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Linux/fs/eventpoll.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  *  fs/eventpoll.c (Efficient event retrieval implementation)
  4  *  Copyright (C) 2001,...,2009  Davide Libenzi
  5  *
  6  *  Davide Libenzi <davidel@xmailserver.org>
  7  */
  8 
  9 #include <linux/init.h>
 10 #include <linux/kernel.h>
 11 #include <linux/sched/signal.h>
 12 #include <linux/fs.h>
 13 #include <linux/file.h>
 14 #include <linux/signal.h>
 15 #include <linux/errno.h>
 16 #include <linux/mm.h>
 17 #include <linux/slab.h>
 18 #include <linux/poll.h>
 19 #include <linux/string.h>
 20 #include <linux/list.h>
 21 #include <linux/hash.h>
 22 #include <linux/spinlock.h>
 23 #include <linux/syscalls.h>
 24 #include <linux/rbtree.h>
 25 #include <linux/wait.h>
 26 #include <linux/eventpoll.h>
 27 #include <linux/mount.h>
 28 #include <linux/bitops.h>
 29 #include <linux/mutex.h>
 30 #include <linux/anon_inodes.h>
 31 #include <linux/device.h>
 32 #include <linux/uaccess.h>
 33 #include <asm/io.h>
 34 #include <asm/mman.h>
 35 #include <linux/atomic.h>
 36 #include <linux/proc_fs.h>
 37 #include <linux/seq_file.h>
 38 #include <linux/compat.h>
 39 #include <linux/rculist.h>
 40 #include <net/busy_poll.h>
 41 
 42 /*
 43  * LOCKING:
 44  * There are three level of locking required by epoll :
 45  *
 46  * 1) epmutex (mutex)
 47  * 2) ep->mtx (mutex)
 48  * 3) ep->lock (rwlock)
 49  *
 50  * The acquire order is the one listed above, from 1 to 3.
 51  * We need a rwlock (ep->lock) because we manipulate objects
 52  * from inside the poll callback, that might be triggered from
 53  * a wake_up() that in turn might be called from IRQ context.
 54  * So we can't sleep inside the poll callback and hence we need
 55  * a spinlock. During the event transfer loop (from kernel to
 56  * user space) we could end up sleeping due a copy_to_user(), so
 57  * we need a lock that will allow us to sleep. This lock is a
 58  * mutex (ep->mtx). It is acquired during the event transfer loop,
 59  * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
 60  * Then we also need a global mutex to serialize eventpoll_release_file()
 61  * and ep_free().
 62  * This mutex is acquired by ep_free() during the epoll file
 63  * cleanup path and it is also acquired by eventpoll_release_file()
 64  * if a file has been pushed inside an epoll set and it is then
 65  * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
 66  * It is also acquired when inserting an epoll fd onto another epoll
 67  * fd. We do this so that we walk the epoll tree and ensure that this
 68  * insertion does not create a cycle of epoll file descriptors, which
 69  * could lead to deadlock. We need a global mutex to prevent two
 70  * simultaneous inserts (A into B and B into A) from racing and
 71  * constructing a cycle without either insert observing that it is
 72  * going to.
 73  * It is necessary to acquire multiple "ep->mtx"es at once in the
 74  * case when one epoll fd is added to another. In this case, we
 75  * always acquire the locks in the order of nesting (i.e. after
 76  * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
 77  * before e2->mtx). Since we disallow cycles of epoll file
 78  * descriptors, this ensures that the mutexes are well-ordered. In
 79  * order to communicate this nesting to lockdep, when walking a tree
 80  * of epoll file descriptors, we use the current recursion depth as
 81  * the lockdep subkey.
 82  * It is possible to drop the "ep->mtx" and to use the global
 83  * mutex "epmutex" (together with "ep->lock") to have it working,
 84  * but having "ep->mtx" will make the interface more scalable.
 85  * Events that require holding "epmutex" are very rare, while for
 86  * normal operations the epoll private "ep->mtx" will guarantee
 87  * a better scalability.
 88  */
 89 
 90 /* Epoll private bits inside the event mask */
 91 #define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE)
 92 
 93 #define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT)
 94 
 95 #define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \
 96                                 EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE)
 97 
 98 /* Maximum number of nesting allowed inside epoll sets */
 99 #define EP_MAX_NESTS 4
100 
101 #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
102 
103 #define EP_UNACTIVE_PTR ((void *) -1L)
104 
105 #define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
106 
107 struct epoll_filefd {
108         struct file *file;
109         int fd;
110 } __packed;
111 
112 /*
113  * Structure used to track possible nested calls, for too deep recursions
114  * and loop cycles.
115  */
116 struct nested_call_node {
117         struct list_head llink;
118         void *cookie;
119         void *ctx;
120 };
121 
122 /*
123  * This structure is used as collector for nested calls, to check for
124  * maximum recursion dept and loop cycles.
125  */
126 struct nested_calls {
127         struct list_head tasks_call_list;
128         spinlock_t lock;
129 };
130 
131 /*
132  * Each file descriptor added to the eventpoll interface will
133  * have an entry of this type linked to the "rbr" RB tree.
134  * Avoid increasing the size of this struct, there can be many thousands
135  * of these on a server and we do not want this to take another cache line.
136  */
137 struct epitem {
138         union {
139                 /* RB tree node links this structure to the eventpoll RB tree */
140                 struct rb_node rbn;
141                 /* Used to free the struct epitem */
142                 struct rcu_head rcu;
143         };
144 
145         /* List header used to link this structure to the eventpoll ready list */
146         struct list_head rdllink;
147 
148         /*
149          * Works together "struct eventpoll"->ovflist in keeping the
150          * single linked chain of items.
151          */
152         struct epitem *next;
153 
154         /* The file descriptor information this item refers to */
155         struct epoll_filefd ffd;
156 
157         /* Number of active wait queue attached to poll operations */
158         int nwait;
159 
160         /* List containing poll wait queues */
161         struct list_head pwqlist;
162 
163         /* The "container" of this item */
164         struct eventpoll *ep;
165 
166         /* List header used to link this item to the "struct file" items list */
167         struct list_head fllink;
168 
169         /* wakeup_source used when EPOLLWAKEUP is set */
170         struct wakeup_source __rcu *ws;
171 
172         /* The structure that describe the interested events and the source fd */
173         struct epoll_event event;
174 };
175 
176 /*
177  * This structure is stored inside the "private_data" member of the file
178  * structure and represents the main data structure for the eventpoll
179  * interface.
180  */
181 struct eventpoll {
182         /*
183          * This mutex is used to ensure that files are not removed
184          * while epoll is using them. This is held during the event
185          * collection loop, the file cleanup path, the epoll file exit
186          * code and the ctl operations.
187          */
188         struct mutex mtx;
189 
190         /* Wait queue used by sys_epoll_wait() */
191         wait_queue_head_t wq;
192 
193         /* Wait queue used by file->poll() */
194         wait_queue_head_t poll_wait;
195 
196         /* List of ready file descriptors */
197         struct list_head rdllist;
198 
199         /* Lock which protects rdllist and ovflist */
200         rwlock_t lock;
201 
202         /* RB tree root used to store monitored fd structs */
203         struct rb_root_cached rbr;
204 
205         /*
206          * This is a single linked list that chains all the "struct epitem" that
207          * happened while transferring ready events to userspace w/out
208          * holding ->lock.
209          */
210         struct epitem *ovflist;
211 
212         /* wakeup_source used when ep_scan_ready_list is running */
213         struct wakeup_source *ws;
214 
215         /* The user that created the eventpoll descriptor */
216         struct user_struct *user;
217 
218         struct file *file;
219 
220         /* used to optimize loop detection check */
221         int visited;
222         struct list_head visited_list_link;
223 
224 #ifdef CONFIG_NET_RX_BUSY_POLL
225         /* used to track busy poll napi_id */
226         unsigned int napi_id;
227 #endif
228 };
229 
230 /* Wait structure used by the poll hooks */
231 struct eppoll_entry {
232         /* List header used to link this structure to the "struct epitem" */
233         struct list_head llink;
234 
235         /* The "base" pointer is set to the container "struct epitem" */
236         struct epitem *base;
237 
238         /*
239          * Wait queue item that will be linked to the target file wait
240          * queue head.
241          */
242         wait_queue_entry_t wait;
243 
244         /* The wait queue head that linked the "wait" wait queue item */
245         wait_queue_head_t *whead;
246 };
247 
248 /* Wrapper struct used by poll queueing */
249 struct ep_pqueue {
250         poll_table pt;
251         struct epitem *epi;
252 };
253 
254 /* Used by the ep_send_events() function as callback private data */
255 struct ep_send_events_data {
256         int maxevents;
257         struct epoll_event __user *events;
258         int res;
259 };
260 
261 /*
262  * Configuration options available inside /proc/sys/fs/epoll/
263  */
264 /* Maximum number of epoll watched descriptors, per user */
265 static long max_user_watches __read_mostly;
266 
267 /*
268  * This mutex is used to serialize ep_free() and eventpoll_release_file().
269  */
270 static DEFINE_MUTEX(epmutex);
271 
272 /* Used to check for epoll file descriptor inclusion loops */
273 static struct nested_calls poll_loop_ncalls;
274 
275 /* Slab cache used to allocate "struct epitem" */
276 static struct kmem_cache *epi_cache __read_mostly;
277 
278 /* Slab cache used to allocate "struct eppoll_entry" */
279 static struct kmem_cache *pwq_cache __read_mostly;
280 
281 /* Visited nodes during ep_loop_check(), so we can unset them when we finish */
282 static LIST_HEAD(visited_list);
283 
284 /*
285  * List of files with newly added links, where we may need to limit the number
286  * of emanating paths. Protected by the epmutex.
