xref: /openbmc/linux/fs/eventpoll.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
1 /*
2  *  fs/eventpoll.c ( Efficent event polling implementation )
3  *  Copyright (C) 2001,...,2006	 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/rwsem.h>
30 #include <linux/rbtree.h>
31 #include <linux/wait.h>
32 #include <linux/eventpoll.h>
33 #include <linux/mount.h>
34 #include <linux/bitops.h>
35 #include <linux/mutex.h>
36 #include <linux/anon_inodes.h>
37 #include <asm/uaccess.h>
38 #include <asm/system.h>
39 #include <asm/io.h>
40 #include <asm/mman.h>
41 #include <asm/atomic.h>
42 #include <asm/semaphore.h>
43 
44 /*
45  * LOCKING:
46  * There are three level of locking required by epoll :
47  *
48  * 1) epmutex (mutex)
49  * 2) ep->sem (rw_semaphore)
50  * 3) ep->lock (rw_lock)
51  *
52  * The acquire order is the one listed above, from 1 to 3.
53  * We need a spinlock (ep->lock) because we manipulate objects
54  * from inside the poll callback, that might be triggered from
55  * a wake_up() that in turn might be called from IRQ context.
56  * So we can't sleep inside the poll callback and hence we need
57  * a spinlock. During the event transfer loop (from kernel to
58  * user space) we could end up sleeping due a copy_to_user(), so
59  * we need a lock that will allow us to sleep. This lock is a
60  * read-write semaphore (ep->sem). It is acquired on read during
61  * the event transfer loop and in write during epoll_ctl(EPOLL_CTL_DEL)
62  * and during eventpoll_release_file(). Then we also need a global
63  * semaphore to serialize eventpoll_release_file() and ep_free().
64  * This semaphore is acquired by ep_free() during the epoll file
65  * cleanup path and it is also acquired by eventpoll_release_file()
66  * if a file has been pushed inside an epoll set and it is then
67  * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL).
68  * It is possible to drop the "ep->sem" and to use the global
69  * semaphore "epmutex" (together with "ep->lock") to have it working,
70  * but having "ep->sem" will make the interface more scalable.
71  * Events that require holding "epmutex" are very rare, while for
72  * normal operations the epoll private "ep->sem" will guarantee
73  * a greater scalability.
74  */
75 
76 #define DEBUG_EPOLL 0
77 
78 #if DEBUG_EPOLL > 0
79 #define DPRINTK(x) printk x
80 #define DNPRINTK(n, x) do { if ((n) <= DEBUG_EPOLL) printk x; } while (0)
81 #else /* #if DEBUG_EPOLL > 0 */
82 #define DPRINTK(x) (void) 0
83 #define DNPRINTK(n, x) (void) 0
84 #endif /* #if DEBUG_EPOLL > 0 */
85 
86 #define DEBUG_EPI 0
87 
88 #if DEBUG_EPI != 0
89 #define EPI_SLAB_DEBUG (SLAB_DEBUG_FREE | SLAB_RED_ZONE /* | SLAB_POISON */)
90 #else /* #if DEBUG_EPI != 0 */
91 #define EPI_SLAB_DEBUG 0
92 #endif /* #if DEBUG_EPI != 0 */
93 
94 /* Epoll private bits inside the event mask */
95 #define EP_PRIVATE_BITS (EPOLLONESHOT | EPOLLET)
96 
97 /* Maximum number of poll wake up nests we are allowing */
98 #define EP_MAX_POLLWAKE_NESTS 4
99 
100 /* Maximum msec timeout value storeable in a long int */
101 #define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ)
102 
103 #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
104 
105 struct epoll_filefd {
106 	struct file *file;
107 	int fd;
108 };
109 
110 /*
111  * Node that is linked into the "wake_task_list" member of the "struct poll_safewake".
112  * It is used to keep track on all tasks that are currently inside the wake_up() code
113  * to 1) short-circuit the one coming from the same task and same wait queue head
114  * ( loop ) 2) allow a maximum number of epoll descriptors inclusion nesting
115  * 3) let go the ones coming from other tasks.
116  */
117 struct wake_task_node {
118 	struct list_head llink;
119 	struct task_struct *task;
120 	wait_queue_head_t *wq;
121 };
122 
123 /*
124  * This is used to implement the safe poll wake up avoiding to reenter
125  * the poll callback from inside wake_up().
126  */
127 struct poll_safewake {
128 	struct list_head wake_task_list;
129 	spinlock_t lock;
130 };
131 
132 /*
133  * This structure is stored inside the "private_data" member of the file
134  * structure and rapresent the main data sructure for the eventpoll
135  * interface.
136  */
137 struct eventpoll {
138 	/* Protect the this structure access */
139 	rwlock_t lock;
140 
141 	/*
142 	 * This semaphore is used to ensure that files are not removed
143 	 * while epoll is using them. This is read-held during the event
144 	 * collection loop and it is write-held during the file cleanup
145 	 * path, the epoll file exit code and the ctl operations.
146 	 */
147 	struct rw_semaphore sem;
148 
149 	/* Wait queue used by sys_epoll_wait() */
150 	wait_queue_head_t wq;
151 
152 	/* Wait queue used by file->poll() */
153 	wait_queue_head_t poll_wait;
154 
155 	/* List of ready file descriptors */
156 	struct list_head rdllist;
157 
158 	/* RB-Tree root used to store monitored fd structs */
159 	struct rb_root rbr;
160 };
161 
162 /* Wait structure used by the poll hooks */
163 struct eppoll_entry {
164 	/* List header used to link this structure to the "struct epitem" */
165 	struct list_head llink;
166 
167 	/* The "base" pointer is set to the container "struct epitem" */
168 	void *base;
169 
170 	/*
171 	 * Wait queue item that will be linked to the target file wait
172 	 * queue head.
173 	 */
174 	wait_queue_t wait;
175 
176 	/* The wait queue head that linked the "wait" wait queue item */
177 	wait_queue_head_t *whead;
178 };
179 
180 /*
181  * Each file descriptor added to the eventpoll interface will
182  * have an entry of this type linked to the "rbr" RB tree.
