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TOMOYO Linux Cross Reference
Linux/fs/eventpoll.c

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  1 /*
  2  *  fs/eventpoll.c (Efficient event retrieval implementation)
  3  *  Copyright (C) 2001,...,2009  Davide Libenzi
  4  *
  5  *  This program is free software; you can redistribute it and/or modify
  6  *  it under the terms of the GNU General Public License as published by
  7  *  the Free Software Foundation; either version 2 of the License, or
  8  *  (at your option) any later version.
  9  *
 10  *  Davide Libenzi <davidel@xmailserver.org>
 11  *
 12  */
 13 
 14 #include <linux/init.h>
 15 #include <linux/kernel.h>
 16 #include <linux/sched.h>
 17 #include <linux/fs.h>
 18 #include <linux/file.h>
 19 #include <linux/signal.h>
 20 #include <linux/errno.h>
 21 #include <linux/mm.h>
 22 #include <linux/slab.h>
 23 #include <linux/poll.h>
 24 #include <linux/string.h>
 25 #include <linux/list.h>
 26 #include <linux/hash.h>
 27 #include <linux/spinlock.h>
 28 #include <linux/syscalls.h>
 29 #include <linux/rbtree.h>
 30 #include <linux/wait.h>
 31 #include <linux/eventpoll.h>
 32 #include <linux/mount.h>
 33 #include <linux/bitops.h>
 34 #include <linux/mutex.h>
 35 #include <linux/anon_inodes.h>
 36 #include <linux/device.h>
 37 #include <asm/uaccess.h>
 38 #include <asm/io.h>
 39 #include <asm/mman.h>
 40 #include <linux/atomic.h>
 41 #include <linux/proc_fs.h>
 42 #include <linux/seq_file.h>
 43 #include <linux/compat.h>
 44 #include <linux/rculist.h>
 45 
 46 /*
 47  * LOCKING:
 48  * There are three level of locking required by epoll :
 49  *
 50  * 1) epmutex (mutex)
 51  * 2) ep->mtx (mutex)
 52  * 3) ep->lock (spinlock)
 53  *
 54  * The acquire order is the one listed above, from 1 to 3.
 55  * We need a spinlock (ep->lock) because we manipulate objects
 56  * from inside the poll callback, that might be triggered from
 57  * a wake_up() that in turn might be called from IRQ context.
 58  * So we can't sleep inside the poll callback and hence we need
 59  * a spinlock. During the event transfer loop (from kernel to
 60  * user space) we could end up sleeping due a copy_to_user(), so
 61  * we need a lock that will allow us to sleep. This lock is a
 62  * mutex (ep->mtx). It is acquired during the event transfer loop,
 63  * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
 64  * Then we also need a global mutex to serialize eventpoll_release_file()
 65  * and ep_free().
 66  * This mutex is acquired by ep_free() during the epoll file
 67  * cleanup path and it is also acquired by eventpoll_release_file()
 68  * if a file has been pushed inside an epoll set and it is then
 69  * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
 70  * It is also acquired when inserting an epoll fd onto another epoll
 71  * fd. We do this so that we walk the epoll tree and ensure that this
 72  * insertion does not create a cycle of epoll file descriptors, which
 73  * could lead to deadlock. We need a global mutex to prevent two
 74  * simultaneous inserts (A into B and B into A) from racing and
 75  * constructing a cycle without either insert observing that it is
 76  * going to.
 77  * It is necessary to acquire multiple "ep->mtx"es at once in the
 78  * case when one epoll fd is added to another. In this case, we
 79  * always acquire the locks in the order of nesting (i.e. after
 80  * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
 81  * before e2->mtx). Since we disallow cycles of epoll file
 82  * descriptors, this ensures that the mutexes are well-ordered. In
 83  * order to communicate this nesting to lockdep, when walking a tree
 84  * of epoll file descriptors, we use the current recursion depth as
 85  * the lockdep subkey.
 86  * It is possible to drop the "ep->mtx" and to use the global
 87  * mutex "epmutex" (together with "ep->lock") to have it working,
 88  * but having "ep->mtx" will make the interface more scalable.
 89  * Events that require holding "epmutex" are very rare, while for
 90  * normal operations the epoll private "ep->mtx" will guarantee
 91  * a better scalability.
 92  */
 93 
 94 /* Epoll private bits inside the event mask */
 95 #define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET)
 96 
 97 /* Maximum number of nesting allowed inside epoll sets */
 98 #define EP_MAX_NESTS 4
 99 
100 #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
101 
102 #define EP_UNACTIVE_PTR ((void *) -1L)
103 
104 #define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
105 
106 struct epoll_filefd {
107         struct file *file;
108         int fd;
109 } __packed;
110 
111 /*
112  * Structure used to track possible nested calls, for too deep recursions
113  * and loop cycles.
114  */
115 struct nested_call_node {
116         struct list_head llink;
117         void *cookie;
118         void *ctx;
119 };
120 
121 /*
122  * This structure is used as collector for nested calls, to check for
123  * maximum recursion dept and loop cycles.
124  */
125 struct nested_calls {
126         struct list_head tasks_call_list;
127         spinlock_t lock;
128 };
129 
130 /*
131  * Each file descriptor added to the eventpoll interface will
132  * have an entry of this type linked to the "rbr" RB tree.
133  * Avoid increasing the size of this struct, there can be many thousands
134  * of these on a server and we do not want this to take another cache line.
135  */
136 struct epitem {
137         union {
138                 /* RB tree node links this structure to the eventpoll RB tree */
139                 struct rb_node rbn;
140                 /* Used to free the struct epitem */
141                 struct rcu_head rcu;
142         };
143 
144         /* List header used to link this structure to the eventpoll ready list */
145         struct list_head rdllink;
146 
147         /*
148          * Works together "struct eventpoll"->ovflist in keeping the
149          * single linked chain of items.
150          */
151         struct epitem *next;
152 
153         /* The file descriptor information this item refers to */
154         struct epoll_filefd ffd;
155 
156         /* Number of active wait queue attached to poll operations */
157         int nwait;
158 
159         /* List containing poll wait queues */
160         struct list_head pwqlist;
161 
162         /* The "container" of this item */
163         struct eventpoll *ep;
164 
165         /* List header used to link this item to the "struct file" items list */
166         struct list_head fllink;
167 
168         /* wakeup_source used when EPOLLWAKEUP is set */
169         struct wakeup_source __rcu *ws;
170 
171         /* The structure that describe the interested events and the source fd */
172         struct epoll_event event;
173 };
174 
175 /*
176  * This structure is stored inside the "private_data" member of the file
177  * structure and represents the main data structure for the eventpoll
178  * interface.
179  */
180 struct eventpoll {
181         /* Protect the access to this structure */
182         spinlock_t lock;
183 
184         /*
185          * This mutex is used to ensure that files are not removed
186          * while epoll is using them. This is held during the event
187          * collection loop, the file cleanup path, the epoll file exit
188          * code and the ctl operations.
189          */
190         struct mutex mtx;
191 
192         /* Wait queue used by sys_epoll_wait() */
193         wait_queue_head_t wq;
194 
195         /* Wait queue used by file->poll() */
196         wait_queue_head_t poll_wait;
197 
198         /* List of ready file descriptors */
199         struct list_head rdllist;
200 
201         /* RB tree root used to store monitored fd structs */
202         struct rb_root rbr;
203 
204         /*
205          * This is a single linked list that chains all the "struct epitem" that
206          * happened while transferring ready events to userspace w/out
207          * holding ->lock.
208          */
209         struct epitem *ovflist;
210 
211         /* wakeup_source used when ep_scan_ready_list is running */
212         struct wakeup_source *ws;
213 
214         /* The user that created the eventpoll descriptor */
215         struct user_struct *user;
216 
217         struct file *file;
218 
219         /* used to optimize loop detection check */
220         int visited;
221         struct list_head visited_list_link;
222 };
223 
224 /* Wait structure used by the poll hooks */
225 struct eppoll_entry {
226         /* List header used to link this structure to the "struct epitem" */
227         struct list_head llink;
228 
229         /* The "base" pointer is set to the container "struct epitem" */
230         struct epitem *base;
231 
232         /*
233          * Wait queue item that will be linked to the target file wait
234          * queue head.
235          */
236         wait_queue_t wait;
237 
238         /* The wait queue head that linked the "wait" wait queue item */
239         wait_queue_head_t *whead;
240 };
241 
242 /* Wrapper struct used by poll queueing */
243 struct ep_pqueue {
244         poll_table pt;
245         struct epitem *epi;
246 };
247 
248 /* Used by the ep_send_events() function as callback private data */
249 struct ep_send_events_data {
250         int maxevents;
251         struct epoll_event __user *events;
252 };
253 
254 /*
255  * Configuration options available inside /proc/sys/fs/epoll/
256  */
257 /* Maximum number of epoll watched descriptors, per user */
258 static long max_user_watches __read_mostly;
259 
260 /*
261  * This mutex is used to serialize ep_free() and eventpoll_release_file().
