1/*
2 * fs/eventpoll.c (Efficient event retrieval implementation)
3 * Copyright (C) 2001,...,2009 Davide Libenzi
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * Davide Libenzi <davidel@xmailserver.org>
11 *
12 */
13
14#include <linux/init.h>
15#include <linux/kernel.h>
16#include <linux/sched/signal.h>
17#include <linux/fs.h>
18#include <linux/file.h>
19#include <linux/signal.h>
20#include <linux/errno.h>
21#include <linux/mm.h>
22#include <linux/slab.h>
23#include <linux/poll.h>
24#include <linux/string.h>
25#include <linux/list.h>
26#include <linux/hash.h>
27#include <linux/spinlock.h>
28#include <linux/syscalls.h>
29#include <linux/rbtree.h>
30#include <linux/wait.h>
31#include <linux/eventpoll.h>
32#include <linux/mount.h>
33#include <linux/bitops.h>
34#include <linux/mutex.h>
35#include <linux/anon_inodes.h>
36#include <linux/device.h>
37#include <linux/uaccess.h>
38#include <asm/io.h>
39#include <asm/mman.h>
40#include <linux/atomic.h>
41#include <linux/proc_fs.h>
42#include <linux/seq_file.h>
43#include <linux/compat.h>
44#include <linux/rculist.h>
45#include <net/busy_poll.h>
46
47/*
48 * LOCKING:
49 * There are three level of locking required by epoll :
50 *
51 * 1) epmutex (mutex)
52 * 2) ep->mtx (mutex)
53 * 3) ep->lock (rwlock)
54 *
55 * The acquire order is the one listed above, from 1 to 3.
56 * We need a rwlock (ep->lock) because we manipulate objects
57 * from inside the poll callback, that might be triggered from
58 * a wake_up() that in turn might be called from IRQ context.
59 * So we can't sleep inside the poll callback and hence we need
60 * a spinlock. During the event transfer loop (from kernel to
61 * user space) we could end up sleeping due a copy_to_user(), so
62 * we need a lock that will allow us to sleep. This lock is a
63 * mutex (ep->mtx). It is acquired during the event transfer loop,
64 * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
65 * Then we also need a global mutex to serialize eventpoll_release_file()
66 * and ep_free().
67 * This mutex is acquired by ep_free() during the epoll file
68 * cleanup path and it is also acquired by eventpoll_release_file()
69 * if a file has been pushed inside an epoll set and it is then
70 * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
71 * It is also acquired when inserting an epoll fd onto another epoll
72 * fd. We do this so that we walk the epoll tree and ensure that this
73 * insertion does not create a cycle of epoll file descriptors, which
74 * could lead to deadlock. We need a global mutex to prevent two
75 * simultaneous inserts (A into B and B into A) from racing and
76 * constructing a cycle without either insert observing that it is
77 * going to.
78 * It is necessary to acquire multiple "ep->mtx"es at once in the
79 * case when one epoll fd is added to another. In this case, we
80 * always acquire the locks in the order of nesting (i.e. after
81 * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
82 * before e2->mtx). Since we disallow cycles of epoll file
83 * descriptors, this ensures that the mutexes are well-ordered. In
84 * order to communicate this nesting to lockdep, when walking a tree
85 * of epoll file descriptors, we use the current recursion depth as
86 * the lockdep subkey.
87 * It is possible to drop the "ep->mtx" and to use the global
88 * mutex "epmutex" (together with "ep->lock") to have it working,
89 * but having "ep->mtx" will make the interface more scalable.
90 * Events that require holding "epmutex" are very rare, while for
91 * normal operations the epoll private "ep->mtx" will guarantee
92 * a better scalability.
93 */
94
95/* Epoll private bits inside the event mask */
96#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE)
97
98#define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT)
99
100#define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \
101 EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE)
102
103/* Maximum number of nesting allowed inside epoll sets */
104#define EP_MAX_NESTS 4
105
106#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
107
108#define EP_UNACTIVE_PTR ((void *) -1L)
109
110#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
111
112struct epoll_filefd {
113 struct file *file;
114 int fd;
115} __packed;
116
117/*
118 * Structure used to track possible nested calls, for too deep recursions
119 * and loop cycles.
120 */
121struct nested_call_node {
122 struct list_head llink;
123 void *cookie;
124 void *ctx;
125};
126
127/*
128 * This structure is used as collector for nested calls, to check for
129 * maximum recursion dept and loop cycles.
130 */
131struct nested_calls {
132 struct list_head tasks_call_list;
133 spinlock_t lock;
134};
135
136/*
137 * Each file descriptor added to the eventpoll interface will
138 * have an entry of this type linked to the "rbr" RB tree.
139 * Avoid increasing the size of this struct, there can be many thousands
140 * of these on a server and we do not want this to take another cache line.
141 */
142struct epitem {
143 union {
144 /* RB tree node links this structure to the eventpoll RB tree */
145 struct rb_node rbn;
146 /* Used to free the struct epitem */
147 struct rcu_head rcu;
148 };
149
150 /* List header used to link this structure to the eventpoll ready list */
151 struct list_head rdllink;
152
153 /*
154 * Works together "struct eventpoll"->ovflist in keeping the
155 * single linked chain of items.
156 */
157 struct epitem *next;
158
159 /* The file descriptor information this item refers to */
160 struct epoll_filefd ffd;
161
162 /* Number of active wait queue attached to poll operations */
163 int nwait;
164
165 /* List containing poll wait queues */
166 struct list_head pwqlist;
167
168 /* The "container" of this item */
169 struct eventpoll *ep;
170
171 /* List header used to link this item to the "struct file" items list */
172 struct list_head fllink;
173
174 /* wakeup_source used when EPOLLWAKEUP is set */
175 struct wakeup_source __rcu *ws;
176
177 /* The structure that describe the interested events and the source fd */
178 struct epoll_event event;
179};
180
181/*
182 * This structure is stored inside the "private_data" member of the file
183 * structure and represents the main data structure for the eventpoll
184 * interface.
185 */
186struct eventpoll {
187 /*
188 * This mutex is used to ensure that files are not removed
189 * while epoll is using them. This is held during the event
190 * collection loop, the file cleanup path, the epoll file exit
191 * code and the ctl operations.
192 */
193 struct mutex mtx;
194
195 /* Wait queue used by sys_epoll_wait() */
196 wait_queue_head_t wq;
197
198 /* Wait queue used by file->poll() */
199 wait_queue_head_t poll_wait;
200
201 /* List of ready file descriptors */
202 struct list_head rdllist;
203
204 /* Lock which protects rdllist and ovflist */
205 rwlock_t lock;
206
207 /* RB tree root used to store monitored fd structs */
208 struct rb_root_cached rbr;
209
210 /*
211 * This is a single linked list that chains all the "struct epitem" that
212 * happened while transferring ready events to userspace w/out
213 * holding ->lock.
214 */
215 struct epitem *ovflist;
216
217 /* wakeup_source used when ep_scan_ready_list is running */
218 struct wakeup_source *ws;
219
220 /* The user that created the eventpoll descriptor */
221 struct user_struct *user;
222
223 struct file *file;
224
225 /* used to optimize loop detection check */
226 int visited;
227 struct list_head visited_list_link;
228
229#ifdef CONFIG_NET_RX_BUSY_POLL
230 /* used to track busy poll napi_id */
231 unsigned int napi_id;
232#endif
233};
234
235/* Wait structure used by the poll hooks */
236struct eppoll_entry {
237 /* List header used to link this structure to the "struct epitem" */
238 struct list_head llink;
239
240 /* The "base" pointer is set to the container "struct epitem" */
241 struct epitem *base;
242
243 /*
244 * Wait queue item that will be linked to the target file wait
245 * queue head.
246 */
247 wait_queue_entry_t wait;
248
249 /* The wait queue head that linked the "wait" wait queue item */
250 wait_queue_head_t *whead;
251};
252
253/* Wrapper struct used by poll queueing */
254struct ep_pqueue {
255 poll_table pt;
256 struct epitem *epi;
257};
258
259/* Used by the ep_send_events() function as callback private data */
260struct ep_send_events_data {
261 int maxevents;
262 struct epoll_event __user *events;
263 int res;
264};
265
266/*
267 * Configuration options available inside /proc/sys/fs/epoll/
268 */
269/* Maximum number of epoll watched descriptors, per user */
270static long max_user_watches __read_mostly;
271
272/*
273 * This mutex is used to serialize ep_free() and eventpoll_release_file().
274 */
275static DEFINE_MUTEX(epmutex);
276
277/* Used to check for epoll file descriptor inclusion loops */
278static struct nested_calls poll_loop_ncalls;
279
280/* Slab cache used to allocate "struct epitem" */
281static struct kmem_cache *epi_cache __read_mostly;
282
283/* Slab cache used to allocate "struct eppoll_entry" */
284static struct kmem_cache *pwq_cache __read_mostly;
285
286/* Visited nodes during ep_loop_check(), so we can unset them when we finish */
287static LIST_HEAD(visited_list);
288
289/*
290 * List of files with newly added links, where we may need to limit the number
291 * of emanating paths. Protected by the epmutex.
