xref: /openbmc/linux/fs/eventpoll.c (revision 643d1f7f)
1 /*
2  *  fs/eventpoll.c (Efficent event polling implementation)
3  *  Copyright (C) 2001,...,2007	 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 <asm/uaccess.h>
37 #include <asm/system.h>
38 #include <asm/io.h>
39 #include <asm/mman.h>
40 #include <asm/atomic.h>
41 
42 /*
43  * LOCKING:
44  * There are three level of locking required by epoll :
45  *
46  * 1) epmutex (mutex)
47  * 2) ep->mtx (mutex)
48  * 3) ep->lock (spinlock)
49  *
50  * The acquire order is the one listed above, from 1 to 3.
51  * We need a spinlock (ep->lock) because we manipulate objects
52  * from inside the poll callback, that might be triggered from
53  * a wake_up() that in turn might be called from IRQ context.
54  * So we can't sleep inside the poll callback and hence we need
55  * a spinlock. During the event transfer loop (from kernel to
56  * user space) we could end up sleeping due a copy_to_user(), so
57  * we need a lock that will allow us to sleep. This lock is a
58  * mutex (ep->mtx). It is acquired during the event transfer loop,
59  * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
60  * Then we also need a global mutex to serialize eventpoll_release_file()
61  * and ep_free().
62  * This mutex is acquired by ep_free() during the epoll file
63  * cleanup path and it is also acquired by eventpoll_release_file()
64  * if a file has been pushed inside an epoll set and it is then
65  * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL).
66  * It is possible to drop the "ep->mtx" and to use the global
67  * mutex "epmutex" (together with "ep->lock") to have it working,
68  * but having "ep->mtx" will make the interface more scalable.
69  * Events that require holding "epmutex" are very rare, while for
70  * normal operations the epoll private "ep->mtx" will guarantee
71  * a better scalability.
72  */
73 
74 #define DEBUG_EPOLL 0
75 
76 #if DEBUG_EPOLL > 0
77 #define DPRINTK(x) printk x
78 #define DNPRINTK(n, x) do { if ((n) <= DEBUG_EPOLL) printk x; } while (0)
79 #else /* #if DEBUG_EPOLL > 0 */
80 #define DPRINTK(x) (void) 0
81 #define DNPRINTK(n, x) (void) 0
82 #endif /* #if DEBUG_EPOLL > 0 */
83 
84 #define DEBUG_EPI 0
85 
86 #if DEBUG_EPI != 0
87 #define EPI_SLAB_DEBUG (SLAB_DEBUG_FREE | SLAB_RED_ZONE /* | SLAB_POISON */)
88 #else /* #if DEBUG_EPI != 0 */
89 #define EPI_SLAB_DEBUG 0
90 #endif /* #if DEBUG_EPI != 0 */
91 
92 /* Epoll private bits inside the event mask */
93 #define EP_PRIVATE_BITS (EPOLLONESHOT | EPOLLET)
94 
95 /* Maximum number of poll wake up nests we are allowing */
96 #define EP_MAX_POLLWAKE_NESTS 4
97 
98 /* Maximum msec timeout value storeable in a long int */
99 #define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ)
100 
101 #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
102 
103 #define EP_UNACTIVE_PTR ((void *) -1L)
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  * Each file descriptor added to the eventpoll interface will
134  * have an entry of this type linked to the "rbr" RB tree.
135  */
136 struct epitem {
137 	/* RB tree node used to link this structure to the eventpoll RB tree */
138 	struct rb_node rbn;
139 
140 	/* List header used to link this structure to the eventpoll ready list */
141 	struct list_head rdllink;
142 
143 	/*
144 	 * Works together "struct eventpoll"->ovflist in keeping the
145 	 * single linked chain of items.
146 	 */
147 	struct epitem *next;
148 
149 	/* The file descriptor information this item refers to */
150 	struct epoll_filefd ffd;
151 
152 	/* Number of active wait queue attached to poll operations */
153 	int nwait;
154 
155 	/* List containing poll wait queues */
156 	struct list_head pwqlist;
157 
158 	/* The "container" of this item */
159 	struct eventpoll *ep;
160 
161 	/* List header used to link this item to the "struct file" items list */
162 	struct list_head fllink;
163 
164 	/* The structure that describe the interested events and the source fd */
165 	struct epoll_event event;
166 };
167 
168 /*
169  * This structure is stored inside the "private_data" member of the file
170  * structure and rapresent the main data sructure for the eventpoll
171  * interface.
172  */
173 struct eventpoll {
174 	/* Protect the this structure access */
175 	spinlock_t lock;
176 
177 	/*
178 	 * This mutex is used to ensure that files are not removed
179 	 * while epoll is using them. This is held during the event
180 	 * collection loop, the file cleanup path, the epoll file exit
181 	 * code and the ctl operations.
182 	 */
183 	struct mutex mtx;
184 
185 	/* Wait queue used by sys_epoll_wait() */
186 	wait_queue_head_t wq;
187 
188 	/* Wait queue used by file->poll() */
189 	wait_queue_head_t poll_wait;
190 
191 	/* List of ready file descriptors */
192 	struct list_head rdllist;
193 
194 	/* RB tree root used to store monitored fd structs */
195 	struct rb_root rbr;
196 
197 	/*
198 	 * This is a single linked list that chains all the "struct epitem" that
199 	 * happened while transfering ready events to userspace w/out
200 	 * holding ->lock.
201 	 */
202 	struct epitem *ovflist;
203 };
204 
205 /* Wait structure used by the poll hooks */
206 struct eppoll_entry {
207 	/* List header used to link this structure to the "struct epitem" */
208 	struct list_head llink;
209 
210 	/* The "base" pointer is set to the container "struct epitem" */
211 	void *base;
212 
213 	/*
214 	 * Wait queue item that will be linked to the target file wait
215 	 * queue head.