183  */
184 struct epitem {
185 	/* RB-Tree node used to link this structure to the eventpoll rb-tree */
186 	struct rb_node rbn;
187 
188 	/* List header used to link this structure to the eventpoll ready list */
189 	struct list_head rdllink;
190 
191 	/* The file descriptor information this item refers to */
192 	struct epoll_filefd ffd;
193 
194 	/* Number of active wait queue attached to poll operations */
195 	int nwait;
196 
197 	/* List containing poll wait queues */
198 	struct list_head pwqlist;
199 
200 	/* The "container" of this item */
201 	struct eventpoll *ep;
202 
203 	/* The structure that describe the interested events and the source fd */
204 	struct epoll_event event;
205 
206 	/*
207 	 * Used to keep track of the usage count of the structure. This avoids
208 	 * that the structure will desappear from underneath our processing.
209 	 */
210 	atomic_t usecnt;
211 
212 	/* List header used to link this item to the "struct file" items list */
213 	struct list_head fllink;
214 };
215 
216 /* Wrapper struct used by poll queueing */
217 struct ep_pqueue {
218 	poll_table pt;
219 	struct epitem *epi;
220 };
221 
222 /*
223  * This semaphore is used to serialize ep_free() and eventpoll_release_file().
224  */
225 static struct mutex epmutex;
226 
227 /* Safe wake up implementation */
228 static struct poll_safewake psw;
229 
230 /* Slab cache used to allocate "struct epitem" */
231 static struct kmem_cache *epi_cache __read_mostly;
232 
233 /* Slab cache used to allocate "struct eppoll_entry" */
234 static struct kmem_cache *pwq_cache __read_mostly;
235 
236 
237 /* Setup the structure that is used as key for the rb-tree */
238 static inline void ep_set_ffd(struct epoll_filefd *ffd,
239 			      struct file *file, int fd)
240 {
241 	ffd->file = file;
242 	ffd->fd = fd;
243 }
244 
245 /* Compare rb-tree keys */
246 static inline int ep_cmp_ffd(struct epoll_filefd *p1,
247 			     struct epoll_filefd *p2)
248 {
249 	return (p1->file > p2->file ? +1:
250 	        (p1->file < p2->file ? -1 : p1->fd - p2->fd));
251 }
252 
253 /* Special initialization for the rb-tree node to detect linkage */
254 static inline void ep_rb_initnode(struct rb_node *n)
255 {
256 	rb_set_parent(n, n);
257 }
258 
259 /* Removes a node from the rb-tree and marks it for a fast is-linked check */
260 static inline void ep_rb_erase(struct rb_node *n, struct rb_root *r)
261 {
262 	rb_erase(n, r);
263 	rb_set_parent(n, n);
264 }
265 
266 /* Fast check to verify that the item is linked to the main rb-tree */
267 static inline int ep_rb_linked(struct rb_node *n)
268 {
269 	return rb_parent(n) != n;
270 }
271 
272 /* Tells us if the item is currently linked */
273 static inline int ep_is_linked(struct list_head *p)
274 {
275 	return !list_empty(p);
276 }
277 
278 /* Get the "struct epitem" from a wait queue pointer */
279 static inline struct epitem * ep_item_from_wait(wait_queue_t *p)
280 {
281 	return container_of(p, struct eppoll_entry, wait)->base;
282 }
283 
284 /* Get the "struct epitem" from an epoll queue wrapper */
285 static inline struct epitem * ep_item_from_epqueue(poll_table *p)
286 {
287 	return container_of(p, struct ep_pqueue, pt)->epi;
288 }
289 
290 /* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
291 static inline int ep_op_has_event(int op)
292 {
293 	return op != EPOLL_CTL_DEL;
294 }
295 
296 /* Initialize the poll safe wake up structure */
297 static void ep_poll_safewake_init(struct poll_safewake *psw)
298 {
299 
300 	INIT_LIST_HEAD(&psw->wake_task_list);
301 	spin_lock_init(&psw->lock);
302 }
303 
304 /*
305  * Perform a safe wake up of the poll wait list. The problem is that
306  * with the new callback'd wake up system, it is possible that the
307  * poll callback is reentered from inside the call to wake_up() done
308  * on the poll wait queue head. The rule is that we cannot reenter the
309  * wake up code from the same task more than EP_MAX_POLLWAKE_NESTS times,
310  * and we cannot reenter the same wait queue head at all. This will
311  * enable to have a hierarchy of epoll file descriptor of no more than
312  * EP_MAX_POLLWAKE_NESTS deep. We need the irq version of the spin lock
313  * because this one gets called by the poll callback, that in turn is called
314  * from inside a wake_up(), that might be called from irq context.
315  */
316 static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq)
317 {
318 	int wake_nests = 0;
319 	unsigned long flags;
320 	struct task_struct *this_task = current;
321 	struct list_head *lsthead = &psw->wake_task_list, *lnk;
322 	struct wake_task_node *tncur;
323 	struct wake_task_node tnode;
324 
325 	spin_lock_irqsave(&psw->lock, flags);
326 
327 	/* Try to see if the current task is already inside this wakeup call */
328 	list_for_each(lnk, lsthead) {
329 		tncur = list_entry(lnk, struct wake_task_node, llink);
330 
331 		if (tncur->wq == wq ||
332 		    (tncur->task == this_task && ++wake_nests > EP_MAX_POLLWAKE_NESTS)) {
333 			/*
334 			 * Ops ... loop detected or maximum nest level reached.
335 			 * We abort this wake by breaking the cycle itself.
336 			 */
337 			spin_unlock_irqrestore(&psw->lock, flags);
338 			return;
339 		}
340 	}
341 
342 	/* Add the current task to the list */
343 	tnode.task = this_task;
344 	tnode.wq = wq;
345 	list_add(&tnode.llink, lsthead);
346 
347 	spin_unlock_irqrestore(&psw->lock, flags);
348 
349 	/* Do really wake up now */
350 	wake_up(wq);
351 
352 	/* Remove the current task from the list */
353 	spin_lock_irqsave(&psw->lock, flags);
354 	list_del(&tnode.llink);
355 	spin_unlock_irqrestore(&psw->lock, flags);
356 }
357 
358 /*
359  * This function unregister poll callbacks from the associated file descriptor.