262  */
263 static DEFINE_MUTEX(epmutex);
264 
265 /* Used to check for epoll file descriptor inclusion loops */
266 static struct nested_calls poll_loop_ncalls;
267 
268 /* Used for safe wake up implementation */
269 static struct nested_calls poll_safewake_ncalls;
270 
271 /* Used to call file's f_op->poll() under the nested calls boundaries */
272 static struct nested_calls poll_readywalk_ncalls;
273 
274 /* Slab cache used to allocate "struct epitem" */
275 static struct kmem_cache *epi_cache __read_mostly;
276 
277 /* Slab cache used to allocate "struct eppoll_entry" */
278 static struct kmem_cache *pwq_cache __read_mostly;
279 
280 /* Visited nodes during ep_loop_check(), so we can unset them when we finish */
281 static LIST_HEAD(visited_list);
282 
283 /*
284  * List of files with newly added links, where we may need to limit the number
285  * of emanating paths. Protected by the epmutex.
286  */
287 static LIST_HEAD(tfile_check_list);
288 
289 #ifdef CONFIG_SYSCTL
290 
291 #include <linux/sysctl.h>
292 
293 static long zero;
294 static long long_max = LONG_MAX;
295 
296 ctl_table epoll_table[] = {
297         {
298                 .procname       = "max_user_watches",
299                 .data           = &max_user_watches,
300                 .maxlen         = sizeof(max_user_watches),
301                 .mode           = 0644,
302                 .proc_handler   = proc_doulongvec_minmax,
303                 .extra1         = &zero,
304                 .extra2         = &long_max,
305         },
306         { }
307 };
308 #endif /* CONFIG_SYSCTL */
309 
310 static const struct file_operations eventpoll_fops;
311 
312 static inline int is_file_epoll(struct file *f)
313 {
314         return f->f_op == &eventpoll_fops;
315 }
316 
317 /* Setup the structure that is used as key for the RB tree */
318 static inline void ep_set_ffd(struct epoll_filefd *ffd,
319                               struct file *file, int fd)
320 {
321         ffd->file = file;
322         ffd->fd = fd;
323 }
324 
325 /* Compare RB tree keys */
326 static inline int ep_cmp_ffd(struct epoll_filefd *p1,
327                              struct epoll_filefd *p2)
328 {
329         return (p1->file > p2->file ? +1:
330                 (p1->file < p2->file ? -1 : p1->fd - p2->fd));
331 }
332 
333 /* Tells us if the item is currently linked */
334 static inline int ep_is_linked(struct list_head *p)
335 {
336         return !list_empty(p);
337 }
338 
339 static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_t *p)
340 {
341         return container_of(p, struct eppoll_entry, wait);
342 }
343 
344 /* Get the "struct epitem" from a wait queue pointer */
345 static inline struct epitem *ep_item_from_wait(wait_queue_t *p)
346 {
347         return container_of(p, struct eppoll_entry, wait)->base;
348 }
349 
350 /* Get the "struct epitem" from an epoll queue wrapper */
351 static inline struct epitem *ep_item_from_epqueue(poll_table *p)
352 {
353         return container_of(p, struct ep_pqueue, pt)->epi;
354 }
355 
356 /* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
357 static inline int ep_op_has_event(int op)
358 {
359         return op != EPOLL_CTL_DEL;
360 }
361 
362 /* Initialize the poll safe wake up structure */
363 static void ep_nested_calls_init(struct nested_calls *ncalls)
364 {
365         INIT_LIST_HEAD(&ncalls->tasks_call_list);
366         spin_lock_init(&ncalls->lock);
367 }
368 
369 /**
370  * ep_events_available - Checks if ready events might be available.
371  *
372  * @ep: Pointer to the eventpoll context.
373  *
374  * Returns: Returns a value different than zero if ready events are available,
375  *          or zero otherwise.
376  */
377 static inline int ep_events_available(struct eventpoll *ep)
378 {
379         return !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
380 }
381 
382 /**
383  * ep_call_nested - Perform a bound (possibly) nested call, by checking
384  *                  that the recursion limit is not exceeded, and that
385  *                  the same nested call (by the meaning of same cookie) is
386  *                  no re-entered.
387  *
388  * @ncalls: Pointer to the nested_calls structure to be used for this call.
389  * @max_nests: Maximum number of allowed nesting calls.
390  * @nproc: Nested call core function pointer.
391  * @priv: Opaque data to be passed to the @nproc callback.
392  * @cookie: Cookie to be used to identify this nested call.
393  * @ctx: This instance context.
394  *
395  * Returns: Returns the code returned by the @nproc callback, or -1 if
396  *          the maximum recursion limit has been exceeded.
397  */
398 static int ep_call_nested(struct nested_calls *ncalls, int max_nests,
399                           int (*nproc)(void *, void *, int), void *priv,
400                           void *cookie, void *ctx)
401 {
402         int error, call_nests = 0;
403         unsigned long flags;
404         struct list_head *lsthead = &ncalls->tasks_call_list;
405         struct nested_call_node *tncur;
406         struct nested_call_node tnode;
407 
408         spin_lock_irqsave(&ncalls->lock, flags);
409 
410         /*
411          * Try to see if the current task is already inside this wakeup call.
412          * We use a list here, since the population inside this set is always
413          * very much limited.
414          */
415         list_for_each_entry(tncur, lsthead, llink) {
416                 if (tncur->ctx == ctx &&
417                     (tncur->cookie == cookie || ++call_nests > max_nests)) {
418                         /*
419                          * Ops ... loop detected or maximum nest level reached.
420                          * We abort this wake by breaking the cycle itself.
421                          */
422                         error = -1;
423                         goto out_unlock;
424                 }
425         }
426 
427         /* Add the current task and cookie to the list */
428         tnode.ctx = ctx;
429         tnode.cookie = cookie;
430         list_add(&tnode.llink, lsthead);
431 
432         spin_unlock_irqrestore(&ncalls->lock, flags);
433 
434         /* Call the nested function */
435         error = (*nproc)(priv, cookie, call_nests);
436 
437         /* Remove the current task from the list */
438         spin_lock_irqsave(&ncalls->lock, flags);
439         list_del(&tnode.llink);
440 out_unlock:
441         spin_unlock_irqrestore(&ncalls->lock, flags);
442 
443         return error;
444 }
445 
446 /*
447  * As described in commit 0ccf831cb lockdep: annotate epoll
448  * the use of wait queues used by epoll is done in a very controlled
449  * manner. Wake ups can nest inside each other, but are never done
450  * with the same locking. For example:
451  *
452  *   dfd = socket(...);
453  *   efd1 = epoll_create();
454  *   efd2 = epoll_create();
455  *   epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
456  *   epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
457  *
458  * When a packet arrives to the device underneath "dfd", the net code will
459  * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
460  * callback wakeup entry on that queue, and the wake_up() performed by the
461  * "dfd" net code will end up in ep_poll_callback(). At this point epoll
462  * (efd1) notices that it may have some event ready, so it needs to wake up
463  * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
464  * that ends up in another wake_up(), after having checked about the
465  * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
466  * avoid stack blasting.
467  *
468  * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
469  * this special case of epoll.
470  */
471 #ifdef CONFIG_DEBUG_LOCK_ALLOC
472 static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
473                                      unsigned long events, int subclass)
474 {
475         unsigned long flags;
476 
477         spin_lock_irqsave_nested(&wqueue->lock, flags, subclass);
478         wake_up_locked_poll(wqueue, events);
479         spin_unlock_irqrestore(&wqueue->lock, flags);
480 }
481 #else
482 static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
483                                      unsigned long events, int subclass)
484 {
485         wake_up_poll(wqueue, events);
486 }
487 #endif
488 
489 static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
490 {
491         ep_wake_up_nested((wait_queue_head_t *) cookie, POLLIN,
492                           1 + call_nests);
493         return 0;
494 }
495 
496 /*
497  * Perform a safe wake up of the poll wait list. The problem is that
498  * with the new callback'd wake up system, it is possible that the
499  * poll callback is reentered from inside the call to wake_up() done
500  * on the poll wait queue head. The rule is that we cannot reenter the
501  * wake up code from the same task more than EP_MAX_NESTS times,
502  * and we cannot reenter the same wait queue head at all. This will
503  * enable to have a hierarchy of epoll file descriptor of no more than
504  * EP_MAX_NESTS deep.
505  */
506 static void ep_poll_safewake(wait_queue_head_t *wq)
507 {
508         int this_cpu = get_cpu();
509 
510         ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS,
511                        ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
512 
513         put_cpu();
514 }
515 
516 static void ep_remove_wait_queue(struct eppoll_entry *pwq)
517 {
518         wait_queue_head_t *whead;
519 
520         rcu_read_lock();
521         /* If it is cleared by POLLFREE, it should be rcu-safe */
522         whead = rcu_dereference(pwq->whead);
523         if (whead)
524                 remove_wait_queue(whead, &pwq->wait);
525         rcu_read_unlock();
526 }
527 
528 /*
529  * This function unregisters poll callbacks from the associated file
530  * descriptor.  Must be called with "mtx" held (or "epmutex" if called from
531  * ep_free).