287  */
288 static LIST_HEAD(tfile_check_list);
289 
290 #ifdef CONFIG_SYSCTL
291 
292 #include <linux/sysctl.h>
293 
294 static long long_zero;
295 static long long_max = LONG_MAX;
296 
297 struct ctl_table epoll_table[] = {
298         {
299                 .procname       = "max_user_watches",
300                 .data           = &max_user_watches,
301                 .maxlen         = sizeof(max_user_watches),
302                 .mode           = 0644,
303                 .proc_handler   = proc_doulongvec_minmax,
304                 .extra1         = &long_zero,
305                 .extra2         = &long_max,
306         },
307         { }
308 };
309 #endif /* CONFIG_SYSCTL */
310 
311 static const struct file_operations eventpoll_fops;
312 
313 static inline int is_file_epoll(struct file *f)
314 {
315         return f->f_op == &eventpoll_fops;
316 }
317 
318 /* Setup the structure that is used as key for the RB tree */
319 static inline void ep_set_ffd(struct epoll_filefd *ffd,
320                               struct file *file, int fd)
321 {
322         ffd->file = file;
323         ffd->fd = fd;
324 }
325 
326 /* Compare RB tree keys */
327 static inline int ep_cmp_ffd(struct epoll_filefd *p1,
328                              struct epoll_filefd *p2)
329 {
330         return (p1->file > p2->file ? +1:
331                 (p1->file < p2->file ? -1 : p1->fd - p2->fd));
332 }
333 
334 /* Tells us if the item is currently linked */
335 static inline int ep_is_linked(struct epitem *epi)
336 {
337         return !list_empty(&epi->rdllink);
338 }
339 
340 static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p)
341 {
342         return container_of(p, struct eppoll_entry, wait);
343 }
344 
345 /* Get the "struct epitem" from a wait queue pointer */
346 static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p)
347 {
348         return container_of(p, struct eppoll_entry, wait)->base;
349 }
350 
351 /* Get the "struct epitem" from an epoll queue wrapper */
352 static inline struct epitem *ep_item_from_epqueue(poll_table *p)
353 {
354         return container_of(p, struct ep_pqueue, pt)->epi;
355 }
356 
357 /* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
358 static inline int ep_op_has_event(int op)
359 {
360         return op != EPOLL_CTL_DEL;
361 }
362 
363 /* Initialize the poll safe wake up structure */
364 static void ep_nested_calls_init(struct nested_calls *ncalls)
365 {
366         INIT_LIST_HEAD(&ncalls->tasks_call_list);
367         spin_lock_init(&ncalls->lock);
368 }
369 
370 /**
371  * ep_events_available - Checks if ready events might be available.
372  *
373  * @ep: Pointer to the eventpoll context.
374  *
375  * Returns: Returns a value different than zero if ready events are available,
376  *          or zero otherwise.
377  */
378 static inline int ep_events_available(struct eventpoll *ep)
379 {
380         return !list_empty_careful(&ep->rdllist) ||
381                 READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR;
382 }
383 
384 #ifdef CONFIG_NET_RX_BUSY_POLL
385 static bool ep_busy_loop_end(void *p, unsigned long start_time)
386 {
387         struct eventpoll *ep = p;
388 
389         return ep_events_available(ep) || busy_loop_timeout(start_time);
390 }
391 
392 /*
393  * Busy poll if globally on and supporting sockets found && no events,
394  * busy loop will return if need_resched or ep_events_available.
395  *
396  * we must do our busy polling with irqs enabled
397  */
398 static void ep_busy_loop(struct eventpoll *ep, int nonblock)
399 {
400         unsigned int napi_id = READ_ONCE(ep->napi_id);
401 
402         if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on())
403                 napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep);
404 }
405 
406 static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
407 {
408         if (ep->napi_id)
409                 ep->napi_id = 0;
410 }
411 
412 /*
413  * Set epoll busy poll NAPI ID from sk.
414  */
415 static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
416 {
417         struct eventpoll *ep;
418         unsigned int napi_id;
419         struct socket *sock;
420         struct sock *sk;
421         int err;
422 
423         if (!net_busy_loop_on())
424                 return;
425 
426         sock = sock_from_file(epi->ffd.file, &err);
427         if (!sock)
428                 return;
429 
430         sk = sock->sk;
431         if (!sk)
432                 return;
433 
434         napi_id = READ_ONCE(sk->sk_napi_id);
435         ep = epi->ep;
436 
437         /* Non-NAPI IDs can be rejected
438          *      or
439          * Nothing to do if we already have this ID
440          */
441         if (napi_id < MIN_NAPI_ID || napi_id == ep->napi_id)
442                 return;
443 
444         /* record NAPI ID for use in next busy poll */
445         ep->napi_id = napi_id;
446 }
447 
448 #else
449 
450 static inline void ep_busy_loop(struct eventpoll *ep, int nonblock)
451 {
452 }
453 
454 static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
455 {
456 }
457 
458 static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
459 {
460 }
461 
462 #endif /* CONFIG_NET_RX_BUSY_POLL */
463 
464 /**
465  * ep_call_nested - Perform a bound (possibly) nested call, by checking
466  *                  that the recursion limit is not exceeded, and that
467  *                  the same nested call (by the meaning of same cookie) is
468  *                  no re-entered.
469  *
470  * @ncalls: Pointer to the nested_calls structure to be used for this call.
471  * @nproc: Nested call core function pointer.
472  * @priv: Opaque data to be passed to the @nproc callback.
473  * @cookie: Cookie to be used to identify this nested call.
474  * @ctx: This instance context.
475  *
476  * Returns: Returns the code returned by the @nproc callback, or -1 if
477  *          the maximum recursion limit has been exceeded.
478  */
479 static int ep_call_nested(struct nested_calls *ncalls,
480                           int (*nproc)(void *, void *, int), void *priv,
481                           void *cookie, void *ctx)
482 {
483         int error, call_nests = 0;
484         unsigned long flags;
485         struct list_head *lsthead = &ncalls->tasks_call_list;
486         struct nested_call_node *tncur;
487         struct nested_call_node tnode;
488 
489         spin_lock_irqsave(&ncalls->lock, flags);
490 
491         /*
492          * Try to see if the current task is already inside this wakeup call.
493          * We use a list here, since the population inside this set is always
494          * very much limited.
495          */
496         list_for_each_entry(tncur, lsthead, llink) {
497                 if (tncur->ctx == ctx &&
498                     (tncur->cookie == cookie || ++call_nests > EP_MAX_NESTS)) {
499                         /*
500                          * Ops ... loop detected or maximum nest level reached.
501                          * We abort this wake by breaking the cycle itself.
502                          */
503                         error = -1;
504                         goto out_unlock;
505                 }
506         }
507 
508         /* Add the current task and cookie to the list */
509         tnode.ctx = ctx;
510         tnode.cookie = cookie;
511         list_add(&tnode.llink, lsthead);
512 
513         spin_unlock_irqrestore(&ncalls->lock, flags);
514 
515         /* Call the nested function */
516         error = (*nproc)(priv, cookie, call_nests);
517 
518         /* Remove the current task from the list */
519         spin_lock_irqsave(&ncalls->lock, flags);
520         list_del(&tnode.llink);
521 out_unlock:
522         spin_unlock_irqrestore(&ncalls->lock, flags);
523 
524         return error;
525 }
526 
527 /*
528  * As described in commit 0ccf831cb lockdep: annotate epoll
529  * the use of wait queues used by epoll is done in a very controlled
530  * manner. Wake ups can nest inside each other, but are never done
531  * with the same locking. For example:
532  *
533  *   dfd = socket(...);
534  *   efd1 = epoll_create();
535  *   efd2 = epoll_create();
536  *   epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
537  *   epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
538  *
539  * When a packet arrives to the device underneath "dfd", the net code will
540  * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
541  * callback wakeup entry on that queue, and the wake_up() performed by the
542  * "dfd" net code will end up in ep_poll_callback(). At this point epoll
543  * (efd1) notices that it may have some event ready, so it needs to wake up
544  * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
545  * that ends up in another wake_up(), after having checked about the
546  * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
547  * avoid stack blasting.
548  *
549  * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
550  * this special case of epoll.
551  */
552 #ifdef CONFIG_DEBUG_LOCK_ALLOC
553 
554 static struct nested_calls poll_safewake_ncalls;
555 
556 static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
557 {
558         unsigned long flags;
559         wait_queue_head_t *wqueue = (wait_queue_head_t *)cookie;
560 
561         spin_lock_irqsave_nested(&wqueue->lock, flags, call_nests + 1);
562         wake_up_locked_poll(wqueue, EPOLLIN);
563         spin_unlock_irqrestore(&wqueue->lock, flags);
564 
565         return 0;
566 }
567 
568 static void ep_poll_safewake(wait_queue_head_t *wq)
569 {
570         int this_cpu = get_cpu();
571 
572         ep_call_nested(&poll_safewake_ncalls,
573                        ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
574 
575         put_cpu();
576 }
577 
578 #else
579 
580 static void ep_poll_safewake(wait_queue_head_t *wq)
581 {
582         wake_up_poll(wq, EPOLLIN);
583 }
584 
585 #endif
586 
587 static void ep_remove_wait_queue(struct eppoll_entry *pwq)
588 {
589         wait_queue_head_t *whead;
590 
591         rcu_read_lock();
592         /*
593          * If it is cleared by POLLFREE, it should be rcu-safe.
594          * If we read NULL we need a barrier paired with
595          * smp_store_release() in ep_poll_callback(), otherwise
596          * we rely on whead->lock.
597          */
598         whead = smp_load_acquire(&pwq->whead);
599         if (whead)
600                 remove_wait_queue(whead, &pwq->wait);
601         rcu_read_unlock();
602 }
603 
604 /*
605  * This function unregisters poll callbacks from the associated file
606  * descriptor.  Must be called with "mtx" held (or "epmutex" if called from
607  * ep_free).