292 */
293static LIST_HEAD(tfile_check_list);
294
295#ifdef CONFIG_SYSCTL
296
297#include <linux/sysctl.h>
298
299static long zero;
300static long long_max = LONG_MAX;
301
302struct ctl_table epoll_table[] = {
303 {
304 .procname = "max_user_watches",
305 .data = &max_user_watches,
306 .maxlen = sizeof(max_user_watches),
307 .mode = 0644,
308 .proc_handler = proc_doulongvec_minmax,
309 .extra1 = &zero,
310 .extra2 = &long_max,
311 },
312 { }
313};
314#endif /* CONFIG_SYSCTL */
315
316static const struct file_operations eventpoll_fops;
317
318static inline int is_file_epoll(struct file *f)
319{
320 return f->f_op == &eventpoll_fops;
321}
322
323/* Setup the structure that is used as key for the RB tree */
324static inline void ep_set_ffd(struct epoll_filefd *ffd,
325 struct file *file, int fd)
326{
327 ffd->file = file;
328 ffd->fd = fd;
329}
330
331/* Compare RB tree keys */
332static inline int ep_cmp_ffd(struct epoll_filefd *p1,
333 struct epoll_filefd *p2)
334{
335 return (p1->file > p2->file ? +1:
336 (p1->file < p2->file ? -1 : p1->fd - p2->fd));
337}
338
339/* Tells us if the item is currently linked */
340static inline int ep_is_linked(struct epitem *epi)
341{
342 return !list_empty(&epi->rdllink);
343}
344
345static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p)
346{
347 return container_of(p, struct eppoll_entry, wait);
348}
349
350/* Get the "struct epitem" from a wait queue pointer */
351static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p)
352{
353 return container_of(p, struct eppoll_entry, wait)->base;
354}
355
356/* Get the "struct epitem" from an epoll queue wrapper */
357static inline struct epitem *ep_item_from_epqueue(poll_table *p)
358{
359 return container_of(p, struct ep_pqueue, pt)->epi;
360}
361
362/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
363static inline int ep_op_has_event(int op)
364{
365 return op != EPOLL_CTL_DEL;
366}
367
368/* Initialize the poll safe wake up structure */
369static void ep_nested_calls_init(struct nested_calls *ncalls)
370{
371 INIT_LIST_HEAD(&ncalls->tasks_call_list);
372 spin_lock_init(&ncalls->lock);
373}
374
375/**
376 * ep_events_available - Checks if ready events might be available.
377 *
378 * @ep: Pointer to the eventpoll context.
379 *
380 * Returns: Returns a value different than zero if ready events are available,
381 * or zero otherwise.
382 */
383static inline int ep_events_available(struct eventpoll *ep)
384{
385 return !list_empty_careful(&ep->rdllist) ||
386 READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR;
387}
388
389#ifdef CONFIG_NET_RX_BUSY_POLL
390static bool ep_busy_loop_end(void *p, unsigned long start_time)
391{
392 struct eventpoll *ep = p;
393
394 return ep_events_available(ep) || busy_loop_timeout(start_time);
395}
396
397/*
398 * Busy poll if globally on and supporting sockets found && no events,
399 * busy loop will return if need_resched or ep_events_available.
400 *
401 * we must do our busy polling with irqs enabled
402 */
403static void ep_busy_loop(struct eventpoll *ep, int nonblock)
404{
405 unsigned int napi_id = READ_ONCE(ep->napi_id);
406
407 if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on())
408 napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep);
409}
410
411static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
412{
413 if (ep->napi_id)
414 ep->napi_id = 0;
415}
416
417/*
418 * Set epoll busy poll NAPI ID from sk.
419 */
420static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
421{
422 struct eventpoll *ep;
423 unsigned int napi_id;
424 struct socket *sock;
425 struct sock *sk;
426 int err;
427
428 if (!net_busy_loop_on())
429 return;
430
431 sock = sock_from_file(epi->ffd.file, &err);
432 if (!sock)
433 return;
434
435 sk = sock->sk;
436 if (!sk)
437 return;
438
439 napi_id = READ_ONCE(sk->sk_napi_id);
440 ep = epi->ep;
441
442 /* Non-NAPI IDs can be rejected
443 * or
444 * Nothing to do if we already have this ID
445 */
446 if (napi_id < MIN_NAPI_ID || napi_id == ep->napi_id)
447 return;
448
449 /* record NAPI ID for use in next busy poll */
450 ep->napi_id = napi_id;
451}
452
453#else
454
455static inline void ep_busy_loop(struct eventpoll *ep, int nonblock)
456{
457}
458
459static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
460{
461}
462
463static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
464{
465}
466
467#endif /* CONFIG_NET_RX_BUSY_POLL */
468
469/**
470 * ep_call_nested - Perform a bound (possibly) nested call, by checking
471 * that the recursion limit is not exceeded, and that
472 * the same nested call (by the meaning of same cookie) is
473 * no re-entered.
474 *
475 * @ncalls: Pointer to the nested_calls structure to be used for this call.
476 * @nproc: Nested call core function pointer.
477 * @priv: Opaque data to be passed to the @nproc callback.
478 * @cookie: Cookie to be used to identify this nested call.
479 * @ctx: This instance context.
480 *
481 * Returns: Returns the code returned by the @nproc callback, or -1 if
482 * the maximum recursion limit has been exceeded.
483 */
484static int ep_call_nested(struct nested_calls *ncalls,
485 int (*nproc)(void *, void *, int), void *priv,
486 void *cookie, void *ctx)
487{
488 int error, call_nests = 0;
489 unsigned long flags;
490 struct list_head *lsthead = &ncalls->tasks_call_list;
491 struct nested_call_node *tncur;
492 struct nested_call_node tnode;
493
494 spin_lock_irqsave(&ncalls->lock, flags);
495
496 /*
497 * Try to see if the current task is already inside this wakeup call.
498 * We use a list here, since the population inside this set is always
499 * very much limited.
500 */
501 list_for_each_entry(tncur, lsthead, llink) {
502 if (tncur->ctx == ctx &&
503 (tncur->cookie == cookie || ++call_nests > EP_MAX_NESTS)) {
504 /*
505 * Ops ... loop detected or maximum nest level reached.
506 * We abort this wake by breaking the cycle itself.
507 */
508 error = -1;
509 goto out_unlock;
510 }
511 }
512
513 /* Add the current task and cookie to the list */
514 tnode.ctx = ctx;
515 tnode.cookie = cookie;
516 list_add(&tnode.llink, lsthead);
517
518 spin_unlock_irqrestore(&ncalls->lock, flags);
519
520 /* Call the nested function */
521 error = (*nproc)(priv, cookie, call_nests);
522
523 /* Remove the current task from the list */
524 spin_lock_irqsave(&ncalls->lock, flags);
525 list_del(&tnode.llink);
526out_unlock:
527 spin_unlock_irqrestore(&ncalls->lock, flags);
528
529 return error;
530}
531
532/*
533 * As described in commit 0ccf831cb lockdep: annotate epoll
534 * the use of wait queues used by epoll is done in a very controlled
535 * manner. Wake ups can nest inside each other, but are never done
536 * with the same locking. For example:
537 *
538 * dfd = socket(...);
539 * efd1 = epoll_create();
540 * efd2 = epoll_create();
541 * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
542 * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
543 *
544 * When a packet arrives to the device underneath "dfd", the net code will
545 * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
546 * callback wakeup entry on that queue, and the wake_up() performed by the
547 * "dfd" net code will end up in ep_poll_callback(). At this point epoll
548 * (efd1) notices that it may have some event ready, so it needs to wake up
549 * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
550 * that ends up in another wake_up(), after having checked about the
551 * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
552 * avoid stack blasting.
553 *
554 * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
555 * this special case of epoll.
556 */
557#ifdef CONFIG_DEBUG_LOCK_ALLOC
558
559static struct nested_calls poll_safewake_ncalls;
560
561static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
562{
563 unsigned long flags;
564 wait_queue_head_t *wqueue = (wait_queue_head_t *)cookie;
565
566 spin_lock_irqsave_nested(&wqueue->lock, flags, call_nests + 1);
567 wake_up_locked_poll(wqueue, EPOLLIN);
568 spin_unlock_irqrestore(&wqueue->lock, flags);
569
570 return 0;
571}
572
573static void ep_poll_safewake(wait_queue_head_t *wq)
574{
575 int this_cpu = get_cpu();
576
577 ep_call_nested(&poll_safewake_ncalls,
578 ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
579
580 put_cpu();
581}
582
583#else
584
585static void ep_poll_safewake(wait_queue_head_t *wq)
586{
587 wake_up_poll(wq, EPOLLIN);
588}
589
590#endif
591
592static void ep_remove_wait_queue(struct eppoll_entry *pwq)
593{
594 wait_queue_head_t *whead;
595
596 rcu_read_lock();
597 /*
598 * If it is cleared by POLLFREE, it should be rcu-safe.
599 * If we read NULL we need a barrier paired with
600 * smp_store_release() in ep_poll_callback(), otherwise
601 * we rely on whead->lock.
602 */
603 whead = smp_load_acquire(&pwq->whead);
604 if (whead)
605 remove_wait_queue(whead, &pwq->wait);
606 rcu_read_unlock();
607}
608
609/*
610 * This function unregisters poll callbacks from the associated file
611 * descriptor. Must be called with "mtx" held (or "epmutex" if called from
612 * ep_free).
613 */
614static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
615{
616 struct list_head *lsthead = &epi->pwqlist;
617 struct eppoll_entry *pwq;
618
619 while (!list_empty(lsthead)) {
620 pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
621
622 list_del(&pwq->llink);
623 ep_remove_wait_queue(pwq);
624 kmem_cache_free(pwq_cache, pwq);
625 }
626}
627
628/* call only when ep->mtx is held */
629static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
630{
631 return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
632}
633
634/* call only when ep->mtx is held */
635static inline void ep_pm_stay_awake(struct epitem *epi)
636{
637 struct wakeup_source *ws = ep_wakeup_source(epi);
638
639 if (ws)
640 __pm_stay_awake(ws);
641}
642
643static inline bool ep_has_wakeup_source(struct epitem *epi)
644{
645 return rcu_access_pointer(epi->ws) ? true : false;
646}
647
648/* call when ep->mtx cannot be held (ep_poll_callback) */
649static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
650{
651 struct wakeup_source *ws;
652
653 rcu_read_lock();
654 ws = rcu_dereference(epi->ws);
655 if (ws)
656 __pm_stay_awake(ws);
657 rcu_read_unlock();
658}
659
660/**
661 * ep_scan_ready_list - Scans the ready list in a way that makes possible for
662 * the scan code, to call f_op->poll(). Also allows for
663 * O(NumReady) performance.