532  */
533 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
534 {
535         struct list_head *lsthead = &epi->pwqlist;
536         struct eppoll_entry *pwq;
537 
538         while (!list_empty(lsthead)) {
539                 pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
540 
541                 list_del(&pwq->llink);
542                 ep_remove_wait_queue(pwq);
543                 kmem_cache_free(pwq_cache, pwq);
544         }
545 }
546 
547 /* call only when ep->mtx is held */
548 static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
549 {
550         return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
551 }
552 
553 /* call only when ep->mtx is held */
554 static inline void ep_pm_stay_awake(struct epitem *epi)
555 {
556         struct wakeup_source *ws = ep_wakeup_source(epi);
557 
558         if (ws)
559                 __pm_stay_awake(ws);
560 }
561 
562 static inline bool ep_has_wakeup_source(struct epitem *epi)
563 {
564         return rcu_access_pointer(epi->ws) ? true : false;
565 }
566 
567 /* call when ep->mtx cannot be held (ep_poll_callback) */
568 static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
569 {
570         struct wakeup_source *ws;
571 
572         rcu_read_lock();
573         ws = rcu_dereference(epi->ws);
574         if (ws)
575                 __pm_stay_awake(ws);
576         rcu_read_unlock();
577 }
578 
579 /**
580  * ep_scan_ready_list - Scans the ready list in a way that makes possible for
581  *                      the scan code, to call f_op->poll(). Also allows for
582  *                      O(NumReady) performance.
583  *
584  * @ep: Pointer to the epoll private data structure.
585  * @sproc: Pointer to the scan callback.
586  * @priv: Private opaque data passed to the @sproc callback.
587  * @depth: The current depth of recursive f_op->poll calls.
588  * @ep_locked: caller already holds ep->mtx
589  *
590  * Returns: The same integer error code returned by the @sproc callback.
591  */
592 static int ep_scan_ready_list(struct eventpoll *ep,
593                               int (*sproc)(struct eventpoll *,
594                                            struct list_head *, void *),
595                               void *priv, int depth, bool ep_locked)
596 {
597         int error, pwake = 0;
598         unsigned long flags;
599         struct epitem *epi, *nepi;
600         LIST_HEAD(txlist);
601 
602         /*
603          * We need to lock this because we could be hit by
604          * eventpoll_release_file() and epoll_ctl().
605          */
606 
607         if (!ep_locked)
608                 mutex_lock_nested(&ep->mtx, depth);
609 
610         /*
611          * Steal the ready list, and re-init the original one to the
612          * empty list. Also, set ep->ovflist to NULL so that events
613          * happening while looping w/out locks, are not lost. We cannot
614          * have the poll callback to queue directly on ep->rdllist,
615          * because we want the "sproc" callback to be able to do it
616          * in a lockless way.
617          */
618         spin_lock_irqsave(&ep->lock, flags);
619         list_splice_init(&ep->rdllist, &txlist);
620         ep->ovflist = NULL;
621         spin_unlock_irqrestore(&ep->lock, flags);
622 
623         /*
624          * Now call the callback function.
625          */
626         error = (*sproc)(ep, &txlist, priv);
627 
628         spin_lock_irqsave(&ep->lock, flags);
629         /*
630          * During the time we spent inside the "sproc" callback, some
631          * other events might have been queued by the poll callback.
632          * We re-insert them inside the main ready-list here.
633          */
634         for (nepi = ep->ovflist; (epi = nepi) != NULL;
635              nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
636                 /*
637                  * We need to check if the item is already in the list.
638                  * During the "sproc" callback execution time, items are
639                  * queued into ->ovflist but the "txlist" might already
640                  * contain them, and the list_splice() below takes care of them.
641                  */
642                 if (!ep_is_linked(&epi->rdllink)) {
643                         list_add_tail(&epi->rdllink, &ep->rdllist);
644                         ep_pm_stay_awake(epi);
645                 }
646         }
647         /*
648          * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
649          * releasing the lock, events will be queued in the normal way inside
650          * ep->rdllist.
651          */
652         ep->ovflist = EP_UNACTIVE_PTR;
653 
654         /*
655          * Quickly re-inject items left on "txlist".
656          */
657         list_splice(&txlist, &ep->rdllist);
658         __pm_relax(ep->ws);
659 
660         if (!list_empty(&ep->rdllist)) {
661                 /*
662                  * Wake up (if active) both the eventpoll wait list and
663                  * the ->poll() wait list (delayed after we release the lock).
664                  */
665                 if (waitqueue_active(&ep->wq))
666                         wake_up_locked(&ep->wq);
667                 if (waitqueue_active(&ep->poll_wait))
668                         pwake++;
669         }
670         spin_unlock_irqrestore(&ep->lock, flags);
671 
672         if (!ep_locked)
673                 mutex_unlock(&ep->mtx);
674 
675         /* We have to call this outside the lock */
676         if (pwake)
677                 ep_poll_safewake(&ep->poll_wait);
678 
679         return error;
680 }
681 
682 static void epi_rcu_free(struct rcu_head *head)
683 {
684         struct epitem *epi = container_of(head, struct epitem, rcu);
685         kmem_cache_free(epi_cache, epi);
686 }
687 
688 /*
689  * Removes a "struct epitem" from the eventpoll RB tree and deallocates
690  * all the associated resources. Must be called with "mtx" held.
691  */
692 static int ep_remove(struct eventpoll *ep, struct epitem *epi)
693 {
694         unsigned long flags;
695         struct file *file = epi->ffd.file;
696 
697         /*
698          * Removes poll wait queue hooks. We _have_ to do this without holding
699          * the "ep->lock" otherwise a deadlock might occur. This because of the
700          * sequence of the lock acquisition. Here we do "ep->lock" then the wait
701          * queue head lock when unregistering the wait queue. The wakeup callback
702          * will run by holding the wait queue head lock and will call our callback
703          * that will try to get "ep->lock".
704          */
705         ep_unregister_pollwait(ep, epi);
706 
707         /* Remove the current item from the list of epoll hooks */
708         spin_lock(&file->f_lock);
709         list_del_rcu(&epi->fllink);
710         spin_unlock(&file->f_lock);
711 
712         rb_erase(&epi->rbn, &ep->rbr);
713 
714         spin_lock_irqsave(&ep->lock, flags);
715         if (ep_is_linked(&epi->rdllink))
716                 list_del_init(&epi->rdllink);
717         spin_unlock_irqrestore(&ep->lock, flags);
718 
719         wakeup_source_unregister(ep_wakeup_source(epi));
720         /*
721          * At this point it is safe to free the eventpoll item. Use the union
722          * field epi->rcu, since we are trying to minimize the size of
723          * 'struct epitem'. The 'rbn' field is no longer in use. Protected by
724          * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
725          * use of the rbn field.
726          */
727         call_rcu(&epi->rcu, epi_rcu_free);
728 
729         atomic_long_dec(&ep->user->epoll_watches);
730 
731         return 0;
732 }
733 
734 static void ep_free(struct eventpoll *ep)
735 {
736         struct rb_node *rbp;
737         struct epitem *epi;
738 
739         /* We need to release all tasks waiting for these file */
740         if (waitqueue_active(&ep->poll_wait))
741                 ep_poll_safewake(&ep->poll_wait);
742 
743         /*
744          * We need to lock this because we could be hit by
745          * eventpoll_release_file() while we're freeing the "struct eventpoll".
746          * We do not need to hold "ep->mtx" here because the epoll file
747          * is on the way to be removed and no one has references to it
748          * anymore. The only hit might come from eventpoll_release_file() but
749          * holding "epmutex" is sufficient here.
750          */
751         mutex_lock(&epmutex);
752 
753         /*
754          * Walks through the whole tree by unregistering poll callbacks.
755          */
756         for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
757                 epi = rb_entry(rbp, struct epitem, rbn);
758 
759                 ep_unregister_pollwait(ep, epi);
760                 cond_resched();
761         }
762 
763         /*
764          * Walks through the whole tree by freeing each "struct epitem". At this
765          * point we are sure no poll callbacks will be lingering around, and also by
766          * holding "epmutex" we can be sure that no file cleanup code will hit
767          * us during this operation. So we can avoid the lock on "ep->lock".
768          * We do not need to lock ep->mtx, either, we only do it to prevent
769          * a lockdep warning.
770          */
771         mutex_lock(&ep->mtx);
772         while ((rbp = rb_first(&ep->rbr)) != NULL) {
773                 epi = rb_entry(rbp, struct epitem, rbn);
774                 ep_remove(ep, epi);
775                 cond_resched();
776         }
777         mutex_unlock(&ep->mtx);
778 
779         mutex_unlock(&epmutex);
780         mutex_destroy(&ep->mtx);
781         free_uid(ep->user);
782         wakeup_source_unregister(ep->ws);
783         kfree(ep);
784 }
785 
786 static int ep_eventpoll_release(struct inode *inode, struct file *file)
787 {
788         struct eventpoll *ep = file->private_data;
789 
790         if (ep)
791                 ep_free(ep);
792 
793         return 0;
794 }
795 
796 static inline unsigned int ep_item_poll(struct epitem *epi, poll_table *pt)
797 {
798         pt->_key = epi->event.events;
799 
800         return epi->ffd.file->f_op->poll(epi->ffd.file, pt) & epi->event.events;
801 }
802 
803 static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
804                                void *priv)
805 {
806         struct epitem *epi, *tmp;
807         poll_table pt;
808 
809         init_poll_funcptr(&pt, NULL);
810 
811         list_for_each_entry_safe(epi, tmp, head, rdllink) {
812                 if (ep_item_poll(epi, &pt))
813                         return POLLIN | POLLRDNORM;
814                 else {
815                         /*
816                          * Item has been dropped into the ready list by the poll
817                          * callback, but it's not actually ready, as far as
818                          * caller requested events goes. We can remove it here.
