~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/fs/eventpoll.c

Version: ~ [ linux-5.4-rc7 ] ~ [ linux-5.3.10 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.83 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.153 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.200 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.200 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.76 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  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 struct 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 void ep_show_fdinfo(struct seq_file *m, struct file *f)
874 {
875         struct eventpoll *ep = f->private_data;
876         struct rb_node *rbp;
877 
878         mutex_lock(&ep->mtx);
879         for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
880                 struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
881 
882                 seq_printf(m, "tfd: %8d events: %8x data: %16llx\n",
883                            epi->ffd.fd, epi->event.events,
884                            (long long)epi->event.data);
885                 if (seq_has_overflowed(m))
886                         break;
887         }
888         mutex_unlock(&ep->mtx);
889 }
890 #endif
891 
892 /* File callbacks that implement the eventpoll file behaviour */
893 static const struct file_operations eventpoll_fops = {
894 #ifdef CONFIG_PROC_FS
895         .show_fdinfo    = ep_show_fdinfo,
896 #endif
897         .release        = ep_eventpoll_release,
898         .poll           = ep_eventpoll_poll,
899         .llseek         = noop_llseek,
900 };
901 
902 /*
903  * This is called from eventpoll_release() to unlink files from the eventpoll
904  * interface. We need to have this facility to cleanup correctly files that are
905  * closed without being removed from the eventpoll interface.
906  */
907 void eventpoll_release_file(struct file *file)
908 {
909         struct eventpoll *ep;
910         struct epitem *epi, *next;
911 
912         /*
913          * We don't want to get "file->f_lock" because it is not
914          * necessary. It is not necessary because we're in the "struct file"
915          * cleanup path, and this means that no one is using this file anymore.
916          * So, for example, epoll_ctl() cannot hit here since if we reach this
917          * point, the file counter already went to zero and fget() would fail.
918          * The only hit might come from ep_free() but by holding the mutex
919          * will correctly serialize the operation. We do need to acquire
920          * "ep->mtx" after "epmutex" because ep_remove() requires it when called
921          * from anywhere but ep_free().
922          *
923          * Besides, ep_remove() acquires the lock, so we can't hold it here.
924          */
925         mutex_lock(&epmutex);
926         list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) {
927                 ep = epi->ep;
928                 mutex_lock_nested(&ep->mtx, 0);
929                 ep_remove(ep, epi);
930                 mutex_unlock(&ep->mtx);
931         }
932         mutex_unlock(&epmutex);
933 }
934 
935 static int ep_alloc(struct eventpoll **pep)
936 {
937         int error;
938         struct user_struct *user;
939         struct eventpoll *ep;
940 
941         user = get_current_user();
942         error = -ENOMEM;
943         ep = kzalloc(sizeof(*ep), GFP_KERNEL);
944         if (unlikely(!ep))
945                 goto free_uid;
946 
947         spin_lock_init(&ep->lock);
948         mutex_init(&ep->mtx);
949         init_waitqueue_head(&ep->wq);
950         init_waitqueue_head(&ep->poll_wait);
951         INIT_LIST_HEAD(&ep->rdllist);
952         ep->rbr = RB_ROOT;
953         ep->ovflist = EP_UNACTIVE_PTR;
954         ep->user = user;
955 
956         *pep = ep;
957 
958         return 0;
959 
960 free_uid:
961         free_uid(user);
962         return error;
963 }
964 
965 /*
966  * Search the file inside the eventpoll tree. The RB tree operations
967  * are protected by the "mtx" mutex, and ep_find() must be called with
968  * "mtx" held.
969  */
970 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
971 {
972         int kcmp;
973         struct rb_node *rbp;
974         struct epitem *epi, *epir = NULL;
975         struct epoll_filefd ffd;
976 
977         ep_set_ffd(&ffd, file, fd);
978         for (rbp = ep->rbr.rb_node; rbp; ) {
979                 epi = rb_entry(rbp, struct epitem, rbn);
980                 kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
981                 if (kcmp > 0)
982                         rbp = rbp->rb_right;
983                 else if (kcmp < 0)
984                         rbp = rbp->rb_left;
985                 else {
986                         epir = epi;
987                         break;
988                 }
989         }
990 
991         return epir;
992 }
993 
994 /*
995  * This is the callback that is passed to the wait queue wakeup
996  * mechanism. It is called by the stored file descriptors when they
997  * have events to report.
998  */
999 static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
1000 {
1001         int pwake = 0;
1002         unsigned long flags;
1003         struct epitem *epi = ep_item_from_wait(wait);
1004         struct eventpoll *ep = epi->ep;
1005 
1006         if ((unsigned long)key & POLLFREE) {
1007                 ep_pwq_from_wait(wait)->whead = NULL;
1008                 /*
1009                  * whead = NULL above can race with ep_remove_wait_queue()
1010                  * which can do another remove_wait_queue() after us, so we
1011                  * can't use __remove_wait_queue(). whead->lock is held by
1012                  * the caller.
1013                  */
1014                 list_del_init(&wait->task_list);
1015         }
1016 
1017         spin_lock_irqsave(&ep->lock, flags);
1018 
1019         /*
1020          * If the event mask does not contain any poll(2) event, we consider the
1021          * descriptor to be disabled. This condition is likely the effect of the
1022          * EPOLLONESHOT bit that disables the descriptor when an event is received,
1023          * until the next EPOLL_CTL_MOD will be issued.