216 	 */
217 	wait_queue_t wait;
218 
219 	/* The wait queue head that linked the "wait" wait queue item */
220 	wait_queue_head_t *whead;
221 };
222 
223 /* Wrapper struct used by poll queueing */
224 struct ep_pqueue {
225 	poll_table pt;
226 	struct epitem *epi;
227 };
228 
229 /*
230  * This mutex is used to serialize ep_free() and eventpoll_release_file().
231  */
232 static struct mutex epmutex;
233 
234 /* Safe wake up implementation */
235 static struct poll_safewake psw;
236 
237 /* Slab cache used to allocate "struct epitem" */
238 static struct kmem_cache *epi_cache __read_mostly;
239 
240 /* Slab cache used to allocate "struct eppoll_entry" */
241 static struct kmem_cache *pwq_cache __read_mostly;
242 
243 
244 /* Setup the structure that is used as key for the RB tree */
245 static inline void ep_set_ffd(struct epoll_filefd *ffd,
246 			      struct file *file, int fd)
247 {
248 	ffd->file = file;
249 	ffd->fd = fd;
250 }
251 
252 /* Compare RB tree keys */
253 static inline int ep_cmp_ffd(struct epoll_filefd *p1,
254 			     struct epoll_filefd *p2)
255 {
256 	return (p1->file > p2->file ? +1:
257 	        (p1->file < p2->file ? -1 : p1->fd - p2->fd));
258 }
259 
260 /* Special initialization for the RB tree node to detect linkage */
261 static inline void ep_rb_initnode(struct rb_node *n)
262 {
263 	rb_set_parent(n, n);
264 }
265 
266 /* Removes a node from the RB tree and marks it for a fast is-linked check */
267 static inline void ep_rb_erase(struct rb_node *n, struct rb_root *r)
268 {
269 	rb_erase(n, r);
270 	rb_set_parent(n, n);
271 }
272 
273 /* Fast check to verify that the item is linked to the main RB tree */
274 static inline int ep_rb_linked(struct rb_node *n)
275 {
276 	return rb_parent(n) != n;
277 }
278 
279 /* Tells us if the item is currently linked */
280 static inline int ep_is_linked(struct list_head *p)
281 {
282 	return !list_empty(p);
283 }
284 
285 /* Get the "struct epitem" from a wait queue pointer */
286 static inline struct epitem * ep_item_from_wait(wait_queue_t *p)
287 {
288 	return container_of(p, struct eppoll_entry, wait)->base;
289 }
290 
291 /* Get the "struct epitem" from an epoll queue wrapper */
292 static inline struct epitem * ep_item_from_epqueue(poll_table *p)
293 {
294 	return container_of(p, struct ep_pqueue, pt)->epi;
295 }
296 
297 /* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
298 static inline int ep_op_has_event(int op)
299 {
300 	return op != EPOLL_CTL_DEL;
301 }
302 
303 /* Initialize the poll safe wake up structure */
304 static void ep_poll_safewake_init(struct poll_safewake *psw)
305 {
306 
307 	INIT_LIST_HEAD(&psw->wake_task_list);
308 	spin_lock_init(&psw->lock);
309 }
310 
311 /*
312  * Perform a safe wake up of the poll wait list. The problem is that
313  * with the new callback'd wake up system, it is possible that the
314  * poll callback is reentered from inside the call to wake_up() done
315  * on the poll wait queue head. The rule is that we cannot reenter the
316  * wake up code from the same task more than EP_MAX_POLLWAKE_NESTS times,
317  * and we cannot reenter the same wait queue head at all. This will
318  * enable to have a hierarchy of epoll file descriptor of no more than
319  * EP_MAX_POLLWAKE_NESTS deep. We need the irq version of the spin lock
320  * because this one gets called by the poll callback, that in turn is called
321  * from inside a wake_up(), that might be called from irq context.
322  */
323 static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq)
324 {
325 	int wake_nests = 0;
326 	unsigned long flags;
327 	struct task_struct *this_task = current;
328 	struct list_head *lsthead = &psw->wake_task_list;
329 	struct wake_task_node *tncur;
330 	struct wake_task_node tnode;
331 
332 	spin_lock_irqsave(&psw->lock, flags);
333 
334 	/* Try to see if the current task is already inside this wakeup call */
335 	list_for_each_entry(tncur, lsthead, llink) {
336 
337 		if (tncur->wq == wq ||
338 		    (tncur->task == this_task && ++wake_nests > EP_MAX_POLLWAKE_NESTS)) {
339 			/*
340 			 * Ops ... loop detected or maximum nest level reached.
341 			 * We abort this wake by breaking the cycle itself.
342 			 */
343 			spin_unlock_irqrestore(&psw->lock, flags);
344 			return;
345 		}
346 	}
347 
348 	/* Add the current task to the list */
349 	tnode.task = this_task;
350 	tnode.wq = wq;
351 	list_add(&tnode.llink, lsthead);
352 
353 	spin_unlock_irqrestore(&psw->lock, flags);
354 
355 	/* Do really wake up now */
356 	wake_up(wq);
357 
358 	/* Remove the current task from the list */
359 	spin_lock_irqsave(&psw->lock, flags);
360 	list_del(&tnode.llink);
361 	spin_unlock_irqrestore(&psw->lock, flags);
362 }
363 
364 /*
365  * This function unregister poll callbacks from the associated file descriptor.
366  * Since this must be called without holding "ep->lock" the atomic exchange trick
367  * will protect us from multiple unregister.