819                          */
820                         __pm_relax(ep_wakeup_source(epi));
821                         list_del_init(&epi->rdllink);
822                 }
823         }
824 
825         return 0;
826 }
827 
828 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
829                                  poll_table *pt);
830 
831 struct readyevents_arg {
832         struct eventpoll *ep;
833         bool locked;
834 };
835 
836 static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
837 {
838         struct readyevents_arg *arg = priv;
839 
840         return ep_scan_ready_list(arg->ep, ep_read_events_proc, NULL,
841                                   call_nests + 1, arg->locked);
842 }
843 
844 static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
845 {
846         int pollflags;
847         struct eventpoll *ep = file->private_data;
848         struct readyevents_arg arg;
849 
850         /*
851          * During ep_insert() we already hold the ep->mtx for the tfile.
852          * Prevent re-aquisition.
853          */
854         arg.locked = wait && (wait->_qproc == ep_ptable_queue_proc);
855         arg.ep = ep;
856 
857         /* Insert inside our poll wait queue */
858         poll_wait(file, &ep->poll_wait, wait);
859 
860         /*
861          * Proceed to find out if wanted events are really available inside
862          * the ready list. This need to be done under ep_call_nested()
863          * supervision, since the call to f_op->poll() done on listed files
864          * could re-enter here.
865          */
866         pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS,
867                                    ep_poll_readyevents_proc, &arg, ep, current);
868 
869         return pollflags != -1 ? pollflags : 0;
870 }
871 
872 #ifdef CONFIG_PROC_FS
873 static int ep_show_fdinfo(struct seq_file *m, struct file *f)
874 {
875         struct eventpoll *ep = f->private_data;
876         struct rb_node *rbp;
877         int ret = 0;
878 
879         mutex_lock(&ep->mtx);
880         for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
881                 struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
882 
883                 ret = seq_printf(m, "tfd: %8d events: %8x data: %16llx\n",
884                                  epi->ffd.fd, epi->event.events,
885                                  (long long)epi->event.data);
886                 if (ret)
887                         break;
888         }
889         mutex_unlock(&ep->mtx);
890 
891         return ret;
892 }
893 #endif
894 
895 /* File callbacks that implement the eventpoll file behaviour */
896 static const struct file_operations eventpoll_fops = {
897 #ifdef CONFIG_PROC_FS
898         .show_fdinfo    = ep_show_fdinfo,
899 #endif
900         .release        = ep_eventpoll_release,
901         .poll           = ep_eventpoll_poll,
902         .llseek         = noop_llseek,
903 };
904 
905 /*
906  * This is called from eventpoll_release() to unlink files from the eventpoll
907  * interface. We need to have this facility to cleanup correctly files that are
908  * closed without being removed from the eventpoll interface.
909  */
910 void eventpoll_release_file(struct file *file)
911 {
912         struct eventpoll *ep;
913         struct epitem *epi, *next;
914 
915         /*
916          * We don't want to get "file->f_lock" because it is not
917          * necessary. It is not necessary because we're in the "struct file"
918          * cleanup path, and this means that no one is using this file anymore.
919          * So, for example, epoll_ctl() cannot hit here since if we reach this
920          * point, the file counter already went to zero and fget() would fail.
921          * The only hit might come from ep_free() but by holding the mutex
922          * will correctly serialize the operation. We do need to acquire
923          * "ep->mtx" after "epmutex" because ep_remove() requires it when called
924          * from anywhere but ep_free().
925          *
926          * Besides, ep_remove() acquires the lock, so we can't hold it here.
927          */
928         mutex_lock(&epmutex);
929         list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) {
930                 ep = epi->ep;
931                 mutex_lock_nested(&ep->mtx, 0);
932                 ep_remove(ep, epi);
933                 mutex_unlock(&ep->mtx);
934         }
935         mutex_unlock(&epmutex);
936 }
937 
938 static int ep_alloc(struct eventpoll **pep)
939 {
940         int error;
941         struct user_struct *user;
942         struct eventpoll *ep;
943 
944         user = get_current_user();
945         error = -ENOMEM;
946         ep = kzalloc(sizeof(*ep), GFP_KERNEL);
947         if (unlikely(!ep))
948                 goto free_uid;
949 
950         spin_lock_init(&ep->lock);
951         mutex_init(&ep->mtx);
952         init_waitqueue_head(&ep->wq);
953         init_waitqueue_head(&ep->poll_wait);
954         INIT_LIST_HEAD(&ep->rdllist);
955         ep->rbr = RB_ROOT;
956         ep->ovflist = EP_UNACTIVE_PTR;
957         ep->user = user;
958 
959         *pep = ep;
960 
961         return 0;
962 
963 free_uid:
964         free_uid(user);
965         return error;
966 }
967 
968 /*
969  * Search the file inside the eventpoll tree. The RB tree operations
970  * are protected by the "mtx" mutex, and ep_find() must be called with
971  * "mtx" held.
972  */
973 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
974 {
975         int kcmp;
976         struct rb_node *rbp;
977         struct epitem *epi, *epir = NULL;
978         struct epoll_filefd ffd;
979 
980         ep_set_ffd(&ffd, file, fd);
981         for (rbp = ep->rbr.rb_node; rbp; ) {
982                 epi = rb_entry(rbp, struct epitem, rbn);
983                 kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
984                 if (kcmp > 0)
985                         rbp = rbp->rb_right;
986                 else if (kcmp < 0)
987                         rbp = rbp->rb_left;
988                 else {
989                         epir = epi;
990                         break;
991                 }
992         }
993 
994         return epir;
995 }
996 
997 /*
998  * This is the callback that is passed to the wait queue wakeup
999  * mechanism. It is called by the stored file descriptors when they
1000  * have events to report.
1001  */
1002 static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
1003 {
1004         int pwake = 0;
1005         unsigned long flags;
1006         struct epitem *epi = ep_item_from_wait(wait);
1007         struct eventpoll *ep = epi->ep;
1008 
1009         if ((unsigned long)key & POLLFREE) {
1010                 ep_pwq_from_wait(wait)->whead = NULL;
1011                 /*
1012                  * whead = NULL above can race with ep_remove_wait_queue()
1013                  * which can do another remove_wait_queue() after us, so we
1014                  * can't use __remove_wait_queue(). whead->lock is held by
1015                  * the caller.
1016                  */
1017                 list_del_init(&wait->task_list);
1018         }
1019 
1020         spin_lock_irqsave(&ep->lock, flags);
1021 
1022         /*
1023          * If the event mask does not contain any poll(2) event, we consider the
1024          * descriptor to be disabled. This condition is likely the effect of the
1025          * EPOLLONESHOT bit that disables the descriptor when an event is received,
1026          * until the next EPOLL_CTL_MOD will be issued.
1027          */
1028         if (!(epi->event.events & ~EP_PRIVATE_BITS))
1029                 goto out_unlock;
1030 
1031         /*
1032          * Check the events coming with the callback. At this stage, not
1033          * every device reports the events in the "key" parameter of the
1034          * callback. We need to be able to handle both cases here, hence the
1035          * test for "key" != NULL before the event match test.
1036          */
1037         if (key && !((unsigned long) key & epi->event.events))
1038                 goto out_unlock;
1039 
1040         /*
1041          * If we are transferring events to userspace, we can hold no locks
1042          * (because we're accessing user memory, and because of linux f_op->poll()
1043          * semantics). All the events that happen during that period of time are
1044          * chained in ep->ovflist and requeued later on.
1045          */
1046         if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
1047                 if (epi->next == EP_UNACTIVE_PTR) {
1048                         epi->next = ep->ovflist;
1049                         ep->ovflist = epi;
1050                         if (epi->ws) {
1051                                 /*
1052                                  * Activate ep->ws since epi->ws may get
1053                                  * deactivated at any time.
1054                                  */
1055                                 __pm_stay_awake(ep->ws);
1056                         }
1057 
1058                 }
1059                 goto out_unlock;
1060         }
1061 
1062         /* If this file is already in the ready list we exit soon */
1063         if (!ep_is_linked(&epi->rdllink)) {
1064                 list_add_tail(&epi->rdllink, &ep->rdllist);
1065                 ep_pm_stay_awake_rcu(epi);
1066         }
1067 
1068         /*
1069          * Wake up ( if active ) both the eventpoll wait list and the ->poll()
1070          * wait list.