1024          */
1025         if (!(epi->event.events & ~EP_PRIVATE_BITS))
1026                 goto out_unlock;
1027 
1028         /*
1029          * Check the events coming with the callback. At this stage, not
1030          * every device reports the events in the "key" parameter of the
1031          * callback. We need to be able to handle both cases here, hence the
1032          * test for "key" != NULL before the event match test.
1033          */
1034         if (key && !((unsigned long) key & epi->event.events))
1035                 goto out_unlock;
1036 
1037         /*
1038          * If we are transferring events to userspace, we can hold no locks
1039          * (because we're accessing user memory, and because of linux f_op->poll()
1040          * semantics). All the events that happen during that period of time are
1041          * chained in ep->ovflist and requeued later on.
1042          */
1043         if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
1044                 if (epi->next == EP_UNACTIVE_PTR) {
1045                         epi->next = ep->ovflist;
1046                         ep->ovflist = epi;
1047                         if (epi->ws) {
1048                                 /*
1049                                  * Activate ep->ws since epi->ws may get
1050                                  * deactivated at any time.
1051                                  */
1052                                 __pm_stay_awake(ep->ws);
1053                         }
1054 
1055                 }
1056                 goto out_unlock;
1057         }
1058 
1059         /* If this file is already in the ready list we exit soon */
1060         if (!ep_is_linked(&epi->rdllink)) {
1061                 list_add_tail(&epi->rdllink, &ep->rdllist);
1062                 ep_pm_stay_awake_rcu(epi);
1063         }
1064 
1065         /*
1066          * Wake up ( if active ) both the eventpoll wait list and the ->poll()
1067          * wait list.
1068          */
1069         if (waitqueue_active(&ep->wq))
1070                 wake_up_locked(&ep->wq);
1071         if (waitqueue_active(&ep->poll_wait))
1072                 pwake++;
1073 
1074 out_unlock:
1075         spin_unlock_irqrestore(&ep->lock, flags);
1076 
1077         /* We have to call this outside the lock */
1078         if (pwake)
1079                 ep_poll_safewake(&ep->poll_wait);
1080 
1081         return 1;
1082 }
1083 
1084 /*
1085  * This is the callback that is used to add our wait queue to the
1086  * target file wakeup lists.
1087  */
1088 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
1089                                  poll_table *pt)
1090 {
1091         struct epitem *epi = ep_item_from_epqueue(pt);
1092         struct eppoll_entry *pwq;
1093 
1094         if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
1095                 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
1096                 pwq->whead = whead;
1097                 pwq->base = epi;
1098                 add_wait_queue(whead, &pwq->wait);
1099                 list_add_tail(&pwq->llink, &epi->pwqlist);
1100                 epi->nwait++;
1101         } else {
1102                 /* We have to signal that an error occurred */
1103                 epi->nwait = -1;
1104         }
1105 }
1106 
1107 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
1108 {
1109         int kcmp;
1110         struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
1111         struct epitem *epic;
1112 
1113         while (*p) {
1114                 parent = *p;
1115                 epic = rb_entry(parent, struct epitem, rbn);
1116                 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
1117                 if (kcmp > 0)
1118                         p = &parent->rb_right;
1119                 else
1120                         p = &parent->rb_left;
1121         }
1122         rb_link_node(&epi->rbn, parent, p);
1123         rb_insert_color(&epi->rbn, &ep->rbr);
1124 }
1125 
1126 
1127 
1128 #define PATH_ARR_SIZE 5
1129 /*
1130  * These are the number paths of length 1 to 5, that we are allowing to emanate
1131  * from a single file of interest. For example, we allow 1000 paths of length
1132  * 1, to emanate from each file of interest. This essentially represents the
1133  * potential wakeup paths, which need to be limited in order to avoid massive
1134  * uncontrolled wakeup storms. The common use case should be a single ep which
1135  * is connected to n file sources. In this case each file source has 1 path
1136  * of length 1. Thus, the numbers below should be more than sufficient. These
1137  * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
1138  * and delete can't add additional paths. Protected by the epmutex.
1139  */
1140 static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
1141 static int path_count[PATH_ARR_SIZE];
1142 
1143 static int path_count_inc(int nests)
1144 {
1145         /* Allow an arbitrary number of depth 1 paths */
1146         if (nests == 0)
1147                 return 0;
1148 
1149         if (++path_count[nests] > path_limits[nests])
1150                 return -1;
1151         return 0;
1152 }
1153 
1154 static void path_count_init(void)
1155 {
1156         int i;
1157 
1158         for (i = 0; i < PATH_ARR_SIZE; i++)
1159                 path_count[i] = 0;
1160 }
1161 
1162 static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
1163 {
1164         int error = 0;
1165         struct file *file = priv;
1166         struct file *child_file;
1167         struct epitem *epi;
1168 
1169         /* CTL_DEL can remove links here, but that can't increase our count */
1170         rcu_read_lock();
1171         list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
1172                 child_file = epi->ep->file;
1173                 if (is_file_epoll(child_file)) {
1174                         if (list_empty(&child_file->f_ep_links)) {
1175                                 if (path_count_inc(call_nests)) {
1176                                         error = -1;
1177                                         break;
1178                                 }
1179                         } else {
1180                                 error = ep_call_nested(&poll_loop_ncalls,
1181                                                         EP_MAX_NESTS,
1182                                                         reverse_path_check_proc,
1183                                                         child_file, child_file,
1184                                                         current);
1185                         }
1186                         if (error != 0)
1187                                 break;
1188                 } else {
1189                         printk(KERN_ERR "reverse_path_check_proc: "
1190                                 "file is not an ep!\n");
1191                 }
1192         }
1193         rcu_read_unlock();
1194         return error;
1195 }
1196 
1197 /**
1198  * reverse_path_check - The tfile_check_list is list of file *, which have
1199  *                      links that are proposed to be newly added. We need to
1200  *                      make sure that those added links don't add too many
1201  *                      paths such that we will spend all our time waking up
1202  *                      eventpoll objects.
