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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.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 <asm/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
46 /*
47 * LOCKING:
48 * There are three level of locking required by epoll :
49 *
50 * 1) epmutex (mutex)
51 * 2) ep->mtx (mutex)
52 * 3) ep->lock (spinlock)
53 *
54 * The acquire order is the one listed above, from 1 to 3.
55 * We need a spinlock (ep->lock) because we manipulate objects
56 * from inside the poll callback, that might be triggered from
57 * a wake_up() that in turn might be called from IRQ context.
58 * So we can't sleep inside the poll callback and hence we need
59 * a spinlock. During the event transfer loop (from kernel to
60 * user space) we could end up sleeping due a copy_to_user(), so
61 * we need a lock that will allow us to sleep. This lock is a
62 * mutex (ep->mtx). It is acquired during the event transfer loop,
63 * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
64 * Then we also need a global mutex to serialize eventpoll_release_file()
65 * and ep_free().
66 * This mutex is acquired by ep_free() during the epoll file
67 * cleanup path and it is also acquired by eventpoll_release_file()
68 * if a file has been pushed inside an epoll set and it is then
69 * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
70 * It is also acquired when inserting an epoll fd onto another epoll
71 * fd. We do this so that we walk the epoll tree and ensure that this
72 * insertion does not create a cycle of epoll file descriptors, which
73 * could lead to deadlock. We need a global mutex to prevent two
74 * simultaneous inserts (A into B and B into A) from racing and
75 * constructing a cycle without either insert observing that it is
76 * going to.
77 * It is necessary to acquire multiple "ep->mtx"es at once in the
78 * case when one epoll fd is added to another. In this case, we
79 * always acquire the locks in the order of nesting (i.e. after
80 * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
81 * before e2->mtx). Since we disallow cycles of epoll file
82 * descriptors, this ensures that the mutexes are well-ordered. In
83 * order to communicate this nesting to lockdep, when walking a tree
84 * of epoll file descriptors, we use the current recursion depth as
85 * the lockdep subkey.
86 * It is possible to drop the "ep->mtx" and to use the global
87 * mutex "epmutex" (together with "ep->lock") to have it working,
88 * but having "ep->mtx" will make the interface more scalable.
89 * Events that require holding "epmutex" are very rare, while for
90 * normal operations the epoll private "ep->mtx" will guarantee
91 * a better scalability.
92 */
93
94 /* Epoll private bits inside the event mask */
95 #define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE)
96
97 #define EPOLLINOUT_BITS (POLLIN | POLLOUT)
98
99 #define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | POLLERR | POLLHUP | \
100 EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE)
101
102 /* Maximum number of nesting allowed inside epoll sets */
103 #define EP_MAX_NESTS 4
104
105 #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
106
107 #define EP_UNACTIVE_PTR ((void *) -1L)
108
109 #define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
110
111 struct epoll_filefd {
112 struct file *file;
113 int fd;
114 } __packed;
115
116 /*
117 * Structure used to track possible nested calls, for too deep recursions
118 * and loop cycles.
119 */
120 struct nested_call_node {
121 struct list_head llink;
122 void *cookie;
123 void *ctx;
124 };
125
126 /*
127 * This structure is used as collector for nested calls, to check for
128 * maximum recursion dept and loop cycles.
129 */
130 struct nested_calls {
131 struct list_head tasks_call_list;
132 spinlock_t lock;
133 };
134
135 /*
136 * Each file descriptor added to the eventpoll interface will
137 * have an entry of this type linked to the "rbr" RB tree.
138 * Avoid increasing the size of this struct, there can be many thousands
139 * of these on a server and we do not want this to take another cache line.
140 */
141 struct epitem {
142 union {
143 /* RB tree node links this structure to the eventpoll RB tree */
144 struct rb_node rbn;
145 /* Used to free the struct epitem */
146 struct rcu_head rcu;
147 };
148
149 /* List header used to link this structure to the eventpoll ready list */
150 struct list_head rdllink;
151
152 /*
153 * Works together "struct eventpoll"->ovflist in keeping the
154 * single linked chain of items.
155 */
156 struct epitem *next;
157
158 /* The file descriptor information this item refers to */
159 struct epoll_filefd ffd;
160
161 /* Number of active wait queue attached to poll operations */
162 int nwait;
163
164 /* List containing poll wait queues */
165 struct list_head pwqlist;
166
167 /* The "container" of this item */
168 struct eventpoll *ep;
169
170 /* List header used to link this item to the "struct file" items list */
171 struct list_head fllink;
172
173 /* wakeup_source used when EPOLLWAKEUP is set */
174 struct wakeup_source __rcu *ws;
175
176 /* The structure that describe the interested events and the source fd */
177 struct epoll_event event;
178 };
179
180 /*
181 * This structure is stored inside the "private_data" member of the file
182 * structure and represents the main data structure for the eventpoll
183 * interface.
184 */
185 struct eventpoll {
186 /* Protect the access to this structure */
187 spinlock_t lock;
188
189 /*
190 * This mutex is used to ensure that files are not removed
191 * while epoll is using them. This is held during the event
192 * collection loop, the file cleanup path, the epoll file exit
193 * code and the ctl operations.
194 */
195 struct mutex mtx;
196
197 /* Wait queue used by sys_epoll_wait() */
198 wait_queue_head_t wq;
199
200 /* Wait queue used by file->poll() */
201 wait_queue_head_t poll_wait;
202
203 /* List of ready file descriptors */
204 struct list_head rdllist;
205
206 /* RB tree root used to store monitored fd structs */
207 struct rb_root rbr;
208
209 /*
210 * This is a single linked list that chains all the "struct epitem" that
211 * happened while transferring ready events to userspace w/out
212 * holding ->lock.
213 */
214 struct epitem *ovflist;
215
216 /* wakeup_source used when ep_scan_ready_list is running */
217 struct wakeup_source *ws;
218
219 /* The user that created the eventpoll descriptor */
220 struct user_struct *user;
221
222 struct file *file;
223
224 /* used to optimize loop detection check */
225 int visited;
226 struct list_head visited_list_link;
227 };
228
229 /* Wait structure used by the poll hooks */
230 struct eppoll_entry {
231 /* List header used to link this structure to the "struct epitem" */
232 struct list_head llink;
233
234 /* The "base" pointer is set to the container "struct epitem" */
235 struct epitem *base;
236
237 /*
238 * Wait queue item that will be linked to the target file wait
239 * queue head.
240 */
241 wait_queue_t wait;
242
243 /* The wait queue head that linked the "wait" wait queue item */
244 wait_queue_head_t *whead;
245 };
246
247 /* Wrapper struct used by poll queueing */
248 struct ep_pqueue {
249 poll_table pt;
250 struct epitem *epi;
251 };
252
253 /* Used by the ep_send_events() function as callback private data */
254 struct ep_send_events_data {
255 int maxevents;
256 struct epoll_event __user *events;
257 };
258
259 /*
260 * Configuration options available inside /proc/sys/fs/epoll/
261 */
262 /* Maximum number of epoll watched descriptors, per user */
263 static long max_user_watches __read_mostly;
264
265 /*
266 * This mutex is used to serialize ep_free() and eventpoll_release_file().
267 */
268 static DEFINE_MUTEX(epmutex);
269
270 /* Used to check for epoll file descriptor inclusion loops */
271 static struct nested_calls poll_loop_ncalls;
272
273 /* Used for safe wake up implementation */
274 static struct nested_calls poll_safewake_ncalls;
275
276 /* Used to call file's f_op->poll() under the nested calls boundaries */
277 static struct nested_calls poll_readywalk_ncalls;
278
279 /* Slab cache used to allocate "struct epitem" */
280 static struct kmem_cache *epi_cache __read_mostly;
281
282 /* Slab cache used to allocate "struct eppoll_entry" */
283 static struct kmem_cache *pwq_cache __read_mostly;
284
285 /* Visited nodes during ep_loop_check(), so we can unset them when we finish */
286 static LIST_HEAD(visited_list);
287
288 /*
289 * List of files with newly added links, where we may need to limit the number
290 * of emanating paths. Protected by the epmutex.