608  */
609 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
610 {
611         struct list_head *lsthead = &epi->pwqlist;
612         struct eppoll_entry *pwq;
613 
614         while (!list_empty(lsthead)) {
615                 pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
616 
617                 list_del(&pwq->llink);
618                 ep_remove_wait_queue(pwq);
619                 kmem_cache_free(pwq_cache, pwq);
620         }
621 }
622 
623 /* call only when ep->mtx is held */
624 static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
625 {
626         return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
627 }
628 
629 /* call only when ep->mtx is held */
630 static inline void ep_pm_stay_awake(struct epitem *epi)
631 {
632         struct wakeup_source *ws = ep_wakeup_source(epi);
633 
634         if (ws)
635                 __pm_stay_awake(ws);
636 }
637 
638 static inline bool ep_has_wakeup_source(struct epitem *epi)
639 {
640         return rcu_access_pointer(epi->ws) ? true : false;
641 }
642 
643 /* call when ep->mtx cannot be held (ep_poll_callback) */
644 static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
645 {
646         struct wakeup_source *ws;
647 
648         rcu_read_lock();
649         ws = rcu_dereference(epi->ws);
650         if (ws)
651                 __pm_stay_awake(ws);
652         rcu_read_unlock();
653 }
654 
655 /**
656  * ep_scan_ready_list - Scans the ready list in a way that makes possible for
657  *                      the scan code, to call f_op->poll(). Also allows for
658  *                      O(NumReady) performance.
659  *
660  * @ep: Pointer to the epoll private data structure.
661  * @sproc: Pointer to the scan callback.
662  * @priv: Private opaque data passed to the @sproc callback.
663  * @depth: The current depth of recursive f_op->poll calls.
664  * @ep_locked: caller already holds ep->mtx
665  *
666  * Returns: The same integer error code returned by the @sproc callback.
667  */
668 static __poll_t ep_scan_ready_list(struct eventpoll *ep,
669                               __poll_t (*sproc)(struct eventpoll *,
670                                            struct list_head *, void *),
671                               void *priv, int depth, bool ep_locked)
672 {
673         __poll_t res;
674         int pwake = 0;
675         struct epitem *epi, *nepi;
676         LIST_HEAD(txlist);
677 
678         lockdep_assert_irqs_enabled();
679 
680         /*
681          * We need to lock this because we could be hit by
682          * eventpoll_release_file() and epoll_ctl().
683          */
684 
685         if (!ep_locked)
686                 mutex_lock_nested(&ep->mtx, depth);
687 
688         /*
689          * Steal the ready list, and re-init the original one to the
690          * empty list. Also, set ep->ovflist to NULL so that events
691          * happening while looping w/out locks, are not lost. We cannot
692          * have the poll callback to queue directly on ep->rdllist,
693          * because we want the "sproc" callback to be able to do it
694          * in a lockless way.
695          */
696         write_lock_irq(&ep->lock);
697         list_splice_init(&ep->rdllist, &txlist);
698         WRITE_ONCE(ep->ovflist, NULL);
699         write_unlock_irq(&ep->lock);
700 
701         /*
702          * Now call the callback function.
703          */
704         res = (*sproc)(ep, &txlist, priv);
705 
706         write_lock_irq(&ep->lock);
707         /*
708          * During the time we spent inside the "sproc" callback, some
709          * other events might have been queued by the poll callback.
710          * We re-insert them inside the main ready-list here.
711          */
712         for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
713              nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
714                 /*
715                  * We need to check if the item is already in the list.
716                  * During the "sproc" callback execution time, items are
717                  * queued into ->ovflist but the "txlist" might already
718                  * contain them, and the list_splice() below takes care of them.
719                  */
720                 if (!ep_is_linked(epi)) {
721                         /*
722                          * ->ovflist is LIFO, so we have to reverse it in order
723                          * to keep in FIFO.
724                          */
725                         list_add(&epi->rdllink, &ep->rdllist);
726                         ep_pm_stay_awake(epi);
727                 }
728         }
729         /*
730          * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
731          * releasing the lock, events will be queued in the normal way inside
732          * ep->rdllist.
733          */
734         WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR);
735 
736         /*
737          * Quickly re-inject items left on "txlist".
738          */
739         list_splice(&txlist, &ep->rdllist);
740         __pm_relax(ep->ws);
741 
742         if (!list_empty(&ep->rdllist)) {
743                 /*
744                  * Wake up (if active) both the eventpoll wait list and
745                  * the ->poll() wait list (delayed after we release the lock).
746                  */
747                 if (waitqueue_active(&ep->wq))
748                         wake_up(&ep->wq);
749                 if (waitqueue_active(&ep->poll_wait))
750                         pwake++;
751         }
752         write_unlock_irq(&ep->lock);
753 
754         if (!ep_locked)
755                 mutex_unlock(&ep->mtx);
756 
757         /* We have to call this outside the lock */
758         if (pwake)
759                 ep_poll_safewake(&ep->poll_wait);
760 
761         return res;
762 }
763 
764 static void epi_rcu_free(struct rcu_head *head)
765 {
766         struct epitem *epi = container_of(head, struct epitem, rcu);
767         kmem_cache_free(epi_cache, epi);
768 }
769 
770 /*
771  * Removes a "struct epitem" from the eventpoll RB tree and deallocates
772  * all the associated resources. Must be called with "mtx" held.
773  */
774 static int ep_remove(struct eventpoll *ep, struct epitem *epi)
775 {
776         struct file *file = epi->ffd.file;
777 
778         lockdep_assert_irqs_enabled();
779 
780         /*
781          * Removes poll wait queue hooks.
782          */
783         ep_unregister_pollwait(ep, epi);
784 
785         /* Remove the current item from the list of epoll hooks */
786         spin_lock(&file->f_lock);
787         list_del_rcu(&epi->fllink);
788         spin_unlock(&file->f_lock);
789 
790         rb_erase_cached(&epi->rbn, &ep->rbr);
791 
792         write_lock_irq(&ep->lock);
793         if (ep_is_linked(epi))
794                 list_del_init(&epi->rdllink);
795         write_unlock_irq(&ep->lock);
796 
797         wakeup_source_unregister(ep_wakeup_source(epi));
798         /*
799          * At this point it is safe to free the eventpoll item. Use the union
800          * field epi->rcu, since we are trying to minimize the size of
801          * 'struct epitem'. The 'rbn' field is no longer in use. Protected by
802          * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
803          * use of the rbn field.
804          */
805         call_rcu(&epi->rcu, epi_rcu_free);
806 
807         atomic_long_dec(&ep->user->epoll_watches);
808 
809         return 0;
810 }
811 
812 static void ep_free(struct eventpoll *ep)
813 {
814         struct rb_node *rbp;
815         struct epitem *epi;
816 
817         /* We need to release all tasks waiting for these file */
818         if (waitqueue_active(&ep->poll_wait))
819                 ep_poll_safewake(&ep->poll_wait);
820 
821         /*
822          * We need to lock this because we could be hit by
823          * eventpoll_release_file() while we're freeing the "struct eventpoll".
824          * We do not need to hold "ep->mtx" here because the epoll file
825          * is on the way to be removed and no one has references to it
826          * anymore. The only hit might come from eventpoll_release_file() but
827          * holding "epmutex" is sufficient here.
828          */
829         mutex_lock(&epmutex);
830 
831         /*
832          * Walks through the whole tree by unregistering poll callbacks.
833          */
834         for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
835                 epi = rb_entry(rbp, struct epitem, rbn);
836 
837                 ep_unregister_pollwait(ep, epi);
838                 cond_resched();
839         }
840 
841         /*
842          * Walks through the whole tree by freeing each "struct epitem". At this
843          * point we are sure no poll callbacks will be lingering around, and also by
844          * holding "epmutex" we can be sure that no file cleanup code will hit
845          * us during this operation. So we can avoid the lock on "ep->lock".
846          * We do not need to lock ep->mtx, either, we only do it to prevent
847          * a lockdep warning.
848          */
849         mutex_lock(&ep->mtx);
850         while ((rbp = rb_first_cached(&ep->rbr)) != NULL) {
851                 epi = rb_entry(rbp, struct epitem, rbn);
852                 ep_remove(ep, epi);
853                 cond_resched();
854         }
855         mutex_unlock(&ep->mtx);
856 
857         mutex_unlock(&epmutex);
858         mutex_destroy(&ep->mtx);
859         free_uid(ep->user);
860         wakeup_source_unregister(ep->ws);
861         kfree(ep);
862 }
863 
864 static int ep_eventpoll_release(struct inode *inode, struct file *file)
865 {
866         struct eventpoll *ep = file->private_data;
867 
868         if (ep)
869                 ep_free(ep);
870 
871         return 0;
872 }
873 
874 static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
875                                void *priv);
876 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
877                                  poll_table *pt);
878 
879 /*
880  * Differs from ep_eventpoll_poll() in that internal callers already have
881  * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested()
882  * is correctly annotated.
883  */
884 static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt,
885                                  int depth)
886 {
887         struct eventpoll *ep;
888         bool locked;
889 
890         pt->_key = epi->event.events;
891         if (!is_file_epoll(epi->ffd.file))
892                 return vfs_poll(epi->ffd.file, pt) & epi->event.events;
893 
894         ep = epi->ffd.file->private_data;
895         poll_wait(epi->ffd.file, &ep->poll_wait, pt);
896         locked = pt && (pt->_qproc == ep_ptable_queue_proc);
897 
898         return ep_scan_ready_list(epi->ffd.file->private_data,
899                                   ep_read_events_proc, &depth, depth,
900                                   locked) & epi->event.events;
901 }
902 
903 static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
904                                void *priv)
905 {
906         struct epitem *epi, *tmp;
907         poll_table pt;
908         int depth = *(int *)priv;
909 
910         init_poll_funcptr(&pt, NULL);
911         depth++;
912 
913         list_for_each_entry_safe(epi, tmp, head, rdllink) {
914                 if (ep_item_poll(epi, &pt, depth)) {
915                         return EPOLLIN | EPOLLRDNORM;
916                 } else {
917                         /*
918                          * Item has been dropped into the ready list by the poll
919                          * callback, but it's not actually ready, as far as
920                          * caller requested events goes. We can remove it here.
921                          */
922                         __pm_relax(ep_wakeup_source(epi));
923                         list_del_init(&epi->rdllink);
924                 }
925         }
926 
927         return 0;
928 }
929 
930 static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait)
931 {
932         struct eventpoll *ep = file->private_data;
933         int depth = 0;
934 
935         /* Insert inside our poll wait queue */
936         poll_wait(file, &ep->poll_wait, wait);
937 
938         /*
939          * Proceed to find out if wanted events are really available inside
940          * the ready list.