360  * Since this must be called without holding "ep->lock" the atomic exchange trick
361  * will protect us from multiple unregister.
362  */
363 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
364 {
365 	int nwait;
366 	struct list_head *lsthead = &epi->pwqlist;
367 	struct eppoll_entry *pwq;
368 
369 	/* This is called without locks, so we need the atomic exchange */
370 	nwait = xchg(&epi->nwait, 0);
371 
372 	if (nwait) {
373 		while (!list_empty(lsthead)) {
374 			pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
375 
376 			list_del_init(&pwq->llink);
377 			remove_wait_queue(pwq->whead, &pwq->wait);
378 			kmem_cache_free(pwq_cache, pwq);
379 		}
380 	}
381 }
382 
383 /*
384  * Unlink the "struct epitem" from all places it might have been hooked up.
385  * This function must be called with write IRQ lock on "ep->lock".
386  */
387 static int ep_unlink(struct eventpoll *ep, struct epitem *epi)
388 {
389 	int error;
390 
391 	/*
392 	 * It can happen that this one is called for an item already unlinked.
393 	 * The check protect us from doing a double unlink ( crash ).
394 	 */
395 	error = -ENOENT;
396 	if (!ep_rb_linked(&epi->rbn))
397 		goto error_return;
398 
399 	/*
400 	 * Clear the event mask for the unlinked item. This will avoid item
401 	 * notifications to be sent after the unlink operation from inside
402 	 * the kernel->userspace event transfer loop.
403 	 */
404 	epi->event.events = 0;
405 
406 	/*
407 	 * At this point is safe to do the job, unlink the item from our rb-tree.
408 	 * This operation togheter with the above check closes the door to
409 	 * double unlinks.
410 	 */
411 	ep_rb_erase(&epi->rbn, &ep->rbr);
412 
413 	/*
414 	 * If the item we are going to remove is inside the ready file descriptors
415 	 * we want to remove it from this list to avoid stale events.
416 	 */
417 	if (ep_is_linked(&epi->rdllink))
418 		list_del_init(&epi->rdllink);
419 
420 	error = 0;
421 error_return:
422 
423 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_unlink(%p, %p) = %d\n",
424 		     current, ep, epi->ffd.file, error));
425 
426 	return error;
427 }
428 
429 /*
430  * Increment the usage count of the "struct epitem" making it sure
431  * that the user will have a valid pointer to reference.
432  */
433 static void ep_use_epitem(struct epitem *epi)
434 {
435 	atomic_inc(&epi->usecnt);
436 }
437 
438 /*
439  * Decrement ( release ) the usage count by signaling that the user
440  * has finished using the structure. It might lead to freeing the
441  * structure itself if the count goes to zero.
442  */
443 static void ep_release_epitem(struct epitem *epi)
444 {
445 	if (atomic_dec_and_test(&epi->usecnt))
446 		kmem_cache_free(epi_cache, epi);
447 }
448 
449 /*
450  * Removes a "struct epitem" from the eventpoll RB tree and deallocates
451  * all the associated resources.
452  */
453 static int ep_remove(struct eventpoll *ep, struct epitem *epi)
454 {
455 	int error;
456 	unsigned long flags;
457 	struct file *file = epi->ffd.file;
458 
459 	/*
460 	 * Removes poll wait queue hooks. We _have_ to do this without holding
461 	 * the "ep->lock" otherwise a deadlock might occur. This because of the
462 	 * sequence of the lock acquisition. Here we do "ep->lock" then the wait
463 	 * queue head lock when unregistering the wait queue. The wakeup callback
464 	 * will run by holding the wait queue head lock and will call our callback
465 	 * that will try to get "ep->lock".
466 	 */
467 	ep_unregister_pollwait(ep, epi);
468 
469 	/* Remove the current item from the list of epoll hooks */
470 	spin_lock(&file->f_ep_lock);
471 	if (ep_is_linked(&epi->fllink))
472 		list_del_init(&epi->fllink);
473 	spin_unlock(&file->f_ep_lock);
474 
475 	/* We need to acquire the write IRQ lock before calling ep_unlink() */
476 	write_lock_irqsave(&ep->lock, flags);
477 
478 	/* Really unlink the item from the RB tree */
479 	error = ep_unlink(ep, epi);
480 
481 	write_unlock_irqrestore(&ep->lock, flags);
482 
483 	if (error)
484 		goto error_return;
485 
486 	/* At this point it is safe to free the eventpoll item */
487 	ep_release_epitem(epi);
488 
489 	error = 0;
490 error_return:
491 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_remove(%p, %p) = %d\n",
492 		     current, ep, file, error));
493 
494 	return error;
495 }
496 
497 static void ep_free(struct eventpoll *ep)
498 {
499 	struct rb_node *rbp;
500 	struct epitem *epi;
501 
502 	/* We need to release all tasks waiting for these file */
503 	if (waitqueue_active(&ep->poll_wait))
504 		ep_poll_safewake(&psw, &ep->poll_wait);
505 
506 	/*
507 	 * We need to lock this because we could be hit by
508 	 * eventpoll_release_file() while we're freeing the "struct eventpoll".
509 	 * We do not need to hold "ep->sem" here because the epoll file
510 	 * is on the way to be removed and no one has references to it
511 	 * anymore. The only hit might come from eventpoll_release_file() but
512 	 * holding "epmutex" is sufficent here.
513 	 */
514 	mutex_lock(&epmutex);
515 
516 	/*
517 	 * Walks through the whole tree by unregistering poll callbacks.
518 	 */
519 	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
520 		epi = rb_entry(rbp, struct epitem, rbn);
521 
522 		ep_unregister_pollwait(ep, epi);
523 	}
524 
525 	/*
526 	 * Walks through the whole tree by freeing each "struct epitem". At this
527 	 * point we are sure no poll callbacks will be lingering around, and also by
528 	 * write-holding "sem" we can be sure that no file cleanup code will hit
529 	 * us during this operation. So we can avoid the lock on "ep->lock".