1071          */
1072         if (waitqueue_active(&ep->wq))
1073                 wake_up_locked(&ep->wq);
1074         if (waitqueue_active(&ep->poll_wait))
1075                 pwake++;
1076 
1077 out_unlock:
1078         spin_unlock_irqrestore(&ep->lock, flags);
1079 
1080         /* We have to call this outside the lock */
1081         if (pwake)
1082                 ep_poll_safewake(&ep->poll_wait);
1083 
1084         return 1;
1085 }
1086 
1087 /*
1088  * This is the callback that is used to add our wait queue to the
1089  * target file wakeup lists.
1090  */
1091 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
1092                                  poll_table *pt)
1093 {
1094         struct epitem *epi = ep_item_from_epqueue(pt);
1095         struct eppoll_entry *pwq;
1096 
1097         if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
1098                 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
1099                 pwq->whead = whead;
1100                 pwq->base = epi;
1101                 add_wait_queue(whead, &pwq->wait);
1102                 list_add_tail(&pwq->llink, &epi->pwqlist);
1103                 epi->nwait++;
1104         } else {
1105                 /* We have to signal that an error occurred */
1106                 epi->nwait = -1;
1107         }
1108 }
1109 
1110 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
1111 {
1112         int kcmp;
1113         struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
1114         struct epitem *epic;
1115 
1116         while (*p) {
1117                 parent = *p;
1118                 epic = rb_entry(parent, struct epitem, rbn);
1119                 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
1120                 if (kcmp > 0)
1121                         p = &parent->rb_right;
1122                 else
1123                         p = &parent->rb_left;
1124         }
1125         rb_link_node(&epi->rbn, parent, p);
1126         rb_insert_color(&epi->rbn, &ep->rbr);
1127 }
1128 
1129 
1130 
1131 #define PATH_ARR_SIZE 5
1132 /*
1133  * These are the number paths of length 1 to 5, that we are allowing to emanate
1134  * from a single file of interest. For example, we allow 1000 paths of length
1135  * 1, to emanate from each file of interest. This essentially represents the
1136  * potential wakeup paths, which need to be limited in order to avoid massive
1137  * uncontrolled wakeup storms. The common use case should be a single ep which
1138  * is connected to n file sources. In this case each file source has 1 path
1139  * of length 1. Thus, the numbers below should be more than sufficient. These
1140  * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
1141  * and delete can't add additional paths. Protected by the epmutex.
1142  */
1143 static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
1144 static int path_count[PATH_ARR_SIZE];
1145 
1146 static int path_count_inc(int nests)
1147 {
1148         /* Allow an arbitrary number of depth 1 paths */
1149         if (nests == 0)
1150                 return 0;
1151 
1152         if (++path_count[nests] > path_limits[nests])
1153                 return -1;
1154         return 0;
1155 }
1156 
1157 static void path_count_init(void)
1158 {
1159         int i;
1160 
1161         for (i = 0; i < PATH_ARR_SIZE; i++)
1162                 path_count[i] = 0;
1163 }
1164 
1165 static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
1166 {
1167         int error = 0;
1168         struct file *file = priv;
1169         struct file *child_file;
1170         struct epitem *epi;
1171 
1172         /* CTL_DEL can remove links here, but that can't increase our count */
1173         rcu_read_lock();
1174         list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
1175                 child_file = epi->ep->file;
1176                 if (is_file_epoll(child_file)) {
1177                         if (list_empty(&child_file->f_ep_links)) {
1178                                 if (path_count_inc(call_nests)) {
1179                                         error = -1;
1180                                         break;
1181                                 }
1182                         } else {
1183                                 error = ep_call_nested(&poll_loop_ncalls,
1184                                                         EP_MAX_NESTS,
1185                                                         reverse_path_check_proc,
1186                                                         child_file, child_file,
1187                                                         current);
1188                         }
1189                         if (error != 0)
1190                                 break;
1191                 } else {
1192                         printk(KERN_ERR "reverse_path_check_proc: "
1193                                 "file is not an ep!\n");
1194                 }
1195         }
1196         rcu_read_unlock();
1197         return error;
1198 }
1199 
1200 /**
1201  * reverse_path_check - The tfile_check_list is list of file *, which have
1202  *                      links that are proposed to be newly added. We need to
1203  *                      make sure that those added links don't add too many
1204  *                      paths such that we will spend all our time waking up
1205  *                      eventpoll objects.
1206  *
1207  * Returns: Returns zero if the proposed links don't create too many paths,
1208  *          -1 otherwise.
1209  */
1210 static int reverse_path_check(void)
1211 {
1212         int error = 0;
1213         struct file *current_file;
1214 
1215         /* let's call this for all tfiles */
1216         list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
1217                 path_count_init();
1218                 error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1219                                         reverse_path_check_proc, current_file,
1220                                         current_file, current);
1221                 if (error)
1222                         break;
1223         }
1224         return error;
1225 }
1226 
1227 static int ep_create_wakeup_source(struct epitem *epi)
1228 {
1229         const char *name;
1230         struct wakeup_source *ws;
1231 
1232         if (!epi->ep->ws) {
1233                 epi->ep->ws = wakeup_source_register("eventpoll");
1234                 if (!epi->ep->ws)
1235                         return -ENOMEM;
1236         }
1237 
1238         name = epi->ffd.file->f_path.dentry->d_name.name;
1239         ws = wakeup_source_register(name);
1240 
1241         if (!ws)
1242                 return -ENOMEM;
1243         rcu_assign_pointer(epi->ws, ws);
1244 
1245         return 0;
1246 }
1247 
1248 /* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
1249 static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1250 {
1251         struct wakeup_source *ws = ep_wakeup_source(epi);
1252 
1253         RCU_INIT_POINTER(epi->ws, NULL);
1254 
1255         /*
1256          * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
1257          * used internally by wakeup_source_remove, too (called by
1258          * wakeup_source_unregister), so we cannot use call_rcu
1259          */
1260         synchronize_rcu();
1261         wakeup_source_unregister(ws);
1262 }
1263 
1264 /*
1265  * Must be called with "mtx" held.
1266  */
1267 static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
1268                      struct file *tfile, int fd, int full_check)
1269 {
1270         int error, revents, pwake = 0;
1271         unsigned long flags;
1272         long user_watches;
1273         struct epitem *epi;
1274         struct ep_pqueue epq;
1275 
1276         user_watches = atomic_long_read(&ep->user->epoll_watches);
1277         if (unlikely(user_watches >= max_user_watches))
1278                 return -ENOSPC;
1279         if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
1280                 return -ENOMEM;
1281 
1282         /* Item initialization follow here ... */
1283         INIT_LIST_HEAD(&epi->rdllink);
1284         INIT_LIST_HEAD(&epi->fllink);
1285         INIT_LIST_HEAD(&epi->pwqlist);
1286         epi->ep = ep;
1287         ep_set_ffd(&epi->ffd, tfile, fd);
1288         epi->event = *event;
1289         epi->nwait = 0;
1290         epi->next = EP_UNACTIVE_PTR;
1291         if (epi->event.events & EPOLLWAKEUP) {
1292                 error = ep_create_wakeup_source(epi);
1293                 if (error)
1294                         goto error_create_wakeup_source;
1295         } else {
1296                 RCU_INIT_POINTER(epi->ws, NULL);
1297         }
1298 
1299         /* Initialize the poll table using the queue callback */
1300         epq.epi = epi;
1301         init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
1302 
1303         /*
1304          * Attach the item to the poll hooks and get current event bits.
1305          * We can safely use the file* here because its usage count has
1306          * been increased by the caller of this function. Note that after
1307          * this operation completes, the poll callback can start hitting
1308          * the new item.
1309          */
1310         revents = ep_item_poll(epi, &epq.pt);
1311 
1312         /*
1313          * We have to check if something went wrong during the poll wait queue
1314          * install process. Namely an allocation for a wait queue failed due
1315          * high memory pressure.
1316          */
1317         error = -ENOMEM;
1318         if (epi->nwait < 0)
1319                 goto error_unregister;
1320 
1321         /* Add the current item to the list of active epoll hook for this file */
1322         spin_lock(&tfile->f_lock);
1323         list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
1324         spin_unlock(&tfile->f_lock);
1325 
1326         /*
1327          * Add the current item to the RB tree. All RB tree operations are
1328          * protected by "mtx", and ep_insert() is called with "mtx" held.
1329          */
1330         ep_rbtree_insert(ep, epi);
1331 
1332         /* now check if we've created too many backpaths */
1333         error = -EINVAL;
1334         if (full_check && reverse_path_check())
1335                 goto error_remove_epi;
1336 
1337         /* We have to drop the new item inside our item list to keep track of it */
1338         spin_lock_irqsave(&ep->lock, flags);
1339 
1340         /* If the file is already "ready" we drop it inside the ready list */
1341         if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
1342                 list_add_tail(&epi->rdllink, &ep->rdllist);
1343                 ep_pm_stay_awake(epi);
1344 
1345                 /* Notify waiting tasks that events are available */
1346                 if (waitqueue_active(&ep->wq))
1347                         wake_up_locked(&ep->wq);
1348                 if (waitqueue_active(&ep->poll_wait))
1349                         pwake++;
1350         }
1351 
1352         spin_unlock_irqrestore(&ep->lock, flags);
1353 
1354         atomic_long_inc(&ep->user->epoll_watches);
1355 
1356         /* We have to call this outside the lock */
1357         if (pwake)
1358                 ep_poll_safewake(&ep->poll_wait);
1359 
1360         return 0;
1361 
1362 error_remove_epi:
1363         spin_lock(&tfile->f_lock);
1364         list_del_rcu(&epi->fllink);
1365         spin_unlock(&tfile->f_lock);
1366 
1367         rb_erase(&epi->rbn, &ep->rbr);
1368 
1369 error_unregister:
1370         ep_unregister_pollwait(ep, epi);
1371 
1372         /*
1373          * We need to do this because an event could have been arrived on some
1374          * allocated wait queue. Note that we don't care about the ep->ovflist
1375          * list, since that is used/cleaned only inside a section bound by "mtx".