1203  *
1204  * Returns: Returns zero if the proposed links don't create too many paths,
1205  *          -1 otherwise.
1206  */
1207 static int reverse_path_check(void)
1208 {
1209         int error = 0;
1210         struct file *current_file;
1211 
1212         /* let's call this for all tfiles */
1213         list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
1214                 path_count_init();
1215                 error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1216                                         reverse_path_check_proc, current_file,
1217                                         current_file, current);
1218                 if (error)
1219                         break;
1220         }
1221         return error;
1222 }
1223 
1224 static int ep_create_wakeup_source(struct epitem *epi)
1225 {
1226         const char *name;
1227         struct wakeup_source *ws;
1228 
1229         if (!epi->ep->ws) {
1230                 epi->ep->ws = wakeup_source_register("eventpoll");
1231                 if (!epi->ep->ws)
1232                         return -ENOMEM;
1233         }
1234 
1235         name = epi->ffd.file->f_path.dentry->d_name.name;
1236         ws = wakeup_source_register(name);
1237 
1238         if (!ws)
1239                 return -ENOMEM;
1240         rcu_assign_pointer(epi->ws, ws);
1241 
1242         return 0;
1243 }
1244 
1245 /* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
1246 static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1247 {
1248         struct wakeup_source *ws = ep_wakeup_source(epi);
1249 
1250         RCU_INIT_POINTER(epi->ws, NULL);
1251 
1252         /*
1253          * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
1254          * used internally by wakeup_source_remove, too (called by
1255          * wakeup_source_unregister), so we cannot use call_rcu
1256          */
1257         synchronize_rcu();
1258         wakeup_source_unregister(ws);
1259 }
1260 
1261 /*
1262  * Must be called with "mtx" held.
1263  */
1264 static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
1265                      struct file *tfile, int fd, int full_check)
1266 {
1267         int error, revents, pwake = 0;
1268         unsigned long flags;
1269         long user_watches;
1270         struct epitem *epi;
1271         struct ep_pqueue epq;
1272 
1273         user_watches = atomic_long_read(&ep->user->epoll_watches);
1274         if (unlikely(user_watches >= max_user_watches))
1275                 return -ENOSPC;
1276         if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
1277                 return -ENOMEM;
1278 
1279         /* Item initialization follow here ... */
1280         INIT_LIST_HEAD(&epi->rdllink);
1281         INIT_LIST_HEAD(&epi->fllink);
1282         INIT_LIST_HEAD(&epi->pwqlist);
1283         epi->ep = ep;
1284         ep_set_ffd(&epi->ffd, tfile, fd);
1285         epi->event = *event;
1286         epi->nwait = 0;
1287         epi->next = EP_UNACTIVE_PTR;
1288         if (epi->event.events & EPOLLWAKEUP) {
1289                 error = ep_create_wakeup_source(epi);
1290                 if (error)
1291                         goto error_create_wakeup_source;
1292         } else {
1293                 RCU_INIT_POINTER(epi->ws, NULL);
1294         }
1295 
1296         /* Initialize the poll table using the queue callback */
1297         epq.epi = epi;
1298         init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
1299 
1300         /*
1301          * Attach the item to the poll hooks and get current event bits.
1302          * We can safely use the file* here because its usage count has
1303          * been increased by the caller of this function. Note that after
1304          * this operation completes, the poll callback can start hitting
1305          * the new item.
1306          */
1307         revents = ep_item_poll(epi, &epq.pt);
1308 
1309         /*
1310          * We have to check if something went wrong during the poll wait queue
1311          * install process. Namely an allocation for a wait queue failed due
1312          * high memory pressure.
1313          */
1314         error = -ENOMEM;
1315         if (epi->nwait < 0)
1316                 goto error_unregister;
1317 
1318         /* Add the current item to the list of active epoll hook for this file */
1319         spin_lock(&tfile->f_lock);
1320         list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
1321         spin_unlock(&tfile->f_lock);
1322 
1323         /*
1324          * Add the current item to the RB tree. All RB tree operations are
1325          * protected by "mtx", and ep_insert() is called with "mtx" held.
1326          */
1327         ep_rbtree_insert(ep, epi);
1328 
1329         /* now check if we've created too many backpaths */
1330         error = -EINVAL;
1331         if (full_check && reverse_path_check())
1332                 goto error_remove_epi;
1333 
1334         /* We have to drop the new item inside our item list to keep track of it */
1335         spin_lock_irqsave(&ep->lock, flags);
1336 
1337         /* If the file is already "ready" we drop it inside the ready list */
1338         if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
1339                 list_add_tail(&epi->rdllink, &ep->rdllist);
1340                 ep_pm_stay_awake(epi);
1341 
1342                 /* Notify waiting tasks that events are available */
1343                 if (waitqueue_active(&ep->wq))
1344                         wake_up_locked(&ep->wq);
1345                 if (waitqueue_active(&ep->poll_wait))
1346                         pwake++;
1347         }
1348 
1349         spin_unlock_irqrestore(&ep->lock, flags);
1350 
1351         atomic_long_inc(&ep->user->epoll_watches);
1352 
1353         /* We have to call this outside the lock */
1354         if (pwake)
1355                 ep_poll_safewake(&ep->poll_wait);
1356 
1357         return 0;
1358 
1359 error_remove_epi:
1360         spin_lock(&tfile->f_lock);
1361         list_del_rcu(&epi->fllink);
1362         spin_unlock(&tfile->f_lock);
1363 
1364         rb_erase(&epi->rbn, &ep->rbr);
1365 
1366 error_unregister:
1367         ep_unregister_pollwait(ep, epi);
1368 
1369         /*
1370          * We need to do this because an event could have been arrived on some
1371          * allocated wait queue. Note that we don't care about the ep->ovflist
1372          * list, since that is used/cleaned only inside a section bound by "mtx".