664 *
665 * @ep: Pointer to the epoll private data structure.
666 * @sproc: Pointer to the scan callback.
667 * @priv: Private opaque data passed to the @sproc callback.
668 * @depth: The current depth of recursive f_op->poll calls.
669 * @ep_locked: caller already holds ep->mtx
670 *
671 * Returns: The same integer error code returned by the @sproc callback.
672 */
673static __poll_t ep_scan_ready_list(struct eventpoll *ep,
674 __poll_t (*sproc)(struct eventpoll *,
675 struct list_head *, void *),
676 void *priv, int depth, bool ep_locked)
677{
678 __poll_t res;
679 int pwake = 0;
680 struct epitem *epi, *nepi;
681 LIST_HEAD(txlist);
682
683 lockdep_assert_irqs_enabled();
684
685 /*
686 * We need to lock this because we could be hit by
687 * eventpoll_release_file() and epoll_ctl().
688 */
689
690 if (!ep_locked)
691 mutex_lock_nested(&ep->mtx, depth);
692
693 /*
694 * Steal the ready list, and re-init the original one to the
695 * empty list. Also, set ep->ovflist to NULL so that events
696 * happening while looping w/out locks, are not lost. We cannot
697 * have the poll callback to queue directly on ep->rdllist,
698 * because we want the "sproc" callback to be able to do it
699 * in a lockless way.
700 */
701 write_lock_irq(&ep->lock);
702 list_splice_init(&ep->rdllist, &txlist);
703 WRITE_ONCE(ep->ovflist, NULL);
704 write_unlock_irq(&ep->lock);
705
706 /*
707 * Now call the callback function.
708 */
709 res = (*sproc)(ep, &txlist, priv);
710
711 write_lock_irq(&ep->lock);
712 /*
713 * During the time we spent inside the "sproc" callback, some
714 * other events might have been queued by the poll callback.
715 * We re-insert them inside the main ready-list here.
716 */
717 for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
718 nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
719 /*
720 * We need to check if the item is already in the list.
721 * During the "sproc" callback execution time, items are
722 * queued into ->ovflist but the "txlist" might already
723 * contain them, and the list_splice() below takes care of them.
724 */
725 if (!ep_is_linked(epi)) {
726 /*
727 * ->ovflist is LIFO, so we have to reverse it in order
728 * to keep in FIFO.
729 */
730 list_add(&epi->rdllink, &ep->rdllist);
731 ep_pm_stay_awake(epi);
732 }
733 }
734 /*
735 * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
736 * releasing the lock, events will be queued in the normal way inside
737 * ep->rdllist.
738 */
739 WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR);
740
741 /*
742 * Quickly re-inject items left on "txlist".
743 */
744 list_splice(&txlist, &ep->rdllist);
745 __pm_relax(ep->ws);
746
747 if (!list_empty(&ep->rdllist)) {
748 /*
749 * Wake up (if active) both the eventpoll wait list and
750 * the ->poll() wait list (delayed after we release the lock).
751 */
752 if (waitqueue_active(&ep->wq))
753 wake_up(&ep->wq);
754 if (waitqueue_active(&ep->poll_wait))
755 pwake++;
756 }
757 write_unlock_irq(&ep->lock);
758
759 if (!ep_locked)
760 mutex_unlock(&ep->mtx);
761
762 /* We have to call this outside the lock */
763 if (pwake)
764 ep_poll_safewake(&ep->poll_wait);
765
766 return res;
767}
768
769static void epi_rcu_free(struct rcu_head *head)
770{
771 struct epitem *epi = container_of(head, struct epitem, rcu);
772 kmem_cache_free(epi_cache, epi);
773}
774
775/*
776 * Removes a "struct epitem" from the eventpoll RB tree and deallocates
777 * all the associated resources. Must be called with "mtx" held.
778 */
779static int ep_remove(struct eventpoll *ep, struct epitem *epi)
780{
781 struct file *file = epi->ffd.file;
782
783 lockdep_assert_irqs_enabled();
784
785 /*
786 * Removes poll wait queue hooks.
787 */
788 ep_unregister_pollwait(ep, epi);
789
790 /* Remove the current item from the list of epoll hooks */
791 spin_lock(&file->f_lock);
792 list_del_rcu(&epi->fllink);
793 spin_unlock(&file->f_lock);
794
795 rb_erase_cached(&epi->rbn, &ep->rbr);
796
797 write_lock_irq(&ep->lock);
798 if (ep_is_linked(epi))
799 list_del_init(&epi->rdllink);
800 write_unlock_irq(&ep->lock);
801
802 wakeup_source_unregister(ep_wakeup_source(epi));
803 /*
804 * At this point it is safe to free the eventpoll item. Use the union
805 * field epi->rcu, since we are trying to minimize the size of
806 * 'struct epitem'. The 'rbn' field is no longer in use. Protected by
807 * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
808 * use of the rbn field.
809 */
810 call_rcu(&epi->rcu, epi_rcu_free);
811
812 atomic_long_dec(&ep->user->epoll_watches);
813
814 return 0;
815}
816
817static void ep_free(struct eventpoll *ep)
818{
819 struct rb_node *rbp;
820 struct epitem *epi;
821
822 /* We need to release all tasks waiting for these file */
823 if (waitqueue_active(&ep->poll_wait))
824 ep_poll_safewake(&ep->poll_wait);
825
826 /*
827 * We need to lock this because we could be hit by
828 * eventpoll_release_file() while we're freeing the "struct eventpoll".
829 * We do not need to hold "ep->mtx" here because the epoll file
830 * is on the way to be removed and no one has references to it
831 * anymore. The only hit might come from eventpoll_release_file() but
832 * holding "epmutex" is sufficient here.
833 */
834 mutex_lock(&epmutex);
835
836 /*
837 * Walks through the whole tree by unregistering poll callbacks.
838 */
839 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
840 epi = rb_entry(rbp, struct epitem, rbn);
841
842 ep_unregister_pollwait(ep, epi);
843 cond_resched();
844 }
845
846 /*
847 * Walks through the whole tree by freeing each "struct epitem". At this
848 * point we are sure no poll callbacks will be lingering around, and also by
849 * holding "epmutex" we can be sure that no file cleanup code will hit
850 * us during this operation. So we can avoid the lock on "ep->lock".
851 * We do not need to lock ep->mtx, either, we only do it to prevent
852 * a lockdep warning.
853 */
854 mutex_lock(&ep->mtx);
855 while ((rbp = rb_first_cached(&ep->rbr)) != NULL) {
856 epi = rb_entry(rbp, struct epitem, rbn);
857 ep_remove(ep, epi);
858 cond_resched();
859 }
860 mutex_unlock(&ep->mtx);
861
862 mutex_unlock(&epmutex);
863 mutex_destroy(&ep->mtx);
864 free_uid(ep->user);
865 wakeup_source_unregister(ep->ws);
866 kfree(ep);
867}
868
869static int ep_eventpoll_release(struct inode *inode, struct file *file)
870{
871 struct eventpoll *ep = file->private_data;
872
873 if (ep)
874 ep_free(ep);
875
876 return 0;
877}
878
879static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
880 void *priv);
881static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
882 poll_table *pt);
883
884/*
885 * Differs from ep_eventpoll_poll() in that internal callers already have
886 * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested()
887 * is correctly annotated.
888 */
889static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt,
890 int depth)
891{
892 struct eventpoll *ep;
893 bool locked;
894
895 pt->_key = epi->event.events;
896 if (!is_file_epoll(epi->ffd.file))
897 return vfs_poll(epi->ffd.file, pt) & epi->event.events;
898
899 ep = epi->ffd.file->private_data;
900 poll_wait(epi->ffd.file, &ep->poll_wait, pt);
901 locked = pt && (pt->_qproc == ep_ptable_queue_proc);
902
903 return ep_scan_ready_list(epi->ffd.file->private_data,
904 ep_read_events_proc, &depth, depth,
905 locked) & epi->event.events;
906}
907
908static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
909 void *priv)
910{
911 struct epitem *epi, *tmp;
912 poll_table pt;
913 int depth = *(int *)priv;
914
915 init_poll_funcptr(&pt, NULL);
916 depth++;
917
918 list_for_each_entry_safe(epi, tmp, head, rdllink) {
919 if (ep_item_poll(epi, &pt, depth)) {
920 return EPOLLIN | EPOLLRDNORM;
921 } else {
922 /*
923 * Item has been dropped into the ready list by the poll
924 * callback, but it's not actually ready, as far as
925 * caller requested events goes. We can remove it here.
926 */
927 __pm_relax(ep_wakeup_source(epi));
928 list_del_init(&epi->rdllink);
929 }
930 }
931
932 return 0;
933}
934
935static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait)
936{
937 struct eventpoll *ep = file->private_data;
938 int depth = 0;
939
940 /* Insert inside our poll wait queue */
941 poll_wait(file, &ep->poll_wait, wait);
942
943 /*
944 * Proceed to find out if wanted events are really available inside
945 * the ready list.