291 */
292 static LIST_HEAD(tfile_check_list);
293
294 #ifdef CONFIG_SYSCTL
295
296 #include <linux/sysctl.h>
297
298 static long zero;
299 static long long_max = LONG_MAX;
300
301 struct ctl_table epoll_table[] = {
302 {
303 .procname = "max_user_watches",
304 .data = &max_user_watches,
305 .maxlen = sizeof(max_user_watches),
306 .mode = 0644,
307 .proc_handler = proc_doulongvec_minmax,
308 .extra1 = &zero,
309 .extra2 = &long_max,
310 },
311 { }
312 };
313 #endif /* CONFIG_SYSCTL */
314
315 static const struct file_operations eventpoll_fops;
316
317 static inline int is_file_epoll(struct file *f)
318 {
319 return f->f_op == &eventpoll_fops;
320 }
321
322 /* Setup the structure that is used as key for the RB tree */
323 static inline void ep_set_ffd(struct epoll_filefd *ffd,
324 struct file *file, int fd)
325 {
326 ffd->file = file;
327 ffd->fd = fd;
328 }
329
330 /* Compare RB tree keys */
331 static inline int ep_cmp_ffd(struct epoll_filefd *p1,
332 struct epoll_filefd *p2)
333 {
334 return (p1->file > p2->file ? +1:
335 (p1->file < p2->file ? -1 : p1->fd - p2->fd));
336 }
337
338 /* Tells us if the item is currently linked */
339 static inline int ep_is_linked(struct list_head *p)
340 {
341 return !list_empty(p);
342 }
343
344 static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_t *p)
345 {
346 return container_of(p, struct eppoll_entry, wait);
347 }
348
349 /* Get the "struct epitem" from a wait queue pointer */
350 static inline struct epitem *ep_item_from_wait(wait_queue_t *p)
351 {
352 return container_of(p, struct eppoll_entry, wait)->base;
353 }
354
355 /* Get the "struct epitem" from an epoll queue wrapper */
356 static inline struct epitem *ep_item_from_epqueue(poll_table *p)
357 {
358 return container_of(p, struct ep_pqueue, pt)->epi;
359 }
360
361 /* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
362 static inline int ep_op_has_event(int op)
363 {
364 return op != EPOLL_CTL_DEL;
365 }
366
367 /* Initialize the poll safe wake up structure */
368 static void ep_nested_calls_init(struct nested_calls *ncalls)
369 {
370 INIT_LIST_HEAD(&ncalls->tasks_call_list);
371 spin_lock_init(&ncalls->lock);
372 }
373
374 /**
375 * ep_events_available - Checks if ready events might be available.
376 *
377 * @ep: Pointer to the eventpoll context.
378 *
379 * Returns: Returns a value different than zero if ready events are available,
380 * or zero otherwise.
381 */
382 static inline int ep_events_available(struct eventpoll *ep)
383 {
384 return !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
385 }
386
387 /**
388 * ep_call_nested - Perform a bound (possibly) nested call, by checking
389 * that the recursion limit is not exceeded, and that
390 * the same nested call (by the meaning of same cookie) is
391 * no re-entered.
392 *
393 * @ncalls: Pointer to the nested_calls structure to be used for this call.
394 * @max_nests: Maximum number of allowed nesting calls.
395 * @nproc: Nested call core function pointer.
396 * @priv: Opaque data to be passed to the @nproc callback.
397 * @cookie: Cookie to be used to identify this nested call.
398 * @ctx: This instance context.
399 *
400 * Returns: Returns the code returned by the @nproc callback, or -1 if
401 * the maximum recursion limit has been exceeded.
402 */
403 static int ep_call_nested(struct nested_calls *ncalls, int max_nests,
404 int (*nproc)(void *, void *, int), void *priv,
405 void *cookie, void *ctx)
406 {
407 int error, call_nests = 0;
408 unsigned long flags;
409 struct list_head *lsthead = &ncalls->tasks_call_list;
410 struct nested_call_node *tncur;
411 struct nested_call_node tnode;
412
413 spin_lock_irqsave(&ncalls->lock, flags);
414
415 /*
416 * Try to see if the current task is already inside this wakeup call.
417 * We use a list here, since the population inside this set is always
418 * very much limited.
419 */
420 list_for_each_entry(tncur, lsthead, llink) {
421 if (tncur->ctx == ctx &&
422 (tncur->cookie == cookie || ++call_nests > max_nests)) {
423 /*
424 * Ops ... loop detected or maximum nest level reached.
425 * We abort this wake by breaking the cycle itself.
426 */
427 error = -1;
428 goto out_unlock;
429 }
430 }
431
432 /* Add the current task and cookie to the list */
433 tnode.ctx = ctx;
434 tnode.cookie = cookie;
435 list_add(&tnode.llink, lsthead);
436
437 spin_unlock_irqrestore(&ncalls->lock, flags);
438
439 /* Call the nested function */
440 error = (*nproc)(priv, cookie, call_nests);
441
442 /* Remove the current task from the list */
443 spin_lock_irqsave(&ncalls->lock, flags);
444 list_del(&tnode.llink);
445 out_unlock:
446 spin_unlock_irqrestore(&ncalls->lock, flags);
447
448 return error;
449 }
450
451 /*
452 * As described in commit 0ccf831cb lockdep: annotate epoll
453 * the use of wait queues used by epoll is done in a very controlled
454 * manner. Wake ups can nest inside each other, but are never done
455 * with the same locking. For example:
456 *
457 * dfd = socket(...);
458 * efd1 = epoll_create();
459 * efd2 = epoll_create();
460 * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
461 * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
462 *
463 * When a packet arrives to the device underneath "dfd", the net code will
464 * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
465 * callback wakeup entry on that queue, and the wake_up() performed by the
466 * "dfd" net code will end up in ep_poll_callback(). At this point epoll
467 * (efd1) notices that it may have some event ready, so it needs to wake up
468 * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
469 * that ends up in another wake_up(), after having checked about the
470 * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
471 * avoid stack blasting.
472 *
473 * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
474 * this special case of epoll.
475 */
476 #ifdef CONFIG_DEBUG_LOCK_ALLOC
477 static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
478 unsigned long events, int subclass)
479 {
480 unsigned long flags;
481
482 spin_lock_irqsave_nested(&wqueue->lock, flags, subclass);
483 wake_up_locked_poll(wqueue, events);
484 spin_unlock_irqrestore(&wqueue->lock, flags);
485 }
486 #else
487 static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
488 unsigned long events, int subclass)
489 {
490 wake_up_poll(wqueue, events);
491 }
492 #endif
493
494 static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
495 {
496 ep_wake_up_nested((wait_queue_head_t *) cookie, POLLIN,
497 1 + call_nests);
498 return 0;
499 }
500
501 /*
502 * Perform a safe wake up of the poll wait list. The problem is that
503 * with the new callback'd wake up system, it is possible that the
504 * poll callback is reentered from inside the call to wake_up() done
505 * on the poll wait queue head. The rule is that we cannot reenter the
506 * wake up code from the same task more than EP_MAX_NESTS times,
507 * and we cannot reenter the same wait queue head at all. This will
508 * enable to have a hierarchy of epoll file descriptor of no more than
509 * EP_MAX_NESTS deep.
510 */
511 static void ep_poll_safewake(wait_queue_head_t *wq)
512 {
513 int this_cpu = get_cpu();
514
515 ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS,
516 ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
517
518 put_cpu();
519 }
520
521 static void ep_remove_wait_queue(struct eppoll_entry *pwq)
522 {
523 wait_queue_head_t *whead;
524
525 rcu_read_lock();
526 /* If it is cleared by POLLFREE, it should be rcu-safe */
527 whead = rcu_dereference(pwq->whead);
528 if (whead)
529 remove_wait_queue(whead, &pwq->wait);
530 rcu_read_unlock();
531 }
532
533 /*
534 * This function unregisters poll callbacks from the associated file
535 * descriptor. Must be called with "mtx" held (or "epmutex" if called from
536 * ep_free).
537 */
538 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
539 {
540 struct list_head *lsthead = &epi->pwqlist;
541 struct eppoll_entry *pwq;
542
543 while (!list_empty(lsthead)) {
544 pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
545
546 list_del(&pwq->llink);
547 ep_remove_wait_queue(pwq);
548 kmem_cache_free(pwq_cache, pwq);
549 }
550 }
551
552 /* call only when ep->mtx is held */
553 static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
554 {
555 return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
556 }
557
558 /* call only when ep->mtx is held */
559 static inline void ep_pm_stay_awake(struct epitem *epi)
560 {
561 struct wakeup_source *ws = ep_wakeup_source(epi);
562
563 if (ws)
564 __pm_stay_awake(ws);
565 }
566
567 static inline bool ep_has_wakeup_source(struct epitem *epi)
568 {
569 return rcu_access_pointer(epi->ws) ? true : false;
570 }
571
572 /* call when ep->mtx cannot be held (ep_poll_callback) */
573 static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
574 {
575 struct wakeup_source *ws;
576
577 rcu_read_lock();
578 ws = rcu_dereference(epi->ws);
579 if (ws)
580 __pm_stay_awake(ws);
581 rcu_read_unlock();
582 }
583
584 /**
585 * ep_scan_ready_list - Scans the ready list in a way that makes possible for
586 * the scan code, to call f_op->poll(). Also allows for
587 * O(NumReady) performance.
588 *
589 * @ep: Pointer to the epoll private data structure.
590 * @sproc: Pointer to the scan callback.
591 * @priv: Private opaque data passed to the @sproc callback.