1373          * And ep_insert() is called with "mtx" held.
1374          */
1375         spin_lock_irqsave(&ep->lock, flags);
1376         if (ep_is_linked(&epi->rdllink))
1377                 list_del_init(&epi->rdllink);
1378         spin_unlock_irqrestore(&ep->lock, flags);
1379 
1380         wakeup_source_unregister(ep_wakeup_source(epi));
1381 
1382 error_create_wakeup_source:
1383         kmem_cache_free(epi_cache, epi);
1384 
1385         return error;
1386 }
1387 
1388 /*
1389  * Modify the interest event mask by dropping an event if the new mask
1390  * has a match in the current file status. Must be called with "mtx" held.
1391  */
1392 static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
1393 {
1394         int pwake = 0;
1395         unsigned int revents;
1396         poll_table pt;
1397 
1398         init_poll_funcptr(&pt, NULL);
1399 
1400         /*
1401          * Set the new event interest mask before calling f_op->poll();
1402          * otherwise we might miss an event that happens between the
1403          * f_op->poll() call and the new event set registering.
1404          */
1405         epi->event.events = event->events; /* need barrier below */
1406         epi->event.data = event->data; /* protected by mtx */
1407         if (epi->event.events & EPOLLWAKEUP) {
1408                 if (!ep_has_wakeup_source(epi))
1409                         ep_create_wakeup_source(epi);
1410         } else if (ep_has_wakeup_source(epi)) {
1411                 ep_destroy_wakeup_source(epi);
1412         }
1413 
1414         /*
1415          * The following barrier has two effects:
1416          *
1417          * 1) Flush epi changes above to other CPUs.  This ensures
1418          *    we do not miss events from ep_poll_callback if an
1419          *    event occurs immediately after we call f_op->poll().
1420          *    We need this because we did not take ep->lock while
1421          *    changing epi above (but ep_poll_callback does take
1422          *    ep->lock).
1423          *
1424          * 2) We also need to ensure we do not miss _past_ events
1425          *    when calling f_op->poll().  This barrier also
1426          *    pairs with the barrier in wq_has_sleeper (see
1427          *    comments for wq_has_sleeper).
1428          *
1429          * This barrier will now guarantee ep_poll_callback or f_op->poll
1430          * (or both) will notice the readiness of an item.
1431          */
1432         smp_mb();
1433 
1434         /*
1435          * Get current event bits. We can safely use the file* here because
1436          * its usage count has been increased by the caller of this function.
1437          */
1438         revents = ep_item_poll(epi, &pt);
1439 
1440         /*
1441          * If the item is "hot" and it is not registered inside the ready
1442          * list, push it inside.
1443          */
1444         if (revents & event->events) {
1445                 spin_lock_irq(&ep->lock);
1446                 if (!ep_is_linked(&epi->rdllink)) {
1447                         list_add_tail(&epi->rdllink, &ep->rdllist);
1448                         ep_pm_stay_awake(epi);
1449 
1450                         /* Notify waiting tasks that events are available */
1451                         if (waitqueue_active(&ep->wq))
1452                                 wake_up_locked(&ep->wq);
1453                         if (waitqueue_active(&ep->poll_wait))
1454                                 pwake++;
1455                 }
1456                 spin_unlock_irq(&ep->lock);
1457         }
1458 
1459         /* We have to call this outside the lock */
1460         if (pwake)
1461                 ep_poll_safewake(&ep->poll_wait);
1462 
1463         return 0;
1464 }
1465 
1466 static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
1467                                void *priv)
1468 {
1469         struct ep_send_events_data *esed = priv;
1470         int eventcnt;
1471         unsigned int revents;
1472         struct epitem *epi;
1473         struct epoll_event __user *uevent;
1474         struct wakeup_source *ws;
1475         poll_table pt;
1476 
1477         init_poll_funcptr(&pt, NULL);
1478 
1479         /*
1480          * We can loop without lock because we are passed a task private list.
1481          * Items cannot vanish during the loop because ep_scan_ready_list() is
1482          * holding "mtx" during this call.
1483          */
1484         for (eventcnt = 0, uevent = esed->events;
1485              !list_empty(head) && eventcnt < esed->maxevents;) {
1486                 epi = list_first_entry(head, struct epitem, rdllink);
1487 
1488                 /*
1489                  * Activate ep->ws before deactivating epi->ws to prevent
1490                  * triggering auto-suspend here (in case we reactive epi->ws
1491                  * below).
1492                  *
1493                  * This could be rearranged to delay the deactivation of epi->ws
1494                  * instead, but then epi->ws would temporarily be out of sync
1495                  * with ep_is_linked().