946 */
947 return ep_scan_ready_list(ep, ep_read_events_proc,
948 &depth, depth, false);
949}
950
951#ifdef CONFIG_PROC_FS
952static void ep_show_fdinfo(struct seq_file *m, struct file *f)
953{
954 struct eventpoll *ep = f->private_data;
955 struct rb_node *rbp;
956
957 mutex_lock(&ep->mtx);
958 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
959 struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
960 struct inode *inode = file_inode(epi->ffd.file);
961
962 seq_printf(m, "tfd: %8d events: %8x data: %16llx "
963 " pos:%lli ino:%lx sdev:%x\n",
964 epi->ffd.fd, epi->event.events,
965 (long long)epi->event.data,
966 (long long)epi->ffd.file->f_pos,
967 inode->i_ino, inode->i_sb->s_dev);
968 if (seq_has_overflowed(m))
969 break;
970 }
971 mutex_unlock(&ep->mtx);
972}
973#endif
974
975/* File callbacks that implement the eventpoll file behaviour */
976static const struct file_operations eventpoll_fops = {
977#ifdef CONFIG_PROC_FS
978 .show_fdinfo = ep_show_fdinfo,
979#endif
980 .release = ep_eventpoll_release,
981 .poll = ep_eventpoll_poll,
982 .llseek = noop_llseek,
983};
984
985/*
986 * This is called from eventpoll_release() to unlink files from the eventpoll
987 * interface. We need to have this facility to cleanup correctly files that are
988 * closed without being removed from the eventpoll interface.
989 */
990void eventpoll_release_file(struct file *file)
991{
992 struct eventpoll *ep;
993 struct epitem *epi, *next;
994
995 /*
996 * We don't want to get "file->f_lock" because it is not
997 * necessary. It is not necessary because we're in the "struct file"
998 * cleanup path, and this means that no one is using this file anymore.
999 * So, for example, epoll_ctl() cannot hit here since if we reach this
1000 * point, the file counter already went to zero and fget() would fail.
1001 * The only hit might come from ep_free() but by holding the mutex
1002 * will correctly serialize the operation. We do need to acquire
1003 * "ep->mtx" after "epmutex" because ep_remove() requires it when called
1004 * from anywhere but ep_free().
1005 *
1006 * Besides, ep_remove() acquires the lock, so we can't hold it here.
1007 */
1008 mutex_lock(&epmutex);
1009 list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) {
1010 ep = epi->ep;
1011 mutex_lock_nested(&ep->mtx, 0);
1012 ep_remove(ep, epi);
1013 mutex_unlock(&ep->mtx);
1014 }
1015 mutex_unlock(&epmutex);
1016}
1017
1018static int ep_alloc(struct eventpoll **pep)
1019{
1020 int error;
1021 struct user_struct *user;
1022 struct eventpoll *ep;
1023
1024 user = get_current_user();
1025 error = -ENOMEM;
1026 ep = kzalloc(sizeof(*ep), GFP_KERNEL);
1027 if (unlikely(!ep))
1028 goto free_uid;
1029
1030 mutex_init(&ep->mtx);
1031 rwlock_init(&ep->lock);
1032 init_waitqueue_head(&ep->wq);
1033 init_waitqueue_head(&ep->poll_wait);
1034 INIT_LIST_HEAD(&ep->rdllist);
1035 ep->rbr = RB_ROOT_CACHED;
1036 ep->ovflist = EP_UNACTIVE_PTR;
1037 ep->user = user;
1038
1039 *pep = ep;
1040
1041 return 0;
1042
1043free_uid:
1044 free_uid(user);
1045 return error;
1046}
1047
1048/*
1049 * Search the file inside the eventpoll tree. The RB tree operations
1050 * are protected by the "mtx" mutex, and ep_find() must be called with
1051 * "mtx" held.
1052 */
1053static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
1054{
1055 int kcmp;
1056 struct rb_node *rbp;
1057 struct epitem *epi, *epir = NULL;
1058 struct epoll_filefd ffd;
1059
1060 ep_set_ffd(&ffd, file, fd);
1061 for (rbp = ep->rbr.rb_root.rb_node; rbp; ) {
1062 epi = rb_entry(rbp, struct epitem, rbn);
1063 kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
1064 if (kcmp > 0)
1065 rbp = rbp->rb_right;
1066 else if (kcmp < 0)
1067 rbp = rbp->rb_left;
1068 else {
1069 epir = epi;
1070 break;
1071 }
1072 }
1073
1074 return epir;
1075}
1076
1077#ifdef CONFIG_CHECKPOINT_RESTORE
1078static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff)
1079{
1080 struct rb_node *rbp;
1081 struct epitem *epi;
1082
1083 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1084 epi = rb_entry(rbp, struct epitem, rbn);
1085 if (epi->ffd.fd == tfd) {
1086 if (toff == 0)
1087 return epi;
1088 else
1089 toff--;
1090 }
1091 cond_resched();
1092 }
1093
1094 return NULL;
1095}
1096
1097struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
1098 unsigned long toff)
1099{
1100 struct file *file_raw;
1101 struct eventpoll *ep;
1102 struct epitem *epi;
1103
1104 if (!is_file_epoll(file))
1105 return ERR_PTR(-EINVAL);
1106
1107 ep = file->private_data;
1108
1109 mutex_lock(&ep->mtx);
1110 epi = ep_find_tfd(ep, tfd, toff);
1111 if (epi)
1112 file_raw = epi->ffd.file;
1113 else
1114 file_raw = ERR_PTR(-ENOENT);
1115 mutex_unlock(&ep->mtx);
1116
1117 return file_raw;
1118}
1119#endif /* CONFIG_CHECKPOINT_RESTORE */
1120
1121/**
1122 * Adds a new entry to the tail of the list in a lockless way, i.e.
1123 * multiple CPUs are allowed to call this function concurrently.
1124 *
1125 * Beware: it is necessary to prevent any other modifications of the
1126 * existing list until all changes are completed, in other words
1127 * concurrent list_add_tail_lockless() calls should be protected
1128 * with a read lock, where write lock acts as a barrier which
1129 * makes sure all list_add_tail_lockless() calls are fully
1130 * completed.
1131 *
1132 * Also an element can be locklessly added to the list only in one
1133 * direction i.e. either to the tail either to the head, otherwise
1134 * concurrent access will corrupt the list.
1135 *
1136 * Returns %false if element has been already added to the list, %true
1137 * otherwise.
1138 */
1139static inline bool list_add_tail_lockless(struct list_head *new,
1140 struct list_head *head)
1141{
1142 struct list_head *prev;
1143
1144 /*
1145 * This is simple 'new->next = head' operation, but cmpxchg()
1146 * is used in order to detect that same element has been just
1147 * added to the list from another CPU: the winner observes
1148 * new->next == new.
1149 */
1150 if (cmpxchg(&new->next, new, head) != new)
1151 return false;
1152
1153 /*
1154 * Initially ->next of a new element must be updated with the head
1155 * (we are inserting to the tail) and only then pointers are atomically
1156 * exchanged. XCHG guarantees memory ordering, thus ->next should be
1157 * updated before pointers are actually swapped and pointers are
1158 * swapped before prev->next is updated.
1159 */
1160
1161 prev = xchg(&head->prev, new);
1162
1163 /*
1164 * It is safe to modify prev->next and new->prev, because a new element
1165 * is added only to the tail and new->next is updated before XCHG.
1166 */
1167
1168 prev->next = new;
1169 new->prev = prev;
1170
1171 return true;
1172}
1173
1174/**
1175 * Chains a new epi entry to the tail of the ep->ovflist in a lockless way,
1176 * i.e. multiple CPUs are allowed to call this function concurrently.
1177 *
1178 * Returns %false if epi element has been already chained, %true otherwise.
1179 */
1180static inline bool chain_epi_lockless(struct epitem *epi)
1181{
1182 struct eventpoll *ep = epi->ep;
1183
1184 /* Check that the same epi has not been just chained from another CPU */
1185 if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR)
1186 return false;
1187
1188 /* Atomically exchange tail */
1189 epi->next = xchg(&ep->ovflist, epi);
1190
1191 return true;
1192}
1193
1194/*
1195 * This is the callback that is passed to the wait queue wakeup
1196 * mechanism. It is called by the stored file descriptors when they
1197 * have events to report.
1198 *
1199 * This callback takes a read lock in order not to content with concurrent
1200 * events from another file descriptors, thus all modifications to ->rdllist
1201 * or ->ovflist are lockless. Read lock is paired with the write lock from
1202 * ep_scan_ready_list(), which stops all list modifications and guarantees
1203 * that lists state is seen correctly.
1204 *
1205 * Another thing worth to mention is that ep_poll_callback() can be called
1206 * concurrently for the same @epi from different CPUs if poll table was inited
1207 * with several wait queues entries. Plural wakeup from different CPUs of a
1208 * single wait queue is serialized by wq.lock, but the case when multiple wait
1209 * queues are used should be detected accordingly. This is detected using
1210 * cmpxchg() operation.
1211 */
1212static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
1213{
1214 int pwake = 0;
1215 struct epitem *epi = ep_item_from_wait(wait);
1216 struct eventpoll *ep = epi->ep;
1217 __poll_t pollflags = key_to_poll(key);
1218 unsigned long flags;
1219 int ewake = 0;
1220
1221 read_lock_irqsave(&ep->lock, flags);
1222
1223 ep_set_busy_poll_napi_id(epi);
1224
1225 /*
1226 * If the event mask does not contain any poll(2) event, we consider the
1227 * descriptor to be disabled. This condition is likely the effect of the
1228 * EPOLLONESHOT bit that disables the descriptor when an event is received,
1229 * until the next EPOLL_CTL_MOD will be issued.