941          */
942         return ep_scan_ready_list(ep, ep_read_events_proc,
943                                   &depth, depth, false);
944 }
945 
946 #ifdef CONFIG_PROC_FS
947 static void ep_show_fdinfo(struct seq_file *m, struct file *f)
948 {
949         struct eventpoll *ep = f->private_data;
950         struct rb_node *rbp;
951 
952         mutex_lock(&ep->mtx);
953         for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
954                 struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
955                 struct inode *inode = file_inode(epi->ffd.file);
956 
957                 seq_printf(m, "tfd: %8d events: %8x data: %16llx "
958                            " pos:%lli ino:%lx sdev:%x\n",
959                            epi->ffd.fd, epi->event.events,
960                            (long long)epi->event.data,
961                            (long long)epi->ffd.file->f_pos,
962                            inode->i_ino, inode->i_sb->s_dev);
963                 if (seq_has_overflowed(m))
964                         break;
965         }
966         mutex_unlock(&ep->mtx);
967 }
968 #endif
969 
970 /* File callbacks that implement the eventpoll file behaviour */
971 static const struct file_operations eventpoll_fops = {
972 #ifdef CONFIG_PROC_FS
973         .show_fdinfo    = ep_show_fdinfo,
974 #endif
975         .release        = ep_eventpoll_release,
976         .poll           = ep_eventpoll_poll,
977         .llseek         = noop_llseek,
978 };
979 
980 /*
981  * This is called from eventpoll_release() to unlink files from the eventpoll
982  * interface. We need to have this facility to cleanup correctly files that are
983  * closed without being removed from the eventpoll interface.
984  */
985 void eventpoll_release_file(struct file *file)
986 {
987         struct eventpoll *ep;
988         struct epitem *epi, *next;
989 
990         /*
991          * We don't want to get "file->f_lock" because it is not
992          * necessary. It is not necessary because we're in the "struct file"
993          * cleanup path, and this means that no one is using this file anymore.
994          * So, for example, epoll_ctl() cannot hit here since if we reach this
995          * point, the file counter already went to zero and fget() would fail.
996          * The only hit might come from ep_free() but by holding the mutex
997          * will correctly serialize the operation. We do need to acquire
998          * "ep->mtx" after "epmutex" because ep_remove() requires it when called
999          * from anywhere but ep_free().
1000          *
1001          * Besides, ep_remove() acquires the lock, so we can't hold it here.
1002          */
1003         mutex_lock(&epmutex);
1004         list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) {
1005                 ep = epi->ep;
1006                 mutex_lock_nested(&ep->mtx, 0);
1007                 ep_remove(ep, epi);
1008                 mutex_unlock(&ep->mtx);
1009         }
1010         mutex_unlock(&epmutex);
1011 }
1012 
1013 static int ep_alloc(struct eventpoll **pep)
1014 {
1015         int error;
1016         struct user_struct *user;
1017         struct eventpoll *ep;
1018 
1019         user = get_current_user();
1020         error = -ENOMEM;
1021         ep = kzalloc(sizeof(*ep), GFP_KERNEL);
1022         if (unlikely(!ep))
1023                 goto free_uid;
1024 
1025         mutex_init(&ep->mtx);
1026         rwlock_init(&ep->lock);
1027         init_waitqueue_head(&ep->wq);
1028         init_waitqueue_head(&ep->poll_wait);
1029         INIT_LIST_HEAD(&ep->rdllist);
1030         ep->rbr = RB_ROOT_CACHED;
1031         ep->ovflist = EP_UNACTIVE_PTR;
1032         ep->user = user;
1033 
1034         *pep = ep;
1035 
1036         return 0;
1037 
1038 free_uid:
1039         free_uid(user);
1040         return error;
1041 }
1042 
1043 /*
1044  * Search the file inside the eventpoll tree. The RB tree operations
1045  * are protected by the "mtx" mutex, and ep_find() must be called with
1046  * "mtx" held.
1047  */
1048 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
1049 {
1050         int kcmp;
1051         struct rb_node *rbp;
1052         struct epitem *epi, *epir = NULL;
1053         struct epoll_filefd ffd;
1054 
1055         ep_set_ffd(&ffd, file, fd);
1056         for (rbp = ep->rbr.rb_root.rb_node; rbp; ) {
1057                 epi = rb_entry(rbp, struct epitem, rbn);
1058                 kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
1059                 if (kcmp > 0)
1060                         rbp = rbp->rb_right;
1061                 else if (kcmp < 0)
1062                         rbp = rbp->rb_left;
1063                 else {
1064                         epir = epi;
1065                         break;
1066                 }
1067         }
1068 
1069         return epir;
1070 }
1071 
1072 #ifdef CONFIG_CHECKPOINT_RESTORE
1073 static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff)
1074 {
1075         struct rb_node *rbp;
1076         struct epitem *epi;
1077 
1078         for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1079                 epi = rb_entry(rbp, struct epitem, rbn);
1080                 if (epi->ffd.fd == tfd) {
1081                         if (toff == 0)
1082                                 return epi;
1083                         else
1084                                 toff--;
1085                 }
1086                 cond_resched();
1087         }
1088 
1089         return NULL;
1090 }
1091 
1092 struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
1093                                      unsigned long toff)
1094 {
1095         struct file *file_raw;
1096         struct eventpoll *ep;
1097         struct epitem *epi;
1098 
1099         if (!is_file_epoll(file))
1100                 return ERR_PTR(-EINVAL);
1101 
1102         ep = file->private_data;
1103 
1104         mutex_lock(&ep->mtx);
1105         epi = ep_find_tfd(ep, tfd, toff);
1106         if (epi)
1107                 file_raw = epi->ffd.file;
1108         else
1109                 file_raw = ERR_PTR(-ENOENT);
1110         mutex_unlock(&ep->mtx);
1111 
1112         return file_raw;
1113 }
1114 #endif /* CONFIG_CHECKPOINT_RESTORE */
1115 
1116 /**
1117  * Adds a new entry to the tail of the list in a lockless way, i.e.
1118  * multiple CPUs are allowed to call this function concurrently.
1119  *
1120  * Beware: it is necessary to prevent any other modifications of the
1121  *         existing list until all changes are completed, in other words
1122  *         concurrent list_add_tail_lockless() calls should be protected
1123  *         with a read lock, where write lock acts as a barrier which
1124  *         makes sure all list_add_tail_lockless() calls are fully
1125  *         completed.
1126  *
1127  *        Also an element can be locklessly added to the list only in one
1128  *        direction i.e. either to the tail either to the head, otherwise
1129  *        concurrent access will corrupt the list.
1130  *
1131  * Returns %false if element has been already added to the list, %true
1132  * otherwise.
1133  */
1134 static inline bool list_add_tail_lockless(struct list_head *new,
1135                                           struct list_head *head)
1136 {
1137         struct list_head *prev;
1138 
1139         /*
1140          * This is simple 'new->next = head' operation, but cmpxchg()
1141          * is used in order to detect that same element has been just
1142          * added to the list from another CPU: the winner observes
1143          * new->next == new.
1144          */
1145         if (cmpxchg(&new->next, new, head) != new)
1146                 return false;
1147 
1148         /*
1149          * Initially ->next of a new element must be updated with the head
1150          * (we are inserting to the tail) and only then pointers are atomically
1151          * exchanged.  XCHG guarantees memory ordering, thus ->next should be
1152          * updated before pointers are actually swapped and pointers are
1153          * swapped before prev->next is updated.
1154          */
1155 
1156         prev = xchg(&head->prev, new);
1157 
1158         /*
1159          * It is safe to modify prev->next and new->prev, because a new element
1160          * is added only to the tail and new->next is updated before XCHG.
1161          */
1162 
1163         prev->next = new;
1164         new->prev = prev;
1165 
1166         return true;
1167 }
1168 
1169 /**
1170  * Chains a new epi entry to the tail of the ep->ovflist in a lockless way,
1171  * i.e. multiple CPUs are allowed to call this function concurrently.
1172  *
1173  * Returns %false if epi element has been already chained, %true otherwise.
1174  */
1175 static inline bool chain_epi_lockless(struct epitem *epi)
1176 {
1177         struct eventpoll *ep = epi->ep;
1178 
1179         /* Check that the same epi has not been just chained from another CPU */
1180         if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR)
1181                 return false;
1182 
1183         /* Atomically exchange tail */
1184         epi->next = xchg(&ep->ovflist, epi);
1185 
1186         return true;
1187 }
1188 
1189 /*
1190  * This is the callback that is passed to the wait queue wakeup
1191  * mechanism. It is called by the stored file descriptors when they
1192  * have events to report.
1193  *
1194  * This callback takes a read lock in order not to content with concurrent
1195  * events from another file descriptors, thus all modifications to ->rdllist
1196  * or ->ovflist are lockless.  Read lock is paired with the write lock from
1197  * ep_scan_ready_list(), which stops all list modifications and guarantees
1198  * that lists state is seen correctly.
1199  *
1200  * Another thing worth to mention is that ep_poll_callback() can be called
1201  * concurrently for the same @epi from different CPUs if poll table was inited
1202  * with several wait queues entries.  Plural wakeup from different CPUs of a
1203  * single wait queue is serialized by wq.lock, but the case when multiple wait
1204  * queues are used should be detected accordingly.  This is detected using
1205  * cmpxchg() operation.
1206  */
1207 static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
1208 {
1209         int pwake = 0;
1210         struct epitem *epi = ep_item_from_wait(wait);
1211         struct eventpoll *ep = epi->ep;
1212         __poll_t pollflags = key_to_poll(key);
1213         unsigned long flags;
1214         int ewake = 0;
1215 
1216         read_lock_irqsave(&ep->lock, flags);
1217 
1218         ep_set_busy_poll_napi_id(epi);
1219 
1220         /*
1221          * If the event mask does not contain any poll(2) event, we consider the
1222          * descriptor to be disabled. This condition is likely the effect of the
1223          * EPOLLONESHOT bit that disables the descriptor when an event is received,
1224          * until the next EPOLL_CTL_MOD will be issued.