1496                  */
1497                 ws = ep_wakeup_source(epi);
1498                 if (ws) {
1499                         if (ws->active)
1500                                 __pm_stay_awake(ep->ws);
1501                         __pm_relax(ws);
1502                 }
1503 
1504                 list_del_init(&epi->rdllink);
1505 
1506                 revents = ep_item_poll(epi, &pt);
1507 
1508                 /*
1509                  * If the event mask intersect the caller-requested one,
1510                  * deliver the event to userspace. Again, ep_scan_ready_list()
1511                  * is holding "mtx", so no operations coming from userspace
1512                  * can change the item.
1513                  */
1514                 if (revents) {
1515                         if (__put_user(revents, &uevent->events) ||
1516                             __put_user(epi->event.data, &uevent->data)) {
1517                                 list_add(&epi->rdllink, head);
1518                                 ep_pm_stay_awake(epi);
1519                                 return eventcnt ? eventcnt : -EFAULT;
1520                         }
1521                         eventcnt++;
1522                         uevent++;
1523                         if (epi->event.events & EPOLLONESHOT)
1524                                 epi->event.events &= EP_PRIVATE_BITS;
1525                         else if (!(epi->event.events & EPOLLET)) {
1526                                 /*
1527                                  * If this file has been added with Level
1528                                  * Trigger mode, we need to insert back inside
1529                                  * the ready list, so that the next call to
1530                                  * epoll_wait() will check again the events
1531                                  * availability. At this point, no one can insert
1532                                  * into ep->rdllist besides us. The epoll_ctl()
1533                                  * callers are locked out by
1534                                  * ep_scan_ready_list() holding "mtx" and the
1535                                  * poll callback will queue them in ep->ovflist.
1536                                  */
1537                                 list_add_tail(&epi->rdllink, &ep->rdllist);
1538                                 ep_pm_stay_awake(epi);
1539                         }
1540                 }
1541         }
1542 
1543         return eventcnt;
1544 }
1545 
1546 static int ep_send_events(struct eventpoll *ep,
1547                           struct epoll_event __user *events, int maxevents)
1548 {
1549         struct ep_send_events_data esed;
1550 
1551         esed.maxevents = maxevents;
1552         esed.events = events;
1553 
1554         return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
1555 }
1556 
1557 static inline struct timespec ep_set_mstimeout(long ms)
1558 {
1559         struct timespec now, ts = {
1560                 .tv_sec = ms / MSEC_PER_SEC,
1561                 .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
1562         };
1563 
1564         ktime_get_ts(&now);
1565         return timespec_add_safe(now, ts);
1566 }
1567 
1568 /**
1569  * ep_poll - Retrieves ready events, and delivers them to the caller supplied
1570  *           event buffer.
1571  *
1572  * @ep: Pointer to the eventpoll context.
1573  * @events: Pointer to the userspace buffer where the ready events should be
1574  *          stored.
1575  * @maxevents: Size (in terms of number of events) of the caller event buffer.
1576  * @timeout: Maximum timeout for the ready events fetch operation, in
1577  *           milliseconds. If the @timeout is zero, the function will not block,
1578  *           while if the @timeout is less than zero, the function will block
1579  *           until at least one event has been retrieved (or an error
1580  *           occurred).
1581  *
1582  * Returns: Returns the number of ready events which have been fetched, or an
1583  *          error code, in case of error.
1584  */
1585 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1586                    int maxevents, long timeout)
1587 {
1588         int res = 0, eavail, timed_out = 0;
1589         unsigned long flags;
1590         long slack = 0;
1591         wait_queue_t wait;
1592         ktime_t expires, *to = NULL;
1593 
1594         if (timeout > 0) {
1595                 struct timespec end_time = ep_set_mstimeout(timeout);
1596 
1597                 slack = select_estimate_accuracy(&end_time);
1598                 to = &expires;
1599                 *to = timespec_to_ktime(end_time);
1600         } else if (timeout == 0) {
1601                 /*
1602                  * Avoid the unnecessary trip to the wait queue loop, if the
1603                  * caller specified a non blocking operation.
1604                  */
1605                 timed_out = 1;
1606                 spin_lock_irqsave(&ep->lock, flags);
1607                 goto check_events;
1608         }
1609 
1610 fetch_events:
1611         spin_lock_irqsave(&ep->lock, flags);
1612 
1613         if (!ep_events_available(ep)) {
1614                 /*
1615                  * We don't have any available event to return to the caller.
1616                  * We need to sleep here, and we will be wake up by
1617                  * ep_poll_callback() when events will become available.
1618                  */
1619                 init_waitqueue_entry(&wait, current);
1620                 __add_wait_queue_exclusive(&ep->wq, &wait);
1621 
1622                 for (;;) {
1623                         /*
1624                          * We don't want to sleep if the ep_poll_callback() sends us
1625                          * a wakeup in between. That's why we set the task state
1626                          * to TASK_INTERRUPTIBLE before doing the checks.
1627                          */
1628                         set_current_state(TASK_INTERRUPTIBLE);
1629                         if (ep_events_available(ep) || timed_out)
1630                                 break;
1631                         if (signal_pending(current)) {
1632                                 res = -EINTR;
1633                                 break;
1634                         }
1635 
1636                         spin_unlock_irqrestore(&ep->lock, flags);
1637                         if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
1638                                 timed_out = 1;
1639 
1640                         spin_lock_irqsave(&ep->lock, flags);
1641                 }
1642 
1643                 __remove_wait_queue(&ep->wq, &wait);
1644                 __set_current_state(TASK_RUNNING);
1645         }
1646 check_events:
1647         /* Is it worth to try to dig for events ? */
1648         eavail = ep_events_available(ep);
1649 
1650         spin_unlock_irqrestore(&ep->lock, flags);
1651 
1652         /*
1653          * Try to transfer events to user space. In case we get 0 events and
1654          * there's still timeout left over, we go trying again in search of
1655          * more luck.