1230 */
1231 if (!(epi->event.events & ~EP_PRIVATE_BITS))
1232 goto out_unlock;
1233
1234 /*
1235 * Check the events coming with the callback. At this stage, not
1236 * every device reports the events in the "key" parameter of the
1237 * callback. We need to be able to handle both cases here, hence the
1238 * test for "key" != NULL before the event match test.
1239 */
1240 if (pollflags && !(pollflags & epi->event.events))
1241 goto out_unlock;
1242
1243 /*
1244 * If we are transferring events to userspace, we can hold no locks
1245 * (because we're accessing user memory, and because of linux f_op->poll()
1246 * semantics). All the events that happen during that period of time are
1247 * chained in ep->ovflist and requeued later on.
1248 */
1249 if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) {
1250 if (epi->next == EP_UNACTIVE_PTR &&
1251 chain_epi_lockless(epi))
1252 ep_pm_stay_awake_rcu(epi);
1253 goto out_unlock;
1254 }
1255
1256 /* If this file is already in the ready list we exit soon */
1257 if (!ep_is_linked(epi) &&
1258 list_add_tail_lockless(&epi->rdllink, &ep->rdllist)) {
1259 ep_pm_stay_awake_rcu(epi);
1260 }
1261
1262 /*
1263 * Wake up ( if active ) both the eventpoll wait list and the ->poll()
1264 * wait list.
1265 */
1266 if (waitqueue_active(&ep->wq)) {
1267 if ((epi->event.events & EPOLLEXCLUSIVE) &&
1268 !(pollflags & POLLFREE)) {
1269 switch (pollflags & EPOLLINOUT_BITS) {
1270 case EPOLLIN:
1271 if (epi->event.events & EPOLLIN)
1272 ewake = 1;
1273 break;
1274 case EPOLLOUT:
1275 if (epi->event.events & EPOLLOUT)
1276 ewake = 1;
1277 break;
1278 case 0:
1279 ewake = 1;
1280 break;
1281 }
1282 }
1283 wake_up(&ep->wq);
1284 }
1285 if (waitqueue_active(&ep->poll_wait))
1286 pwake++;
1287
1288out_unlock:
1289 read_unlock_irqrestore(&ep->lock, flags);
1290
1291 /* We have to call this outside the lock */
1292 if (pwake)
1293 ep_poll_safewake(&ep->poll_wait);
1294
1295 if (!(epi->event.events & EPOLLEXCLUSIVE))
1296 ewake = 1;
1297
1298 if (pollflags & POLLFREE) {
1299 /*
1300 * If we race with ep_remove_wait_queue() it can miss
1301 * ->whead = NULL and do another remove_wait_queue() after
1302 * us, so we can't use __remove_wait_queue().
1303 */
1304 list_del_init(&wait->entry);
1305 /*
1306 * ->whead != NULL protects us from the race with ep_free()
1307 * or ep_remove(), ep_remove_wait_queue() takes whead->lock
1308 * held by the caller. Once we nullify it, nothing protects
1309 * ep/epi or even wait.
1310 */
1311 smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL);
1312 }
1313
1314 return ewake;
1315}
1316
1317/*
1318 * This is the callback that is used to add our wait queue to the
1319 * target file wakeup lists.
1320 */
1321static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
1322 poll_table *pt)
1323{
1324 struct epitem *epi = ep_item_from_epqueue(pt);
1325 struct eppoll_entry *pwq;
1326
1327 if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
1328 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
1329 pwq->whead = whead;
1330 pwq->base = epi;
1331 if (epi->event.events & EPOLLEXCLUSIVE)
1332 add_wait_queue_exclusive(whead, &pwq->wait);
1333 else
1334 add_wait_queue(whead, &pwq->wait);
1335 list_add_tail(&pwq->llink, &epi->pwqlist);
1336 epi->nwait++;
1337 } else {
1338 /* We have to signal that an error occurred */
1339 epi->nwait = -1;
1340 }
1341}
1342
1343static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
1344{
1345 int kcmp;
1346 struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL;
1347 struct epitem *epic;
1348 bool leftmost = true;
1349
1350 while (*p) {
1351 parent = *p;
1352 epic = rb_entry(parent, struct epitem, rbn);
1353 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
1354 if (kcmp > 0) {
1355 p = &parent->rb_right;
1356 leftmost = false;
1357 } else
1358 p = &parent->rb_left;
1359 }
1360 rb_link_node(&epi->rbn, parent, p);
1361 rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost);
1362}
1363
1364
1365
1366#define PATH_ARR_SIZE 5
1367/*
1368 * These are the number paths of length 1 to 5, that we are allowing to emanate
1369 * from a single file of interest. For example, we allow 1000 paths of length
1370 * 1, to emanate from each file of interest. This essentially represents the
1371 * potential wakeup paths, which need to be limited in order to avoid massive
1372 * uncontrolled wakeup storms. The common use case should be a single ep which
1373 * is connected to n file sources. In this case each file source has 1 path
1374 * of length 1. Thus, the numbers below should be more than sufficient. These
1375 * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
1376 * and delete can't add additional paths. Protected by the epmutex.
1377 */
1378static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
1379static int path_count[PATH_ARR_SIZE];
1380
1381static int path_count_inc(int nests)
1382{
1383 /* Allow an arbitrary number of depth 1 paths */
1384 if (nests == 0)
1385 return 0;
1386
1387 if (++path_count[nests] > path_limits[nests])
1388 return -1;
1389 return 0;
1390}
1391
1392static void path_count_init(void)
1393{
1394 int i;
1395
1396 for (i = 0; i < PATH_ARR_SIZE; i++)
1397 path_count[i] = 0;
1398}
1399
1400static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
1401{
1402 int error = 0;
1403 struct file *file = priv;
1404 struct file *child_file;
1405 struct epitem *epi;
1406
1407 /* CTL_DEL can remove links here, but that can't increase our count */
1408 rcu_read_lock();
1409 list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
1410 child_file = epi->ep->file;
1411 if (is_file_epoll(child_file)) {
1412 if (list_empty(&child_file->f_ep_links)) {
1413 if (path_count_inc(call_nests)) {
1414 error = -1;
1415 break;
1416 }
1417 } else {
1418 error = ep_call_nested(&poll_loop_ncalls,
1419 reverse_path_check_proc,
1420 child_file, child_file,
1421 current);
1422 }
1423 if (error != 0)
1424 break;
1425 } else {
1426 printk(KERN_ERR "reverse_path_check_proc: "
1427 "file is not an ep!\n");
1428 }
1429 }
1430 rcu_read_unlock();
1431 return error;
1432}
1433
1434/**
1435 * reverse_path_check - The tfile_check_list is list of file *, which have
1436 * links that are proposed to be newly added. We need to
1437 * make sure that those added links don't add too many
1438 * paths such that we will spend all our time waking up
1439 * eventpoll objects.
1440 *
1441 * Returns: Returns zero if the proposed links don't create too many paths,
1442 * -1 otherwise.
1443 */
1444static int reverse_path_check(void)
1445{
1446 int error = 0;
1447 struct file *current_file;
1448
1449 /* let's call this for all tfiles */
1450 list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
1451 path_count_init();
1452 error = ep_call_nested(&poll_loop_ncalls,
1453 reverse_path_check_proc, current_file,
1454 current_file, current);
1455 if (error)
1456 break;
1457 }
1458 return error;
1459}
1460
1461static int ep_create_wakeup_source(struct epitem *epi)
1462{
1463 const char *name;
1464 struct wakeup_source *ws;
1465
1466 if (!epi->ep->ws) {
1467 epi->ep->ws = wakeup_source_register("eventpoll");
1468 if (!epi->ep->ws)
1469 return -ENOMEM;
1470 }
1471
1472 name = epi->ffd.file->f_path.dentry->d_name.name;
1473 ws = wakeup_source_register(name);
1474
1475 if (!ws)
1476 return -ENOMEM;
1477 rcu_assign_pointer(epi->ws, ws);
1478
1479 return 0;
1480}
1481
1482/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
1483static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1484{
1485 struct wakeup_source *ws = ep_wakeup_source(epi);
1486
1487 RCU_INIT_POINTER(epi->ws, NULL);
1488
1489 /*
1490 * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
1491 * used internally by wakeup_source_remove, too (called by
1492 * wakeup_source_unregister), so we cannot use call_rcu
1493 */
1494 synchronize_rcu();
1495 wakeup_source_unregister(ws);
1496}
1497
1498/*
1499 * Must be called with "mtx" held.
1500 */
1501static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
1502 struct file *tfile, int fd, int full_check)
1503{
1504 int error, pwake = 0;
1505 __poll_t revents;
1506 long user_watches;
1507 struct epitem *epi;
1508 struct ep_pqueue epq;
1509
1510 lockdep_assert_irqs_enabled();
1511
1512 user_watches = atomic_long_read(&ep->user->epoll_watches);
1513 if (unlikely(user_watches >= max_user_watches))
1514 return -ENOSPC;
1515 if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
1516 return -ENOMEM;
1517
1518 /* Item initialization follow here ... */
1519 INIT_LIST_HEAD(&epi->rdllink);
1520 INIT_LIST_HEAD(&epi->fllink);
1521 INIT_LIST_HEAD(&epi->pwqlist);
1522 epi->ep = ep;
1523 ep_set_ffd(&epi->ffd, tfile, fd);
1524 epi->event = *event;
1525 epi->nwait = 0;
1526 epi->next = EP_UNACTIVE_PTR;
1527 if (epi->event.events & EPOLLWAKEUP) {
1528 error = ep_create_wakeup_source(epi);
1529 if (error)
1530 goto error_create_wakeup_source;
1531 } else {
1532 RCU_INIT_POINTER(epi->ws, NULL);
1533 }
1534
1535 /* Initialize the poll table using the queue callback */
1536 epq.epi = epi;
1537 init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
1538
1539 /*
1540 * Attach the item to the poll hooks and get current event bits.