1225          */
1226         if (!(epi->event.events & ~EP_PRIVATE_BITS))
1227                 goto out_unlock;
1228 
1229         /*
1230          * Check the events coming with the callback. At this stage, not
1231          * every device reports the events in the "key" parameter of the
1232          * callback. We need to be able to handle both cases here, hence the
1233          * test for "key" != NULL before the event match test.
1234          */
1235         if (pollflags && !(pollflags & epi->event.events))
1236                 goto out_unlock;
1237 
1238         /*
1239          * If we are transferring events to userspace, we can hold no locks
1240          * (because we're accessing user memory, and because of linux f_op->poll()
1241          * semantics). All the events that happen during that period of time are
1242          * chained in ep->ovflist and requeued later on.
1243          */
1244         if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) {
1245                 if (epi->next == EP_UNACTIVE_PTR &&
1246                     chain_epi_lockless(epi))
1247                         ep_pm_stay_awake_rcu(epi);
1248                 goto out_unlock;
1249         }
1250 
1251         /* If this file is already in the ready list we exit soon */
1252         if (!ep_is_linked(epi) &&
1253             list_add_tail_lockless(&epi->rdllink, &ep->rdllist)) {
1254                 ep_pm_stay_awake_rcu(epi);
1255         }
1256 
1257         /*
1258          * Wake up ( if active ) both the eventpoll wait list and the ->poll()
1259          * wait list.
1260          */
1261         if (waitqueue_active(&ep->wq)) {
1262                 if ((epi->event.events & EPOLLEXCLUSIVE) &&
1263                                         !(pollflags & POLLFREE)) {
1264                         switch (pollflags & EPOLLINOUT_BITS) {
1265                         case EPOLLIN:
1266                                 if (epi->event.events & EPOLLIN)
1267                                         ewake = 1;
1268                                 break;
1269                         case EPOLLOUT:
1270                                 if (epi->event.events & EPOLLOUT)
1271                                         ewake = 1;
1272                                 break;
1273                         case 0:
1274                                 ewake = 1;
1275                                 break;
1276                         }
1277                 }
1278                 wake_up(&ep->wq);
1279         }
1280         if (waitqueue_active(&ep->poll_wait))
1281                 pwake++;
1282 
1283 out_unlock:
1284         read_unlock_irqrestore(&ep->lock, flags);
1285 
1286         /* We have to call this outside the lock */
1287         if (pwake)
1288                 ep_poll_safewake(&ep->poll_wait);
1289 
1290         if (!(epi->event.events & EPOLLEXCLUSIVE))
1291                 ewake = 1;
1292 
1293         if (pollflags & POLLFREE) {
1294                 /*
1295                  * If we race with ep_remove_wait_queue() it can miss
1296                  * ->whead = NULL and do another remove_wait_queue() after
1297                  * us, so we can't use __remove_wait_queue().
1298                  */
1299                 list_del_init(&wait->entry);
1300                 /*
1301                  * ->whead != NULL protects us from the race with ep_free()
1302                  * or ep_remove(), ep_remove_wait_queue() takes whead->lock
1303                  * held by the caller. Once we nullify it, nothing protects
1304                  * ep/epi or even wait.
1305                  */
1306                 smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL);
1307         }
1308 
1309         return ewake;
1310 }
1311 
1312 /*
1313  * This is the callback that is used to add our wait queue to the
1314  * target file wakeup lists.
1315  */
1316 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
1317                                  poll_table *pt)
1318 {
1319         struct epitem *epi = ep_item_from_epqueue(pt);
1320         struct eppoll_entry *pwq;
1321 
1322         if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
1323                 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
1324                 pwq->whead = whead;
1325                 pwq->base = epi;
1326                 if (epi->event.events & EPOLLEXCLUSIVE)
1327                         add_wait_queue_exclusive(whead, &pwq->wait);
1328                 else
1329                         add_wait_queue(whead, &pwq->wait);
1330                 list_add_tail(&pwq->llink, &epi->pwqlist);
1331                 epi->nwait++;
1332         } else {
1333                 /* We have to signal that an error occurred */
1334                 epi->nwait = -1;
1335         }
1336 }
1337 
1338 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
1339 {
1340         int kcmp;
1341         struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL;
1342         struct epitem *epic;
1343         bool leftmost = true;
1344 
1345         while (*p) {
1346                 parent = *p;
1347                 epic = rb_entry(parent, struct epitem, rbn);
1348                 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
1349                 if (kcmp > 0) {
1350                         p = &parent->rb_right;
1351                         leftmost = false;
1352                 } else
1353                         p = &parent->rb_left;
1354         }
1355         rb_link_node(&epi->rbn, parent, p);
1356         rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost);
1357 }
1358 
1359 
1360 
1361 #define PATH_ARR_SIZE 5
1362 /*
1363  * These are the number paths of length 1 to 5, that we are allowing to emanate
1364  * from a single file of interest. For example, we allow 1000 paths of length
1365  * 1, to emanate from each file of interest. This essentially represents the
1366  * potential wakeup paths, which need to be limited in order to avoid massive
1367  * uncontrolled wakeup storms. The common use case should be a single ep which
1368  * is connected to n file sources. In this case each file source has 1 path
1369  * of length 1. Thus, the numbers below should be more than sufficient. These
1370  * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
1371  * and delete can't add additional paths. Protected by the epmutex.
1372  */
1373 static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
1374 static int path_count[PATH_ARR_SIZE];
1375 
1376 static int path_count_inc(int nests)
1377 {
1378         /* Allow an arbitrary number of depth 1 paths */
1379         if (nests == 0)
1380                 return 0;
1381 
1382         if (++path_count[nests] > path_limits[nests])
1383                 return -1;
1384         return 0;
1385 }
1386 
1387 static void path_count_init(void)
1388 {
1389         int i;
1390 
1391         for (i = 0; i < PATH_ARR_SIZE; i++)
1392                 path_count[i] = 0;
1393 }
1394 
1395 static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
1396 {
1397         int error = 0;
1398         struct file *file = priv;
1399         struct file *child_file;
1400         struct epitem *epi;
1401 
1402         /* CTL_DEL can remove links here, but that can't increase our count */
1403         rcu_read_lock();
1404         list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
1405                 child_file = epi->ep->file;
1406                 if (is_file_epoll(child_file)) {
1407                         if (list_empty(&child_file->f_ep_links)) {
1408                                 if (path_count_inc(call_nests)) {
1409                                         error = -1;
1410                                         break;
1411                                 }
1412                         } else {
1413                                 error = ep_call_nested(&poll_loop_ncalls,
1414                                                         reverse_path_check_proc,
1415                                                         child_file, child_file,
1416                                                         current);
1417                         }
1418                         if (error != 0)
1419                                 break;
1420                 } else {
1421                         printk(KERN_ERR "reverse_path_check_proc: "
1422                                 "file is not an ep!\n");
1423                 }
1424         }
1425         rcu_read_unlock();
1426         return error;
1427 }
1428 
1429 /**
1430  * reverse_path_check - The tfile_check_list is list of file *, which have
1431  *                      links that are proposed to be newly added. We need to
1432  *                      make sure that those added links don't add too many
1433  *                      paths such that we will spend all our time waking up
1434  *                      eventpoll objects.
1435  *
1436  * Returns: Returns zero if the proposed links don't create too many paths,
1437  *          -1 otherwise.
1438  */
1439 static int reverse_path_check(void)
1440 {
1441         int error = 0;
1442         struct file *current_file;
1443 
1444         /* let's call this for all tfiles */
1445         list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
1446                 path_count_init();
1447                 error = ep_call_nested(&poll_loop_ncalls,
1448                                         reverse_path_check_proc, current_file,
1449                                         current_file, current);
1450                 if (error)
1451                         break;
1452         }
1453         return error;
1454 }
1455 
1456 static int ep_create_wakeup_source(struct epitem *epi)
1457 {
1458         const char *name;
1459         struct wakeup_source *ws;
1460 
1461         if (!epi->ep->ws) {
1462                 epi->ep->ws = wakeup_source_register("eventpoll");
1463                 if (!epi->ep->ws)
1464                         return -ENOMEM;
1465         }
1466 
1467         name = epi->ffd.file->f_path.dentry->d_name.name;
1468         ws = wakeup_source_register(name);
1469 
1470         if (!ws)
1471                 return -ENOMEM;
1472         rcu_assign_pointer(epi->ws, ws);
1473 
1474         return 0;
1475 }
1476 
1477 /* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
1478 static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1479 {
1480         struct wakeup_source *ws = ep_wakeup_source(epi);
1481 
1482         RCU_INIT_POINTER(epi->ws, NULL);
1483 
1484         /*
1485          * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
1486          * used internally by wakeup_source_remove, too (called by
1487          * wakeup_source_unregister), so we cannot use call_rcu
1488          */
1489         synchronize_rcu();
1490         wakeup_source_unregister(ws);
1491 }
1492 
1493 /*
1494  * Must be called with "mtx" held.
1495  */
1496 static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
1497                      struct file *tfile, int fd, int full_check)
1498 {
1499         int error, pwake = 0;
1500         __poll_t revents;
1501         long user_watches;
1502         struct epitem *epi;
1503         struct ep_pqueue epq;
1504 
1505         lockdep_assert_irqs_enabled();
1506 
1507         user_watches = atomic_long_read(&ep->user->epoll_watches);
1508         if (unlikely(user_watches >= max_user_watches))
1509                 return -ENOSPC;
1510         if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
1511                 return -ENOMEM;
1512 
1513         /* Item initialization follow here ... */
1514         INIT_LIST_HEAD(&epi->rdllink);
1515         INIT_LIST_HEAD(&epi->fllink);
1516         INIT_LIST_HEAD(&epi->pwqlist);
1517         epi->ep = ep;
1518         ep_set_ffd(&epi->ffd, tfile, fd);
1519         epi->event = *event;
1520         epi->nwait = 0;
1521         epi->next = EP_UNACTIVE_PTR;
1522         if (epi->event.events & EPOLLWAKEUP) {
1523                 error = ep_create_wakeup_source(epi);
1524                 if (error)
1525                         goto error_create_wakeup_source;
1526         } else {
1527                 RCU_INIT_POINTER(epi->ws, NULL);
1528         }
1529 
1530         /* Initialize the poll table using the queue callback */
1531         epq.epi = epi;
1532         init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
1533 
1534         /*
1535          * Attach the item to the poll hooks and get current event bits.