592 * @depth: The current depth of recursive f_op->poll calls.
593 * @ep_locked: caller already holds ep->mtx
594 *
595 * Returns: The same integer error code returned by the @sproc callback.
596 */
597 static int ep_scan_ready_list(struct eventpoll *ep,
598 int (*sproc)(struct eventpoll *,
599 struct list_head *, void *),
600 void *priv, int depth, bool ep_locked)
601 {
602 int error, pwake = 0;
603 unsigned long flags;
604 struct epitem *epi, *nepi;
605 LIST_HEAD(txlist);
606
607 /*
608 * We need to lock this because we could be hit by
609 * eventpoll_release_file() and epoll_ctl().
610 */
611
612 if (!ep_locked)
613 mutex_lock_nested(&ep->mtx, depth);
614
615 /*
616 * Steal the ready list, and re-init the original one to the
617 * empty list. Also, set ep->ovflist to NULL so that events
618 * happening while looping w/out locks, are not lost. We cannot
619 * have the poll callback to queue directly on ep->rdllist,
620 * because we want the "sproc" callback to be able to do it
621 * in a lockless way.
622 */
623 spin_lock_irqsave(&ep->lock, flags);
624 list_splice_init(&ep->rdllist, &txlist);
625 ep->ovflist = NULL;
626 spin_unlock_irqrestore(&ep->lock, flags);
627
628 /*
629 * Now call the callback function.
630 */
631 error = (*sproc)(ep, &txlist, priv);
632
633 spin_lock_irqsave(&ep->lock, flags);
634 /*
635 * During the time we spent inside the "sproc" callback, some
636 * other events might have been queued by the poll callback.
637 * We re-insert them inside the main ready-list here.
638 */
639 for (nepi = ep->ovflist; (epi = nepi) != NULL;
640 nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
641 /*
642 * We need to check if the item is already in the list.
643 * During the "sproc" callback execution time, items are
644 * queued into ->ovflist but the "txlist" might already
645 * contain them, and the list_splice() below takes care of them.
646 */
647 if (!ep_is_linked(&epi->rdllink)) {
648 list_add_tail(&epi->rdllink, &ep->rdllist);
649 ep_pm_stay_awake(epi);
650 }
651 }
652 /*
653 * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
654 * releasing the lock, events will be queued in the normal way inside
655 * ep->rdllist.
656 */
657 ep->ovflist = EP_UNACTIVE_PTR;
658
659 /*
660 * Quickly re-inject items left on "txlist".
661 */
662 list_splice(&txlist, &ep->rdllist);
663 __pm_relax(ep->ws);
664
665 if (!list_empty(&ep->rdllist)) {
666 /*
667 * Wake up (if active) both the eventpoll wait list and
668 * the ->poll() wait list (delayed after we release the lock).
669 */
670 if (waitqueue_active(&ep->wq))
671 wake_up_locked(&ep->wq);
672 if (waitqueue_active(&ep->poll_wait))
673 pwake++;
674 }
675 spin_unlock_irqrestore(&ep->lock, flags);
676
677 if (!ep_locked)
678 mutex_unlock(&ep->mtx);
679
680 /* We have to call this outside the lock */
681 if (pwake)
682 ep_poll_safewake(&ep->poll_wait);
683
684 return error;
685 }
686
687 static void epi_rcu_free(struct rcu_head *head)
688 {
689 struct epitem *epi = container_of(head, struct epitem, rcu);
690 kmem_cache_free(epi_cache, epi);
691 }
692
693 /*
694 * Removes a "struct epitem" from the eventpoll RB tree and deallocates
695 * all the associated resources. Must be called with "mtx" held.
696 */
697 static int ep_remove(struct eventpoll *ep, struct epitem *epi)
698 {
699 unsigned long flags;
700 struct file *file = epi->ffd.file;
701
702 /*
703 * Removes poll wait queue hooks. We _have_ to do this without holding
704 * the "ep->lock" otherwise a deadlock might occur. This because of the
705 * sequence of the lock acquisition. Here we do "ep->lock" then the wait
706 * queue head lock when unregistering the wait queue. The wakeup callback
707 * will run by holding the wait queue head lock and will call our callback
708 * that will try to get "ep->lock".
709 */
710 ep_unregister_pollwait(ep, epi);
711
712 /* Remove the current item from the list of epoll hooks */
713 spin_lock(&file->f_lock);
714 list_del_rcu(&epi->fllink);
715 spin_unlock(&file->f_lock);
716
717 rb_erase(&epi->rbn, &ep->rbr);
718
719 spin_lock_irqsave(&ep->lock, flags);
720 if (ep_is_linked(&epi->rdllink))
721 list_del_init(&epi->rdllink);
722 spin_unlock_irqrestore(&ep->lock, flags);
723
724 wakeup_source_unregister(ep_wakeup_source(epi));
725 /*
726 * At this point it is safe to free the eventpoll item. Use the union
727 * field epi->rcu, since we are trying to minimize the size of
728 * 'struct epitem'. The 'rbn' field is no longer in use. Protected by
729 * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
730 * use of the rbn field.
731 */
732 call_rcu(&epi->rcu, epi_rcu_free);
733
734 atomic_long_dec(&ep->user->epoll_watches);
735
736 return 0;
737 }
738
739 static void ep_free(struct eventpoll *ep)
740 {
741 struct rb_node *rbp;
742 struct epitem *epi;
743
744 /* We need to release all tasks waiting for these file */
745 if (waitqueue_active(&ep->poll_wait))
746 ep_poll_safewake(&ep->poll_wait);
747
748 /*
749 * We need to lock this because we could be hit by
750 * eventpoll_release_file() while we're freeing the "struct eventpoll".
751 * We do not need to hold "ep->mtx" here because the epoll file
752 * is on the way to be removed and no one has references to it
753 * anymore. The only hit might come from eventpoll_release_file() but
754 * holding "epmutex" is sufficient here.
755 */
756 mutex_lock(&epmutex);
757
758 /*
759 * Walks through the whole tree by unregistering poll callbacks.
760 */
761 for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
762 epi = rb_entry(rbp, struct epitem, rbn);
763
764 ep_unregister_pollwait(ep, epi);
765 cond_resched();
766 }
767
768 /*
769 * Walks through the whole tree by freeing each "struct epitem". At this
770 * point we are sure no poll callbacks will be lingering around, and also by
771 * holding "epmutex" we can be sure that no file cleanup code will hit
772 * us during this operation. So we can avoid the lock on "ep->lock".
773 * We do not need to lock ep->mtx, either, we only do it to prevent
774 * a lockdep warning.
775 */
776 mutex_lock(&ep->mtx);
777 while ((rbp = rb_first(&ep->rbr)) != NULL) {
778 epi = rb_entry(rbp, struct epitem, rbn);
779 ep_remove(ep, epi);
780 cond_resched();
781 }
782 mutex_unlock(&ep->mtx);
783
784 mutex_unlock(&epmutex);
785 mutex_destroy(&ep->mtx);
786 free_uid(ep->user);
787 wakeup_source_unregister(ep->ws);
788 kfree(ep);
789 }
790
791 static int ep_eventpoll_release(struct inode *inode, struct file *file)
792 {
793 struct eventpoll *ep = file->private_data;
794
795 if (ep)
796 ep_free(ep);
797
798 return 0;
799 }
800
801 static inline unsigned int ep_item_poll(struct epitem *epi, poll_table *pt)
802 {
803 pt->_key = epi->event.events;
804
805 return epi->ffd.file->f_op->poll(epi->ffd.file, pt) & epi->event.events;
806 }
807
808 static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
809 void *priv)
810 {
811 struct epitem *epi, *tmp;
812 poll_table pt;
813
814 init_poll_funcptr(&pt, NULL);
815
816 list_for_each_entry_safe(epi, tmp, head, rdllink) {
817 if (ep_item_poll(epi, &pt))
818 return POLLIN | POLLRDNORM;
819 else {
820 /*
821 * Item has been dropped into the ready list by the poll
822 * callback, but it's not actually ready, as far as
823 * caller requested events goes. We can remove it here.
824 */
825 __pm_relax(ep_wakeup_source(epi));
826 list_del_init(&epi->rdllink);
827 }
828 }
829
830 return 0;
831 }
832
833 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
834 poll_table *pt);
835
836 struct readyevents_arg {
837 struct eventpoll *ep;
838 bool locked;
839 };
840
841 static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
842 {
843 struct readyevents_arg *arg = priv;
844
845 return ep_scan_ready_list(arg->ep, ep_read_events_proc, NULL,
846 call_nests + 1, arg->locked);
847 }
848
849 static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
850 {
851 int pollflags;
852 struct eventpoll *ep = file->private_data;
853 struct readyevents_arg arg;
854
855 /*
856 * During ep_insert() we already hold the ep->mtx for the tfile.
857 * Prevent re-aquisition.