1541 * We can safely use the file* here because its usage count has
1542 * been increased by the caller of this function. Note that after
1543 * this operation completes, the poll callback can start hitting
1544 * the new item.
1545 */
1546 revents = ep_item_poll(epi, &epq.pt, 1);
1547
1548 /*
1549 * We have to check if something went wrong during the poll wait queue
1550 * install process. Namely an allocation for a wait queue failed due
1551 * high memory pressure.
1552 */
1553 error = -ENOMEM;
1554 if (epi->nwait < 0)
1555 goto error_unregister;
1556
1557 /* Add the current item to the list of active epoll hook for this file */
1558 spin_lock(&tfile->f_lock);
1559 list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
1560 spin_unlock(&tfile->f_lock);
1561
1562 /*
1563 * Add the current item to the RB tree. All RB tree operations are
1564 * protected by "mtx", and ep_insert() is called with "mtx" held.
1565 */
1566 ep_rbtree_insert(ep, epi);
1567
1568 /* now check if we've created too many backpaths */
1569 error = -EINVAL;
1570 if (full_check && reverse_path_check())
1571 goto error_remove_epi;
1572
1573 /* We have to drop the new item inside our item list to keep track of it */
1574 write_lock_irq(&ep->lock);
1575
1576 /* record NAPI ID of new item if present */
1577 ep_set_busy_poll_napi_id(epi);
1578
1579 /* If the file is already "ready" we drop it inside the ready list */
1580 if (revents && !ep_is_linked(epi)) {
1581 list_add_tail(&epi->rdllink, &ep->rdllist);
1582 ep_pm_stay_awake(epi);
1583
1584 /* Notify waiting tasks that events are available */
1585 if (waitqueue_active(&ep->wq))
1586 wake_up(&ep->wq);
1587 if (waitqueue_active(&ep->poll_wait))
1588 pwake++;
1589 }
1590
1591 write_unlock_irq(&ep->lock);
1592
1593 atomic_long_inc(&ep->user->epoll_watches);
1594
1595 /* We have to call this outside the lock */
1596 if (pwake)
1597 ep_poll_safewake(&ep->poll_wait);
1598
1599 return 0;
1600
1601error_remove_epi:
1602 spin_lock(&tfile->f_lock);
1603 list_del_rcu(&epi->fllink);
1604 spin_unlock(&tfile->f_lock);
1605
1606 rb_erase_cached(&epi->rbn, &ep->rbr);
1607
1608error_unregister:
1609 ep_unregister_pollwait(ep, epi);
1610
1611 /*
1612 * We need to do this because an event could have been arrived on some
1613 * allocated wait queue. Note that we don't care about the ep->ovflist
1614 * list, since that is used/cleaned only inside a section bound by "mtx".
1615 * And ep_insert() is called with "mtx" held.
1616 */
1617 write_lock_irq(&ep->lock);
1618 if (ep_is_linked(epi))
1619 list_del_init(&epi->rdllink);
1620 write_unlock_irq(&ep->lock);
1621
1622 wakeup_source_unregister(ep_wakeup_source(epi));
1623
1624error_create_wakeup_source:
1625 kmem_cache_free(epi_cache, epi);
1626
1627 return error;
1628}
1629
1630/*
1631 * Modify the interest event mask by dropping an event if the new mask
1632 * has a match in the current file status. Must be called with "mtx" held.
1633 */
1634static int ep_modify(struct eventpoll *ep, struct epitem *epi,
1635 const struct epoll_event *event)
1636{
1637 int pwake = 0;
1638 poll_table pt;
1639
1640 lockdep_assert_irqs_enabled();
1641
1642 init_poll_funcptr(&pt, NULL);
1643
1644 /*
1645 * Set the new event interest mask before calling f_op->poll();
1646 * otherwise we might miss an event that happens between the
1647 * f_op->poll() call and the new event set registering.
1648 */
1649 epi->event.events = event->events; /* need barrier below */
1650 epi->event.data = event->data; /* protected by mtx */
1651 if (epi->event.events & EPOLLWAKEUP) {
1652 if (!ep_has_wakeup_source(epi))
1653 ep_create_wakeup_source(epi);
1654 } else if (ep_has_wakeup_source(epi)) {
1655 ep_destroy_wakeup_source(epi);
1656 }
1657
1658 /*
1659 * The following barrier has two effects:
1660 *
1661 * 1) Flush epi changes above to other CPUs. This ensures
1662 * we do not miss events from ep_poll_callback if an
1663 * event occurs immediately after we call f_op->poll().
1664 * We need this because we did not take ep->lock while
1665 * changing epi above (but ep_poll_callback does take
1666 * ep->lock).
1667 *
1668 * 2) We also need to ensure we do not miss _past_ events
1669 * when calling f_op->poll(). This barrier also
1670 * pairs with the barrier in wq_has_sleeper (see
1671 * comments for wq_has_sleeper).
1672 *
1673 * This barrier will now guarantee ep_poll_callback or f_op->poll
1674 * (or both) will notice the readiness of an item.
1675 */
1676 smp_mb();
1677
1678 /*
1679 * Get current event bits. We can safely use the file* here because
1680 * its usage count has been increased by the caller of this function.
1681 * If the item is "hot" and it is not registered inside the ready
1682 * list, push it inside.
1683 */
1684 if (ep_item_poll(epi, &pt, 1)) {
1685 write_lock_irq(&ep->lock);
1686 if (!ep_is_linked(epi)) {
1687 list_add_tail(&epi->rdllink, &ep->rdllist);
1688 ep_pm_stay_awake(epi);
1689
1690 /* Notify waiting tasks that events are available */
1691 if (waitqueue_active(&ep->wq))
1692 wake_up(&ep->wq);
1693 if (waitqueue_active(&ep->poll_wait))
1694 pwake++;
1695 }
1696 write_unlock_irq(&ep->lock);
1697 }
1698
1699 /* We have to call this outside the lock */
1700 if (pwake)
1701 ep_poll_safewake(&ep->poll_wait);
1702
1703 return 0;
1704}
1705
1706static __poll_t ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
1707 void *priv)
1708{
1709 struct ep_send_events_data *esed = priv;
1710 __poll_t revents;
1711 struct epitem *epi, *tmp;
1712 struct epoll_event __user *uevent = esed->events;
1713 struct wakeup_source *ws;
1714 poll_table pt;
1715
1716 init_poll_funcptr(&pt, NULL);
1717 esed->res = 0;
1718
1719 /*
1720 * We can loop without lock because we are passed a task private list.
1721 * Items cannot vanish during the loop because ep_scan_ready_list() is
1722 * holding "mtx" during this call.
1723 */
1724 lockdep_assert_held(&ep->mtx);
1725
1726 list_for_each_entry_safe(epi, tmp, head, rdllink) {
1727 if (esed->res >= esed->maxevents)
1728 break;
1729
1730 /*
1731 * Activate ep->ws before deactivating epi->ws to prevent
1732 * triggering auto-suspend here (in case we reactive epi->ws
1733 * below).
1734 *
1735 * This could be rearranged to delay the deactivation of epi->ws
1736 * instead, but then epi->ws would temporarily be out of sync
1737 * with ep_is_linked().
1738 */
1739 ws = ep_wakeup_source(epi);
1740 if (ws) {
1741 if (ws->active)
1742 __pm_stay_awake(ep->ws);
1743 __pm_relax(ws);
1744 }
1745
1746 list_del_init(&epi->rdllink);
1747
1748 /*
1749 * If the event mask intersect the caller-requested one,
1750 * deliver the event to userspace. Again, ep_scan_ready_list()
1751 * is holding ep->mtx, so no operations coming from userspace
1752 * can change the item.
1753 */
1754 revents = ep_item_poll(epi, &pt, 1);
1755 if (!revents)
1756 continue;
1757
1758 if (__put_user(revents, &uevent->events) ||
1759 __put_user(epi->event.data, &uevent->data)) {
1760 list_add(&epi->rdllink, head);
1761 ep_pm_stay_awake(epi);
1762 if (!esed->res)
1763 esed->res = -EFAULT;
1764 return 0;
1765 }
1766 esed->res++;
1767 uevent++;
1768 if (epi->event.events & EPOLLONESHOT)
1769 epi->event.events &= EP_PRIVATE_BITS;
1770 else if (!(epi->event.events & EPOLLET)) {
1771 /*
1772 * If this file has been added with Level
1773 * Trigger mode, we need to insert back inside
1774 * the ready list, so that the next call to
1775 * epoll_wait() will check again the events
1776 * availability. At this point, no one can insert
1777 * into ep->rdllist besides us. The epoll_ctl()
1778 * callers are locked out by
1779 * ep_scan_ready_list() holding "mtx" and the
1780 * poll callback will queue them in ep->ovflist.
1781 */
1782 list_add_tail(&epi->rdllink, &ep->rdllist);
1783 ep_pm_stay_awake(epi);
1784 }
1785 }
1786
1787 return 0;
1788}
1789
1790static int ep_send_events(struct eventpoll *ep,
1791 struct epoll_event __user *events, int maxevents)
1792{
1793 struct ep_send_events_data esed;
1794
1795 esed.maxevents = maxevents;
1796 esed.events = events;
1797
1798 ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
1799 return esed.res;
1800}
1801
1802static inline struct timespec64 ep_set_mstimeout(long ms)
1803{
1804 struct timespec64 now, ts = {
1805 .tv_sec = ms / MSEC_PER_SEC,
1806 .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
1807 };
1808
1809 ktime_get_ts64(&now);
1810 return timespec64_add_safe(now, ts);
1811}
1812
1813/**
1814 * ep_poll - Retrieves ready events, and delivers them to the caller supplied
1815 * event buffer.