1536          * We can safely use the file* here because its usage count has
1537          * been increased by the caller of this function. Note that after
1538          * this operation completes, the poll callback can start hitting
1539          * the new item.
1540          */
1541         revents = ep_item_poll(epi, &epq.pt, 1);
1542 
1543         /*
1544          * We have to check if something went wrong during the poll wait queue
1545          * install process. Namely an allocation for a wait queue failed due
1546          * high memory pressure.
1547          */
1548         error = -ENOMEM;
1549         if (epi->nwait < 0)
1550                 goto error_unregister;
1551 
1552         /* Add the current item to the list of active epoll hook for this file */
1553         spin_lock(&tfile->f_lock);
1554         list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
1555         spin_unlock(&tfile->f_lock);
1556 
1557         /*
1558          * Add the current item to the RB tree. All RB tree operations are
1559          * protected by "mtx", and ep_insert() is called with "mtx" held.
1560          */
1561         ep_rbtree_insert(ep, epi);
1562 
1563         /* now check if we've created too many backpaths */
1564         error = -EINVAL;
1565         if (full_check && reverse_path_check())
1566                 goto error_remove_epi;
1567 
1568         /* We have to drop the new item inside our item list to keep track of it */
1569         write_lock_irq(&ep->lock);
1570 
1571         /* record NAPI ID of new item if present */
1572         ep_set_busy_poll_napi_id(epi);
1573 
1574         /* If the file is already "ready" we drop it inside the ready list */
1575         if (revents && !ep_is_linked(epi)) {
1576                 list_add_tail(&epi->rdllink, &ep->rdllist);
1577                 ep_pm_stay_awake(epi);
1578 
1579                 /* Notify waiting tasks that events are available */
1580                 if (waitqueue_active(&ep->wq))
1581                         wake_up(&ep->wq);
1582                 if (waitqueue_active(&ep->poll_wait))
1583                         pwake++;
1584         }
1585 
1586         write_unlock_irq(&ep->lock);
1587 
1588         atomic_long_inc(&ep->user->epoll_watches);
1589 
1590         /* We have to call this outside the lock */
1591         if (pwake)
1592                 ep_poll_safewake(&ep->poll_wait);
1593 
1594         return 0;
1595 
1596 error_remove_epi:
1597         spin_lock(&tfile->f_lock);
1598         list_del_rcu(&epi->fllink);
1599         spin_unlock(&tfile->f_lock);
1600 
1601         rb_erase_cached(&epi->rbn, &ep->rbr);
1602 
1603 error_unregister:
1604         ep_unregister_pollwait(ep, epi);
1605 
1606         /*
1607          * We need to do this because an event could have been arrived on some
1608          * allocated wait queue. Note that we don't care about the ep->ovflist
1609          * list, since that is used/cleaned only inside a section bound by "mtx".
1610          * And ep_insert() is called with "mtx" held.
1611          */
1612         write_lock_irq(&ep->lock);
1613         if (ep_is_linked(epi))
1614                 list_del_init(&epi->rdllink);
1615         write_unlock_irq(&ep->lock);
1616 
1617         wakeup_source_unregister(ep_wakeup_source(epi));
1618 
1619 error_create_wakeup_source:
1620         kmem_cache_free(epi_cache, epi);
1621 
1622         return error;
1623 }
1624 
1625 /*
1626  * Modify the interest event mask by dropping an event if the new mask
1627  * has a match in the current file status. Must be called with "mtx" held.
1628  */
1629 static int ep_modify(struct eventpoll *ep, struct epitem *epi,
1630                      const struct epoll_event *event)
1631 {
1632         int pwake = 0;
1633         poll_table pt;
1634 
1635         lockdep_assert_irqs_enabled();
1636 
1637         init_poll_funcptr(&pt, NULL);
1638 
1639         /*
1640          * Set the new event interest mask before calling f_op->poll();
1641          * otherwise we might miss an event that happens between the
1642          * f_op->poll() call and the new event set registering.
1643          */
1644         epi->event.events = event->events; /* need barrier below */
1645         epi->event.data = event->data; /* protected by mtx */
1646         if (epi->event.events & EPOLLWAKEUP) {
1647                 if (!ep_has_wakeup_source(epi))
1648                         ep_create_wakeup_source(epi);
1649         } else if (ep_has_wakeup_source(epi)) {
1650                 ep_destroy_wakeup_source(epi);
1651         }
1652 
1653         /*
1654          * The following barrier has two effects:
1655          *
1656          * 1) Flush epi changes above to other CPUs.  This ensures
1657          *    we do not miss events from ep_poll_callback if an
1658          *    event occurs immediately after we call f_op->poll().
1659          *    We need this because we did not take ep->lock while
1660          *    changing epi above (but ep_poll_callback does take
1661          *    ep->lock).
1662          *
1663          * 2) We also need to ensure we do not miss _past_ events
1664          *    when calling f_op->poll().  This barrier also
1665          *    pairs with the barrier in wq_has_sleeper (see
1666          *    comments for wq_has_sleeper).
1667          *
1668          * This barrier will now guarantee ep_poll_callback or f_op->poll
1669          * (or both) will notice the readiness of an item.
1670          */
1671         smp_mb();
1672 
1673         /*
1674          * Get current event bits. We can safely use the file* here because
1675          * its usage count has been increased by the caller of this function.
1676          * If the item is "hot" and it is not registered inside the ready
1677          * list, push it inside.
1678          */
1679         if (ep_item_poll(epi, &pt, 1)) {
1680                 write_lock_irq(&ep->lock);
1681                 if (!ep_is_linked(epi)) {
1682                         list_add_tail(&epi->rdllink, &ep->rdllist);
1683                         ep_pm_stay_awake(epi);
1684 
1685                         /* Notify waiting tasks that events are available */
1686                         if (waitqueue_active(&ep->wq))
1687                                 wake_up(&ep->wq);
1688                         if (waitqueue_active(&ep->poll_wait))
1689                                 pwake++;
1690                 }
1691                 write_unlock_irq(&ep->lock);
1692         }
1693 
1694         /* We have to call this outside the lock */
1695         if (pwake)
1696                 ep_poll_safewake(&ep->poll_wait);
1697 
1698         return 0;
1699 }
1700 
1701 static __poll_t ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
1702                                void *priv)
1703 {
1704         struct ep_send_events_data *esed = priv;
1705         __poll_t revents;
1706         struct epitem *epi, *tmp;
1707         struct epoll_event __user *uevent = esed->events;
1708         struct wakeup_source *ws;
1709         poll_table pt;
1710 
1711         init_poll_funcptr(&pt, NULL);
1712         esed->res = 0;
1713 
1714         /*
1715          * We can loop without lock because we are passed a task private list.
1716          * Items cannot vanish during the loop because ep_scan_ready_list() is
1717          * holding "mtx" during this call.
1718          */
1719         lockdep_assert_held(&ep->mtx);
1720 
1721         list_for_each_entry_safe(epi, tmp, head, rdllink) {
1722                 if (esed->res >= esed->maxevents)
1723                         break;
1724 
1725                 /*
1726                  * Activate ep->ws before deactivating epi->ws to prevent
1727                  * triggering auto-suspend here (in case we reactive epi->ws
1728                  * below).
1729                  *
1730                  * This could be rearranged to delay the deactivation of epi->ws
1731                  * instead, but then epi->ws would temporarily be out of sync
1732                  * with ep_is_linked().
1733                  */
1734                 ws = ep_wakeup_source(epi);
1735                 if (ws) {
1736                         if (ws->active)
1737                                 __pm_stay_awake(ep->ws);
1738                         __pm_relax(ws);
1739                 }
1740 
1741                 list_del_init(&epi->rdllink);
1742 
1743                 /*
1744                  * If the event mask intersect the caller-requested one,
1745                  * deliver the event to userspace. Again, ep_scan_ready_list()
1746                  * is holding ep->mtx, so no operations coming from userspace
1747                  * can change the item.
1748                  */
1749                 revents = ep_item_poll(epi, &pt, 1);
1750                 if (!revents)
1751                         continue;
1752 
1753                 if (__put_user(revents, &uevent->events) ||
1754                     __put_user(epi->event.data, &uevent->data)) {
1755                         list_add(&epi->rdllink, head);
1756                         ep_pm_stay_awake(epi);
1757                         if (!esed->res)
1758                                 esed->res = -EFAULT;
1759                         return 0;
1760                 }
1761                 esed->res++;
1762                 uevent++;
1763                 if (epi->event.events & EPOLLONESHOT)
1764                         epi->event.events &= EP_PRIVATE_BITS;
1765                 else if (!(epi->event.events & EPOLLET)) {
1766                         /*
1767                          * If this file has been added with Level
1768                          * Trigger mode, we need to insert back inside
1769                          * the ready list, so that the next call to
1770                          * epoll_wait() will check again the events
1771                          * availability. At this point, no one can insert
1772                          * into ep->rdllist besides us. The epoll_ctl()
1773                          * callers are locked out by
1774                          * ep_scan_ready_list() holding "mtx" and the
1775                          * poll callback will queue them in ep->ovflist.
1776                          */
1777                         list_add_tail(&epi->rdllink, &ep->rdllist);
1778                         ep_pm_stay_awake(epi);
1779                 }
1780         }
1781 
1782         return 0;
1783 }
1784 
1785 static int ep_send_events(struct eventpoll *ep,
1786                           struct epoll_event __user *events, int maxevents)
1787 {
1788         struct ep_send_events_data esed;
1789 
1790         esed.maxevents = maxevents;
1791         esed.events = events;
1792 
1793         ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
1794         return esed.res;
1795 }
1796 
1797 static inline struct timespec64 ep_set_mstimeout(long ms)
1798 {
1799         struct timespec64 now, ts = {
1800                 .tv_sec = ms / MSEC_PER_SEC,
1801                 .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
1802         };
1803 
1804         ktime_get_ts64(&now);
1805         return timespec64_add_safe(now, ts);
1806 }
1807 
1808 /**
1809  * ep_poll - Retrieves ready events, and delivers them to the caller supplied
1810  *           event buffer.