858 */
859 arg.locked = wait && (wait->_qproc == ep_ptable_queue_proc);
860 arg.ep = ep;
861
862 /* Insert inside our poll wait queue */
863 poll_wait(file, &ep->poll_wait, wait);
864
865 /*
866 * Proceed to find out if wanted events are really available inside
867 * the ready list. This need to be done under ep_call_nested()
868 * supervision, since the call to f_op->poll() done on listed files
869 * could re-enter here.
870 */
871 pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS,
872 ep_poll_readyevents_proc, &arg, ep, current);
873
874 return pollflags != -1 ? pollflags : 0;
875 }
876
877 #ifdef CONFIG_PROC_FS
878 static void ep_show_fdinfo(struct seq_file *m, struct file *f)
879 {
880 struct eventpoll *ep = f->private_data;
881 struct rb_node *rbp;
882
883 mutex_lock(&ep->mtx);
884 for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
885 struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
886
887 seq_printf(m, "tfd: %8d events: %8x data: %16llx\n",
888 epi->ffd.fd, epi->event.events,
889 (long long)epi->event.data);
890 if (seq_has_overflowed(m))
891 break;
892 }
893 mutex_unlock(&ep->mtx);
894 }
895 #endif
896
897 /* File callbacks that implement the eventpoll file behaviour */
898 static const struct file_operations eventpoll_fops = {
899 #ifdef CONFIG_PROC_FS
900 .show_fdinfo = ep_show_fdinfo,
901 #endif
902 .release = ep_eventpoll_release,
903 .poll = ep_eventpoll_poll,
904 .llseek = noop_llseek,
905 };
906
907 /*
908 * This is called from eventpoll_release() to unlink files from the eventpoll
909 * interface. We need to have this facility to cleanup correctly files that are
910 * closed without being removed from the eventpoll interface.
911 */
912 void eventpoll_release_file(struct file *file)
913 {
914 struct eventpoll *ep;
915 struct epitem *epi, *next;
916
917 /*
918 * We don't want to get "file->f_lock" because it is not
919 * necessary. It is not necessary because we're in the "struct file"
920 * cleanup path, and this means that no one is using this file anymore.
921 * So, for example, epoll_ctl() cannot hit here since if we reach this
922 * point, the file counter already went to zero and fget() would fail.
923 * The only hit might come from ep_free() but by holding the mutex
924 * will correctly serialize the operation. We do need to acquire
925 * "ep->mtx" after "epmutex" because ep_remove() requires it when called
926 * from anywhere but ep_free().
927 *
928 * Besides, ep_remove() acquires the lock, so we can't hold it here.
929 */
930 mutex_lock(&epmutex);
931 list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) {
932 ep = epi->ep;
933 mutex_lock_nested(&ep->mtx, 0);
934 ep_remove(ep, epi);
935 mutex_unlock(&ep->mtx);
936 }
937 mutex_unlock(&epmutex);
938 }
939
940 static int ep_alloc(struct eventpoll **pep)
941 {
942 int error;
943 struct user_struct *user;
944 struct eventpoll *ep;
945
946 user = get_current_user();
947 error = -ENOMEM;
948 ep = kzalloc(sizeof(*ep), GFP_KERNEL);
949 if (unlikely(!ep))
950 goto free_uid;
951
952 spin_lock_init(&ep->lock);
953 mutex_init(&ep->mtx);
954 init_waitqueue_head(&ep->wq);
955 init_waitqueue_head(&ep->poll_wait);
956 INIT_LIST_HEAD(&ep->rdllist);
957 ep->rbr = RB_ROOT;
958 ep->ovflist = EP_UNACTIVE_PTR;
959 ep->user = user;
960
961 *pep = ep;
962
963 return 0;
964
965 free_uid:
966 free_uid(user);
967 return error;
968 }
969
970 /*
971 * Search the file inside the eventpoll tree. The RB tree operations
972 * are protected by the "mtx" mutex, and ep_find() must be called with
973 * "mtx" held.
974 */
975 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
976 {
977 int kcmp;
978 struct rb_node *rbp;
979 struct epitem *epi, *epir = NULL;
980 struct epoll_filefd ffd;
981
982 ep_set_ffd(&ffd, file, fd);
983 for (rbp = ep->rbr.rb_node; rbp; ) {
984 epi = rb_entry(rbp, struct epitem, rbn);
985 kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
986 if (kcmp > 0)
987 rbp = rbp->rb_right;
988 else if (kcmp < 0)
989 rbp = rbp->rb_left;
990 else {
991 epir = epi;
992 break;
993 }
994 }
995
996 return epir;
997 }
998
999 /*
1000 * This is the callback that is passed to the wait queue wakeup
1001 * mechanism. It is called by the stored file descriptors when they
1002 * have events to report.
1003 */
1004 static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
1005 {
1006 int pwake = 0;
1007 unsigned long flags;
1008 struct epitem *epi = ep_item_from_wait(wait);
1009 struct eventpoll *ep = epi->ep;
1010 int ewake = 0;
1011
1012 if ((unsigned long)key & POLLFREE) {
1013 ep_pwq_from_wait(wait)->whead = NULL;
1014 /*
1015 * whead = NULL above can race with ep_remove_wait_queue()
1016 * which can do another remove_wait_queue() after us, so we
1017 * can't use __remove_wait_queue(). whead->lock is held by
1018 * the caller.
1019 */
1020 list_del_init(&wait->task_list);
1021 }
1022
1023 spin_lock_irqsave(&ep->lock, flags);
1024
1025 /*
1026 * If the event mask does not contain any poll(2) event, we consider the
1027 * descriptor to be disabled. This condition is likely the effect of the
1028 * EPOLLONESHOT bit that disables the descriptor when an event is received,
1029 * until the next EPOLL_CTL_MOD will be issued.
1030 */
1031 if (!(epi->event.events & ~EP_PRIVATE_BITS))
1032 goto out_unlock;
1033
1034 /*
1035 * Check the events coming with the callback. At this stage, not
1036 * every device reports the events in the "key" parameter of the
1037 * callback. We need to be able to handle both cases here, hence the
1038 * test for "key" != NULL before the event match test.
1039 */
1040 if (key && !((unsigned long) key & epi->event.events))
1041 goto out_unlock;
1042
1043 /*
1044 * If we are transferring events to userspace, we can hold no locks
1045 * (because we're accessing user memory, and because of linux f_op->poll()
1046 * semantics). All the events that happen during that period of time are
1047 * chained in ep->ovflist and requeued later on.
1048 */
1049 if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
1050 if (epi->next == EP_UNACTIVE_PTR) {
1051 epi->next = ep->ovflist;
1052 ep->ovflist = epi;
1053 if (epi->ws) {
1054 /*
1055 * Activate ep->ws since epi->ws may get
1056 * deactivated at any time.
1057 */
1058 __pm_stay_awake(ep->ws);
1059 }
1060
1061 }
1062 goto out_unlock;
1063 }
1064
1065 /* If this file is already in the ready list we exit soon */
1066 if (!ep_is_linked(&epi->rdllink)) {
1067 list_add_tail(&epi->rdllink, &ep->rdllist);
1068 ep_pm_stay_awake_rcu(epi);
1069 }
1070
1071 /*
1072 * Wake up ( if active ) both the eventpoll wait list and the ->poll()
1073 * wait list.
1074 */
1075 if (waitqueue_active(&ep->wq)) {
1076 if ((epi->event.events & EPOLLEXCLUSIVE) &&
1077 !((unsigned long)key & POLLFREE)) {
1078 switch ((unsigned long)key & EPOLLINOUT_BITS) {
1079 case POLLIN:
1080 if (epi->event.events & POLLIN)
1081 ewake = 1;
1082 break;
1083 case POLLOUT:
1084 if (epi->event.events & POLLOUT)
1085 ewake = 1;
1086 break;
1087 case 0:
1088 ewake = 1;
1089 break;
1090 }
1091 }
1092 wake_up_locked(&ep->wq);
1093 }
1094 if (waitqueue_active(&ep->poll_wait))
1095 pwake++;
1096
1097 out_unlock:
1098 spin_unlock_irqrestore(&ep->lock, flags);
1099
1100 /* We have to call this outside the lock */
1101 if (pwake)
1102 ep_poll_safewake(&ep->poll_wait);
1103
1104 if (epi->event.events & EPOLLEXCLUSIVE)
1105 return ewake;
1106
1107 return 1;
1108 }
1109
1110 /*
1111 * This is the callback that is used to add our wait queue to the
1112 * target file wakeup lists.