1816 *
1817 * @ep: Pointer to the eventpoll context.
1818 * @events: Pointer to the userspace buffer where the ready events should be
1819 * stored.
1820 * @maxevents: Size (in terms of number of events) of the caller event buffer.
1821 * @timeout: Maximum timeout for the ready events fetch operation, in
1822 * milliseconds. If the @timeout is zero, the function will not block,
1823 * while if the @timeout is less than zero, the function will block
1824 * until at least one event has been retrieved (or an error
1825 * occurred).
1826 *
1827 * Returns: Returns the number of ready events which have been fetched, or an
1828 * error code, in case of error.
1829 */
1830static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1831 int maxevents, long timeout)
1832{
1833 int res = 0, eavail, timed_out = 0;
1834 u64 slack = 0;
1835 bool waiter = false;
1836 wait_queue_entry_t wait;
1837 ktime_t expires, *to = NULL;
1838
1839 lockdep_assert_irqs_enabled();
1840
1841 if (timeout > 0) {
1842 struct timespec64 end_time = ep_set_mstimeout(timeout);
1843
1844 slack = select_estimate_accuracy(&end_time);
1845 to = &expires;
1846 *to = timespec64_to_ktime(end_time);
1847 } else if (timeout == 0) {
1848 /*
1849 * Avoid the unnecessary trip to the wait queue loop, if the
1850 * caller specified a non blocking operation. We still need
1851 * lock because we could race and not see an epi being added
1852 * to the ready list while in irq callback. Thus incorrectly
1853 * returning 0 back to userspace.
1854 */
1855 timed_out = 1;
1856
1857 write_lock_irq(&ep->lock);
1858 eavail = ep_events_available(ep);
1859 write_unlock_irq(&ep->lock);
1860
1861 goto send_events;
1862 }
1863
1864fetch_events:
1865
1866 if (!ep_events_available(ep))
1867 ep_busy_loop(ep, timed_out);
1868
1869 eavail = ep_events_available(ep);
1870 if (eavail)
1871 goto send_events;
1872
1873 /*
1874 * Busy poll timed out. Drop NAPI ID for now, we can add
1875 * it back in when we have moved a socket with a valid NAPI
1876 * ID onto the ready list.
1877 */
1878 ep_reset_busy_poll_napi_id(ep);
1879
1880 /*
1881 * We don't have any available event to return to the caller. We need
1882 * to sleep here, and we will be woken by ep_poll_callback() when events
1883 * become available.
1884 */
1885 if (!waiter) {
1886 waiter = true;
1887 init_waitqueue_entry(&wait, current);
1888
1889 spin_lock_irq(&ep->wq.lock);
1890 __add_wait_queue_exclusive(&ep->wq, &wait);
1891 spin_unlock_irq(&ep->wq.lock);
1892 }
1893
1894 for (;;) {
1895 /*
1896 * We don't want to sleep if the ep_poll_callback() sends us
1897 * a wakeup in between. That's why we set the task state
1898 * to TASK_INTERRUPTIBLE before doing the checks.
1899 */
1900 set_current_state(TASK_INTERRUPTIBLE);
1901 /*
1902 * Always short-circuit for fatal signals to allow
1903 * threads to make a timely exit without the chance of
1904 * finding more events available and fetching
1905 * repeatedly.
1906 */
1907 if (fatal_signal_pending(current)) {
1908 res = -EINTR;
1909 break;
1910 }
1911
1912 eavail = ep_events_available(ep);
1913 if (eavail)
1914 break;
1915 if (signal_pending(current)) {
1916 res = -EINTR;
1917 break;
1918 }
1919
1920 if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) {
1921 timed_out = 1;
1922 break;
1923 }
1924 }
1925
1926 __set_current_state(TASK_RUNNING);
1927
1928send_events:
1929 /*
1930 * Try to transfer events to user space. In case we get 0 events and
1931 * there's still timeout left over, we go trying again in search of
1932 * more luck.
1933 */
1934 if (!res && eavail &&
1935 !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
1936 goto fetch_events;
1937
1938 if (waiter) {
1939 spin_lock_irq(&ep->wq.lock);
1940 __remove_wait_queue(&ep->wq, &wait);
1941 spin_unlock_irq(&ep->wq.lock);
1942 }
1943
1944 return res;
1945}
1946
1947/**
1948 * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
1949 * API, to verify that adding an epoll file inside another
1950 * epoll structure, does not violate the constraints, in
1951 * terms of closed loops, or too deep chains (which can
1952 * result in excessive stack usage).
1953 *
1954 * @priv: Pointer to the epoll file to be currently checked.
1955 * @cookie: Original cookie for this call. This is the top-of-the-chain epoll
1956 * data structure pointer.
1957 * @call_nests: Current dept of the @ep_call_nested() call stack.
1958 *
1959 * Returns: Returns zero if adding the epoll @file inside current epoll
1960 * structure @ep does not violate the constraints, or -1 otherwise.
1961 */
1962static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
1963{
1964 int error = 0;
1965 struct file *file = priv;
1966 struct eventpoll *ep = file->private_data;
1967 struct eventpoll *ep_tovisit;
1968 struct rb_node *rbp;
1969 struct epitem *epi;
1970
1971 mutex_lock_nested(&ep->mtx, call_nests + 1);
1972 ep->visited = 1;
1973 list_add(&ep->visited_list_link, &visited_list);
1974 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1975 epi = rb_entry(rbp, struct epitem, rbn);
1976 if (unlikely(is_file_epoll(epi->ffd.file))) {
1977 ep_tovisit = epi->ffd.file->private_data;
1978 if (ep_tovisit->visited)
1979 continue;
1980 error = ep_call_nested(&poll_loop_ncalls,
1981 ep_loop_check_proc, epi->ffd.file,
1982 ep_tovisit, current);
1983 if (error != 0)
1984 break;
1985 } else {
1986 /*
1987 * If we've reached a file that is not associated with
1988 * an ep, then we need to check if the newly added
1989 * links are going to add too many wakeup paths. We do
1990 * this by adding it to the tfile_check_list, if it's
1991 * not already there, and calling reverse_path_check()
1992 * during ep_insert().
1993 */
1994 if (list_empty(&epi->ffd.file->f_tfile_llink))
1995 list_add(&epi->ffd.file->f_tfile_llink,
1996 &tfile_check_list);
1997 }
1998 }
1999 mutex_unlock(&ep->mtx);
2000
2001 return error;
2002}
2003
2004/**
2005 * ep_loop_check - Performs a check to verify that adding an epoll file (@file)
2006 * another epoll file (represented by @ep) does not create
2007 * closed loops or too deep chains.
2008 *
2009 * @ep: Pointer to the epoll private data structure.
2010 * @file: Pointer to the epoll file to be checked.
2011 *
2012 * Returns: Returns zero if adding the epoll @file inside current epoll
2013 * structure @ep does not violate the constraints, or -1 otherwise.
2014 */
2015static int ep_loop_check(struct eventpoll *ep, struct file *file)
2016{
2017 int ret;
2018 struct eventpoll *ep_cur, *ep_next;
2019
2020 ret = ep_call_nested(&poll_loop_ncalls,
2021 ep_loop_check_proc, file, ep, current);
2022 /* clear visited list */
2023 list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
2024 visited_list_link) {
2025 ep_cur->visited = 0;
2026 list_del(&ep_cur->visited_list_link);
2027 }
2028 return ret;
2029}
2030
2031static void clear_tfile_check_list(void)
2032{
2033 struct file *file;
2034
2035 /* first clear the tfile_check_list */
2036 while (!list_empty(&tfile_check_list)) {
2037 file = list_first_entry(&tfile_check_list, struct file,
2038 f_tfile_llink);
2039 list_del_init(&file->f_tfile_llink);
2040 }
2041 INIT_LIST_HEAD(&tfile_check_list);
2042}
2043
2044/*
2045 * Open an eventpoll file descriptor.
2046 */
2047static int do_epoll_create(int flags)
2048{
2049 int error, fd;
2050 struct eventpoll *ep = NULL;
2051 struct file *file;
2052
2053 /* Check the EPOLL_* constant for consistency. */
2054 BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
2055
2056 if (flags & ~EPOLL_CLOEXEC)
2057 return -EINVAL;
2058 /*
2059 * Create the internal data structure ("struct eventpoll").
2060 */
2061 error = ep_alloc(&ep);
2062 if (error < 0)
2063 return error;
2064 /*
2065 * Creates all the items needed to setup an eventpoll file. That is,
2066 * a file structure and a free file descriptor.
2067 */
2068 fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
2069 if (fd < 0) {
2070 error = fd;
2071 goto out_free_ep;
2072 }
2073 file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
2074 O_RDWR | (flags & O_CLOEXEC));
2075 if (IS_ERR(file)) {
2076 error = PTR_ERR(file);
2077 goto out_free_fd;
2078 }
2079 ep->file = file;
2080 fd_install(fd, file);
2081 return fd;
2082
2083out_free_fd:
2084 put_unused_fd(fd);
2085out_free_ep:
2086 ep_free(ep);
2087 return error;
2088}
2089
2090SYSCALL_DEFINE1(epoll_create1, int, flags)
2091{
2092 return do_epoll_create(flags);
2093}
2094
2095SYSCALL_DEFINE1(epoll_create, int, size)
2096{
2097 if (size <= 0)
2098 return -EINVAL;
2099
2100 return do_epoll_create(0);
2101}
2102
2103/*
2104 * The following function implements the controller interface for
2105 * the eventpoll file that enables the insertion/removal/change of
2106 * file descriptors inside the interest set.