1656          */
1657         if (!res && eavail &&
1658             !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
1659                 goto fetch_events;
1660 
1661         return res;
1662 }
1663 
1664 /**
1665  * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
1666  *                      API, to verify that adding an epoll file inside another
1667  *                      epoll structure, does not violate the constraints, in
1668  *                      terms of closed loops, or too deep chains (which can
1669  *                      result in excessive stack usage).
1670  *
1671  * @priv: Pointer to the epoll file to be currently checked.
1672  * @cookie: Original cookie for this call. This is the top-of-the-chain epoll
1673  *          data structure pointer.
1674  * @call_nests: Current dept of the @ep_call_nested() call stack.
1675  *
1676  * Returns: Returns zero if adding the epoll @file inside current epoll
1677  *          structure @ep does not violate the constraints, or -1 otherwise.
1678  */
1679 static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
1680 {
1681         int error = 0;
1682         struct file *file = priv;
1683         struct eventpoll *ep = file->private_data;
1684         struct eventpoll *ep_tovisit;
1685         struct rb_node *rbp;
1686         struct epitem *epi;
1687 
1688         mutex_lock_nested(&ep->mtx, call_nests + 1);
1689         ep->visited = 1;
1690         list_add(&ep->visited_list_link, &visited_list);
1691         for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1692                 epi = rb_entry(rbp, struct epitem, rbn);
1693                 if (unlikely(is_file_epoll(epi->ffd.file))) {
1694                         ep_tovisit = epi->ffd.file->private_data;
1695                         if (ep_tovisit->visited)
1696                                 continue;
1697                         error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1698                                         ep_loop_check_proc, epi->ffd.file,
1699                                         ep_tovisit, current);
1700                         if (error != 0)
1701                                 break;
1702                 } else {
1703                         /*
1704                          * If we've reached a file that is not associated with
1705                          * an ep, then we need to check if the newly added
1706                          * links are going to add too many wakeup paths. We do
1707                          * this by adding it to the tfile_check_list, if it's
1708                          * not already there, and calling reverse_path_check()
1709                          * during ep_insert().
1710                          */
1711                         if (list_empty(&epi->ffd.file->f_tfile_llink))
1712                                 list_add(&epi->ffd.file->f_tfile_llink,
1713                                          &tfile_check_list);
1714                 }
1715         }
1716         mutex_unlock(&ep->mtx);
1717 
1718         return error;
1719 }
1720 
1721 /**
1722  * ep_loop_check - Performs a check to verify that adding an epoll file (@file)
1723  *                 another epoll file (represented by @ep) does not create
1724  *                 closed loops or too deep chains.
1725  *
1726  * @ep: Pointer to the epoll private data structure.
1727  * @file: Pointer to the epoll file to be checked.
1728  *
1729  * Returns: Returns zero if adding the epoll @file inside current epoll
1730  *          structure @ep does not violate the constraints, or -1 otherwise.
1731  */
1732 static int ep_loop_check(struct eventpoll *ep, struct file *file)
1733 {
1734         int ret;
1735         struct eventpoll *ep_cur, *ep_next;
1736 
1737         ret = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1738                               ep_loop_check_proc, file, ep, current);
1739         /* clear visited list */
1740         list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
1741                                                         visited_list_link) {
1742                 ep_cur->visited = 0;
1743                 list_del(&ep_cur->visited_list_link);
1744         }
1745         return ret;
1746 }
1747 
1748 static void clear_tfile_check_list(void)
1749 {
1750         struct file *file;
1751 
1752         /* first clear the tfile_check_list */
1753         while (!list_empty(&tfile_check_list)) {
1754                 file = list_first_entry(&tfile_check_list, struct file,
1755                                         f_tfile_llink);
1756                 list_del_init(&file->f_tfile_llink);
1757         }
1758         INIT_LIST_HEAD(&tfile_check_list);
1759 }
1760 
1761 /*
1762  * Open an eventpoll file descriptor.
1763  */
1764 SYSCALL_DEFINE1(epoll_create1, int, flags)
1765 {
1766         int error, fd;
1767         struct eventpoll *ep = NULL;
1768         struct file *file;
1769 
1770         /* Check the EPOLL_* constant for consistency.  */
1771         BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
1772 
1773         if (flags & ~EPOLL_CLOEXEC)
1774                 return -EINVAL;
1775         /*
1776          * Create the internal data structure ("struct eventpoll").
1777          */
1778         error = ep_alloc(&ep);
1779         if (error < 0)
1780                 return error;
1781         /*
1782          * Creates all the items needed to setup an eventpoll file. That is,
1783          * a file structure and a free file descriptor.
1784          */
1785         fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
1786         if (fd < 0) {
1787                 error = fd;
1788                 goto out_free_ep;
1789         }
1790         file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
1791                                  O_RDWR | (flags & O_CLOEXEC));
1792         if (IS_ERR(file)) {
1793                 error = PTR_ERR(file);
1794                 goto out_free_fd;
1795         }
1796         ep->file = file;
1797         fd_install(fd, file);
1798         return fd;
1799 
1800 out_free_fd:
1801         put_unused_fd(fd);
1802 out_free_ep:
1803         ep_free(ep);
1804         return error;
1805 }
1806 
1807 SYSCALL_DEFINE1(epoll_create, int, size)
1808 {
1809         if (size <= 0)
1810                 return -EINVAL;
1811 
1812         return sys_epoll_create1(0);
1813 }
1814 
1815 /*
1816  * The following function implements the controller interface for
1817  * the eventpoll file that enables the insertion/removal/change of
1818  * file descriptors inside the interest set.