1113 */
1114 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
1115 poll_table *pt)
1116 {
1117 struct epitem *epi = ep_item_from_epqueue(pt);
1118 struct eppoll_entry *pwq;
1119
1120 if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
1121 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
1122 pwq->whead = whead;
1123 pwq->base = epi;
1124 if (epi->event.events & EPOLLEXCLUSIVE)
1125 add_wait_queue_exclusive(whead, &pwq->wait);
1126 else
1127 add_wait_queue(whead, &pwq->wait);
1128 list_add_tail(&pwq->llink, &epi->pwqlist);
1129 epi->nwait++;
1130 } else {
1131 /* We have to signal that an error occurred */
1132 epi->nwait = -1;
1133 }
1134 }
1135
1136 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
1137 {
1138 int kcmp;
1139 struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
1140 struct epitem *epic;
1141
1142 while (*p) {
1143 parent = *p;
1144 epic = rb_entry(parent, struct epitem, rbn);
1145 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
1146 if (kcmp > 0)
1147 p = &parent->rb_right;
1148 else
1149 p = &parent->rb_left;
1150 }
1151 rb_link_node(&epi->rbn, parent, p);
1152 rb_insert_color(&epi->rbn, &ep->rbr);
1153 }
1154
1155
1156
1157 #define PATH_ARR_SIZE 5
1158 /*
1159 * These are the number paths of length 1 to 5, that we are allowing to emanate
1160 * from a single file of interest. For example, we allow 1000 paths of length
1161 * 1, to emanate from each file of interest. This essentially represents the
1162 * potential wakeup paths, which need to be limited in order to avoid massive
1163 * uncontrolled wakeup storms. The common use case should be a single ep which
1164 * is connected to n file sources. In this case each file source has 1 path
1165 * of length 1. Thus, the numbers below should be more than sufficient. These
1166 * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
1167 * and delete can't add additional paths. Protected by the epmutex.
1168 */
1169 static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
1170 static int path_count[PATH_ARR_SIZE];
1171
1172 static int path_count_inc(int nests)
1173 {
1174 /* Allow an arbitrary number of depth 1 paths */
1175 if (nests == 0)
1176 return 0;
1177
1178 if (++path_count[nests] > path_limits[nests])
1179 return -1;
1180 return 0;
1181 }
1182
1183 static void path_count_init(void)
1184 {
1185 int i;
1186
1187 for (i = 0; i < PATH_ARR_SIZE; i++)
1188 path_count[i] = 0;
1189 }
1190
1191 static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
1192 {
1193 int error = 0;
1194 struct file *file = priv;
1195 struct file *child_file;
1196 struct epitem *epi;
1197
1198 /* CTL_DEL can remove links here, but that can't increase our count */
1199 rcu_read_lock();
1200 list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
1201 child_file = epi->ep->file;
1202 if (is_file_epoll(child_file)) {
1203 if (list_empty(&child_file->f_ep_links)) {
1204 if (path_count_inc(call_nests)) {
1205 error = -1;
1206 break;
1207 }
1208 } else {
1209 error = ep_call_nested(&poll_loop_ncalls,
1210 EP_MAX_NESTS,
1211 reverse_path_check_proc,
1212 child_file, child_file,
1213 current);
1214 }
1215 if (error != 0)
1216 break;
1217 } else {
1218 printk(KERN_ERR "reverse_path_check_proc: "
1219 "file is not an ep!\n");
1220 }
1221 }
1222 rcu_read_unlock();
1223 return error;
1224 }
1225
1226 /**
1227 * reverse_path_check - The tfile_check_list is list of file *, which have
1228 * links that are proposed to be newly added. We need to
1229 * make sure that those added links don't add too many
1230 * paths such that we will spend all our time waking up
1231 * eventpoll objects.
1232 *
1233 * Returns: Returns zero if the proposed links don't create too many paths,
1234 * -1 otherwise.
1235 */
1236 static int reverse_path_check(void)
1237 {
1238 int error = 0;
1239 struct file *current_file;
1240
1241 /* let's call this for all tfiles */
1242 list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
1243 path_count_init();
1244 error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1245 reverse_path_check_proc, current_file,
1246 current_file, current);
1247 if (error)
1248 break;
1249 }
1250 return error;
1251 }
1252
1253 static int ep_create_wakeup_source(struct epitem *epi)
1254 {
1255 const char *name;
1256 struct wakeup_source *ws;
1257
1258 if (!epi->ep->ws) {
1259 epi->ep->ws = wakeup_source_register("eventpoll");
1260 if (!epi->ep->ws)
1261 return -ENOMEM;
1262 }
1263
1264 name = epi->ffd.file->f_path.dentry->d_name.name;
1265 ws = wakeup_source_register(name);
1266
1267 if (!ws)
1268 return -ENOMEM;
1269 rcu_assign_pointer(epi->ws, ws);
1270
1271 return 0;
1272 }
1273
1274 /* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
1275 static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1276 {
1277 struct wakeup_source *ws = ep_wakeup_source(epi);
1278
1279 RCU_INIT_POINTER(epi->ws, NULL);
1280
1281 /*
1282 * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
1283 * used internally by wakeup_source_remove, too (called by
1284 * wakeup_source_unregister), so we cannot use call_rcu
1285 */
1286 synchronize_rcu();
1287 wakeup_source_unregister(ws);
1288 }
1289
1290 /*
1291 * Must be called with "mtx" held.
1292 */
1293 static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
1294 struct file *tfile, int fd, int full_check)
1295 {
1296 int error, revents, pwake = 0;
1297 unsigned long flags;
1298 long user_watches;
1299 struct epitem *epi;
1300 struct ep_pqueue epq;
1301
1302 user_watches = atomic_long_read(&ep->user->epoll_watches);
1303 if (unlikely(user_watches >= max_user_watches))
1304 return -ENOSPC;
1305 if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
1306 return -ENOMEM;
1307
1308 /* Item initialization follow here ... */
1309 INIT_LIST_HEAD(&epi->rdllink);
1310 INIT_LIST_HEAD(&epi->fllink);
1311 INIT_LIST_HEAD(&epi->pwqlist);
1312 epi->ep = ep;
1313 ep_set_ffd(&epi->ffd, tfile, fd);
1314 epi->event = *event;
1315 epi->nwait = 0;
1316 epi->next = EP_UNACTIVE_PTR;
1317 if (epi->event.events & EPOLLWAKEUP) {
1318 error = ep_create_wakeup_source(epi);
1319 if (error)
1320 goto error_create_wakeup_source;
1321 } else {
1322 RCU_INIT_POINTER(epi->ws, NULL);
1323 }
1324
1325 /* Initialize the poll table using the queue callback */
1326 epq.epi = epi;
1327 init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
1328
1329 /*
1330 * Attach the item to the poll hooks and get current event bits.
1331 * We can safely use the file* here because its usage count has
1332 * been increased by the caller of this function. Note that after
1333 * this operation completes, the poll callback can start hitting
1334 * the new item.
1335 */
1336 revents = ep_item_poll(epi, &epq.pt);
1337
1338 /*
1339 * We have to check if something went wrong during the poll wait queue
1340 * install process. Namely an allocation for a wait queue failed due
1341 * high memory pressure.
1342 */
1343 error = -ENOMEM;
1344 if (epi->nwait < 0)
1345 goto error_unregister;
1346
1347 /* Add the current item to the list of active epoll hook for this file */
1348 spin_lock(&tfile->f_lock);
1349 list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
1350 spin_unlock(&tfile->f_lock);
1351
1352 /*
1353 * Add the current item to the RB tree. All RB tree operations are
1354 * protected by "mtx", and ep_insert() is called with "mtx" held.
1355 */
1356 ep_rbtree_insert(ep, epi);
1357
1358 /* now check if we've created too many backpaths */
1359 error = -EINVAL;
1360 if (full_check && reverse_path_check())
1361 goto error_remove_epi;
1362
1363 /* We have to drop the new item inside our item list to keep track of it */
1364 spin_lock_irqsave(&ep->lock, flags);
1365
1366 /* If the file is already "ready" we drop it inside the ready list */
1367 if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
1368 list_add_tail(&epi->rdllink, &ep->rdllist);
1369 ep_pm_stay_awake(epi);
1370
1371 /* Notify waiting tasks that events are available */
1372 if (waitqueue_active(&ep->wq))
1373 wake_up_locked(&ep->wq);
1374 if (waitqueue_active(&ep->poll_wait))
1375 pwake++;
1376 }
1377
1378 spin_unlock_irqrestore(&ep->lock, flags);
1379
1380 atomic_long_inc(&ep->user->epoll_watches);
1381
1382 /* We have to call this outside the lock */
1383 if (pwake)
1384 ep_poll_safewake(&ep->poll_wait);
1385
1386 return 0;
1387
1388 error_remove_epi:
1389 spin_lock(&tfile->f_lock);
1390 list_del_rcu(&epi->fllink);
1391 spin_unlock(&tfile->f_lock);
1392
1393 rb_erase(&epi->rbn, &ep->rbr);
1394
1395 error_unregister:
1396 ep_unregister_pollwait(ep, epi);
1397
1398 /*
1399 * We need to do this because an event could have been arrived on some
1400 * allocated wait queue. Note that we don't care about the ep->ovflist
1401 * list, since that is used/cleaned only inside a section bound by "mtx".
1402 * And ep_insert() is called with "mtx" held.
1403 */
1404 spin_lock_irqsave(&ep->lock, flags);
1405 if (ep_is_linked(&epi->rdllink))
1406 list_del_init(&epi->rdllink);
1407 spin_unlock_irqrestore(&ep->lock, flags);
1408
1409 wakeup_source_unregister(ep_wakeup_source(epi));
1410
1411 error_create_wakeup_source:
1412 kmem_cache_free(epi_cache, epi);
1413
1414 return error;
1415 }
1416
1417 /*
1418 * Modify the interest event mask by dropping an event if the new mask
1419 * has a match in the current file status. Must be called with "mtx" held.
1420 */
1421 static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
1422 {
1423 int pwake = 0;
1424 unsigned int revents;
1425 poll_table pt;
1426
1427 init_poll_funcptr(&pt, NULL);
1428
1429 /*
1430 * Set the new event interest mask before calling f_op->poll();
1431 * otherwise we might miss an event that happens between the
1432 * f_op->poll() call and the new event set registering.
1433 */
1434 epi->event.events = event->events; /* need barrier below */
1435 epi->event.data = event->data; /* protected by mtx */
1436 if (epi->event.events & EPOLLWAKEUP) {
1437 if (!ep_has_wakeup_source(epi))
1438 ep_create_wakeup_source(epi);
1439 } else if (ep_has_wakeup_source(epi)) {
1440 ep_destroy_wakeup_source(epi);
1441 }
1442
1443 /*
1444 * The following barrier has two effects:
1445 *
1446 * 1) Flush epi changes above to other CPUs. This ensures
1447 * we do not miss events from ep_poll_callback if an
1448 * event occurs immediately after we call f_op->poll().
1449 * We need this because we did not take ep->lock while
1450 * changing epi above (but ep_poll_callback does take
1451 * ep->lock).
1452 *
1453 * 2) We also need to ensure we do not miss _past_ events
1454 * when calling f_op->poll(). This barrier also
1455 * pairs with the barrier in wq_has_sleeper (see
1456 * comments for wq_has_sleeper).
1457 *
1458 * This barrier will now guarantee ep_poll_callback or f_op->poll
1459 * (or both) will notice the readiness of an item.
1460 */
1461 smp_mb();
1462
1463 /*
1464 * Get current event bits. We can safely use the file* here because
1465 * its usage count has been increased by the caller of this function.
1466 */
1467 revents = ep_item_poll(epi, &pt);
1468
1469 /*
1470 * If the item is "hot" and it is not registered inside the ready
1471 * list, push it inside.
1472 */
1473 if (revents & event->events) {
1474 spin_lock_irq(&ep->lock);
1475 if (!ep_is_linked(&epi->rdllink)) {
1476 list_add_tail(&epi->rdllink, &ep->rdllist);
1477 ep_pm_stay_awake(epi);
1478
1479 /* Notify waiting tasks that events are available */
1480 if (waitqueue_active(&ep->wq))
1481 wake_up_locked(&ep->wq);
1482 if (waitqueue_active(&ep->poll_wait))
1483 pwake++;
1484 }
1485 spin_unlock_irq(&ep->lock);
1486 }
1487
1488 /* We have to call this outside the lock */
1489 if (pwake)
1490 ep_poll_safewake(&ep->poll_wait);
1491
1492 return 0;
1493 }
1494
1495 static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
1496 void *priv)
1497 {
1498 struct ep_send_events_data *esed = priv;
1499 int eventcnt;
1500 unsigned int revents;
1501 struct epitem *epi;
1502 struct epoll_event __user *uevent;
1503 struct wakeup_source *ws;
1504 poll_table pt;
1505
1506 init_poll_funcptr(&pt, NULL);
1507
1508 /*
1509 * We can loop without lock because we are passed a task private list.
1510 * Items cannot vanish during the loop because ep_scan_ready_list() is
1511 * holding "mtx" during this call.
1512 */
1513 for (eventcnt = 0, uevent = esed->events;
1514 !list_empty(head) && eventcnt < esed->maxevents;) {
1515 epi = list_first_entry(head, struct epitem, rdllink);
1516
1517 /*
1518 * Activate ep->ws before deactivating epi->ws to prevent
1519 * triggering auto-suspend here (in case we reactive epi->ws
1520 * below).
1521 *
1522 * This could be rearranged to delay the deactivation of epi->ws
1523 * instead, but then epi->ws would temporarily be out of sync
1524 * with ep_is_linked().
1525 */
1526 ws = ep_wakeup_source(epi);
1527 if (ws) {
1528 if (ws->active)
1529 __pm_stay_awake(ep->ws);
1530 __pm_relax(ws);
1531 }
1532
1533 list_del_init(&epi->rdllink);
1534
1535 revents = ep_item_poll(epi, &pt);
1536
1537 /*
1538 * If the event mask intersect the caller-requested one,
1539 * deliver the event to userspace. Again, ep_scan_ready_list()
1540 * is holding "mtx", so no operations coming from userspace
1541 * can change the item.
1542 */
1543 if (revents) {
1544 if (__put_user(revents, &uevent->events) ||
1545 __put_user(epi->event.data, &uevent->data)) {
1546 list_add(&epi->rdllink, head);
1547 ep_pm_stay_awake(epi);
1548 return eventcnt ? eventcnt : -EFAULT;
1549 }
1550 eventcnt++;
1551 uevent++;
1552 if (epi->event.events & EPOLLONESHOT)
1553 epi->event.events &= EP_PRIVATE_BITS;
1554 else if (!(epi->event.events & EPOLLET)) {
1555 /*
1556 * If this file has been added with Level
1557 * Trigger mode, we need to insert back inside
1558 * the ready list, so that the next call to
1559 * epoll_wait() will check again the events
1560 * availability. At this point, no one can insert
1561 * into ep->rdllist besides us. The epoll_ctl()
1562 * callers are locked out by
1563 * ep_scan_ready_list() holding "mtx" and the
1564 * poll callback will queue them in ep->ovflist.
1565 */
1566 list_add_tail(&epi->rdllink, &ep->rdllist);
1567 ep_pm_stay_awake(epi);
1568 }
1569 }
1570 }
1571
1572 return eventcnt;
1573 }
1574
1575 static int ep_send_events(struct eventpoll *ep,
1576 struct epoll_event __user *events, int maxevents)
1577 {
1578 struct ep_send_events_data esed;
1579
1580 esed.maxevents = maxevents;
1581 esed.events = events;
1582
1583 return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
1584 }
1585
1586 static inline struct timespec64 ep_set_mstimeout(long ms)
1587 {
1588 struct timespec64 now, ts = {
1589 .tv_sec = ms / MSEC_PER_SEC,
1590 .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
1591 };
1592
1593 ktime_get_ts64(&now);
1594 return timespec64_add_safe(now, ts);
1595 }
1596
1597 /**
1598 * ep_poll - Retrieves ready events, and delivers them to the caller supplied
1599 * event buffer.
1600 *
1601 * @ep: Pointer to the eventpoll context.
1602 * @events: Pointer to the userspace buffer where the ready events should be
1603 * stored.
1604 * @maxevents: Size (in terms of number of events) of the caller event buffer.
1605 * @timeout: Maximum timeout for the ready events fetch operation, in
1606 * milliseconds. If the @timeout is zero, the function will not block,
1607 * while if the @timeout is less than zero, the function will block
1608 * until at least one event has been retrieved (or an error
1609 * occurred).
1610 *
1611 * Returns: Returns the number of ready events which have been fetched, or an
1612 * error code, in case of error.
1613 */
1614 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1615 int maxevents, long timeout)
1616 {
1617 int res = 0, eavail, timed_out = 0;
1618 unsigned long flags;
1619 u64 slack = 0;
1620 wait_queue_t wait;
1621 ktime_t expires, *to = NULL;
1622
1623 if (timeout > 0) {
1624 struct timespec64 end_time = ep_set_mstimeout(timeout);
1625
1626 slack = select_estimate_accuracy(&end_time);
1627 to = &expires;
1628 *to = timespec64_to_ktime(end_time);
1629 } else if (timeout == 0) {
1630 /*
1631 * Avoid the unnecessary trip to the wait queue loop, if the
1632 * caller specified a non blocking operation.
1633 */
1634 timed_out = 1;
1635 spin_lock_irqsave(&ep->lock, flags);
1636 goto check_events;
1637 }
1638
1639 fetch_events:
1640 spin_lock_irqsave(&ep->lock, flags);
1641
1642 if (!ep_events_available(ep)) {
1643 /*
1644 * We don't have any available event to return to the caller.
1645 * We need to sleep here, and we will be wake up by
1646 * ep_poll_callback() when events will become available.
1647 */
1648 init_waitqueue_entry(&wait, current);
1649 __add_wait_queue_exclusive(&ep->wq, &wait);
1650
1651 for (;;) {
1652 /*
1653 * We don't want to sleep if the ep_poll_callback() sends us
1654 * a wakeup in between. That's why we set the task state
1655 * to TASK_INTERRUPTIBLE before doing the checks.
1656 */
1657 set_current_state(TASK_INTERRUPTIBLE);
1658 if (ep_events_available(ep) || timed_out)
1659 break;
1660 if (signal_pending(current)) {
1661 res = -EINTR;
1662 break;
1663 }
1664
1665 spin_unlock_irqrestore(&ep->lock, flags);
1666 if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
1667 timed_out = 1;
1668
1669 spin_lock_irqsave(&ep->lock, flags);
1670 }
1671
1672 __remove_wait_queue(&ep->wq, &wait);
1673 __set_current_state(TASK_RUNNING);
1674 }
1675 check_events:
1676 /* Is it worth to try to dig for events ? */
1677 eavail = ep_events_available(ep);
1678
1679 spin_unlock_irqrestore(&ep->lock, flags);
1680
1681 /*
1682 * Try to transfer events to user space. In case we get 0 events and
1683 * there's still timeout left over, we go trying again in search of
1684 * more luck.
1685 */
1686 if (!res && eavail &&
1687 !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
1688 goto fetch_events;
1689
1690 return res;
1691 }
1692
1693 /**
1694 * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
1695 * API, to verify that adding an epoll file inside another
1696 * epoll structure, does not violate the constraints, in
1697 * terms of closed loops, or too deep chains (which can
1698 * result in excessive stack usage).
1699 *
1700 * @priv: Pointer to the epoll file to be currently checked.
1701 * @cookie: Original cookie for this call. This is the top-of-the-chain epoll
1702 * data structure pointer.
1703 * @call_nests: Current dept of the @ep_call_nested() call stack.
1704 *
1705 * Returns: Returns zero if adding the epoll @file inside current epoll
1706 * structure @ep does not violate the constraints, or -1 otherwise.
1707 */
1708 static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
1709 {
1710 int error = 0;
1711 struct file *file = priv;
1712 struct eventpoll *ep = file->private_data;
1713 struct eventpoll *ep_tovisit;
1714 struct rb_node *rbp;
1715 struct epitem *epi;
1716
1717 mutex_lock_nested(&ep->mtx, call_nests + 1);
1718 ep->visited = 1;
1719 list_add(&ep->visited_list_link, &visited_list);
1720 for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1721 epi = rb_entry(rbp, struct epitem, rbn);
1722 if (unlikely(is_file_epoll(epi->ffd.file))) {
1723 ep_tovisit = epi->ffd.file->private_data;
1724 if (ep_tovisit->visited)
1725 continue;
1726 error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1727 ep_loop_check_proc, epi->ffd.file,
1728 ep_tovisit, current);
1729 if (error != 0)
1730 break;
1731 } else {
1732 /*
1733 * If we've reached a file that is not associated with
1734 * an ep, then we need to check if the newly added
1735 * links are going to add too many wakeup paths. We do
1736 * this by adding it to the tfile_check_list, if it's
1737 * not already there, and calling reverse_path_check()
1738 * during ep_insert().
1739 */
1740 if (list_empty(&epi->ffd.file->f_tfile_llink))
1741 list_add(&epi->ffd.file->f_tfile_llink,
1742 &tfile_check_list);
1743 }
1744 }
1745 mutex_unlock(&ep->mtx);
1746
1747 return error;
1748 }
1749
1750 /**
1751 * ep_loop_check - Performs a check to verify that adding an epoll file (@file)
1752 * another epoll file (represented by @ep) does not create
1753 * closed loops or too deep chains.
1754 *
1755 * @ep: Pointer to the epoll private data structure.
1756 * @file: Pointer to the epoll file to be checked.
1757 *
1758 * Returns: Returns zero if adding the epoll @file inside current epoll
1759 * structure @ep does not violate the constraints, or -1 otherwise.
1760 */
1761 static int ep_loop_check(struct eventpoll *ep, struct file *file)
1762 {
1763 int ret;
1764 struct eventpoll *ep_cur, *ep_next;
1765
1766 ret = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1767 ep_loop_check_proc, file, ep, current);
1768 /* clear visited list */
1769 list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
1770 visited_list_link) {
1771 ep_cur->visited = 0;
1772 list_del(&ep_cur->visited_list_link);
1773 }
1774 return ret;
1775 }
1776
1777 static void clear_tfile_check_list(void)
1778 {
1779 struct file *file;
1780
1781 /* first clear the tfile_check_list */
1782 while (!list_empty(&tfile_check_list)) {
1783 file = list_first_entry(&tfile_check_list, struct file,
1784 f_tfile_llink);
1785 list_del_init(&file->f_tfile_llink);
1786 }
1787 INIT_LIST_HEAD(&tfile_check_list);
1788 }
1789
1790 /*
1791 * Open an eventpoll file descriptor.
1792 */
1793 SYSCALL_DEFINE1(epoll_create1, int, flags)
1794 {
1795 int error, fd;
1796 struct eventpoll *ep = NULL;
1797 struct file *file;
1798
1799 /* Check the EPOLL_* constant for consistency. */
1800 BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
1801
1802 if (flags & ~EPOLL_CLOEXEC)
1803 return -EINVAL;
1804 /*
1805 * Create the internal data structure ("struct eventpoll").
1806 */
1807 error = ep_alloc(&ep);
1808 if (error < 0)
1809 return error;
1810 /*
1811 * Creates all the items needed to setup an eventpoll file. That is,
1812 * a file structure and a free file descriptor.
1813 */
1814 fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
1815 if (fd < 0) {
1816 error = fd;
1817 goto out_free_ep;
1818 }
1819 file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
1820 O_RDWR | (flags & O_CLOEXEC));
1821 if (IS_ERR(file)) {
1822 error = PTR_ERR(file);
1823 goto out_free_fd;
1824 }
1825 ep->file = file;
1826 fd_install(fd, file);
1827 return fd;
1828
1829 out_free_fd:
1830 put_unused_fd(fd);
1831 out_free_ep:
1832 ep_free(ep);
1833 return error;
1834 }
1835
1836 SYSCALL_DEFINE1(epoll_create, int, size)
1837 {
1838 if (size <= 0)
1839 return -EINVAL;
1840
1841 return sys_epoll_create1(0);
1842 }
1843
1844 /*
1845 * The following function implements the controller interface for
1846 * the eventpoll file that enables the insertion/removal/change of
1847 * file descriptors inside the interest set.
1848 */
1849 SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
1850 struct epoll_event __user *, event)
1851 {
1852 int error;
1853 int full_check = 0;
1854 struct fd f, tf;
1855 struct eventpoll *ep;
1856 struct epitem *epi;
1857 struct epoll_event epds;
1858 struct eventpoll *tep = NULL;
1859
1860 error = -EFAULT;
1861 if (ep_op_has_event(op) &&
1862 copy_from_user(&epds, event, sizeof(struct epoll_event)))
1863 goto error_return;
1864
1865 error = -EBADF;
1866 f = fdget(epfd);
1867 if (!f.file)
1868 goto error_return;
1869
1870 /* Get the "struct file *" for the target file */
1871 tf = fdget(fd);
1872 if (!tf.file)
1873 goto error_fput;
1874
1875 /* The target file descriptor must support poll */
1876 error = -EPERM;
1877 if (!tf.file->f_op->poll)
1878 goto error_tgt_fput;
1879
1880 /* Check if EPOLLWAKEUP is allowed */
1881 if (ep_op_has_event(op))
1882 ep_take_care_of_epollwakeup(&epds);
1883
1884 /*
1885 * We have to check that the file structure underneath the file descriptor
1886 * the user passed to us _is_ an eventpoll file. And also we do not permit
1887 * adding an epoll file descriptor inside itself.
1888 */
1889 error = -EINVAL;
1890 if (f.file == tf.file || !is_file_epoll(f.file))
1891 goto error_tgt_fput;
1892
1893 /*
1894 * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only,
1895 * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
1896 * Also, we do not currently supported nested exclusive wakeups.
1897 */
1898 if (epds.events & EPOLLEXCLUSIVE) {
1899 if (op == EPOLL_CTL_MOD)
1900 goto error_tgt_fput;
1901 if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
1902 (epds.events & ~EPOLLEXCLUSIVE_OK_BITS)))
1903 goto error_tgt_fput;
1904 }
1905
1906 /*
1907 * At this point it is safe to assume that the "private_data" contains
1908 * our own data structure.