1376          * And ep_insert() is called with "mtx" held.
1377          */
1378         spin_lock_irqsave(&ep->lock, flags);
1379         if (ep_is_linked(&epi->rdllink))
1380                 list_del_init(&epi->rdllink);
1381         spin_unlock_irqrestore(&ep->lock, flags);
1382 
1383         wakeup_source_unregister(ep_wakeup_source(epi));
1384 
1385 error_create_wakeup_source:
1386         kmem_cache_free(epi_cache, epi);
1387 
1388         return error;
1389 }
1390 
1391 /*
1392  * Modify the interest event mask by dropping an event if the new mask
1393  * has a match in the current file status. Must be called with "mtx" held.
1394  */
1395 static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
1396 {
1397         int pwake = 0;
1398         unsigned int revents;
1399         poll_table pt;
1400 
1401         init_poll_funcptr(&pt, NULL);
1402 
1403         /*
1404          * Set the new event interest mask before calling f_op->poll();
1405          * otherwise we might miss an event that happens between the
1406          * f_op->poll() call and the new event set registering.
1407          */
1408         epi->event.events = event->events; /* need barrier below */
1409         epi->event.data = event->data; /* protected by mtx */
1410         if (epi->event.events & EPOLLWAKEUP) {
1411                 if (!ep_has_wakeup_source(epi))
1412                         ep_create_wakeup_source(epi);
1413         } else if (ep_has_wakeup_source(epi)) {
1414                 ep_destroy_wakeup_source(epi);
1415         }
1416 
1417         /*
1418          * The following barrier has two effects:
1419          *
1420          * 1) Flush epi changes above to other CPUs.  This ensures
1421          *    we do not miss events from ep_poll_callback if an
1422          *    event occurs immediately after we call f_op->poll().
1423          *    We need this because we did not take ep->lock while
1424          *    changing epi above (but ep_poll_callback does take
1425          *    ep->lock).
1426          *
1427          * 2) We also need to ensure we do not miss _past_ events
1428          *    when calling f_op->poll().  This barrier also
1429          *    pairs with the barrier in wq_has_sleeper (see
1430          *    comments for wq_has_sleeper).
1431          *
1432          * This barrier will now guarantee ep_poll_callback or f_op->poll
1433          * (or both) will notice the readiness of an item.
1434          */
1435         smp_mb();
1436 
1437         /*
1438          * Get current event bits. We can safely use the file* here because
1439          * its usage count has been increased by the caller of this function.
1440          */
1441         revents = ep_item_poll(epi, &pt);
1442 
1443         /*
1444          * If the item is "hot" and it is not registered inside the ready
1445          * list, push it inside.
1446          */
1447         if (revents & event->events) {
1448                 spin_lock_irq(&ep->lock);
1449                 if (!ep_is_linked(&epi->rdllink)) {
1450                         list_add_tail(&epi->rdllink, &ep->rdllist);
1451                         ep_pm_stay_awake(epi);
1452 
1453                         /* Notify waiting tasks that events are available */
1454                         if (waitqueue_active(&ep->wq))
1455                                 wake_up_locked(&ep->wq);
1456                         if (waitqueue_active(&ep->poll_wait))
1457                                 pwake++;
1458                 }
1459                 spin_unlock_irq(&ep->lock);
1460         }
1461 
1462         /* We have to call this outside the lock */
1463         if (pwake)
1464                 ep_poll_safewake(&ep->poll_wait);
1465 
1466         return 0;
1467 }
1468 
1469 static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
1470                                void *priv)
1471 {
1472         struct ep_send_events_data *esed = priv;
1473         int eventcnt;
1474         unsigned int revents;
1475         struct epitem *epi;
1476         struct epoll_event __user *uevent;
1477         struct wakeup_source *ws;
1478         poll_table pt;
1479 
1480         init_poll_funcptr(&pt, NULL);
1481 
1482         /*
1483          * We can loop without lock because we are passed a task private list.
1484          * Items cannot vanish during the loop because ep_scan_ready_list() is
1485          * holding "mtx" during this call.
1486          */
1487         for (eventcnt = 0, uevent = esed->events;
1488              !list_empty(head) && eventcnt < esed->maxevents;) {
1489                 epi = list_first_entry(head, struct epitem, rdllink);
1490 
1491                 /*
1492                  * Activate ep->ws before deactivating epi->ws to prevent
1493                  * triggering auto-suspend here (in case we reactive epi->ws
1494                  * below).
1495                  *
1496                  * This could be rearranged to delay the deactivation of epi->ws
1497                  * instead, but then epi->ws would temporarily be out of sync
1498                  * with ep_is_linked().
1499                  */
1500                 ws = ep_wakeup_source(epi);
1501                 if (ws) {
1502                         if (ws->active)
1503                                 __pm_stay_awake(ep->ws);
1504                         __pm_relax(ws);
1505                 }
1506 
1507                 list_del_init(&epi->rdllink);
1508 
1509                 revents = ep_item_poll(epi, &pt);
1510 
1511                 /*
1512                  * If the event mask intersect the caller-requested one,
1513                  * deliver the event to userspace. Again, ep_scan_ready_list()
1514                  * is holding "mtx", so no operations coming from userspace
1515                  * can change the item.
1516                  */
1517                 if (revents) {
1518                         if (__put_user(revents, &uevent->events) ||
1519                             __put_user(epi->event.data, &uevent->data)) {
1520                                 list_add(&epi->rdllink, head);
1521                                 ep_pm_stay_awake(epi);
1522                                 return eventcnt ? eventcnt : -EFAULT;
1523                         }
1524                         eventcnt++;
1525                         uevent++;
1526                         if (epi->event.events & EPOLLONESHOT)
1527                                 epi->event.events &= EP_PRIVATE_BITS;
1528                         else if (!(epi->event.events & EPOLLET)) {
1529                                 /*
1530                                  * If this file has been added with Level
1531                                  * Trigger mode, we need to insert back inside
1532                                  * the ready list, so that the next call to
1533                                  * epoll_wait() will check again the events
1534                                  * availability. At this point, no one can insert
1535                                  * into ep->rdllist besides us. The epoll_ctl()
1536                                  * callers are locked out by
1537                                  * ep_scan_ready_list() holding "mtx" and the
1538                                  * poll callback will queue them in ep->ovflist.
1539                                  */
1540                                 list_add_tail(&epi->rdllink, &ep->rdllist);
1541                                 ep_pm_stay_awake(epi);
1542                         }
1543                 }
1544         }
1545 
1546         return eventcnt;
1547 }
1548 
1549 static int ep_send_events(struct eventpoll *ep,
1550                           struct epoll_event __user *events, int maxevents)
1551 {
1552         struct ep_send_events_data esed;
1553 
1554         esed.maxevents = maxevents;
1555         esed.events = events;
1556 
1557         return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
1558 }
1559 
1560 static inline struct timespec ep_set_mstimeout(long ms)
1561 {
1562         struct timespec now, ts = {
1563                 .tv_sec = ms / MSEC_PER_SEC,
1564                 .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
1565         };
1566 
1567         ktime_get_ts(&now);
1568         return timespec_add_safe(now, ts);
1569 }
1570 
1571 /**
1572  * ep_poll - Retrieves ready events, and delivers them to the caller supplied
1573  *           event buffer.
1574  *
1575  * @ep: Pointer to the eventpoll context.
1576  * @events: Pointer to the userspace buffer where the ready events should be
1577  *          stored.
1578  * @maxevents: Size (in terms of number of events) of the caller event buffer.
1579  * @timeout: Maximum timeout for the ready events fetch operation, in
1580  *           milliseconds. If the @timeout is zero, the function will not block,
1581  *           while if the @timeout is less than zero, the function will block
1582  *           until at least one event has been retrieved (or an error
1583  *           occurred).
1584  *
1585  * Returns: Returns the number of ready events which have been fetched, or an
1586  *          error code, in case of error.
1587  */
1588 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1589                    int maxevents, long timeout)
1590 {
1591         int res = 0, eavail, timed_out = 0;
1592         unsigned long flags;
1593         long slack = 0;
1594         wait_queue_t wait;
1595         ktime_t expires, *to = NULL;
1596 
1597         if (timeout > 0) {
1598                 struct timespec end_time = ep_set_mstimeout(timeout);
1599 
1600                 slack = select_estimate_accuracy(&end_time);
1601                 to = &expires;
1602                 *to = timespec_to_ktime(end_time);
1603         } else if (timeout == 0) {
1604                 /*
1605                  * Avoid the unnecessary trip to the wait queue loop, if the
1606                  * caller specified a non blocking operation.
