858 * Barrierless variant, waitqueue_active() is called under
1859 * the same lock on wakeup ep_poll_callback() side, so it
1860 * is safe to avoid an explicit barrier.
1861 */
1862 __set_current_state(TASK_INTERRUPTIBLE);
1863
1864 /*
1865 * Do the final check under the lock. ep_scan_ready_list()
1866 * plays with two lists (->rdllist and ->ovflist) and there
1867 * is always a race when both lists are empty for short
1868 * period of time although events are pending, so lock is
1869 * important.
1870 */
1871 eavail = ep_events_available(ep);
1872 if (!eavail)
1873 __add_wait_queue_exclusive(&ep->wq, &wait);
1874
1875 write_unlock_irq(&ep->lock);
1876
1877 if (!eavail)
1878 timed_out = !schedule_hrtimeout_range(to, slack,
1879 HRTIMER_MODE_ABS);
1880 __set_current_state(TASK_RUNNING);
1881
1882 /*
1883 * We were woken up, thus go and try to harvest some events.
1884 * If timed out and still on the wait queue, recheck eavail
1885 * carefully under lock, below.
1886 */
1887 eavail = 1;
1888
1889 if (!list_empty_careful(&wait.entry)) {
1890 write_lock_irq(&ep->lock);
1891 /*
1892 * If the thread timed out and is not on the wait queue,
1893 * it means that the thread was woken up after its
1894 * timeout expired before it could reacquire the lock.
1895 * Thus, when wait.entry is empty, it needs to harvest
1896 * events.
1897 */
1898 if (timed_out)
1899 eavail = list_empty(&wait.entry);
1900 __remove_wait_queue(&ep->wq, &wait);
1901 write_unlock_irq(&ep->lock);
1902 }
1903 }
1904}
1905
1906/**
1907 * ep_loop_check_proc - verify that adding an epoll file inside another
1908 * epoll structure does not violate the constraints, in
1909 * terms of closed loops, or too deep chains (which can
1910 * result in excessive stack usage).
1911 *
1912 * @ep: the &struct eventpoll to be currently checked.
1913 * @depth: Current depth of the path being checked.
1914 *
1915 * Return: %zero if adding the epoll @file inside current epoll
1916 * structure @ep does not violate the constraints, or %-1 otherwise.
1917 */
1918static int ep_loop_check_proc(struct eventpoll *ep, int depth)
1919{
1920 int error = 0;
1921 struct rb_node *rbp;
1922 struct epitem *epi;
1923
1924 mutex_lock_nested(&ep->mtx, depth + 1);
1925 ep->gen = loop_check_gen;
1926 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1927 epi = rb_entry(rbp, struct epitem, rbn);
1928 if (unlikely(is_file_epoll(epi->ffd.file))) {
1929 struct eventpoll *ep_tovisit;
1930 ep_tovisit = epi->ffd.file->private_data;
1931 if (ep_tovisit->gen == loop_check_gen)
1932 continue;
1933 if (ep_tovisit == inserting_into || depth > EP_MAX_NESTS)
1934 error = -1;
1935 else
1936 error = ep_loop_check_proc(ep_tovisit, depth + 1);
1937 if (error != 0)
1938 break;
1939 } else {
1940 /*
1941 * If we've reached a file that is not associated with
1942 * an ep, then we need to check if the newly added
1943 * links are going to add too many wakeup paths. We do
1944 * this by adding it to the tfile_check_list, if it's
1945 * not already there, and calling reverse_path_check()
1946 * during ep_insert().
1947 */
1948 list_file(epi->ffd.file);
1949 }
1950 }
1951 mutex_unlock(&ep->mtx);
1952
1953 return error;
1954}
1955
1956/**
1957 * ep_loop_check - Performs a check to verify that adding an epoll file (@to)
1958 * into another epoll file (represented by @ep) does not create
1959 * closed loops or too deep chains.
1960 *
1961 * @ep: Pointer to the epoll we are inserting into.
1962 * @to: Pointer to the epoll to be inserted.
1963 *
1964 * Return: %zero if adding the epoll @to inside the epoll @from
1965 * does not violate the constraints, or %-1 otherwise.
1966 */
1967static int ep_loop_check(struct eventpoll *ep, struct eventpoll *to)
1968{
1969 inserting_into = ep;
1970 return ep_loop_check_proc(to, 0);
1971}
1972
1973static void clear_tfile_check_list(void)
1974{
1975 rcu_read_lock();
1976 while (tfile_check_list != EP_UNACTIVE_PTR) {
1977 struct epitems_head *head = tfile_check_list;
1978 tfile_check_list = head->next;
1979 unlist_file(head);
1980 }
1981 rcu_read_unlock();
1982}
1983
1984/*
1985 * Open an eventpoll file descriptor.