1811  *
1812  * @ep: Pointer to the eventpoll context.
1813  * @events: Pointer to the userspace buffer where the ready events should be
1814  *          stored.
1815  * @maxevents: Size (in terms of number of events) of the caller event buffer.
1816  * @timeout: Maximum timeout for the ready events fetch operation, in
1817  *           milliseconds. If the @timeout is zero, the function will not block,
1818  *           while if the @timeout is less than zero, the function will block
1819  *           until at least one event has been retrieved (or an error
1820  *           occurred).
1821  *
1822  * Returns: Returns the number of ready events which have been fetched, or an
1823  *          error code, in case of error.
1824  */
1825 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1826                    int maxevents, long timeout)
1827 {
1828         int res = 0, eavail, timed_out = 0;
1829         u64 slack = 0;
1830         bool waiter = false;
1831         wait_queue_entry_t wait;
1832         ktime_t expires, *to = NULL;
1833 
1834         lockdep_assert_irqs_enabled();
1835 
1836         if (timeout > 0) {
1837                 struct timespec64 end_time = ep_set_mstimeout(timeout);
1838 
1839                 slack = select_estimate_accuracy(&end_time);
1840                 to = &expires;
1841                 *to = timespec64_to_ktime(end_time);
1842         } else if (timeout == 0) {
1843                 /*
1844                  * Avoid the unnecessary trip to the wait queue loop, if the
1845                  * caller specified a non blocking operation. We still need
1846                  * lock because we could race and not see an epi being added
1847                  * to the ready list while in irq callback. Thus incorrectly
1848                  * returning 0 back to userspace.
1849                  */
1850                 timed_out = 1;
1851 
1852                 write_lock_irq(&ep->lock);
1853                 eavail = ep_events_available(ep);
1854                 write_unlock_irq(&ep->lock);
1855 
1856                 goto send_events;
1857         }
1858 
1859 fetch_events:
1860 
1861         if (!ep_events_available(ep))
1862                 ep_busy_loop(ep, timed_out);
1863 
1864         eavail = ep_events_available(ep);
1865         if (eavail)
1866                 goto send_events;
1867 
1868         /*
1869          * Busy poll timed out.  Drop NAPI ID for now, we can add
1870          * it back in when we have moved a socket with a valid NAPI
1871          * ID onto the ready list.
1872          */
1873         ep_reset_busy_poll_napi_id(ep);
1874 
1875         /*
1876          * We don't have any available event to return to the caller.  We need
1877          * to sleep here, and we will be woken by ep_poll_callback() when events
1878          * become available.
1879          */
1880         if (!waiter) {
1881                 waiter = true;
1882                 init_waitqueue_entry(&wait, current);
1883 
1884                 spin_lock_irq(&ep->wq.lock);
1885                 __add_wait_queue_exclusive(&ep->wq, &wait);
1886                 spin_unlock_irq(&ep->wq.lock);
1887         }
1888 
1889         for (;;) {
1890                 /*
1891                  * We don't want to sleep if the ep_poll_callback() sends us
1892                  * a wakeup in between. That's why we set the task state
1893                  * to TASK_INTERRUPTIBLE before doing the checks.
1894                  */
1895                 set_current_state(TASK_INTERRUPTIBLE);
1896                 /*
1897                  * Always short-circuit for fatal signals to allow
1898                  * threads to make a timely exit without the chance of
1899                  * finding more events available and fetching
1900                  * repeatedly.
1901                  */
1902                 if (fatal_signal_pending(current)) {
1903                         res = -EINTR;
1904                         break;
1905                 }
1906 
1907                 eavail = ep_events_available(ep);
1908                 if (eavail)
1909                         break;
1910                 if (signal_pending(current)) {
1911                         res = -EINTR;
1912                         break;
1913                 }
1914 
1915                 if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) {
1916                         timed_out = 1;
1917                         break;
1918                 }
1919         }
1920 
1921         __set_current_state(TASK_RUNNING);
1922 
1923 send_events:
1924         /*
1925          * Try to transfer events to user space. In case we get 0 events and
1926          * there's still timeout left over, we go trying again in search of
1927          * more luck.
1928          */
1929         if (!res && eavail &&
1930             !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
1931                 goto fetch_events;
1932 
1933         if (waiter) {
1934                 spin_lock_irq(&ep->wq.lock);
1935                 __remove_wait_queue(&ep->wq, &wait);
1936                 spin_unlock_irq(&ep->wq.lock);
1937         }
1938 
1939         return res;
1940 }
1941 
1942 /**
1943  * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
1944  *                      API, to verify that adding an epoll file inside another
1945  *                      epoll structure, does not violate the constraints, in
1946  *                      terms of closed loops, or too deep chains (which can
1947  *                      result in excessive stack usage).
1948  *
1949  * @priv: Pointer to the epoll file to be currently checked.
1950  * @cookie: Original cookie for this call. This is the top-of-the-chain epoll
1951  *          data structure pointer.
1952  * @call_nests: Current dept of the @ep_call_nested() call stack.
1953  *
1954  * Returns: Returns zero if adding the epoll @file inside current epoll
1955  *          structure @ep does not violate the constraints, or -1 otherwise.
1956  */
1957 static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
1958 {
1959         int error = 0;
1960         struct file *file = priv;
1961         struct eventpoll *ep = file->private_data;
1962         struct eventpoll *ep_tovisit;
1963         struct rb_node *rbp;
1964         struct epitem *epi;
1965 
1966         mutex_lock_nested(&ep->mtx, call_nests + 1);
1967         ep->visited = 1;
1968         list_add(&ep->visited_list_link, &visited_list);
1969         for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1970                 epi = rb_entry(rbp, struct epitem, rbn);
1971                 if (unlikely(is_file_epoll(epi->ffd.file))) {
1972                         ep_tovisit = epi->ffd.file->private_data;
1973                         if (ep_tovisit->visited)
1974                                 continue;
1975                         error = ep_call_nested(&poll_loop_ncalls,
1976                                         ep_loop_check_proc, epi->ffd.file,
1977                                         ep_tovisit, current);
1978                         if (error != 0)
1979                                 break;
1980                 } else {
1981                         /*
1982                          * If we've reached a file that is not associated with
1983                          * an ep, then we need to check if the newly added
1984                          * links are going to add too many wakeup paths. We do
1985                          * this by adding it to the tfile_check_list, if it's
1986                          * not already there, and calling reverse_path_check()
1987                          * during ep_insert().
1988                          */
1989                         if (list_empty(&epi->ffd.file->f_tfile_llink))
1990                                 list_add(&epi->ffd.file->f_tfile_llink,
1991                                          &tfile_check_list);
1992                 }
1993         }
1994         mutex_unlock(&ep->mtx);
1995 
1996         return error;
1997 }
1998 
1999 /**
2000  * ep_loop_check - Performs a check to verify that adding an epoll file (@file)
2001  *                 another epoll file (represented by @ep) does not create
2002  *                 closed loops or too deep chains.
2003  *
2004  * @ep: Pointer to the epoll private data structure.
2005  * @file: Pointer to the epoll file to be checked.
2006  *
2007  * Returns: Returns zero if adding the epoll @file inside current epoll
2008  *          structure @ep does not violate the constraints, or -1 otherwise.
2009  */
2010 static int ep_loop_check(struct eventpoll *ep, struct file *file)
2011 {
2012         int ret;
2013         struct eventpoll *ep_cur, *ep_next;
2014 
2015         ret = ep_call_nested(&poll_loop_ncalls,
2016                               ep_loop_check_proc, file, ep, current);
2017         /* clear visited list */
2018         list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
2019                                                         visited_list_link) {
2020                 ep_cur->visited = 0;
2021                 list_del(&ep_cur->visited_list_link);
2022         }
2023         return ret;
2024 }
2025 
2026 static void clear_tfile_check_list(void)
2027 {
2028         struct file *file;
2029 
2030         /* first clear the tfile_check_list */
2031         while (!list_empty(&tfile_check_list)) {
2032                 file = list_first_entry(&tfile_check_list, struct file,
2033                                         f_tfile_llink);
2034                 list_del_init(&file->f_tfile_llink);
2035         }
2036         INIT_LIST_HEAD(&tfile_check_list);
2037 }
2038 
2039 /*
2040  * Open an eventpoll file descriptor.
2041  */
2042 static int do_epoll_create(int flags)
2043 {
2044         int error, fd;
2045         struct eventpoll *ep = NULL;
2046         struct file *file;
2047 
2048         /* Check the EPOLL_* constant for consistency.  */
2049         BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
2050 
2051         if (flags & ~EPOLL_CLOEXEC)
2052                 return -EINVAL;
2053         /*
2054          * Create the internal data structure ("struct eventpoll").
2055          */
2056         error = ep_alloc(&ep);
2057         if (error < 0)
2058                 return error;
2059         /*
2060          * Creates all the items needed to setup an eventpoll file. That is,
2061          * a file structure and a free file descriptor.
2062          */
2063         fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
2064         if (fd < 0) {
2065                 error = fd;
2066                 goto out_free_ep;
2067         }
2068         file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
2069                                  O_RDWR | (flags & O_CLOEXEC));
2070         if (IS_ERR(file)) {
2071                 error = PTR_ERR(file);
2072                 goto out_free_fd;
2073         }
2074         ep->file = file;
2075         fd_install(fd, file);
2076         return fd;
2077 
2078 out_free_fd:
2079         put_unused_fd(fd);
2080 out_free_ep:
2081         ep_free(ep);
2082         return error;
2083 }
2084 
2085 SYSCALL_DEFINE1(epoll_create1, int, flags)
2086 {
2087         return do_epoll_create(flags);
2088 }
2089 
2090 SYSCALL_DEFINE1(epoll_create, int, size)
2091 {
2092         if (size <= 0)
2093                 return -EINVAL;
2094 
2095         return do_epoll_create(0);
2096 }
2097 
2098 /*
2099  * The following function implements the controller interface for
2100  * the eventpoll file that enables the insertion/removal/change of
2101  * file descriptors inside the interest set.
