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Linux/fs/eventpoll.c

  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 <linux/uaccess.h>
 38 #include <asm/io.h>
 39 #include <asm/mman.h>
 40 #include <linux/atomic.h>
 41 #include <linux/proc_fs.h>
 42 #include <linux/seq_file.h>
 43 #include <linux/compat.h>
 44 #include <linux/rculist.h>
 45 
 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);
2178 

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