1986 */
1987static int do_epoll_create(int flags)
1988{
1989 int error, fd;
1990 struct eventpoll *ep = NULL;
1991 struct file *file;
1992
1993 /* Check the EPOLL_* constant for consistency. */
1994 BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
1995
1996 if (flags & ~EPOLL_CLOEXEC)
1997 return -EINVAL;
1998 /*
1999 * Create the internal data structure ("struct eventpoll").
2000 */
2001 error = ep_alloc(&ep);
2002 if (error < 0)
2003 return error;
2004 /*
2005 * Creates all the items needed to setup an eventpoll file. That is,
2006 * a file structure and a free file descriptor.
2007 */
2008 fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
2009 if (fd < 0) {
2010 error = fd;
2011 goto out_free_ep;
2012 }
2013 file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
2014 O_RDWR | (flags & O_CLOEXEC));
2015 if (IS_ERR(file)) {
2016 error = PTR_ERR(file);
2017 goto out_free_fd;
2018 }
2019 ep->file = file;
2020 fd_install(fd, file);
2021 return fd;
2022
2023out_free_fd:
2024 put_unused_fd(fd);
2025out_free_ep:
2026 ep_free(ep);
2027 return error;
2028}
2029
2030SYSCALL_DEFINE1(epoll_create1, int, flags)
2031{
2032 return do_epoll_create(flags);
2033}
2034
2035SYSCALL_DEFINE1(epoll_create, int, size)
2036{
2037 if (size <= 0)
2038 return -EINVAL;
2039
2040 return do_epoll_create(0);
2041}
2042
2043static inline int epoll_mutex_lock(struct mutex *mutex, int depth,
2044 bool nonblock)
2045{
2046 if (!nonblock) {
2047 mutex_lock_nested(mutex, depth);
2048 return 0;
2049 }
2050 if (mutex_trylock(mutex))
2051 return 0;
2052 return -EAGAIN;
2053}
2054
2055int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
2056 bool nonblock)
2057{
2058 int error;
2059 int full_check = 0;
2060 struct fd f, tf;
2061 struct eventpoll *ep;
2062 struct epitem *epi;
2063 struct eventpoll *tep = NULL;
2064
2065 error = -EBADF;
2066 f = fdget(epfd);
2067 if (!f.file)
2068 goto error_return;
2069
2070 /* Get the "struct file *" for the target file */
2071 tf = fdget(fd);
2072 if (!tf.file)
2073 goto error_fput;
2074
2075 /* The target file descriptor must support poll */
2076 error = -EPERM;
2077 if (!file_can_poll(tf.file))
2078 goto error_tgt_fput;
2079
2080 /* Check if EPOLLWAKEUP is allowed */
2081 if (ep_op_has_event(op))
2082 ep_take_care_of_epollwakeup(epds);
2083
2084 /*
2085 * We have to check that the file structure underneath the file descriptor
2086 * the user passed to us _is_ an eventpoll file. And also we do not permit
2087 * adding an epoll file descriptor inside itself.
2088 */
2089 error = -EINVAL;
2090 if (f.file == tf.file || !is_file_epoll(f.file))
2091 goto error_tgt_fput;
2092
2093 /*
2094 * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only,
2095 * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
2096 * Also, we do not currently supported nested exclusive wakeups.
2097 */
2098 if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) {
2099 if (op == EPOLL_CTL_MOD)
2100 goto error_tgt_fput;
2101 if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
2102 (epds->events & ~EPOLLEXCLUSIVE_OK_BITS)))
2103 goto error_tgt_fput;
2104 }
2105
2106 /*
2107 * At this point it is safe to assume that the "private_data" contains
2108 * our own data structure.
2109 */
2110 ep = f.file->private_data;
2111
2112 /*
2113 * When we insert an epoll file descriptor inside another epoll file
2114 * descriptor, there is the chance of creating closed loops, which are
2115 * better be handled here, than in more critical paths. While we are
2116 * checking for loops we also determine the list of files reachable
2117 * and hang them on the tfile_check_list, so we can check that we
2118 * haven't created too many possible wakeup paths.
2119 *
2120 * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
2121 * the epoll file descriptor is attaching directly to a wakeup source,
2122 * unless the epoll file descriptor is nested. The purpose of taking the
2123 * 'epmutex' on add is to prevent complex toplogies such as loops and
2124 * deep wakeup paths from forming in parallel through multiple
2125 * EPOLL_CTL_ADD operations.