2102  */
2103 SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
2104                 struct epoll_event __user *, event)
2105 {
2106         int error;
2107         int full_check = 0;
2108         struct fd f, tf;
2109         struct eventpoll *ep;
2110         struct epitem *epi;
2111         struct epoll_event epds;
2112         struct eventpoll *tep = NULL;
2113 
2114         error = -EFAULT;
2115         if (ep_op_has_event(op) &&
2116             copy_from_user(&epds, event, sizeof(struct epoll_event)))
2117                 goto error_return;
2118 
2119         error = -EBADF;
2120         f = fdget(epfd);
2121         if (!f.file)
2122                 goto error_return;
2123 
2124         /* Get the "struct file *" for the target file */
2125         tf = fdget(fd);
2126         if (!tf.file)
2127                 goto error_fput;
2128 
2129         /* The target file descriptor must support poll */
2130         error = -EPERM;
2131         if (!file_can_poll(tf.file))
2132                 goto error_tgt_fput;
2133 
2134         /* Check if EPOLLWAKEUP is allowed */
2135         if (ep_op_has_event(op))
2136                 ep_take_care_of_epollwakeup(&epds);
2137 
2138         /*
2139          * We have to check that the file structure underneath the file descriptor
2140          * the user passed to us _is_ an eventpoll file. And also we do not permit
2141          * adding an epoll file descriptor inside itself.
2142          */
2143         error = -EINVAL;
2144         if (f.file == tf.file || !is_file_epoll(f.file))
2145                 goto error_tgt_fput;
2146 
2147         /*
2148          * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only,
2149          * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
2150          * Also, we do not currently supported nested exclusive wakeups.
2151          */
2152         if (ep_op_has_event(op) && (epds.events & EPOLLEXCLUSIVE)) {
2153                 if (op == EPOLL_CTL_MOD)
2154                         goto error_tgt_fput;
2155                 if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
2156                                 (epds.events & ~EPOLLEXCLUSIVE_OK_BITS)))
2157                         goto error_tgt_fput;
2158         }
2159 
2160         /*
2161          * At this point it is safe to assume that the "private_data" contains
2162          * our own data structure.
2163          */
2164         ep = f.file->private_data;
2165 
2166         /*
2167          * When we insert an epoll file descriptor, inside another epoll file
2168          * descriptor, there is the change of creating closed loops, which are
2169          * better be handled here, than in more critical paths. While we are
2170          * checking for loops we also determine the list of files reachable
2171          * and hang them on the tfile_check_list, so we can check that we
2172          * haven't created too many possible wakeup paths.
2173          *
2174          * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
2175          * the epoll file descriptor is attaching directly to a wakeup source,
2176          * unless the epoll file descriptor is nested. The purpose of taking the
2177          * 'epmutex' on add is to prevent complex toplogies such as loops and
2178          * deep wakeup paths from forming in parallel through multiple
2179          * EPOLL_CTL_ADD operations.
2180          */
2181         mutex_lock_nested(&ep->mtx, 0);
2182         if (op == EPOLL_CTL_ADD) {
2183                 if (!list_empty(&f.file->f_ep_links) ||
2184                                                 is_file_epoll(tf.file)) {
2185                         full_check = 1;
2186                         mutex_unlock(&ep->mtx);
2187                         mutex_lock(&epmutex);
2188                         if (is_file_epoll(tf.file)) {
2189                                 error = -ELOOP;
2190                                 if (ep_loop_check(ep, tf.file) != 0) {
2191                                         clear_tfile_check_list();
2192                                         goto error_tgt_fput;
2193                                 }
2194                         } else
2195                                 list_add(&tf.file->f_tfile_llink,
2196                                                         &tfile_check_list);
2197                         mutex_lock_nested(&ep->mtx, 0);
2198                         if (is_file_epoll(tf.file)) {
2199                                 tep = tf.file->private_data;
2200                                 mutex_lock_nested(&tep->mtx, 1);
2201                         }
2202                 }
2203         }
2204 
2205         /*
2206          * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
2207          * above, we can be sure to be able to use the item looked up by
2208          * ep_find() till we release the mutex.
2209          */
2210         epi = ep_find(ep, tf.file, fd);
2211 
2212         error = -EINVAL;
2213         switch (op) {
2214         case EPOLL_CTL_ADD:
2215                 if (!epi) {
2216                         epds.events |= EPOLLERR | EPOLLHUP;
2217                         error = ep_insert(ep, &epds, tf.file, fd, full_check);
2218                 } else
2219                         error = -EEXIST;
2220                 if (full_check)
2221                         clear_tfile_check_list();
2222                 break;
2223         case EPOLL_CTL_DEL:
2224                 if (epi)
2225                         error = ep_remove(ep, epi);
2226                 else
2227                         error = -ENOENT;
2228                 break;
2229         case EPOLL_CTL_MOD:
2230                 if (epi) {
2231                         if (!(epi->event.events & EPOLLEXCLUSIVE)) {
2232                                 epds.events |= EPOLLERR | EPOLLHUP;
2233                                 error = ep_modify(ep, epi, &epds);
2234                         }
2235                 } else
2236                         error = -ENOENT;
2237                 break;
2238         }
2239         if (tep != NULL)
2240                 mutex_unlock(&tep->mtx);
2241         mutex_unlock(&ep->mtx);
2242 
2243 error_tgt_fput:
2244         if (full_check)
2245                 mutex_unlock(&epmutex);
2246 
2247         fdput(tf);
2248 error_fput:
2249         fdput(f);
2250 error_return:
2251 
2252         return error;
2253 }
2254 
2255 /*
2256  * Implement the event wait interface for the eventpoll file. It is the kernel
2257  * part of the user space epoll_wait(2).
2258  */
2259 static int do_epoll_wait(int epfd, struct epoll_event __user *events,
2260                          int maxevents, int timeout)
2261 {
2262         int error;
2263         struct fd f;
2264         struct eventpoll *ep;
2265 
2266         /* The maximum number of event must be greater than zero */
2267         if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
2268                 return -EINVAL;
2269 
2270         /* Verify that the area passed by the user is writeable */
2271         if (!access_ok(events, maxevents * sizeof(struct epoll_event)))
2272                 return -EFAULT;
2273 
2274         /* Get the "struct file *" for the eventpoll file */
2275         f = fdget(epfd);
2276         if (!f.file)
2277                 return -EBADF;
2278 
2279         /*
2280          * We have to check that the file structure underneath the fd
2281          * the user passed to us _is_ an eventpoll file.
2282          */
2283         error = -EINVAL;
2284         if (!is_file_epoll(f.file))
2285                 goto error_fput;
2286 
2287         /*
2288          * At this point it is safe to assume that the "private_data" contains
2289          * our own data structure.
2290          */
2291         ep = f.file->private_data;
2292 
2293         /* Time to fish for events ... */
2294         error = ep_poll(ep, events, maxevents, timeout);
2295 
2296 error_fput:
2297         fdput(f);
2298         return error;
2299 }
2300 
2301 SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
2302                 int, maxevents, int, timeout)
2303 {
2304         return do_epoll_wait(epfd, events, maxevents, timeout);
2305 }
2306 
2307 /*
2308  * Implement the event wait interface for the eventpoll file. It is the kernel
2309  * part of the user space epoll_pwait(2).
2310  */
2311 SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
2312                 int, maxevents, int, timeout, const sigset_t __user *, sigmask,
2313                 size_t, sigsetsize)
2314 {
2315         int error;
2316 
2317         /*
2318          * If the caller wants a certain signal mask to be set during the wait,
2319          * we apply it here.
2320          */
2321         error = set_user_sigmask(sigmask, sigsetsize);
2322         if (error)
2323                 return error;
2324 
2325         error = do_epoll_wait(epfd, events, maxevents, timeout);
2326         restore_saved_sigmask_unless(error == -EINTR);
2327 
2328         return error;
2329 }
2330 
2331 #ifdef CONFIG_COMPAT
2332 COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
2333                         struct epoll_event __user *, events,
2334                         int, maxevents, int, timeout,
2335                         const compat_sigset_t __user *, sigmask,
2336                         compat_size_t, sigsetsize)
2337 {
2338         long err;
2339 
2340         /*
2341          * If the caller wants a certain signal mask to be set during the wait,
2342          * we apply it here.
2343          */
2344         err = set_compat_user_sigmask(sigmask, sigsetsize);
2345         if (err)
2346                 return err;
2347 
2348         err = do_epoll_wait(epfd, events, maxevents, timeout);
2349         restore_saved_sigmask_unless(err == -EINTR);
2350 
2351         return err;
2352 }
2353 #endif
2354 
2355 static int __init eventpoll_init(void)
2356 {
2357         struct sysinfo si;
2358 
2359         si_meminfo(&si);
2360         /*
2361          * Allows top 4% of lomem to be allocated for epoll watches (per user).
2362          */
2363         max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2364                 EP_ITEM_COST;
2365         BUG_ON(max_user_watches < 0);
2366 
2367         /*
2368          * Initialize the structure used to perform epoll file descriptor
2369          * inclusion loops checks.
2370          */
2371         ep_nested_calls_init(&poll_loop_ncalls);
2372 
2373 #ifdef CONFIG_DEBUG_LOCK_ALLOC
2374         /* Initialize the structure used to perform safe poll wait head wake ups */
2375         ep_nested_calls_init(&poll_safewake_ncalls);
2376 #endif
2377 
2378         /*
2379          * We can have many thousands of epitems, so prevent this from
2380          * using an extra cache line on 64-bit (and smaller) CPUs
2381          */
2382         BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
2383 
2384         /* Allocates slab cache used to allocate "struct epitem" items */
2385         epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
2386                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
2387 
2388         /* Allocates slab cache used to allocate "struct eppoll_entry" */
2389         pwq_cache = kmem_cache_create("eventpoll_pwq",
2390                 sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
2391 
2392         return 0;
2393 }
2394 fs_initcall(eventpoll_init);
2395 

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