530 	 */
531 	while ((rbp = rb_first(&ep->rbr)) != 0) {
532 		epi = rb_entry(rbp, struct epitem, rbn);
533 		ep_remove(ep, epi);
534 	}
535 
536 	mutex_unlock(&epmutex);
537 }
538 
539 static int ep_eventpoll_release(struct inode *inode, struct file *file)
540 {
541 	struct eventpoll *ep = file->private_data;
542 
543 	if (ep) {
544 		ep_free(ep);
545 		kfree(ep);
546 	}
547 
548 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: close() ep=%p\n", current, ep));
549 	return 0;
550 }
551 
552 static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
553 {
554 	unsigned int pollflags = 0;
555 	unsigned long flags;
556 	struct eventpoll *ep = file->private_data;
557 
558 	/* Insert inside our poll wait queue */
559 	poll_wait(file, &ep->poll_wait, wait);
560 
561 	/* Check our condition */
562 	read_lock_irqsave(&ep->lock, flags);
563 	if (!list_empty(&ep->rdllist))
564 		pollflags = POLLIN | POLLRDNORM;
565 	read_unlock_irqrestore(&ep->lock, flags);
566 
567 	return pollflags;
568 }
569 
570 /* File callbacks that implement the eventpoll file behaviour */
571 static const struct file_operations eventpoll_fops = {
572 	.release	= ep_eventpoll_release,
573 	.poll		= ep_eventpoll_poll
574 };
575 
576 /* Fast test to see if the file is an evenpoll file */
577 static inline int is_file_epoll(struct file *f)
578 {
579 	return f->f_op == &eventpoll_fops;
580 }
581 
582 /*
583  * This is called from eventpoll_release() to unlink files from the eventpoll
584  * interface. We need to have this facility to cleanup correctly files that are
585  * closed without being removed from the eventpoll interface.
586  */
587 void eventpoll_release_file(struct file *file)
588 {
589 	struct list_head *lsthead = &file->f_ep_links;
590 	struct eventpoll *ep;
591 	struct epitem *epi;
592 
593 	/*
594 	 * We don't want to get "file->f_ep_lock" because it is not
595 	 * necessary. It is not necessary because we're in the "struct file"
596 	 * cleanup path, and this means that noone is using this file anymore.
597 	 * The only hit might come from ep_free() but by holding the semaphore
598 	 * will correctly serialize the operation. We do need to acquire
599 	 * "ep->sem" after "epmutex" because ep_remove() requires it when called
600 	 * from anywhere but ep_free().
601 	 */
602 	mutex_lock(&epmutex);
603 
604 	while (!list_empty(lsthead)) {
605 		epi = list_first_entry(lsthead, struct epitem, fllink);
606 
607 		ep = epi->ep;
608 		list_del_init(&epi->fllink);
609 		down_write(&ep->sem);
610 		ep_remove(ep, epi);
611 		up_write(&ep->sem);
612 	}
613 
614 	mutex_unlock(&epmutex);
615 }
616 
617 static int ep_alloc(struct eventpoll **pep)
618 {
619 	struct eventpoll *ep = kzalloc(sizeof(*ep), GFP_KERNEL);
620 
621 	if (!ep)
622 		return -ENOMEM;
623 
624 	rwlock_init(&ep->lock);
625 	init_rwsem(&ep->sem);
626 	init_waitqueue_head(&ep->wq);
627 	init_waitqueue_head(&ep->poll_wait);
628 	INIT_LIST_HEAD(&ep->rdllist);
629 	ep->rbr = RB_ROOT;
630 
631 	*pep = ep;
632 
633 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_alloc() ep=%p\n",
634 		     current, ep));
635 	return 0;
636 }
637 
638 /*
639  * Search the file inside the eventpoll tree. It add usage count to
640  * the returned item, so the caller must call ep_release_epitem()
641  * after finished using the "struct epitem".
642  */
643 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
644 {
645 	int kcmp;
646 	unsigned long flags;
647 	struct rb_node *rbp;
648 	struct epitem *epi, *epir = NULL;
649 	struct epoll_filefd ffd;
650 
651 	ep_set_ffd(&ffd, file, fd);
652 	read_lock_irqsave(&ep->lock, flags);
653 	for (rbp = ep->rbr.rb_node; rbp; ) {
654 		epi = rb_entry(rbp, struct epitem, rbn);
655 		kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
656 		if (kcmp > 0)
657 			rbp = rbp->rb_right;
658 		else if (kcmp < 0)
659 			rbp = rbp->rb_left;
660 		else {
661 			ep_use_epitem(epi);
662 			epir = epi;
663 			break;
664 		}
665 	}
666 	read_unlock_irqrestore(&ep->lock, flags);
667 
668 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_find(%p) -> %p\n",
669 		     current, file, epir));
670 
671 	return epir;
672 }
673 
674 /*
675  * This is the callback that is passed to the wait queue wakeup
676  * machanism. It is called by the stored file descriptors when they
677  * have events to report.
678  */
679 static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
680 {
681 	int pwake = 0;
682 	unsigned long flags;
683 	struct epitem *epi = ep_item_from_wait(wait);
684 	struct eventpoll *ep = epi->ep;
685 
686 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: poll_callback(%p) epi=%p ep=%p\n",
687 		     current, epi->ffd.file, epi, ep));
688 
689 	write_lock_irqsave(&ep->lock, flags);
690 
691 	/*
692 	 * If the event mask does not contain any poll(2) event, we consider the
693 	 * descriptor to be disabled. This condition is likely the effect of the
694 	 * EPOLLONESHOT bit that disables the descriptor when an event is received,
695 	 * until the next EPOLL_CTL_MOD will be issued.
696 	 */
697 	if (!(epi->event.events & ~EP_PRIVATE_BITS))
698 		goto is_disabled;
699 
700 	/* If this file is already in the ready list we exit soon */
701 	if (ep_is_linked(&epi->rdllink))
702 		goto is_linked;
703 
704 	list_add_tail(&epi->rdllink, &ep->rdllist);
705 
706 is_linked:
707 	/*
708 	 * Wake up ( if active ) both the eventpoll wait list and the ->poll()
709 	 * wait list.