1607                  */
1608                 timed_out = 1;
1609                 spin_lock_irqsave(&ep->lock, flags);
1610                 goto check_events;
1611         }
1612 
1613 fetch_events:
1614         spin_lock_irqsave(&ep->lock, flags);
1615 
1616         if (!ep_events_available(ep)) {
1617                 /*
1618                  * We don't have any available event to return to the caller.
1619                  * We need to sleep here, and we will be wake up by
1620                  * ep_poll_callback() when events will become available.
1621                  */
1622                 init_waitqueue_entry(&wait, current);
1623                 __add_wait_queue_exclusive(&ep->wq, &wait);
1624 
1625                 for (;;) {
1626                         /*
1627                          * We don't want to sleep if the ep_poll_callback() sends us
1628                          * a wakeup in between. That's why we set the task state
1629                          * to TASK_INTERRUPTIBLE before doing the checks.
1630                          */
1631                         set_current_state(TASK_INTERRUPTIBLE);
1632                         if (ep_events_available(ep) || timed_out)
1633                                 break;
1634                         if (signal_pending(current)) {
1635                                 res = -EINTR;
1636                                 break;
1637                         }
1638 
1639                         spin_unlock_irqrestore(&ep->lock, flags);
1640                         if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
1641                                 timed_out = 1;
1642 
1643                         spin_lock_irqsave(&ep->lock, flags);
1644                 }
1645                 __remove_wait_queue(&ep->wq, &wait);
1646 
1647                 set_current_state(TASK_RUNNING);
1648         }
1649 check_events:
1650         /* Is it worth to try to dig for events ? */
1651         eavail = ep_events_available(ep);
1652 
1653         spin_unlock_irqrestore(&ep->lock, flags);
1654 
1655         /*
1656          * Try to transfer events to user space. In case we get 0 events and
1657          * there's still timeout left over, we go trying again in search of
1658          * more luck.
1659          */
1660         if (!res && eavail &&
1661             !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
1662                 goto fetch_events;
1663 
1664         return res;
1665 }
1666 
1667 /**
1668  * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
1669  *                      API, to verify that adding an epoll file inside another
1670  *                      epoll structure, does not violate the constraints, in
1671  *                      terms of closed loops, or too deep chains (which can
1672  *                      result in excessive stack usage).
1673  *
1674  * @priv: Pointer to the epoll file to be currently checked.
1675  * @cookie: Original cookie for this call. This is the top-of-the-chain epoll
1676  *          data structure pointer.
1677  * @call_nests: Current dept of the @ep_call_nested() call stack.
1678  *
1679  * Returns: Returns zero if adding the epoll @file inside current epoll
1680  *          structure @ep does not violate the constraints, or -1 otherwise.
1681  */
1682 static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
1683 {
1684         int error = 0;
1685         struct file *file = priv;
1686         struct eventpoll *ep = file->private_data;
1687         struct eventpoll *ep_tovisit;
1688         struct rb_node *rbp;
1689         struct epitem *epi;
1690 
1691         mutex_lock_nested(&ep->mtx, call_nests + 1);
1692         ep->visited = 1;
1693         list_add(&ep->visited_list_link, &visited_list);
1694         for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1695                 epi = rb_entry(rbp, struct epitem, rbn);
1696                 if (unlikely(is_file_epoll(epi->ffd.file))) {
1697                         ep_tovisit = epi->ffd.file->private_data;
1698                         if (ep_tovisit->visited)
1699                                 continue;
1700                         error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1701                                         ep_loop_check_proc, epi->ffd.file,
1702                                         ep_tovisit, current);
1703                         if (error != 0)
1704                                 break;
1705                 } else {
1706                         /*
1707                          * If we've reached a file that is not associated with
1708                          * an ep, then we need to check if the newly added
1709                          * links are going to add too many wakeup paths. We do
1710                          * this by adding it to the tfile_check_list, if it's
1711                          * not already there, and calling reverse_path_check()
1712                          * during ep_insert().
1713                          */
1714                         if (list_empty(&epi->ffd.file->f_tfile_llink))
1715                                 list_add(&epi->ffd.file->f_tfile_llink,
1716                                          &tfile_check_list);
1717                 }
1718         }
1719         mutex_unlock(&ep->mtx);
1720 
1721         return error;
1722 }
1723 
1724 /**
1725  * ep_loop_check - Performs a check to verify that adding an epoll file (@file)
1726  *                 another epoll file (represented by @ep) does not create
1727  *                 closed loops or too deep chains.
1728  *
1729  * @ep: Pointer to the epoll private data structure.
1730  * @file: Pointer to the epoll file to be checked.
1731  *
1732  * Returns: Returns zero if adding the epoll @file inside current epoll
1733  *          structure @ep does not violate the constraints, or -1 otherwise.
1734  */
1735 static int ep_loop_check(struct eventpoll *ep, struct file *file)
1736 {
1737         int ret;
1738         struct eventpoll *ep_cur, *ep_next;
1739 
1740         ret = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1741                               ep_loop_check_proc, file, ep, current);
1742         /* clear visited list */
1743         list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
1744                                                         visited_list_link) {
1745                 ep_cur->visited = 0;
1746                 list_del(&ep_cur->visited_list_link);
1747         }
1748         return ret;
1749 }
1750 
1751 static void clear_tfile_check_list(void)
1752 {
1753         struct file *file;
1754 
1755         /* first clear the tfile_check_list */
1756         while (!list_empty(&tfile_check_list)) {
1757                 file = list_first_entry(&tfile_check_list, struct file,
1758                                         f_tfile_llink);
1759                 list_del_init(&file->f_tfile_llink);
1760         }
1761         INIT_LIST_HEAD(&tfile_check_list);
1762 }
1763 
1764 /*
1765  * Open an eventpoll file descriptor.
1766  */
1767 SYSCALL_DEFINE1(epoll_create1, int, flags)
1768 {
1769         int error, fd;
1770         struct eventpoll *ep = NULL;
1771         struct file *file;
1772 
1773         /* Check the EPOLL_* constant for consistency.  */
1774         BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
1775 
1776         if (flags & ~EPOLL_CLOEXEC)
1777                 return -EINVAL;
1778         /*
1779          * Create the internal data structure ("struct eventpoll").
1780          */
1781         error = ep_alloc(&ep);
1782         if (error < 0)
1783                 return error;
1784         /*
1785          * Creates all the items needed to setup an eventpoll file. That is,
1786          * a file structure and a free file descriptor.
1787          */
1788         fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
1789         if (fd < 0) {
1790                 error = fd;
1791                 goto out_free_ep;
1792         }
1793         file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
1794                                  O_RDWR | (flags & O_CLOEXEC));
1795         if (IS_ERR(file)) {
1796                 error = PTR_ERR(file);
1797                 goto out_free_fd;
1798         }
1799         ep->file = file;
1800         fd_install(fd, file);
1801         return fd;
1802 
1803 out_free_fd:
1804         put_unused_fd(fd);
1805 out_free_ep:
1806         ep_free(ep);
1807         return error;
1808 }
1809 
1810 SYSCALL_DEFINE1(epoll_create, int, size)
1811 {
1812         if (size <= 0)
1813                 return -EINVAL;
1814 
1815         return sys_epoll_create1(0);
1816 }
1817 
1818 /*
1819  * The following function implements the controller interface for
1820  * the eventpoll file that enables the insertion/removal/change of
1821  * file descriptors inside the interest set.
1822  */
1823 SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
1824                 struct epoll_event __user *, event)
1825 {
1826         int error;
1827         int full_check = 0;
1828         struct fd f, tf;
1829         struct eventpoll *ep;
1830         struct epitem *epi;
1831         struct epoll_event epds;
1832         struct eventpoll *tep = NULL;
1833 
1834         error = -EFAULT;
1835         if (ep_op_has_event(op) &&
1836             copy_from_user(&epds, event, sizeof(struct epoll_event)))
1837                 goto error_return;
1838 
1839         error = -EBADF;
1840         f = fdget(epfd);
1841         if (!f.file)
1842                 goto error_return;
1843 
1844         /* Get the "struct file *" for the target file */
1845         tf = fdget(fd);
1846         if (!tf.file)
1847                 goto error_fput;
1848 
1849         /* The target file descriptor must support poll */
1850         error = -EPERM;
1851         if (!tf.file->f_op->poll)
1852                 goto error_tgt_fput;
1853 
1854         /* Check if EPOLLWAKEUP is allowed */
1855         if (ep_op_has_event(op))
1856                 ep_take_care_of_epollwakeup(&epds);
1857 
1858         /*
1859          * We have to check that the file structure underneath the file descriptor
1860          * the user passed to us _is_ an eventpoll file. And also we do not permit
1861          * adding an epoll file descriptor inside itself.
1862          */
1863         error = -EINVAL;
1864         if (f.file == tf.file || !is_file_epoll(f.file))
1865                 goto error_tgt_fput;
1866 
1867         /*
1868          * At this point it is safe to assume that the "private_data" contains
1869          * our own data structure.