1909 */
1910 ep = f.file->private_data;
1911
1912 /*
1913 * When we insert an epoll file descriptor, inside another epoll file
1914 * descriptor, there is the change of creating closed loops, which are
1915 * better be handled here, than in more critical paths. While we are
1916 * checking for loops we also determine the list of files reachable
1917 * and hang them on the tfile_check_list, so we can check that we
1918 * haven't created too many possible wakeup paths.
1919 *
1920 * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
1921 * the epoll file descriptor is attaching directly to a wakeup source,
1922 * unless the epoll file descriptor is nested. The purpose of taking the
1923 * 'epmutex' on add is to prevent complex toplogies such as loops and
1924 * deep wakeup paths from forming in parallel through multiple
1925 * EPOLL_CTL_ADD operations.
1926 */
1927 mutex_lock_nested(&ep->mtx, 0);
1928 if (op == EPOLL_CTL_ADD) {
1929 if (!list_empty(&f.file->f_ep_links) ||
1930 is_file_epoll(tf.file)) {
1931 full_check = 1;
1932 mutex_unlock(&ep->mtx);
1933 mutex_lock(&epmutex);
1934 if (is_file_epoll(tf.file)) {
1935 error = -ELOOP;
1936 if (ep_loop_check(ep, tf.file) != 0) {
1937 clear_tfile_check_list();
1938 goto error_tgt_fput;
1939 }
1940 } else
1941 list_add(&tf.file->f_tfile_llink,
1942 &tfile_check_list);
1943 mutex_lock_nested(&ep->mtx, 0);
1944 if (is_file_epoll(tf.file)) {
1945 tep = tf.file->private_data;
1946 mutex_lock_nested(&tep->mtx, 1);
1947 }
1948 }
1949 }
1950
1951 /*
1952 * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
1953 * above, we can be sure to be able to use the item looked up by
1954 * ep_find() till we release the mutex.
1955 */
1956 epi = ep_find(ep, tf.file, fd);
1957
1958 error = -EINVAL;
1959 switch (op) {
1960 case EPOLL_CTL_ADD:
1961 if (!epi) {
1962 epds.events |= POLLERR | POLLHUP;
1963 error = ep_insert(ep, &epds, tf.file, fd, full_check);
1964 } else
1965 error = -EEXIST;
1966 if (full_check)
1967 clear_tfile_check_list();
1968 break;
1969 case EPOLL_CTL_DEL:
1970 if (epi)
1971 error = ep_remove(ep, epi);
1972 else
1973 error = -ENOENT;
1974 break;
1975 case EPOLL_CTL_MOD:
1976 if (epi) {
1977 if (!(epi->event.events & EPOLLEXCLUSIVE)) {
1978 epds.events |= POLLERR | POLLHUP;
1979 error = ep_modify(ep, epi, &epds);
1980 }
1981 } else
1982 error = -ENOENT;
1983 break;
1984 }
1985 if (tep != NULL)
1986 mutex_unlock(&tep->mtx);
1987 mutex_unlock(&ep->mtx);
1988
1989 error_tgt_fput:
1990 if (full_check)
1991 mutex_unlock(&epmutex);
1992
1993 fdput(tf);
1994 error_fput:
1995 fdput(f);
1996 error_return:
1997
1998 return error;
1999 }
2000
2001 /*
2002 * Implement the event wait interface for the eventpoll file. It is the kernel
2003 * part of the user space epoll_wait(2).
2004 */
2005 SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
2006 int, maxevents, int, timeout)
2007 {
2008 int error;
2009 struct fd f;
2010 struct eventpoll *ep;
2011
2012 /* The maximum number of event must be greater than zero */
2013 if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
2014 return -EINVAL;
2015
2016 /* Verify that the area passed by the user is writeable */
2017 if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event)))
2018 return -EFAULT;
2019
2020 /* Get the "struct file *" for the eventpoll file */
2021 f = fdget(epfd);
2022 if (!f.file)
2023 return -EBADF;
2024
2025 /*
2026 * We have to check that the file structure underneath the fd
2027 * the user passed to us _is_ an eventpoll file.
2028 */
2029 error = -EINVAL;
2030 if (!is_file_epoll(f.file))
2031 goto error_fput;
2032
2033 /*
2034 * At this point it is safe to assume that the "private_data" contains
2035 * our own data structure.
2036 */
2037 ep = f.file->private_data;
2038
2039 /* Time to fish for events ... */
2040 error = ep_poll(ep, events, maxevents, timeout);
2041
2042 error_fput:
2043 fdput(f);
2044 return error;
2045 }
2046
2047 /*
2048 * Implement the event wait interface for the eventpoll file. It is the kernel
2049 * part of the user space epoll_pwait(2).
2050 */
2051 SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
2052 int, maxevents, int, timeout, const sigset_t __user *, sigmask,
2053 size_t, sigsetsize)
2054 {
2055 int error;
2056 sigset_t ksigmask, sigsaved;
2057
2058 /*
2059 * If the caller wants a certain signal mask to be set during the wait,
2060 * we apply it here.
2061 */
2062 if (sigmask) {
2063 if (sigsetsize != sizeof(sigset_t))
2064 return -EINVAL;
2065 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
2066 return -EFAULT;
2067 sigsaved = current->blocked;
2068 set_current_blocked(&ksigmask);
2069 }
2070
2071 error = sys_epoll_wait(epfd, events, maxevents, timeout);
2072
2073 /*
2074 * If we changed the signal mask, we need to restore the original one.
2075 * In case we've got a signal while waiting, we do not restore the
2076 * signal mask yet, and we allow do_signal() to deliver the signal on
2077 * the way back to userspace, before the signal mask is restored.
2078 */
2079 if (sigmask) {
2080 if (error == -EINTR) {
2081 memcpy(&current->saved_sigmask, &sigsaved,
2082 sizeof(sigsaved));
2083 set_restore_sigmask();
2084 } else
2085 set_current_blocked(&sigsaved);
2086 }
2087
2088 return error;
2089 }
2090
2091 #ifdef CONFIG_COMPAT
2092 COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
2093 struct epoll_event __user *, events,
2094 int, maxevents, int, timeout,
2095 const compat_sigset_t __user *, sigmask,
2096 compat_size_t, sigsetsize)
2097 {
2098 long err;
2099 compat_sigset_t csigmask;
2100 sigset_t ksigmask, sigsaved;
2101
2102 /*
2103 * If the caller wants a certain signal mask to be set during the wait,
2104 * we apply it here.
2105 */
2106 if (sigmask) {
2107 if (sigsetsize != sizeof(compat_sigset_t))
2108 return -EINVAL;
2109 if (copy_from_user(&csigmask, sigmask, sizeof(csigmask)))
2110 return -EFAULT;
2111 sigset_from_compat(&ksigmask, &csigmask);
2112 sigsaved = current->blocked;
2113 set_current_blocked(&ksigmask);
2114 }
2115
2116 err = sys_epoll_wait(epfd, events, maxevents, timeout);
2117
2118 /*
2119 * If we changed the signal mask, we need to restore the original one.
2120 * In case we've got a signal while waiting, we do not restore the
2121 * signal mask yet, and we allow do_signal() to deliver the signal on
2122 * the way back to userspace, before the signal mask is restored.
2123 */
2124 if (sigmask) {
2125 if (err == -EINTR) {
2126 memcpy(&current->saved_sigmask, &sigsaved,
2127 sizeof(sigsaved));
2128 set_restore_sigmask();
2129 } else
2130 set_current_blocked(&sigsaved);
2131 }
2132
2133 return err;
2134 }
2135 #endif
2136
2137 static int __init eventpoll_init(void)
2138 {
2139 struct sysinfo si;
2140
2141 si_meminfo(&si);
2142 /*
2143 * Allows top 4% of lomem to be allocated for epoll watches (per user).
2144 */
2145 max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2146 EP_ITEM_COST;
2147 BUG_ON(max_user_watches < 0);
2148
2149 /*
2150 * Initialize the structure used to perform epoll file descriptor
2151 * inclusion loops checks.
2152 */
2153 ep_nested_calls_init(&poll_loop_ncalls);
2154
2155 /* Initialize the structure used to perform safe poll wait head wake ups */
2156 ep_nested_calls_init(&poll_safewake_ncalls);
2157
2158 /* Initialize the structure used to perform file's f_op->poll() calls */
2159 ep_nested_calls_init(&poll_readywalk_ncalls);
2160
2161 /*
2162 * We can have many thousands of epitems, so prevent this from
2163 * using an extra cache line on 64-bit (and smaller) CPUs
2164 */
2165 BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
2166
2167 /* Allocates slab cache used to allocate "struct epitem" items */
2168 epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
2169 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
2170
2171 /* Allocates slab cache used to allocate "struct eppoll_entry" */
2172 pwq_cache = kmem_cache_create("eventpoll_pwq",
2173 sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL);
2174
2175 return 0;
2176 }
2177 fs_initcall(eventpoll_init);