710 	 */
711 	if (waitqueue_active(&ep->wq))
712 		__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
713 				 TASK_INTERRUPTIBLE);
714 	if (waitqueue_active(&ep->poll_wait))
715 		pwake++;
716 
717 is_disabled:
718 	write_unlock_irqrestore(&ep->lock, flags);
719 
720 	/* We have to call this outside the lock */
721 	if (pwake)
722 		ep_poll_safewake(&psw, &ep->poll_wait);
723 
724 	return 1;
725 }
726 
727 /*
728  * This is the callback that is used to add our wait queue to the
729  * target file wakeup lists.
730  */
731 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
732 				 poll_table *pt)
733 {
734 	struct epitem *epi = ep_item_from_epqueue(pt);
735 	struct eppoll_entry *pwq;
736 
737 	if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
738 		init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
739 		pwq->whead = whead;
740 		pwq->base = epi;
741 		add_wait_queue(whead, &pwq->wait);
742 		list_add_tail(&pwq->llink, &epi->pwqlist);
743 		epi->nwait++;
744 	} else {
745 		/* We have to signal that an error occurred */
746 		epi->nwait = -1;
747 	}
748 }
749 
750 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
751 {
752 	int kcmp;
753 	struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
754 	struct epitem *epic;
755 
756 	while (*p) {
757 		parent = *p;
758 		epic = rb_entry(parent, struct epitem, rbn);
759 		kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
760 		if (kcmp > 0)
761 			p = &parent->rb_right;
762 		else
763 			p = &parent->rb_left;
764 	}
765 	rb_link_node(&epi->rbn, parent, p);
766 	rb_insert_color(&epi->rbn, &ep->rbr);
767 }
768 
769 static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
770 		     struct file *tfile, int fd)
771 {
772 	int error, revents, pwake = 0;
773 	unsigned long flags;
774 	struct epitem *epi;
775 	struct ep_pqueue epq;
776 
777 	error = -ENOMEM;
778 	if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
779 		goto error_return;
780 
781 	/* Item initialization follow here ... */
782 	ep_rb_initnode(&epi->rbn);
783 	INIT_LIST_HEAD(&epi->rdllink);
784 	INIT_LIST_HEAD(&epi->fllink);
785 	INIT_LIST_HEAD(&epi->pwqlist);
786 	epi->ep = ep;
787 	ep_set_ffd(&epi->ffd, tfile, fd);
788 	epi->event = *event;
789 	atomic_set(&epi->usecnt, 1);
790 	epi->nwait = 0;
791 
792 	/* Initialize the poll table using the queue callback */
793 	epq.epi = epi;
794 	init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
795 
796 	/*
797 	 * Attach the item to the poll hooks and get current event bits.
798 	 * We can safely use the file* here because its usage count has
799 	 * been increased by the caller of this function.
800 	 */
801 	revents = tfile->f_op->poll(tfile, &epq.pt);
802 
803 	/*
804 	 * We have to check if something went wrong during the poll wait queue
805 	 * install process. Namely an allocation for a wait queue failed due
806 	 * high memory pressure.
807 	 */
808 	if (epi->nwait < 0)
809 		goto error_unregister;
810 
811 	/* Add the current item to the list of active epoll hook for this file */
812 	spin_lock(&tfile->f_ep_lock);
813 	list_add_tail(&epi->fllink, &tfile->f_ep_links);
814 	spin_unlock(&tfile->f_ep_lock);
815 
816 	/* We have to drop the new item inside our item list to keep track of it */
817 	write_lock_irqsave(&ep->lock, flags);
818 
819 	/* Add the current item to the rb-tree */
820 	ep_rbtree_insert(ep, epi);
821 
822 	/* If the file is already "ready" we drop it inside the ready list */
823 	if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
824 		list_add_tail(&epi->rdllink, &ep->rdllist);
825 
826 		/* Notify waiting tasks that events are available */
827 		if (waitqueue_active(&ep->wq))
828 			__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE);
829 		if (waitqueue_active(&ep->poll_wait))
830 			pwake++;
831 	}
832 
833 	write_unlock_irqrestore(&ep->lock, flags);
834 
835 	/* We have to call this outside the lock */
836 	if (pwake)
837 		ep_poll_safewake(&psw, &ep->poll_wait);
838 
839 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_insert(%p, %p, %d)\n",
840 		     current, ep, tfile, fd));
841 
842 	return 0;
843 
844 error_unregister:
845 	ep_unregister_pollwait(ep, epi);
846 
847 	/*
848 	 * We need to do this because an event could have been arrived on some
849 	 * allocated wait queue.
850 	 */
851 	write_lock_irqsave(&ep->lock, flags);
852 	if (ep_is_linked(&epi->rdllink))
853 		list_del_init(&epi->rdllink);
854 	write_unlock_irqrestore(&ep->lock, flags);
855 
856 	kmem_cache_free(epi_cache, epi);
857 error_return:
858 	return error;
859 }
860 
861 /*
862  * Modify the interest event mask by dropping an event if the new mask
863  * has a match in the current file status.
864  */
865 static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
866 {
867 	int pwake = 0;
868 	unsigned int revents;
869 	unsigned long flags;
870 
871 	/*
872 	 * Set the new event interest mask before calling f_op->poll(), otherwise
873 	 * a potential race might occur. In fact if we do this operation inside
874 	 * the lock, an event might happen between the f_op->poll() call and the
875 	 * new event set registering.
876 	 */
877 	epi->event.events = event->events;
878 
879 	/*
880 	 * Get current event bits. We can safely use the file* here because
881 	 * its usage count has been increased by the caller of this function.
882 	 */
883 	revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
884 
885 	write_lock_irqsave(&ep->lock, flags);
886 
887 	/* Copy the data member from inside the lock */
888 	epi->event.data = event->data;
889 
890 	/*
891 	 * If the item is not linked to the RB tree it means that it's on its
892 	 * way toward the removal. Do nothing in this case.
893 	 */
894 	if (ep_rb_linked(&epi->rbn)) {
895 		/*
896 		 * If the item is "hot" and it is not registered inside the ready
897 		 * list, push it inside. If the item is not "hot" and it is currently
898 		 * registered inside the ready list, unlink it.
899 		 */
900 		if (revents & event->events) {
901 			if (!ep_is_linked(&epi->rdllink)) {
902 				list_add_tail(&epi->rdllink, &ep->rdllist);
903 
904 				/* Notify waiting tasks that events are available */
905 				if (waitqueue_active(&ep->wq))
906 					__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
907 							 TASK_INTERRUPTIBLE);
908 				if (waitqueue_active(&ep->poll_wait))
909 					pwake++;
910 			}
911 		}
912 	}
913 
914 	write_unlock_irqrestore(&ep->lock, flags);
915 
916 	/* We have to call this outside the lock */
917 	if (pwake)
918 		ep_poll_safewake(&psw, &ep->poll_wait);
919 
920 	return 0;
921 }
922 
923 /*
924  * This function is called without holding the "ep->lock" since the call to
925  * __copy_to_user() might sleep, and also f_op->poll() might reenable the IRQ
926  * because of the way poll() is traditionally implemented in Linux.
927  */
928 static int ep_send_events(struct eventpoll *ep, struct list_head *txlist,
929 			  struct epoll_event __user *events, int maxevents)
930 {
931 	int eventcnt, error = -EFAULT, pwake = 0;
932 	unsigned int revents;
933 	unsigned long flags;
934 	struct epitem *epi;
935 	struct list_head injlist;
936 
937 	INIT_LIST_HEAD(&injlist);
938 
939 	/*
940 	 * We can loop without lock because this is a task private list.
941 	 * We just splice'd out the ep->rdllist in ep_collect_ready_items().
942 	 * Items cannot vanish during the loop because we are holding "sem" in
943 	 * read.
944 	 */
945 	for (eventcnt = 0; !list_empty(txlist) && eventcnt < maxevents;) {
946 		epi = list_first_entry(txlist, struct epitem, rdllink);
947 		prefetch(epi->rdllink.next);
948 
949 		/*
950 		 * Get the ready file event set. We can safely use the file
951 		 * because we are holding the "sem" in read and this will
952 		 * guarantee that both the file and the item will not vanish.
953 		 */
954 		revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
955 		revents &= epi->event.events;
956 
957 		/*
958 		 * Is the event mask intersect the caller-requested one,
959 		 * deliver the event to userspace. Again, we are holding
960 		 * "sem" in read, so no operations coming from userspace
961 		 * can change the item.
962 		 */
963 		if (revents) {
964 			if (__put_user(revents,
965 				       &events[eventcnt].events) ||
966 			    __put_user(epi->event.data,
967 				       &events[eventcnt].data))
968 				goto errxit;
969 			if (epi->event.events & EPOLLONESHOT)
970 				epi->event.events &= EP_PRIVATE_BITS;
971 			eventcnt++;
972 		}
973 
974 		/*
975 		 * This is tricky. We are holding the "sem" in read, and this
976 		 * means that the operations that can change the "linked" status
977 		 * of the epoll item (epi->rbn and epi->rdllink), cannot touch
978 		 * them.  Also, since we are "linked" from a epi->rdllink POV
979 		 * (the item is linked to our transmission list we just
980 		 * spliced), the ep_poll_callback() cannot touch us either,
981 		 * because of the check present in there. Another parallel
982 		 * epoll_wait() will not get the same result set, since we
983 		 * spliced the ready list before.  Note that list_del() still
984 		 * shows the item as linked to the test in ep_poll_callback().
985 		 */
986 		list_del(&epi->rdllink);
987 		if (!(epi->event.events & EPOLLET) &&
988 				(revents & epi->event.events))
989 			list_add_tail(&epi->rdllink, &injlist);
990 		else {
991 			/*
992 			 * Be sure the item is totally detached before re-init
993 			 * the list_head. After INIT_LIST_HEAD() is committed,
994 			 * the ep_poll_callback() can requeue the item again,
995 			 * but we don't care since we are already past it.
996 			 */
997 			smp_mb();
998 			INIT_LIST_HEAD(&epi->rdllink);
999 		}
1000 	}
1001 	error = 0;
1002 
1003 	errxit:
1004 
1005 	/*
1006 	 * If the re-injection list or the txlist are not empty, re-splice
1007 	 * them to the ready list and do proper wakeups.
1008 	 */
1009 	if (!list_empty(&injlist) || !list_empty(txlist)) {
1010 		write_lock_irqsave(&ep->lock, flags);
1011 
1012 		list_splice(txlist, &ep->rdllist);
1013 		list_splice(&injlist, &ep->rdllist);
1014 		/*
1015 		 * Wake up ( if active ) both the eventpoll wait list and the ->poll()
1016 		 * wait list.
1017 		 */
1018 		if (waitqueue_active(&ep->wq))
1019 			__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
1020 					 TASK_INTERRUPTIBLE);
1021 		if (waitqueue_active(&ep->poll_wait))
1022 			pwake++;
1023 
1024 		write_unlock_irqrestore(&ep->lock, flags);
1025 	}
1026 
1027 	/* We have to call this outside the lock */
1028 	if (pwake)
1029 		ep_poll_safewake(&psw, &ep->poll_wait);
1030 
1031 	return eventcnt == 0 ? error: eventcnt;
1032 }
1033 
1034 /*
1035  * Perform the transfer of events to user space.
1036  */
1037 static int ep_events_transfer(struct eventpoll *ep,
1038 			      struct epoll_event __user *events, int maxevents)
1039 {
1040 	int eventcnt;
1041 	unsigned long flags;
1042 	struct list_head txlist;
1043 
1044 	INIT_LIST_HEAD(&txlist);
1045 
1046 	/*
1047 	 * We need to lock this because we could be hit by
1048 	 * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL).
1049 	 */
1050 	down_read(&ep->sem);
1051 
1052 	/*
1053 	 * Steal the ready list, and re-init the original one to the
1054 	 * empty list.
1055 	 */
1056 	write_lock_irqsave(&ep->lock, flags);
1057 	list_splice(&ep->rdllist, &txlist);
1058 	INIT_LIST_HEAD(&ep->rdllist);
1059 	write_unlock_irqrestore(&ep->lock, flags);
1060 
1061 	/* Build result set in userspace */
1062 	eventcnt = ep_send_events(ep, &txlist, events, maxevents);
1063 
1064 	up_read(&ep->sem);
1065 
1066 	return eventcnt;
1067 }
1068 
1069 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1070 		   int maxevents, long timeout)
1071 {
1072 	int res, eavail;
1073 	unsigned long flags;
1074 	long jtimeout;
1075 	wait_queue_t wait;
1076 
1077 	/*
1078 	 * Calculate the timeout by checking for the "infinite" value ( -1 )
1079 	 * and the overflow condition. The passed timeout is in milliseconds,
1080 	 * that why (t * HZ) / 1000.
1081 	 */
1082 	jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ?
1083 		MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000;
1084 
1085 retry:
1086 	write_lock_irqsave(&ep->lock, flags);
1087 
1088 	res = 0;
1089 	if (list_empty(&ep->rdllist)) {
1090 		/*
1091 		 * We don't have any available event to return to the caller.
1092 		 * We need to sleep here, and we will be wake up by
1093 		 * ep_poll_callback() when events will become available.
1094 		 */
1095 		init_waitqueue_entry(&wait, current);
1096 		__add_wait_queue(&ep->wq, &wait);
1097 
1098 		for (;;) {
1099 			/*
1100 			 * We don't want to sleep if the ep_poll_callback() sends us
1101 			 * a wakeup in between. That's why we set the task state
1102 			 * to TASK_INTERRUPTIBLE before doing the checks.
1103 			 */
1104 			set_current_state(TASK_INTERRUPTIBLE);
1105 			if (!list_empty(&ep->rdllist) || !jtimeout)
1106 				break;
1107 			if (signal_pending(current)) {
1108 				res = -EINTR;
1109 				break;
1110 			}
1111 
1112 			write_unlock_irqrestore(&ep->lock, flags);
1113 			jtimeout = schedule_timeout(jtimeout);
1114 			write_lock_irqsave(&ep->lock, flags);
1115 		}
1116 		__remove_wait_queue(&ep->wq, &wait);
1117 
1118 		set_current_state(TASK_RUNNING);
1119 	}
1120 
1121 	/* Is it worth to try to dig for events ? */
1122 	eavail = !list_empty(&ep->rdllist);
1123 
1124 	write_unlock_irqrestore(&ep->lock, flags);
1125 
1126 	/*
1127 	 * Try to transfer events to user space. In case we get 0 events and
1128 	 * there's still timeout left over, we go trying again in search of
1129 	 * more luck.
1130 	 */
1131 	if (!res && eavail &&
1132 	    !(res = ep_events_transfer(ep, events, maxevents)) && jtimeout)
1133 		goto retry;
1134 
1135 	return res;
1136 }
1137 
1138 /*
1139  * It opens an eventpoll file descriptor by suggesting a storage of "size"
1140  * file descriptors. The size parameter is just an hint about how to size
1141  * data structures. It won't prevent the user to store more than "size"
1142  * file descriptors inside the epoll interface. It is the kernel part of
1143  * the userspace epoll_create(2).
1144  */
1145 asmlinkage long sys_epoll_create(int size)
1146 {
1147 	int error, fd = -1;
1148 	struct eventpoll *ep;
1149 	struct inode *inode;
1150 	struct file *file;
1151 
1152 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n",
1153 		     current, size));
1154 
1155 	/*
1156 	 * Sanity check on the size parameter, and create the internal data
1157 	 * structure ( "struct eventpoll" ).
1158 	 */
1159 	error = -EINVAL;
1160 	if (size <= 0 || (error = ep_alloc(&ep)) != 0)
1161 		goto error_return;
1162 
1163 	/*
1164 	 * Creates all the items needed to setup an eventpoll file. That is,
1165 	 * a file structure, and inode and a free file descriptor.
1166 	 */
1167 	error = anon_inode_getfd(&fd, &inode, &file, "[eventpoll]",
1168 				 &eventpoll_fops, ep);
1169 	if (error)
1170 		goto error_free;
1171 
1172 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
1173 		     current, size, fd));
1174 
1175 	return fd;
1176 
1177 error_free:
1178 	ep_free(ep);
1179 	kfree(ep);
1180 error_return:
1181 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
1182 		     current, size, error));
1183 	return error;
1184 }
1185 
1186 /*
1187  * The following function implements the controller interface for
1188  * the eventpoll file that enables the insertion/removal/change of
1189  * file descriptors inside the interest set.  It represents
1190  * the kernel part of the user space epoll_ctl(2).
1191  */
1192 asmlinkage long sys_epoll_ctl(int epfd, int op, int fd,
1193 			      struct epoll_event __user *event)
1194 {
1195 	int error;
1196 	struct file *file, *tfile;
1197 	struct eventpoll *ep;
1198 	struct epitem *epi;
1199 	struct epoll_event epds;
1200 
1201 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p)\n",
1202 		     current, epfd, op, fd, event));
1203 
1204 	error = -EFAULT;
1205 	if (ep_op_has_event(op) &&
1206 	    copy_from_user(&epds, event, sizeof(struct epoll_event)))
1207 		goto error_return;
1208 
1209 	/* Get the "struct file *" for the eventpoll file */
1210 	error = -EBADF;
1211 	file = fget(epfd);
1212 	if (!file)
1213 		goto error_return;
1214 
1215 	/* Get the "struct file *" for the target file */
1216 	tfile = fget(fd);
1217 	if (!tfile)
1218 		goto error_fput;
1219 
1220 	/* The target file descriptor must support poll */
1221 	error = -EPERM;
1222 	if (!tfile->f_op || !tfile->f_op->poll)
1223 		goto error_tgt_fput;
1224 
1225 	/*
1226 	 * We have to check that the file structure underneath the file descriptor
1227 	 * the user passed to us _is_ an eventpoll file. And also we do not permit
1228 	 * adding an epoll file descriptor inside itself.
1229 	 */
1230 	error = -EINVAL;
1231 	if (file == tfile || !is_file_epoll(file))
1232 		goto error_tgt_fput;
1233 
1234 	/*
1235 	 * At this point it is safe to assume that the "private_data" contains
1236 	 * our own data structure.
1237 	 */
1238 	ep = file->private_data;
1239 
1240 	down_write(&ep->sem);
1241 
1242 	/* Try to lookup the file inside our RB tree */
1243 	epi = ep_find(ep, tfile, fd);
1244 
1245 	error = -EINVAL;
1246 	switch (op) {
1247 	case EPOLL_CTL_ADD:
1248 		if (!epi) {
1249 			epds.events |= POLLERR | POLLHUP;
1250 
1251 			error = ep_insert(ep, &epds, tfile, fd);
1252 		} else
1253 			error = -EEXIST;
1254 		break;
1255 	case EPOLL_CTL_DEL:
1256 		if (epi)
1257 			error = ep_remove(ep, epi);
1258 		else
1259 			error = -ENOENT;
1260 		break;
1261 	case EPOLL_CTL_MOD:
1262 		if (epi) {
1263 			epds.events |= POLLERR | POLLHUP;
1264 			error = ep_modify(ep, epi, &epds);
1265 		} else
1266 			error = -ENOENT;
1267 		break;
1268 	}
1269 	/*
1270 	 * The function ep_find() increments the usage count of the structure
1271 	 * so, if this is not NULL, we need to release it.
1272 	 */
1273 	if (epi)
1274 		ep_release_epitem(epi);
1275 	up_write(&ep->sem);
1276 
1277 error_tgt_fput:
1278 	fput(tfile);
1279 error_fput:
1280 	fput(file);
1281 error_return:
1282 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p) = %d\n",
1283 		     current, epfd, op, fd, event, error));
1284 
1285 	return error;
1286 }
1287 
1288 /*
1289  * Implement the event wait interface for the eventpoll file. It is the kernel
1290  * part of the user space epoll_wait(2).
1291  */
1292 asmlinkage long sys_epoll_wait(int epfd, struct epoll_event __user *events,
1293 			       int maxevents, int timeout)
1294 {
1295 	int error;
1296 	struct file *file;
1297 	struct eventpoll *ep;
1298 
1299 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d)\n",
1300 		     current, epfd, events, maxevents, timeout));
1301 
1302 	/* The maximum number of event must be greater than zero */
1303 	if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
1304 		return -EINVAL;
1305 
1306 	/* Verify that the area passed by the user is writeable */
1307 	if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event))) {
1308 		error = -EFAULT;
1309 		goto error_return;
1310 	}
1311 
1312 	/* Get the "struct file *" for the eventpoll file */
1313 	error = -EBADF;
1314 	file = fget(epfd);
1315 	if (!file)
1316 		goto error_return;
1317 
1318 	/*
1319 	 * We have to check that the file structure underneath the fd
1320 	 * the user passed to us _is_ an eventpoll file.
1321 	 */
1322 	error = -EINVAL;
1323 	if (!is_file_epoll(file))
1324 		goto error_fput;
1325 
1326 	/*
1327 	 * At this point it is safe to assume that the "private_data" contains
1328 	 * our own data structure.
1329 	 */
1330 	ep = file->private_data;
1331 
1332 	/* Time to fish for events ... */
1333 	error = ep_poll(ep, events, maxevents, timeout);
1334 
1335 error_fput:
1336 	fput(file);
1337 error_return:
1338 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d) = %d\n",
1339 		     current, epfd, events, maxevents, timeout, error));
1340 
1341 	return error;
1342 }
1343 
1344 #ifdef TIF_RESTORE_SIGMASK
1345 
1346 /*
1347  * Implement the event wait interface for the eventpoll file. It is the kernel
1348  * part of the user space epoll_pwait(2).
1349  */
1350 asmlinkage long sys_epoll_pwait(int epfd, struct epoll_event __user *events,
1351 		int maxevents, int timeout, const sigset_t __user *sigmask,
1352 		size_t sigsetsize)
1353 {
1354 	int error;
1355 	sigset_t ksigmask, sigsaved;
1356 
1357 	/*
1358 	 * If the caller wants a certain signal mask to be set during the wait,
1359 	 * we apply it here.
1360 	 */
1361 	if (sigmask) {
1362 		if (sigsetsize != sizeof(sigset_t))
1363 			return -EINVAL;
1364 		if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
1365 			return -EFAULT;
1366 		sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
1367 		sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
1368 	}
1369 
1370 	error = sys_epoll_wait(epfd, events, maxevents, timeout);
1371 
1372 	/*
1373 	 * If we changed the signal mask, we need to restore the original one.
1374 	 * In case we've got a signal while waiting, we do not restore the
1375 	 * signal mask yet, and we allow do_signal() to deliver the signal on
1376 	 * the way back to userspace, before the signal mask is restored.
1377 	 */
1378 	if (sigmask) {
1379 		if (error == -EINTR) {
1380 			memcpy(&current->saved_sigmask, &sigsaved,
1381 				sizeof(sigsaved));
1382 			set_thread_flag(TIF_RESTORE_SIGMASK);
1383 		} else
1384 			sigprocmask(SIG_SETMASK, &sigsaved, NULL);
1385 	}
1386 
1387 	return error;
1388 }
1389 
1390 #endif /* #ifdef TIF_RESTORE_SIGMASK */
1391 
1392 static int __init eventpoll_init(void)
1393 {
1394 	mutex_init(&epmutex);
1395 
1396 	/* Initialize the structure used to perform safe poll wait head wake ups */
1397 	ep_poll_safewake_init(&psw);
1398 
1399 	/* Allocates slab cache used to allocate "struct epitem" items */
1400 	epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
1401 			0, SLAB_HWCACHE_ALIGN|EPI_SLAB_DEBUG|SLAB_PANIC,
1402 			NULL, NULL);
1403 
1404 	/* Allocates slab cache used to allocate "struct eppoll_entry" */
1405 	pwq_cache = kmem_cache_create("eventpoll_pwq",
1406 			sizeof(struct eppoll_entry), 0,
1407 			EPI_SLAB_DEBUG|SLAB_PANIC, NULL, NULL);
1408 
1409 	return 0;
1410 }
1411 fs_initcall(eventpoll_init);
1412 
1413