1870          */
1871         ep = f.file->private_data;
1872 
1873         /*
1874          * When we insert an epoll file descriptor, inside another epoll file
1875          * descriptor, there is the change of creating closed loops, which are
1876          * better be handled here, than in more critical paths. While we are
1877          * checking for loops we also determine the list of files reachable
1878          * and hang them on the tfile_check_list, so we can check that we
1879          * haven't created too many possible wakeup paths.
1880          *
1881          * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
1882          * the epoll file descriptor is attaching directly to a wakeup source,
1883          * unless the epoll file descriptor is nested. The purpose of taking the
1884          * 'epmutex' on add is to prevent complex toplogies such as loops and
1885          * deep wakeup paths from forming in parallel through multiple
1886          * EPOLL_CTL_ADD operations.
1887          */
1888         mutex_lock_nested(&ep->mtx, 0);
1889         if (op == EPOLL_CTL_ADD) {
1890                 if (!list_empty(&f.file->f_ep_links) ||
1891                                                 is_file_epoll(tf.file)) {
1892                         full_check = 1;
1893                         mutex_unlock(&ep->mtx);
1894                         mutex_lock(&epmutex);
1895                         if (is_file_epoll(tf.file)) {
1896                                 error = -ELOOP;
1897                                 if (ep_loop_check(ep, tf.file) != 0) {
1898                                         clear_tfile_check_list();
1899                                         goto error_tgt_fput;
1900                                 }
1901                         } else
1902                                 list_add(&tf.file->f_tfile_llink,
1903                                                         &tfile_check_list);
1904                         mutex_lock_nested(&ep->mtx, 0);
1905                         if (is_file_epoll(tf.file)) {
1906                                 tep = tf.file->private_data;
1907                                 mutex_lock_nested(&tep->mtx, 1);
1908                         }
1909                 }
1910         }
1911 
1912         /*
1913          * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
1914          * above, we can be sure to be able to use the item looked up by
1915          * ep_find() till we release the mutex.
1916          */
1917         epi = ep_find(ep, tf.file, fd);
1918 
1919         error = -EINVAL;
1920         switch (op) {
1921         case EPOLL_CTL_ADD:
1922                 if (!epi) {
1923                         epds.events |= POLLERR | POLLHUP;
1924                         error = ep_insert(ep, &epds, tf.file, fd, full_check);
1925                 } else
1926                         error = -EEXIST;
1927                 if (full_check)
1928                         clear_tfile_check_list();
1929                 break;
1930         case EPOLL_CTL_DEL:
1931                 if (epi)
1932                         error = ep_remove(ep, epi);
1933                 else
1934                         error = -ENOENT;
1935                 break;
1936         case EPOLL_CTL_MOD:
1937                 if (epi) {
1938                         epds.events |= POLLERR | POLLHUP;
1939                         error = ep_modify(ep, epi, &epds);
1940                 } else
1941                         error = -ENOENT;
1942                 break;
1943         }
1944         if (tep != NULL)
1945                 mutex_unlock(&tep->mtx);
1946         mutex_unlock(&ep->mtx);
1947 
1948 error_tgt_fput:
1949         if (full_check)
1950                 mutex_unlock(&epmutex);
1951 
1952         fdput(tf);
1953 error_fput:
1954         fdput(f);
1955 error_return:
1956 
1957         return error;
1958 }
1959 
1960 /*
1961  * Implement the event wait interface for the eventpoll file. It is the kernel
1962  * part of the user space epoll_wait(2).
1963  */
1964 SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
1965                 int, maxevents, int, timeout)
1966 {
1967         int error;
1968         struct fd f;
1969         struct eventpoll *ep;
1970 
1971         /* The maximum number of event must be greater than zero */
1972         if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
1973                 return -EINVAL;
1974 
1975         /* Verify that the area passed by the user is writeable */
1976         if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event)))
1977                 return -EFAULT;
1978 
1979         /* Get the "struct file *" for the eventpoll file */
1980         f = fdget(epfd);
1981         if (!f.file)
1982                 return -EBADF;
1983 
1984         /*
1985          * We have to check that the file structure underneath the fd
1986          * the user passed to us _is_ an eventpoll file.
1987          */
1988         error = -EINVAL;
1989         if (!is_file_epoll(f.file))
1990                 goto error_fput;
1991 
1992         /*
1993          * At this point it is safe to assume that the "private_data" contains
1994          * our own data structure.
1995          */
1996         ep = f.file->private_data;
1997 
1998         /* Time to fish for events ... */
1999         error = ep_poll(ep, events, maxevents, timeout);
2000 
2001 error_fput:
2002         fdput(f);
2003         return error;
2004 }
2005 
2006 /*
2007  * Implement the event wait interface for the eventpoll file. It is the kernel
2008  * part of the user space epoll_pwait(2).
2009  */
2010 SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
2011                 int, maxevents, int, timeout, const sigset_t __user *, sigmask,
2012                 size_t, sigsetsize)
2013 {
2014         int error;
2015         sigset_t ksigmask, sigsaved;
2016 
2017         /*
2018          * If the caller wants a certain signal mask to be set during the wait,
2019          * we apply it here.
2020          */
2021         if (sigmask) {
2022                 if (sigsetsize != sizeof(sigset_t))
2023                         return -EINVAL;
2024                 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
2025                         return -EFAULT;
2026                 sigsaved = current->blocked;
2027                 set_current_blocked(&ksigmask);
2028         }
2029 
2030         error = sys_epoll_wait(epfd, events, maxevents, timeout);
2031 
2032         /*
2033          * If we changed the signal mask, we need to restore the original one.
2034          * In case we've got a signal while waiting, we do not restore the
2035          * signal mask yet, and we allow do_signal() to deliver the signal on
2036          * the way back to userspace, before the signal mask is restored.
2037          */
2038         if (sigmask) {
2039                 if (error == -EINTR) {
2040                         memcpy(&current->saved_sigmask, &sigsaved,
2041                                sizeof(sigsaved));
2042                         set_restore_sigmask();
2043                 } else
2044                         set_current_blocked(&sigsaved);
2045         }
2046 
2047         return error;
2048 }
2049 
2050 #ifdef CONFIG_COMPAT
2051 COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
2052                         struct epoll_event __user *, events,
2053                         int, maxevents, int, timeout,
2054                         const compat_sigset_t __user *, sigmask,
2055                         compat_size_t, sigsetsize)
2056 {
2057         long err;
2058         compat_sigset_t csigmask;
2059         sigset_t ksigmask, sigsaved;
2060 
2061         /*
2062          * If the caller wants a certain signal mask to be set during the wait,
2063          * we apply it here.
2064          */
2065         if (sigmask) {
2066                 if (sigsetsize != sizeof(compat_sigset_t))
2067                         return -EINVAL;
2068                 if (copy_from_user(&csigmask, sigmask, sizeof(csigmask)))
2069                         return -EFAULT;
2070                 sigset_from_compat(&ksigmask, &csigmask);
2071                 sigsaved = current->blocked;
2072                 set_current_blocked(&ksigmask);
2073         }
2074 
2075         err = sys_epoll_wait(epfd, events, maxevents, timeout);
2076 
2077         /*
2078          * If we changed the signal mask, we need to restore the original one.
2079          * In case we've got a signal while waiting, we do not restore the
2080          * signal mask yet, and we allow do_signal() to deliver the signal on
2081          * the way back to userspace, before the signal mask is restored.
2082          */
2083         if (sigmask) {
2084                 if (err == -EINTR) {
2085                         memcpy(&current->saved_sigmask, &sigsaved,
2086                                sizeof(sigsaved));
2087                         set_restore_sigmask();
2088                 } else
2089                         set_current_blocked(&sigsaved);
2090         }
2091 
2092         return err;
2093 }
2094 #endif
2095 
2096 static int __init eventpoll_init(void)
2097 {
2098         struct sysinfo si;
2099 
2100         si_meminfo(&si);
2101         /*
2102          * Allows top 4% of lomem to be allocated for epoll watches (per user).
2103          */
2104         max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2105                 EP_ITEM_COST;
2106         BUG_ON(max_user_watches < 0);
2107 
2108         /*
2109          * Initialize the structure used to perform epoll file descriptor
2110          * inclusion loops checks.
2111          */
2112         ep_nested_calls_init(&poll_loop_ncalls);
2113 
2114         /* Initialize the structure used to perform safe poll wait head wake ups */
2115         ep_nested_calls_init(&poll_safewake_ncalls);
2116 
2117         /* Initialize the structure used to perform file's f_op->poll() calls */
2118         ep_nested_calls_init(&poll_readywalk_ncalls);
2119 
2120         /*
2121          * We can have many thousands of epitems, so prevent this from
2122          * using an extra cache line on 64-bit (and smaller) CPUs
2123          */
2124         BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
2125 
2126         /* Allocates slab cache used to allocate "struct epitem" items */
2127         epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
2128                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
2129 
2130         /* Allocates slab cache used to allocate "struct eppoll_entry" */
2131         pwq_cache = kmem_cache_create("eventpoll_pwq",
2132                         sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL);
2133 
2134         return 0;
2135 }
2136 fs_initcall(eventpoll_init);
2137 

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