2126 */
2127 error = epoll_mutex_lock(&ep->mtx, 0, nonblock);
2128 if (error)
2129 goto error_tgt_fput;
2130 if (op == EPOLL_CTL_ADD) {
2131 if (READ_ONCE(f.file->f_ep) || ep->gen == loop_check_gen ||
2132 is_file_epoll(tf.file)) {
2133 mutex_unlock(&ep->mtx);
2134 error = epoll_mutex_lock(&epmutex, 0, nonblock);
2135 if (error)
2136 goto error_tgt_fput;
2137 loop_check_gen++;
2138 full_check = 1;
2139 if (is_file_epoll(tf.file)) {
2140 tep = tf.file->private_data;
2141 error = -ELOOP;
2142 if (ep_loop_check(ep, tep) != 0)
2143 goto error_tgt_fput;
2144 }
2145 error = epoll_mutex_lock(&ep->mtx, 0, nonblock);
2146 if (error)
2147 goto error_tgt_fput;
2148 }
2149 }
2150
2151 /*
2152 * Try to lookup the file inside our RB tree. Since we grabbed "mtx"
2153 * above, we can be sure to be able to use the item looked up by
2154 * ep_find() till we release the mutex.
2155 */
2156 epi = ep_find(ep, tf.file, fd);
2157
2158 error = -EINVAL;
2159 switch (op) {
2160 case EPOLL_CTL_ADD:
2161 if (!epi) {
2162 epds->events |= EPOLLERR | EPOLLHUP;
2163 error = ep_insert(ep, epds, tf.file, fd, full_check);
2164 } else
2165 error = -EEXIST;
2166 break;
2167 case EPOLL_CTL_DEL:
2168 if (epi)
2169 error = ep_remove(ep, epi);
2170 else
2171 error = -ENOENT;
2172 break;
2173 case EPOLL_CTL_MOD:
2174 if (epi) {
2175 if (!(epi->event.events & EPOLLEXCLUSIVE)) {
2176 epds->events |= EPOLLERR | EPOLLHUP;
2177 error = ep_modify(ep, epi, epds);
2178 }
2179 } else
2180 error = -ENOENT;
2181 break;
2182 }
2183 mutex_unlock(&ep->mtx);
2184
2185error_tgt_fput:
2186 if (full_check) {
2187 clear_tfile_check_list();
2188 loop_check_gen++;
2189 mutex_unlock(&epmutex);
2190 }
2191
2192 fdput(tf);
2193error_fput:
2194 fdput(f);
2195error_return:
2196
2197 return error;
2198}
2199
2200/*
2201 * The following function implements the controller interface for
2202 * the eventpoll file that enables the insertion/removal/change of
2203 * file descriptors inside the interest set.
2204 */
2205SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
2206 struct epoll_event __user *, event)
2207{
2208 struct epoll_event epds;
2209
2210 if (ep_op_has_event(op) &&
2211 copy_from_user(&epds, event, sizeof(struct epoll_event)))
2212 return -EFAULT;
2213
2214 return do_epoll_ctl(epfd, op, fd, &epds, false);
2215}
2216
2217/*
2218 * Implement the event wait interface for the eventpoll file. It is the kernel
2219 * part of the user space epoll_wait(2).
2220 */
2221static int do_epoll_wait(int epfd, struct epoll_event __user *events,
2222 int maxevents, struct timespec64 *to)
2223{
2224 int error;
2225 struct fd f;
2226 struct eventpoll *ep;
2227
2228 /* The maximum number of event must be greater than zero */
2229 if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
2230 return -EINVAL;
2231
2232 /* Verify that the area passed by the user is writeable */
2233 if (!access_ok(events, maxevents * sizeof(struct epoll_event)))
2234 return -EFAULT;
2235
2236 /* Get the "struct file *" for the eventpoll file */
2237 f = fdget(epfd);
2238 if (!f.file)
2239 return -EBADF;
2240
2241 /*
2242 * We have to check that the file structure underneath the fd
2243 * the user passed to us _is_ an eventpoll file.
2244 */
2245 error = -EINVAL;
2246 if (!is_file_epoll(f.file))
2247 goto error_fput;
2248
2249 /*
2250 * At this point it is safe to assume that the "private_data" contains
2251 * our own data structure.
2252 */
2253 ep = f.file->private_data;
2254
2255 /* Time to fish for events ... */
2256 error = ep_poll(ep, events, maxevents, to);
2257
2258error_fput:
2259 fdput(f);
2260 return error;
2261}
2262
2263SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
2264 int, maxevents, int, timeout)
2265{
2266 struct timespec64 to;
2267
2268 return do_epoll_wait(epfd, events, maxevents,
2269 ep_timeout_to_timespec(&to, timeout));
2270}
2271
2272/*
2273 * Implement the event wait interface for the eventpoll file. It is the kernel
2274 * part of the user space epoll_pwait(2).