1819  */
1820 SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
1821                 struct epoll_event __user *, event)
1822 {
1823         int error;
1824         int full_check = 0;
1825         struct fd f, tf;
1826         struct eventpoll *ep;
1827         struct epitem *epi;
1828         struct epoll_event epds;
1829         struct eventpoll *tep = NULL;
1830 
1831         error = -EFAULT;
1832         if (ep_op_has_event(op) &&
1833             copy_from_user(&epds, event, sizeof(struct epoll_event)))
1834                 goto error_return;
1835 
1836         error = -EBADF;
1837         f = fdget(epfd);
1838         if (!f.file)
1839                 goto error_return;
1840 
1841         /* Get the "struct file *" for the target file */
1842         tf = fdget(fd);
1843         if (!tf.file)
1844                 goto error_fput;
1845 
1846         /* The target file descriptor must support poll */
1847         error = -EPERM;
1848         if (!tf.file->f_op->poll)
1849                 goto error_tgt_fput;
1850 
1851         /* Check if EPOLLWAKEUP is allowed */
1852         if (ep_op_has_event(op))
1853                 ep_take_care_of_epollwakeup(&epds);
1854 
1855         /*
1856          * We have to check that the file structure underneath the file descriptor
1857          * the user passed to us _is_ an eventpoll file. And also we do not permit
1858          * adding an epoll file descriptor inside itself.
1859          */
1860         error = -EINVAL;
1861         if (f.file == tf.file || !is_file_epoll(f.file))
1862                 goto error_tgt_fput;
1863 
1864         /*
1865          * At this point it is safe to assume that the "private_data" contains
1866          * our own data structure.
1867          */
1868         ep = f.file->private_data;
1869 
1870         /*
1871          * When we insert an epoll file descriptor, inside another epoll file
1872          * descriptor, there is the change of creating closed loops, which are
1873          * better be handled here, than in more critical paths. While we are
1874          * checking for loops we also determine the list of files reachable
1875          * and hang them on the tfile_check_list, so we can check that we
1876          * haven't created too many possible wakeup paths.
1877          *
1878          * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
1879          * the epoll file descriptor is attaching directly to a wakeup source,
1880          * unless the epoll file descriptor is nested. The purpose of taking the
1881          * 'epmutex' on add is to prevent complex toplogies such as loops and
1882          * deep wakeup paths from forming in parallel through multiple
1883          * EPOLL_CTL_ADD operations.
1884          */
1885         mutex_lock_nested(&ep->mtx, 0);
1886         if (op == EPOLL_CTL_ADD) {
1887                 if (!list_empty(&f.file->f_ep_links) ||
1888                                                 is_file_epoll(tf.file)) {
1889                         full_check = 1;
1890                         mutex_unlock(&ep->mtx);
1891                         mutex_lock(&epmutex);
1892                         if (is_file_epoll(tf.file)) {
1893                                 error = -ELOOP;
1894                                 if (ep_loop_check(ep, tf.file) != 0) {
1895                                         clear_tfile_check_list();
1896                                         goto error_tgt_fput;
1897                                 }
1898                         } else
1899                                 list_add(&tf.file->f_tfile_llink,
1900                                                         &tfile_check_list);
1901                         mutex_lock_nested(&ep->mtx, 0);
1902                         if (is_file_epoll(tf.file)) {
1903                                 tep = tf.file->private_data;
1904                                 mutex_lock_nested(&tep->mtx, 1);
1905                         }
1906                 }
1907         }
1908 
1909         /*
1910          * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
1911          * above, we can be sure to be able to use the item looked up by
1912          * ep_find() till we release the mutex.
1913          */
1914         epi = ep_find(ep, tf.file, fd);
1915 
1916         error = -EINVAL;
1917         switch (op) {
1918         case EPOLL_CTL_ADD:
1919                 if (!epi) {
1920                         epds.events |= POLLERR | POLLHUP;
1921                         error = ep_insert(ep, &epds, tf.file, fd, full_check);
1922                 } else
1923                         error = -EEXIST;
1924                 if (full_check)
1925                         clear_tfile_check_list();
1926                 break;
1927         case EPOLL_CTL_DEL:
1928                 if (epi)
1929                         error = ep_remove(ep, epi);
1930                 else
1931                         error = -ENOENT;
1932                 break;
1933         case EPOLL_CTL_MOD:
1934                 if (epi) {
1935                         epds.events |= POLLERR | POLLHUP;
1936                         error = ep_modify(ep, epi, &epds);
1937                 } else
1938                         error = -ENOENT;
1939                 break;
1940         }
1941         if (tep != NULL)
1942                 mutex_unlock(&tep->mtx);
1943         mutex_unlock(&ep->mtx);
1944 
1945 error_tgt_fput:
1946         if (full_check)
1947                 mutex_unlock(&epmutex);
1948 
1949         fdput(tf);
1950 error_fput:
1951         fdput(f);
1952 error_return:
1953 
1954         return error;
1955 }
1956 
1957 /*
1958  * Implement the event wait interface for the eventpoll file. It is the kernel
1959  * part of the user space epoll_wait(2).