368  */
369 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
370 {
371 	int nwait;
372 	struct list_head *lsthead = &epi->pwqlist;
373 	struct eppoll_entry *pwq;
374 
375 	/* This is called without locks, so we need the atomic exchange */
376 	nwait = xchg(&epi->nwait, 0);
377 
378 	if (nwait) {
379 		while (!list_empty(lsthead)) {
380 			pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
381 
382 			list_del_init(&pwq->llink);
383 			remove_wait_queue(pwq->whead, &pwq->wait);
384 			kmem_cache_free(pwq_cache, pwq);
385 		}
386 	}
387 }
388 
389 /*
390  * Removes a "struct epitem" from the eventpoll RB tree and deallocates
391  * all the associated resources. Must be called with "mtx" held.
392  */
393 static int ep_remove(struct eventpoll *ep, struct epitem *epi)
394 {
395 	unsigned long flags;
396 	struct file *file = epi->ffd.file;
397 
398 	/*
399 	 * Removes poll wait queue hooks. We _have_ to do this without holding
400 	 * the "ep->lock" otherwise a deadlock might occur. This because of the
401 	 * sequence of the lock acquisition. Here we do "ep->lock" then the wait
402 	 * queue head lock when unregistering the wait queue. The wakeup callback
403 	 * will run by holding the wait queue head lock and will call our callback
404 	 * that will try to get "ep->lock".
405 	 */
406 	ep_unregister_pollwait(ep, epi);
407 
408 	/* Remove the current item from the list of epoll hooks */
409 	spin_lock(&file->f_ep_lock);
410 	if (ep_is_linked(&epi->fllink))
411 		list_del_init(&epi->fllink);
412 	spin_unlock(&file->f_ep_lock);
413 
414 	if (ep_rb_linked(&epi->rbn))
415 		ep_rb_erase(&epi->rbn, &ep->rbr);
416 
417 	spin_lock_irqsave(&ep->lock, flags);
418 	if (ep_is_linked(&epi->rdllink))
419 		list_del_init(&epi->rdllink);
420 	spin_unlock_irqrestore(&ep->lock, flags);
421 
422 	/* At this point it is safe to free the eventpoll item */
423 	kmem_cache_free(epi_cache, epi);
424 
425 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_remove(%p, %p)\n",
426 		     current, ep, file));
427 
428 	return 0;
429 }
430 
431 static void ep_free(struct eventpoll *ep)
432 {
433 	struct rb_node *rbp;
434 	struct epitem *epi;
435 
436 	/* We need to release all tasks waiting for these file */
437 	if (waitqueue_active(&ep->poll_wait))
438 		ep_poll_safewake(&psw, &ep->poll_wait);
439 
440 	/*
441 	 * We need to lock this because we could be hit by
442 	 * eventpoll_release_file() while we're freeing the "struct eventpoll".
443 	 * We do not need to hold "ep->mtx" here because the epoll file
444 	 * is on the way to be removed and no one has references to it
445 	 * anymore. The only hit might come from eventpoll_release_file() but
446 	 * holding "epmutex" is sufficent here.
447 	 */
448 	mutex_lock(&epmutex);
449 
450 	/*
451 	 * Walks through the whole tree by unregistering poll callbacks.
452 	 */
453 	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
454 		epi = rb_entry(rbp, struct epitem, rbn);
455 
456 		ep_unregister_pollwait(ep, epi);
457 	}
458 
459 	/*
460 	 * Walks through the whole tree by freeing each "struct epitem". At this
461 	 * point we are sure no poll callbacks will be lingering around, and also by
462 	 * holding "epmutex" we can be sure that no file cleanup code will hit
463 	 * us during this operation. So we can avoid the lock on "ep->lock".
464 	 */
465 	while ((rbp = rb_first(&ep->rbr)) != NULL) {
466 		epi = rb_entry(rbp, struct epitem, rbn);
467 		ep_remove(ep, epi);
468 	}
469 
470 	mutex_unlock(&epmutex);
471 	mutex_destroy(&ep->mtx);
472 	kfree(ep);
473 }
474 
475 static int ep_eventpoll_release(struct inode *inode, struct file *file)
476 {
477 	struct eventpoll *ep = file->private_data;
478 
479 	if (ep)
480 		ep_free(ep);
481 
482 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: close() ep=%p\n", current, ep));
483 	return 0;
484 }
485 
486 static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
487 {
488 	unsigned int pollflags = 0;
489 	unsigned long flags;
490 	struct eventpoll *ep = file->private_data;
491 
492 	/* Insert inside our poll wait queue */
493 	poll_wait(file, &ep->poll_wait, wait);
494 
495 	/* Check our condition */
496 	spin_lock_irqsave(&ep->lock, flags);
497 	if (!list_empty(&ep->rdllist))
498 		pollflags = POLLIN | POLLRDNORM;
499 	spin_unlock_irqrestore(&ep->lock, flags);
500 
501 	return pollflags;
502 }
503 
504 /* File callbacks that implement the eventpoll file behaviour */
505 static const struct file_operations eventpoll_fops = {
506 	.release	= ep_eventpoll_release,
507 	.poll		= ep_eventpoll_poll
508 };
509 
510 /* Fast test to see if the file is an evenpoll file */
511 static inline int is_file_epoll(struct file *f)
512 {
513 	return f->f_op == &eventpoll_fops;
514 }
515 
516 /*
517  * This is called from eventpoll_release() to unlink files from the eventpoll
518  * interface. We need to have this facility to cleanup correctly files that are
519  * closed without being removed from the eventpoll interface.
520  */
521 void eventpoll_release_file(struct file *file)
522 {
523 	struct list_head *lsthead = &file->f_ep_links;
524 	struct eventpoll *ep;
525 	struct epitem *epi;
526 
527 	/*
528 	 * We don't want to get "file->f_ep_lock" because it is not
529 	 * necessary. It is not necessary because we're in the "struct file"
530 	 * cleanup path, and this means that noone is using this file anymore.
531 	 * So, for example, epoll_ctl() cannot hit here sicne if we reach this
532 	 * point, the file counter already went to zero and fget() would fail.
533 	 * The only hit might come from ep_free() but by holding the mutex
534 	 * will correctly serialize the operation. We do need to acquire
535 	 * "ep->mtx" after "epmutex" because ep_remove() requires it when called
536 	 * from anywhere but ep_free().
537 	 */
538 	mutex_lock(&epmutex);
539 
540 	while (!list_empty(lsthead)) {
541 		epi = list_first_entry(lsthead, struct epitem, fllink);
542 
543 		ep = epi->ep;
544 		list_del_init(&epi->fllink);
545 		mutex_lock(&ep->mtx);
546 		ep_remove(ep, epi);
547 		mutex_unlock(&ep->mtx);
548 	}
549 
550 	mutex_unlock(&epmutex);
551 }
552 
553 static int ep_alloc(struct eventpoll **pep)
554 {
555 	struct eventpoll *ep = kzalloc(sizeof(*ep), GFP_KERNEL);
556 
557 	if (!ep)
558 		return -ENOMEM;
559 
560 	spin_lock_init(&ep->lock);
561 	mutex_init(&ep->mtx);
562 	init_waitqueue_head(&ep->wq);
563 	init_waitqueue_head(&ep->poll_wait);
564 	INIT_LIST_HEAD(&ep->rdllist);
565 	ep->rbr = RB_ROOT;
566 	ep->ovflist = EP_UNACTIVE_PTR;
567 
568 	*pep = ep;
569 
570 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_alloc() ep=%p\n",
571 		     current, ep));
572 	return 0;
573 }
574 
575 /*
576  * Search the file inside the eventpoll tree. The RB tree operations
577  * are protected by the "mtx" mutex, and ep_find() must be called with
578  * "mtx" held.
579  */
580 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
581 {
582 	int kcmp;
583 	struct rb_node *rbp;
584 	struct epitem *epi, *epir = NULL;
585 	struct epoll_filefd ffd;
586 
587 	ep_set_ffd(&ffd, file, fd);
588 	for (rbp = ep->rbr.rb_node; rbp; ) {
589 		epi = rb_entry(rbp, struct epitem, rbn);
590 		kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
591 		if (kcmp > 0)
592 			rbp = rbp->rb_right;
593 		else if (kcmp < 0)
594 			rbp = rbp->rb_left;
595 		else {
596 			epir = epi;
597 			break;
598 		}
599 	}
600 
601 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_find(%p) -> %p\n",
602 		     current, file, epir));
603 
604 	return epir;
605 }
606 
607 /*
608  * This is the callback that is passed to the wait queue wakeup
609  * machanism. It is called by the stored file descriptors when they
610  * have events to report.
611  */
612 static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
613 {
614 	int pwake = 0;
615 	unsigned long flags;
616 	struct epitem *epi = ep_item_from_wait(wait);
617 	struct eventpoll *ep = epi->ep;
618 
619 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: poll_callback(%p) epi=%p ep=%p\n",
620 		     current, epi->ffd.file, epi, ep));
621 
622 	spin_lock_irqsave(&ep->lock, flags);
623 
624 	/*
625 	 * If the event mask does not contain any poll(2) event, we consider the
626 	 * descriptor to be disabled. This condition is likely the effect of the
627 	 * EPOLLONESHOT bit that disables the descriptor when an event is received,
628 	 * until the next EPOLL_CTL_MOD will be issued.
629 	 */
630 	if (!(epi->event.events & ~EP_PRIVATE_BITS))
631 		goto out_unlock;
632 
633 	/*
634 	 * If we are trasfering events to userspace, we can hold no locks
635 	 * (because we're accessing user memory, and because of linux f_op->poll()
636 	 * semantics). All the events that happens during that period of time are
637 	 * chained in ep->ovflist and requeued later on.
638 	 */
639 	if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
640 		if (epi->next == EP_UNACTIVE_PTR) {
641 			epi->next = ep->ovflist;
642 			ep->ovflist = epi;
643 		}
644 		goto out_unlock;
645 	}
646 
647 	/* If this file is already in the ready list we exit soon */
648 	if (ep_is_linked(&epi->rdllink))
649 		goto is_linked;
650 
651 	list_add_tail(&epi->rdllink, &ep->rdllist);
652 
653 is_linked:
654 	/*
655 	 * Wake up ( if active ) both the eventpoll wait list and the ->poll()
656 	 * wait list.
657 	 */
658 	if (waitqueue_active(&ep->wq))
659 		wake_up_locked(&ep->wq);
660 	if (waitqueue_active(&ep->poll_wait))
661 		pwake++;
662 
663 out_unlock:
664 	spin_unlock_irqrestore(&ep->lock, flags);
665 
666 	/* We have to call this outside the lock */
667 	if (pwake)
668 		ep_poll_safewake(&psw, &ep->poll_wait);
669 
670 	return 1;
671 }
672 
673 /*
674  * This is the callback that is used to add our wait queue to the
675  * target file wakeup lists.
676  */
677 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
678 				 poll_table *pt)
679 {
680 	struct epitem *epi = ep_item_from_epqueue(pt);
681 	struct eppoll_entry *pwq;
682 
683 	if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
684 		init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
685 		pwq->whead = whead;
686 		pwq->base = epi;
687 		add_wait_queue(whead, &pwq->wait);
688 		list_add_tail(&pwq->llink, &epi->pwqlist);
689 		epi->nwait++;
690 	} else {
691 		/* We have to signal that an error occurred */
692 		epi->nwait = -1;
693 	}
694 }
695 
696 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
697 {
698 	int kcmp;
699 	struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
700 	struct epitem *epic;
701 
702 	while (*p) {
703 		parent = *p;
704 		epic = rb_entry(parent, struct epitem, rbn);
705 		kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
706 		if (kcmp > 0)
707 			p = &parent->rb_right;
708 		else
709 			p = &parent->rb_left;
710 	}
711 	rb_link_node(&epi->rbn, parent, p);
712 	rb_insert_color(&epi->rbn, &ep->rbr);
713 }
714 
715 /*
716  * Must be called with "mtx" held.
717  */
718 static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
719 		     struct file *tfile, int fd)
720 {
721 	int error, revents, pwake = 0;
722 	unsigned long flags;
723 	struct epitem *epi;
724 	struct ep_pqueue epq;
725 
726 	error = -ENOMEM;
727 	if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
728 		goto error_return;
729 
730 	/* Item initialization follow here ... */
731 	ep_rb_initnode(&epi->rbn);
732 	INIT_LIST_HEAD(&epi->rdllink);
733 	INIT_LIST_HEAD(&epi->fllink);
734 	INIT_LIST_HEAD(&epi->pwqlist);
735 	epi->ep = ep;
736 	ep_set_ffd(&epi->ffd, tfile, fd);
737 	epi->event = *event;
738 	epi->nwait = 0;
739 	epi->next = EP_UNACTIVE_PTR;
740 
741 	/* Initialize the poll table using the queue callback */
742 	epq.epi = epi;
743 	init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
744 
745 	/*
746 	 * Attach the item to the poll hooks and get current event bits.
747 	 * We can safely use the file* here because its usage count has
748 	 * been increased by the caller of this function. Note that after
749 	 * this operation completes, the poll callback can start hitting
750 	 * the new item.
751 	 */
752 	revents = tfile->f_op->poll(tfile, &epq.pt);
753 
754 	/*
755 	 * We have to check if something went wrong during the poll wait queue
756 	 * install process. Namely an allocation for a wait queue failed due
757 	 * high memory pressure.
758 	 */
759 	if (epi->nwait < 0)
760 		goto error_unregister;
761 
762 	/* Add the current item to the list of active epoll hook for this file */
763 	spin_lock(&tfile->f_ep_lock);
764 	list_add_tail(&epi->fllink, &tfile->f_ep_links);
765 	spin_unlock(&tfile->f_ep_lock);
766 
767 	/*
768 	 * Add the current item to the RB tree. All RB tree operations are
769 	 * protected by "mtx", and ep_insert() is called with "mtx" held.
770 	 */
771 	ep_rbtree_insert(ep, epi);
772 
773 	/* We have to drop the new item inside our item list to keep track of it */
774 	spin_lock_irqsave(&ep->lock, flags);
775 
776 	/* If the file is already "ready" we drop it inside the ready list */
777 	if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
778 		list_add_tail(&epi->rdllink, &ep->rdllist);
779 
780 		/* Notify waiting tasks that events are available */
781 		if (waitqueue_active(&ep->wq))
782 			wake_up_locked(&ep->wq);
783 		if (waitqueue_active(&ep->poll_wait))
784 			pwake++;
785 	}
786 
787 	spin_unlock_irqrestore(&ep->lock, flags);
788 
789 	/* We have to call this outside the lock */
790 	if (pwake)
791 		ep_poll_safewake(&psw, &ep->poll_wait);
792 
793 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_insert(%p, %p, %d)\n",
794 		     current, ep, tfile, fd));
795 
796 	return 0;
797 
798 error_unregister:
799 	ep_unregister_pollwait(ep, epi);
800 
801 	/*
802 	 * We need to do this because an event could have been arrived on some
803 	 * allocated wait queue. Note that we don't care about the ep->ovflist
804 	 * list, since that is used/cleaned only inside a section bound by "mtx".
805 	 * And ep_insert() is called with "mtx" held.
806 	 */
807 	spin_lock_irqsave(&ep->lock, flags);
808 	if (ep_is_linked(&epi->rdllink))
809 		list_del_init(&epi->rdllink);
810 	spin_unlock_irqrestore(&ep->lock, flags);
811 
812 	kmem_cache_free(epi_cache, epi);
813 error_return:
814 	return error;
815 }
816 
817 /*
818  * Modify the interest event mask by dropping an event if the new mask
819  * has a match in the current file status. Must be called with "mtx" held.
820  */
821 static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
822 {
823 	int pwake = 0;
824 	unsigned int revents;
825 	unsigned long flags;
826 
827 	/*
828 	 * Set the new event interest mask before calling f_op->poll(), otherwise
829 	 * a potential race might occur. In fact if we do this operation inside
830 	 * the lock, an event might happen between the f_op->poll() call and the
831 	 * new event set registering.
832 	 */
833 	epi->event.events = event->events;
834 
835 	/*
836 	 * Get current event bits. We can safely use the file* here because
837 	 * its usage count has been increased by the caller of this function.
838 	 */
839 	revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
840 
841 	spin_lock_irqsave(&ep->lock, flags);
842 
843 	/* Copy the data member from inside the lock */
844 	epi->event.data = event->data;
845 
846 	/*
847 	 * If the item is "hot" and it is not registered inside the ready
848 	 * list, push it inside.
849 	 */
850 	if (revents & event->events) {
851 		if (!ep_is_linked(&epi->rdllink)) {
852 			list_add_tail(&epi->rdllink, &ep->rdllist);
853 
854 			/* Notify waiting tasks that events are available */
855 			if (waitqueue_active(&ep->wq))
856 				wake_up_locked(&ep->wq);
857 			if (waitqueue_active(&ep->poll_wait))
858 				pwake++;
859 		}
860 	}
861 	spin_unlock_irqrestore(&ep->lock, flags);
862 
863 	/* We have to call this outside the lock */
864 	if (pwake)
865 		ep_poll_safewake(&psw, &ep->poll_wait);
866 
867 	return 0;
868 }
869 
870 static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *events,
871 			  int maxevents)
872 {
873 	int eventcnt, error = -EFAULT, pwake = 0;
874 	unsigned int revents;
875 	unsigned long flags;
876 	struct epitem *epi, *nepi;
877 	struct list_head txlist;
878 
879 	INIT_LIST_HEAD(&txlist);
880 
881 	/*
882 	 * We need to lock this because we could be hit by
883 	 * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL).
884 	 */
885 	mutex_lock(&ep->mtx);
886 
887 	/*
888 	 * Steal the ready list, and re-init the original one to the
889 	 * empty list. Also, set ep->ovflist to NULL so that events
890 	 * happening while looping w/out locks, are not lost. We cannot
891 	 * have the poll callback to queue directly on ep->rdllist,
892 	 * because we are doing it in the loop below, in a lockless way.
893 	 */
894 	spin_lock_irqsave(&ep->lock, flags);
895 	list_splice(&ep->rdllist, &txlist);
896 	INIT_LIST_HEAD(&ep->rdllist);
897 	ep->ovflist = NULL;
898 	spin_unlock_irqrestore(&ep->lock, flags);
899 
900 	/*
901 	 * We can loop without lock because this is a task private list.
902 	 * We just splice'd out the ep->rdllist in ep_collect_ready_items().
903 	 * Items cannot vanish during the loop because we are holding "mtx".
904 	 */
905 	for (eventcnt = 0; !list_empty(&txlist) && eventcnt < maxevents;) {
906 		epi = list_first_entry(&txlist, struct epitem, rdllink);
907 
908 		list_del_init(&epi->rdllink);
909 
910 		/*
911 		 * Get the ready file event set. We can safely use the file
912 		 * because we are holding the "mtx" and this will guarantee
913 		 * that both the file and the item will not vanish.
914 		 */
915 		revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
916 		revents &= epi->event.events;
917 
918 		/*
919 		 * Is the event mask intersect the caller-requested one,
920 		 * deliver the event to userspace. Again, we are holding
921 		 * "mtx", so no operations coming from userspace can change
922 		 * the item.
923 		 */
924 		if (revents) {
925 			if (__put_user(revents,
926 				       &events[eventcnt].events) ||
927 			    __put_user(epi->event.data,
928 				       &events[eventcnt].data))
929 				goto errxit;
930 			if (epi->event.events & EPOLLONESHOT)
931 				epi->event.events &= EP_PRIVATE_BITS;
932 			eventcnt++;
933 		}
934 		/*
935 		 * At this point, noone can insert into ep->rdllist besides
936 		 * us. The epoll_ctl() callers are locked out by us holding
937 		 * "mtx" and the poll callback will queue them in ep->ovflist.
938 		 */
939 		if (!(epi->event.events & EPOLLET) &&
940 		    (revents & epi->event.events))
941 			list_add_tail(&epi->rdllink, &ep->rdllist);
942 	}
943 	error = 0;
944 
945 errxit:
946 
947 	spin_lock_irqsave(&ep->lock, flags);
948 	/*
949 	 * During the time we spent in the loop above, some other events
950 	 * might have been queued by the poll callback. We re-insert them
951 	 * here (in case they are not already queued, or they're one-shot).
952 	 */
953 	for (nepi = ep->ovflist; (epi = nepi) != NULL;
954 	     nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
955 		if (!ep_is_linked(&epi->rdllink) &&
956 		    (epi->event.events & ~EP_PRIVATE_BITS))
957 			list_add_tail(&epi->rdllink, &ep->rdllist);
958 	}
959 	/*
960 	 * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
961 	 * releasing the lock, events will be queued in the normal way inside
962 	 * ep->rdllist.
963 	 */
964 	ep->ovflist = EP_UNACTIVE_PTR;
965 
966 	/*
967 	 * In case of error in the event-send loop, or in case the number of
968 	 * ready events exceeds the userspace limit, we need to splice the
969 	 * "txlist" back inside ep->rdllist.
970 	 */
971 	list_splice(&txlist, &ep->rdllist);
972 
973 	if (!list_empty(&ep->rdllist)) {
974 		/*
975 		 * Wake up (if active) both the eventpoll wait list and the ->poll()
976 		 * wait list (delayed after we release the lock).
977 		 */
978 		if (waitqueue_active(&ep->wq))
979 			wake_up_locked(&ep->wq);
980 		if (waitqueue_active(&ep->poll_wait))
981 			pwake++;
982 	}
983 	spin_unlock_irqrestore(&ep->lock, flags);
984 
985 	mutex_unlock(&ep->mtx);
986 
987 	/* We have to call this outside the lock */
988 	if (pwake)
989 		ep_poll_safewake(&psw, &ep->poll_wait);
990 
991 	return eventcnt == 0 ? error: eventcnt;
992 }
993 
994 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
995 		   int maxevents, long timeout)
996 {
997 	int res, eavail;
998 	unsigned long flags;
999 	long jtimeout;
1000 	wait_queue_t wait;
1001 
1002 	/*
1003 	 * Calculate the timeout by checking for the "infinite" value ( -1 )
1004 	 * and the overflow condition. The passed timeout is in milliseconds,
1005 	 * that why (t * HZ) / 1000.
1006 	 */
1007 	jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ?
1008 		MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000;
1009 
1010 retry:
1011 	spin_lock_irqsave(&ep->lock, flags);
1012 
1013 	res = 0;
1014 	if (list_empty(&ep->rdllist)) {
1015 		/*
1016 		 * We don't have any available event to return to the caller.
1017 		 * We need to sleep here, and we will be wake up by
1018 		 * ep_poll_callback() when events will become available.
1019 		 */
1020 		init_waitqueue_entry(&wait, current);
1021 		wait.flags |= WQ_FLAG_EXCLUSIVE;
1022 		__add_wait_queue(&ep->wq, &wait);
1023 
1024 		for (;;) {
1025 			/*
1026 			 * We don't want to sleep if the ep_poll_callback() sends us
1027 			 * a wakeup in between. That's why we set the task state
1028 			 * to TASK_INTERRUPTIBLE before doing the checks.
1029 			 */
1030 			set_current_state(TASK_INTERRUPTIBLE);
1031 			if (!list_empty(&ep->rdllist) || !jtimeout)
1032 				break;
1033 			if (signal_pending(current)) {
1034 				res = -EINTR;
1035 				break;
1036 			}
1037 
1038 			spin_unlock_irqrestore(&ep->lock, flags);
1039 			jtimeout = schedule_timeout(jtimeout);
1040 			spin_lock_irqsave(&ep->lock, flags);
1041 		}
1042 		__remove_wait_queue(&ep->wq, &wait);
1043 
1044 		set_current_state(TASK_RUNNING);
1045 	}
1046 
1047 	/* Is it worth to try to dig for events ? */
1048 	eavail = !list_empty(&ep->rdllist);
1049 
1050 	spin_unlock_irqrestore(&ep->lock, flags);
1051 
1052 	/*
1053 	 * Try to transfer events to user space. In case we get 0 events and
1054 	 * there's still timeout left over, we go trying again in search of
1055 	 * more luck.
1056 	 */
1057 	if (!res && eavail &&
1058 	    !(res = ep_send_events(ep, events, maxevents)) && jtimeout)
1059 		goto retry;
1060 
1061 	return res;
1062 }
1063 
1064 /*
1065  * It opens an eventpoll file descriptor. The "size" parameter is there
1066  * for historical reasons, when epoll was using an hash instead of an
1067  * RB tree. With the current implementation, the "size" parameter is ignored
1068  * (besides sanity checks).
1069  */
1070 asmlinkage long sys_epoll_create(int size)
1071 {
1072 	int error, fd = -1;
1073 	struct eventpoll *ep;
1074 	struct inode *inode;
1075 	struct file *file;
1076 
1077 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n",
1078 		     current, size));
1079 
1080 	/*
1081 	 * Sanity check on the size parameter, and create the internal data
1082 	 * structure ( "struct eventpoll" ).
1083 	 */
1084 	error = -EINVAL;
1085 	if (size <= 0 || (error = ep_alloc(&ep)) != 0)
1086 		goto error_return;
1087 
1088 	/*
1089 	 * Creates all the items needed to setup an eventpoll file. That is,
1090 	 * a file structure, and inode and a free file descriptor.
1091 	 */
1092 	error = anon_inode_getfd(&fd, &inode, &file, "[eventpoll]",
1093 				 &eventpoll_fops, ep);
1094 	if (error)
1095 		goto error_free;
1096 
1097 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
1098 		     current, size, fd));
1099 
1100 	return fd;
1101 
1102 error_free:
1103 	ep_free(ep);
1104 error_return:
1105 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
1106 		     current, size, error));
1107 	return error;
1108 }
1109 
1110 /*
1111  * The following function implements the controller interface for
1112  * the eventpoll file that enables the insertion/removal/change of
1113  * file descriptors inside the interest set.
1114  */
1115 asmlinkage long sys_epoll_ctl(int epfd, int op, int fd,
1116 			      struct epoll_event __user *event)
1117 {
1118 	int error;
1119 	struct file *file, *tfile;
1120 	struct eventpoll *ep;
1121 	struct epitem *epi;
1122 	struct epoll_event epds;
1123 
1124 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p)\n",
1125 		     current, epfd, op, fd, event));
1126 
1127 	error = -EFAULT;
1128 	if (ep_op_has_event(op) &&
1129 	    copy_from_user(&epds, event, sizeof(struct epoll_event)))
1130 		goto error_return;
1131 
1132 	/* Get the "struct file *" for the eventpoll file */
1133 	error = -EBADF;
1134 	file = fget(epfd);
1135 	if (!file)
1136 		goto error_return;
1137 
1138 	/* Get the "struct file *" for the target file */
1139 	tfile = fget(fd);
1140 	if (!tfile)
1141 		goto error_fput;
1142 
1143 	/* The target file descriptor must support poll */
1144 	error = -EPERM;
1145 	if (!tfile->f_op || !tfile->f_op->poll)
1146 		goto error_tgt_fput;
1147 
1148 	/*
1149 	 * We have to check that the file structure underneath the file descriptor
1150 	 * the user passed to us _is_ an eventpoll file. And also we do not permit
1151 	 * adding an epoll file descriptor inside itself.
1152 	 */
1153 	error = -EINVAL;
1154 	if (file == tfile || !is_file_epoll(file))
1155 		goto error_tgt_fput;
1156 
1157 	/*
1158 	 * At this point it is safe to assume that the "private_data" contains
1159 	 * our own data structure.
1160 	 */
1161 	ep = file->private_data;
1162 
1163 	mutex_lock(&ep->mtx);
1164 
1165 	/*
1166 	 * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
1167 	 * above, we can be sure to be able to use the item looked up by
1168 	 * ep_find() till we release the mutex.
1169 	 */
1170 	epi = ep_find(ep, tfile, fd);
1171 
1172 	error = -EINVAL;
1173 	switch (op) {
1174 	case EPOLL_CTL_ADD:
1175 		if (!epi) {
1176 			epds.events |= POLLERR | POLLHUP;
1177 
1178 			error = ep_insert(ep, &epds, tfile, fd);
1179 		} else
1180 			error = -EEXIST;
1181 		break;
1182 	case EPOLL_CTL_DEL:
1183 		if (epi)
1184 			error = ep_remove(ep, epi);
1185 		else
1186 			error = -ENOENT;
1187 		break;
1188 	case EPOLL_CTL_MOD:
1189 		if (epi) {
1190 			epds.events |= POLLERR | POLLHUP;
1191 			error = ep_modify(ep, epi, &epds);
1192 		} else
1193 			error = -ENOENT;
1194 		break;
1195 	}
1196 	mutex_unlock(&ep->mtx);
1197 
1198 error_tgt_fput:
1199 	fput(tfile);
1200 error_fput:
1201 	fput(file);
1202 error_return:
1203 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p) = %d\n",
1204 		     current, epfd, op, fd, event, error));
1205 
1206 	return error;
1207 }
1208 
1209 /*
1210  * Implement the event wait interface for the eventpoll file. It is the kernel
1211  * part of the user space epoll_wait(2).
1212  */
1213 asmlinkage long sys_epoll_wait(int epfd, struct epoll_event __user *events,
1214 			       int maxevents, int timeout)
1215 {
1216 	int error;
1217 	struct file *file;
1218 	struct eventpoll *ep;
1219 
1220 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d)\n",
1221 		     current, epfd, events, maxevents, timeout));
1222 
1223 	/* The maximum number of event must be greater than zero */
1224 	if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
1225 		return -EINVAL;
1226 
1227 	/* Verify that the area passed by the user is writeable */
1228 	if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event))) {
1229 		error = -EFAULT;
1230 		goto error_return;
1231 	}
1232 
1233 	/* Get the "struct file *" for the eventpoll file */
1234 	error = -EBADF;
1235 	file = fget(epfd);
1236 	if (!file)
1237 		goto error_return;
1238 
1239 	/*
1240 	 * We have to check that the file structure underneath the fd
1241 	 * the user passed to us _is_ an eventpoll file.
1242 	 */
1243 	error = -EINVAL;
1244 	if (!is_file_epoll(file))
1245 		goto error_fput;
1246 
1247 	/*
1248 	 * At this point it is safe to assume that the "private_data" contains
1249 	 * our own data structure.
1250 	 */
1251 	ep = file->private_data;
1252 
1253 	/* Time to fish for events ... */
1254 	error = ep_poll(ep, events, maxevents, timeout);
1255 
1256 error_fput:
1257 	fput(file);
1258 error_return:
1259 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d) = %d\n",
1260 		     current, epfd, events, maxevents, timeout, error));
1261 
1262 	return error;
1263 }
1264 
1265 #ifdef TIF_RESTORE_SIGMASK
1266 
1267 /*
1268  * Implement the event wait interface for the eventpoll file. It is the kernel
1269  * part of the user space epoll_pwait(2).
1270  */
1271 asmlinkage long sys_epoll_pwait(int epfd, struct epoll_event __user *events,
1272 		int maxevents, int timeout, const sigset_t __user *sigmask,
1273 		size_t sigsetsize)
1274 {
1275 	int error;
1276 	sigset_t ksigmask, sigsaved;
1277 
1278 	/*
1279 	 * If the caller wants a certain signal mask to be set during the wait,
1280 	 * we apply it here.
1281 	 */
1282 	if (sigmask) {
1283 		if (sigsetsize != sizeof(sigset_t))
1284 			return -EINVAL;
1285 		if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
1286 			return -EFAULT;
1287 		sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
1288 		sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
1289 	}
1290 
1291 	error = sys_epoll_wait(epfd, events, maxevents, timeout);
1292 
1293 	/*
1294 	 * If we changed the signal mask, we need to restore the original one.
1295 	 * In case we've got a signal while waiting, we do not restore the
1296 	 * signal mask yet, and we allow do_signal() to deliver the signal on
1297 	 * the way back to userspace, before the signal mask is restored.
1298 	 */
1299 	if (sigmask) {
1300 		if (error == -EINTR) {
1301 			memcpy(&current->saved_sigmask, &sigsaved,
1302 			       sizeof(sigsaved));
1303 			set_thread_flag(TIF_RESTORE_SIGMASK);
1304 		} else
1305 			sigprocmask(SIG_SETMASK, &sigsaved, NULL);
1306 	}
1307 
1308 	return error;
1309 }
1310 
1311 #endif /* #ifdef TIF_RESTORE_SIGMASK */
1312 
1313 static int __init eventpoll_init(void)
1314 {
1315 	mutex_init(&epmutex);
1316 
1317 	/* Initialize the structure used to perform safe poll wait head wake ups */
1318 	ep_poll_safewake_init(&psw);
1319 
1320 	/* Allocates slab cache used to allocate "struct epitem" items */
1321 	epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
1322 			0, SLAB_HWCACHE_ALIGN|EPI_SLAB_DEBUG|SLAB_PANIC,
1323 			NULL);
1324 
1325 	/* Allocates slab cache used to allocate "struct eppoll_entry" */
1326 	pwq_cache = kmem_cache_create("eventpoll_pwq",
1327 			sizeof(struct eppoll_entry), 0,
1328 			EPI_SLAB_DEBUG|SLAB_PANIC, NULL);
1329 
1330 	return 0;
1331 }
1332 fs_initcall(eventpoll_init);
1333 
1334