2275 */
2276static int do_epoll_pwait(int epfd, struct epoll_event __user *events,
2277 int maxevents, struct timespec64 *to,
2278 const sigset_t __user *sigmask, size_t sigsetsize)
2279{
2280 int error;
2281
2282 /*
2283 * If the caller wants a certain signal mask to be set during the wait,
2284 * we apply it here.
2285 */
2286 error = set_user_sigmask(sigmask, sigsetsize);
2287 if (error)
2288 return error;
2289
2290 error = do_epoll_wait(epfd, events, maxevents, to);
2291
2292 restore_saved_sigmask_unless(error == -EINTR);
2293
2294 return error;
2295}
2296
2297SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
2298 int, maxevents, int, timeout, const sigset_t __user *, sigmask,
2299 size_t, sigsetsize)
2300{
2301 struct timespec64 to;
2302
2303 return do_epoll_pwait(epfd, events, maxevents,
2304 ep_timeout_to_timespec(&to, timeout),
2305 sigmask, sigsetsize);
2306}
2307
2308SYSCALL_DEFINE6(epoll_pwait2, int, epfd, struct epoll_event __user *, events,
2309 int, maxevents, const struct __kernel_timespec __user *, timeout,
2310 const sigset_t __user *, sigmask, size_t, sigsetsize)
2311{
2312 struct timespec64 ts, *to = NULL;
2313
2314 if (timeout) {
2315 if (get_timespec64(&ts, timeout))
2316 return -EFAULT;
2317 to = &ts;
2318 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
2319 return -EINVAL;
2320 }
2321
2322 return do_epoll_pwait(epfd, events, maxevents, to,
2323 sigmask, sigsetsize);
2324}
2325
2326#ifdef CONFIG_COMPAT
2327static int do_compat_epoll_pwait(int epfd, struct epoll_event __user *events,
2328 int maxevents, struct timespec64 *timeout,
2329 const compat_sigset_t __user *sigmask,
2330 compat_size_t sigsetsize)
2331{
2332 long err;
2333
2334 /*
2335 * If the caller wants a certain signal mask to be set during the wait,
2336 * we apply it here.
2337 */
2338 err = set_compat_user_sigmask(sigmask, sigsetsize);
2339 if (err)
2340 return err;
2341
2342 err = do_epoll_wait(epfd, events, maxevents, timeout);
2343
2344 restore_saved_sigmask_unless(err == -EINTR);
2345
2346 return err;
2347}
2348
2349COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
2350 struct epoll_event __user *, events,
2351 int, maxevents, int, timeout,
2352 const compat_sigset_t __user *, sigmask,
2353 compat_size_t, sigsetsize)
2354{
2355 struct timespec64 to;
2356
2357 return do_compat_epoll_pwait(epfd, events, maxevents,
2358 ep_timeout_to_timespec(&to, timeout),
2359 sigmask, sigsetsize);
2360}
2361
2362COMPAT_SYSCALL_DEFINE6(epoll_pwait2, int, epfd,
2363 struct epoll_event __user *, events,
2364 int, maxevents,
2365 const struct __kernel_timespec __user *, timeout,
2366 const compat_sigset_t __user *, sigmask,
2367 compat_size_t, sigsetsize)
2368{
2369 struct timespec64 ts, *to = NULL;
2370
2371 if (timeout) {
2372 if (get_timespec64(&ts, timeout))
2373 return -EFAULT;
2374 to = &ts;
2375 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
2376 return -EINVAL;
2377 }
2378
2379 return do_compat_epoll_pwait(epfd, events, maxevents, to,
2380 sigmask, sigsetsize);
2381}
2382
2383#endif
2384
2385static int __init eventpoll_init(void)
2386{
2387 struct sysinfo si;
2388
2389 si_meminfo(&si);
2390 /*
2391 * Allows top 4% of lomem to be allocated for epoll watches (per user).
2392 */
2393 max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2394 EP_ITEM_COST;
2395 BUG_ON(max_user_watches < 0);
2396
2397 /*
2398 * We can have many thousands of epitems, so prevent this from
2399 * using an extra cache line on 64-bit (and smaller) CPUs
2400 */
2401 BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
2402
2403 /* Allocates slab cache used to allocate "struct epitem" items */
2404 epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
2405 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
2406
2407 /* Allocates slab cache used to allocate "struct eppoll_entry" */
2408 pwq_cache = kmem_cache_create("eventpoll_pwq",
2409 sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
2410 epoll_sysctls_init();
2411
2412 ephead_cache = kmem_cache_create("ep_head",
2413 sizeof(struct epitems_head), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
2414
2415 return 0;
2416}
2417fs_initcall(eventpoll_init);
2418

source code of linux/fs/eventpoll.c