2107 */
2108SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
2109 struct epoll_event __user *, event)
2110{
2111 int error;
2112 int full_check = 0;
2113 struct fd f, tf;
2114 struct eventpoll *ep;
2115 struct epitem *epi;
2116 struct epoll_event epds;
2117 struct eventpoll *tep = NULL;
2118
2119 error = -EFAULT;
2120 if (ep_op_has_event(op) &&
2121 copy_from_user(&epds, event, sizeof(struct epoll_event)))
2122 goto error_return;
2123
2124 error = -EBADF;
2125 f = fdget(epfd);
2126 if (!f.file)
2127 goto error_return;
2128
2129 /* Get the "struct file *" for the target file */
2130 tf = fdget(fd);
2131 if (!tf.file)
2132 goto error_fput;
2133
2134 /* The target file descriptor must support poll */
2135 error = -EPERM;
2136 if (!file_can_poll(tf.file))
2137 goto error_tgt_fput;
2138
2139 /* Check if EPOLLWAKEUP is allowed */
2140 if (ep_op_has_event(op))
2141 ep_take_care_of_epollwakeup(&epds);
2142
2143 /*
2144 * We have to check that the file structure underneath the file descriptor
2145 * the user passed to us _is_ an eventpoll file. And also we do not permit
2146 * adding an epoll file descriptor inside itself.
2147 */
2148 error = -EINVAL;
2149 if (f.file == tf.file || !is_file_epoll(f.file))
2150 goto error_tgt_fput;
2151
2152 /*
2153 * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only,
2154 * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
2155 * Also, we do not currently supported nested exclusive wakeups.
2156 */
2157 if (ep_op_has_event(op) && (epds.events & EPOLLEXCLUSIVE)) {
2158 if (op == EPOLL_CTL_MOD)
2159 goto error_tgt_fput;
2160 if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
2161 (epds.events & ~EPOLLEXCLUSIVE_OK_BITS)))
2162 goto error_tgt_fput;
2163 }
2164
2165 /*
2166 * At this point it is safe to assume that the "private_data" contains
2167 * our own data structure.
2168 */
2169 ep = f.file->private_data;
2170
2171 /*
2172 * When we insert an epoll file descriptor, inside another epoll file
2173 * descriptor, there is the change of creating closed loops, which are
2174 * better be handled here, than in more critical paths. While we are
2175 * checking for loops we also determine the list of files reachable
2176 * and hang them on the tfile_check_list, so we can check that we
2177 * haven't created too many possible wakeup paths.
2178 *
2179 * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
2180 * the epoll file descriptor is attaching directly to a wakeup source,
2181 * unless the epoll file descriptor is nested. The purpose of taking the
2182 * 'epmutex' on add is to prevent complex toplogies such as loops and
2183 * deep wakeup paths from forming in parallel through multiple
2184 * EPOLL_CTL_ADD operations.
2185 */
2186 mutex_lock_nested(&ep->mtx, 0);
2187 if (op == EPOLL_CTL_ADD) {
2188 if (!list_empty(&f.file->f_ep_links) ||
2189 is_file_epoll(tf.file)) {
2190 full_check = 1;
2191 mutex_unlock(&ep->mtx);
2192 mutex_lock(&epmutex);
2193 if (is_file_epoll(tf.file)) {
2194 error = -ELOOP;
2195 if (ep_loop_check(ep, tf.file) != 0) {
2196 clear_tfile_check_list();
2197 goto error_tgt_fput;
2198 }
2199 } else
2200 list_add(&tf.file->f_tfile_llink,
2201 &tfile_check_list);
2202 mutex_lock_nested(&ep->mtx, 0);
2203 if (is_file_epoll(tf.file)) {
2204 tep = tf.file->private_data;
2205 mutex_lock_nested(&tep->mtx, 1);
2206 }
2207 }
2208 }
2209
2210 /*
2211 * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
2212 * above, we can be sure to be able to use the item looked up by
2213 * ep_find() till we release the mutex.
2214 */
2215 epi = ep_find(ep, tf.file, fd);
2216
2217 error = -EINVAL;
2218 switch (op) {
2219 case EPOLL_CTL_ADD:
2220 if (!epi) {
2221 epds.events |= EPOLLERR | EPOLLHUP;
2222 error = ep_insert(ep, &epds, tf.file, fd, full_check);
2223 } else
2224 error = -EEXIST;
2225 if (full_check)
2226 clear_tfile_check_list();
2227 break;
2228 case EPOLL_CTL_DEL:
2229 if (epi)
2230 error = ep_remove(ep, epi);
2231 else
2232 error = -ENOENT;
2233 break;
2234 case EPOLL_CTL_MOD:
2235 if (epi) {
2236 if (!(epi->event.events & EPOLLEXCLUSIVE)) {
2237 epds.events |= EPOLLERR | EPOLLHUP;
2238 error = ep_modify(ep, epi, &epds);
2239 }
2240 } else
2241 error = -ENOENT;
2242 break;
2243 }
2244 if (tep != NULL)
2245 mutex_unlock(&tep->mtx);
2246 mutex_unlock(&ep->mtx);
2247
2248error_tgt_fput:
2249 if (full_check)
2250 mutex_unlock(&epmutex);
2251
2252 fdput(tf);
2253error_fput:
2254 fdput(f);
2255error_return:
2256
2257 return error;
2258}
2259
2260/*
2261 * Implement the event wait interface for the eventpoll file. It is the kernel
2262 * part of the user space epoll_wait(2).
2263 */
2264static int do_epoll_wait(int epfd, struct epoll_event __user *events,
2265 int maxevents, int timeout)
2266{
2267 int error;
2268 struct fd f;
2269 struct eventpoll *ep;
2270
2271 /* The maximum number of event must be greater than zero */
2272 if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
2273 return -EINVAL;
2274
2275 /* Verify that the area passed by the user is writeable */
2276 if (!access_ok(events, maxevents * sizeof(struct epoll_event)))
2277 return -EFAULT;
2278
2279 /* Get the "struct file *" for the eventpoll file */
2280 f = fdget(epfd);
2281 if (!f.file)
2282 return -EBADF;
2283
2284 /*
2285 * We have to check that the file structure underneath the fd
2286 * the user passed to us _is_ an eventpoll file.
2287 */
2288 error = -EINVAL;
2289 if (!is_file_epoll(f.file))
2290 goto error_fput;
2291
2292 /*
2293 * At this point it is safe to assume that the "private_data" contains
2294 * our own data structure.
2295 */
2296 ep = f.file->private_data;
2297
2298 /* Time to fish for events ... */
2299 error = ep_poll(ep, events, maxevents, timeout);
2300
2301error_fput:
2302 fdput(f);
2303 return error;
2304}
2305
2306SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
2307 int, maxevents, int, timeout)
2308{
2309 return do_epoll_wait(epfd, events, maxevents, timeout);
2310}
2311
2312/*
2313 * Implement the event wait interface for the eventpoll file. It is the kernel
2314 * part of the user space epoll_pwait(2).
2315 */
2316SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
2317 int, maxevents, int, timeout, const sigset_t __user *, sigmask,
2318 size_t, sigsetsize)
2319{
2320 int error;
2321 sigset_t ksigmask, sigsaved;
2322
2323 /*
2324 * If the caller wants a certain signal mask to be set during the wait,
2325 * we apply it here.
2326 */
2327 error = set_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
2328 if (error)
2329 return error;
2330
2331 error = do_epoll_wait(epfd, events, maxevents, timeout);
2332
2333 restore_user_sigmask(sigmask, &sigsaved);
2334
2335 return error;
2336}
2337
2338#ifdef CONFIG_COMPAT
2339COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
2340 struct epoll_event __user *, events,
2341 int, maxevents, int, timeout,
2342 const compat_sigset_t __user *, sigmask,
2343 compat_size_t, sigsetsize)
2344{
2345 long err;
2346 sigset_t ksigmask, sigsaved;
2347
2348 /*
2349 * If the caller wants a certain signal mask to be set during the wait,
2350 * we apply it here.
2351 */
2352 err = set_compat_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
2353 if (err)
2354 return err;
2355
2356 err = do_epoll_wait(epfd, events, maxevents, timeout);
2357
2358 restore_user_sigmask(sigmask, &sigsaved);
2359
2360 return err;
2361}
2362#endif
2363
2364static int __init eventpoll_init(void)
2365{
2366 struct sysinfo si;
2367
2368 si_meminfo(&si);
2369 /*
2370 * Allows top 4% of lomem to be allocated for epoll watches (per user).
2371 */
2372 max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2373 EP_ITEM_COST;
2374 BUG_ON(max_user_watches < 0);
2375
2376 /*
2377 * Initialize the structure used to perform epoll file descriptor
2378 * inclusion loops checks.
2379 */
2380 ep_nested_calls_init(&poll_loop_ncalls);
2381
2382#ifdef CONFIG_DEBUG_LOCK_ALLOC
2383 /* Initialize the structure used to perform safe poll wait head wake ups */
2384 ep_nested_calls_init(&poll_safewake_ncalls);
2385#endif
2386
2387 /*
2388 * We can have many thousands of epitems, so prevent this from
2389 * using an extra cache line on 64-bit (and smaller) CPUs
2390 */
2391 BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
2392
2393 /* Allocates slab cache used to allocate "struct epitem" items */
2394 epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
2395 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
2396
2397 /* Allocates slab cache used to allocate "struct eppoll_entry" */
2398 pwq_cache = kmem_cache_create("eventpoll_pwq",
2399 sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
2400
2401 return 0;
2402}
2403fs_initcall(eventpoll_init);
2404