1960  */
1961 SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
1962                 int, maxevents, int, timeout)
1963 {
1964         int error;
1965         struct fd f;
1966         struct eventpoll *ep;
1967 
1968         /* The maximum number of event must be greater than zero */
1969         if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
1970                 return -EINVAL;
1971 
1972         /* Verify that the area passed by the user is writeable */
1973         if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event)))
1974                 return -EFAULT;
1975 
1976         /* Get the "struct file *" for the eventpoll file */
1977         f = fdget(epfd);
1978         if (!f.file)
1979                 return -EBADF;
1980 
1981         /*
1982          * We have to check that the file structure underneath the fd
1983          * the user passed to us _is_ an eventpoll file.
1984          */
1985         error = -EINVAL;
1986         if (!is_file_epoll(f.file))
1987                 goto error_fput;
1988 
1989         /*
1990          * At this point it is safe to assume that the "private_data" contains
1991          * our own data structure.
1992          */
1993         ep = f.file->private_data;
1994 
1995         /* Time to fish for events ... */
1996         error = ep_poll(ep, events, maxevents, timeout);
1997 
1998 error_fput:
1999         fdput(f);
2000         return error;
2001 }
2002 
2003 /*
2004  * Implement the event wait interface for the eventpoll file. It is the kernel
2005  * part of the user space epoll_pwait(2).
2006  */
2007 SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
2008                 int, maxevents, int, timeout, const sigset_t __user *, sigmask,
2009                 size_t, sigsetsize)
2010 {
2011         int error;
2012         sigset_t ksigmask, sigsaved;
2013 
2014         /*
2015          * If the caller wants a certain signal mask to be set during the wait,
2016          * we apply it here.
2017          */
2018         if (sigmask) {
2019                 if (sigsetsize != sizeof(sigset_t))
2020                         return -EINVAL;
2021                 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
2022                         return -EFAULT;
2023                 sigsaved = current->blocked;
2024                 set_current_blocked(&ksigmask);
2025         }
2026 
2027         error = sys_epoll_wait(epfd, events, maxevents, timeout);
2028 
2029         /*
2030          * If we changed the signal mask, we need to restore the original one.
2031          * In case we've got a signal while waiting, we do not restore the
2032          * signal mask yet, and we allow do_signal() to deliver the signal on
2033          * the way back to userspace, before the signal mask is restored.
2034          */
2035         if (sigmask) {
2036                 if (error == -EINTR) {
2037                         memcpy(&current->saved_sigmask, &sigsaved,
2038                                sizeof(sigsaved));
2039                         set_restore_sigmask();
2040                 } else
2041                         set_current_blocked(&sigsaved);
2042         }
2043 
2044         return error;
2045 }
2046 
2047 #ifdef CONFIG_COMPAT
2048 COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
2049                         struct epoll_event __user *, events,
2050                         int, maxevents, int, timeout,
2051                         const compat_sigset_t __user *, sigmask,
2052                         compat_size_t, sigsetsize)
2053 {
2054         long err;
2055         compat_sigset_t csigmask;
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(compat_sigset_t))
2064                         return -EINVAL;
2065                 if (copy_from_user(&csigmask, sigmask, sizeof(csigmask)))
2066                         return -EFAULT;
2067                 sigset_from_compat(&ksigmask, &csigmask);
2068                 sigsaved = current->blocked;
2069                 set_current_blocked(&ksigmask);
2070         }
2071 
2072         err = sys_epoll_wait(epfd, events, maxevents, timeout);
2073 
2074         /*
2075          * If we changed the signal mask, we need to restore the original one.
2076          * In case we've got a signal while waiting, we do not restore the
2077          * signal mask yet, and we allow do_signal() to deliver the signal on
2078          * the way back to userspace, before the signal mask is restored.
2079          */
2080         if (sigmask) {
2081                 if (err == -EINTR) {
2082                         memcpy(&current->saved_sigmask, &sigsaved,
2083                                sizeof(sigsaved));
2084                         set_restore_sigmask();
2085                 } else
2086                         set_current_blocked(&sigsaved);
2087         }
2088 
2089         return err;
2090 }
2091 #endif
2092 
2093 static int __init eventpoll_init(void)
2094 {
2095         struct sysinfo si;
2096 
2097         si_meminfo(&si);
2098         /*
2099          * Allows top 4% of lomem to be allocated for epoll watches (per user).
2100          */
2101         max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2102                 EP_ITEM_COST;
2103         BUG_ON(max_user_watches < 0);
2104 
2105         /*
2106          * Initialize the structure used to perform epoll file descriptor
2107          * inclusion loops checks.
2108          */
2109         ep_nested_calls_init(&poll_loop_ncalls);
2110 
2111         /* Initialize the structure used to perform safe poll wait head wake ups */
2112         ep_nested_calls_init(&poll_safewake_ncalls);
2113 
2114         /* Initialize the structure used to perform file's f_op->poll() calls */
2115         ep_nested_calls_init(&poll_readywalk_ncalls);
2116 
2117         /*
2118          * We can have many thousands of epitems, so prevent this from
2119          * using an extra cache line on 64-bit (and smaller) CPUs
2120          */
2121         BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
2122 
2123         /* Allocates slab cache used to allocate "struct epitem" items */
2124         epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
2125                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
2126 
2127         /* Allocates slab cache used to allocate "struct eppoll_entry" */
2128         pwq_cache = kmem_cache_create("eventpoll_pwq",
2129                         sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL);
2130 
2131         return 0;
2132 }
2133 fs_initcall(eventpoll_init);
2134 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp