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 struct list_head visited_list_link; 222 int visited; 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 #ifdef CONFIG_DEBUG_LOCK_ALLOC 230 /* tracks wakeup nests for lockdep validation */ 231 u8 nests; 232 #endif 233 }; 234 235 /* Wait structure used by the poll hooks */ 236 struct eppoll_entry { 237 /* List header used to link this structure to the "struct epitem" */ 238 struct list_head llink; 239 240 /* The "base" pointer is set to the container "struct epitem" */ 241 struct epitem *base; 242 243 /* 244 * Wait queue item that will be linked to the target file wait 245 * queue head. 246 */ 247 wait_queue_entry_t wait; 248 249 /* The wait queue head that linked the "wait" wait queue item */ 250 wait_queue_head_t *whead; 251 }; 252 253 /* Wrapper struct used by poll queueing */ 254 struct ep_pqueue { 255 poll_table pt; 256 struct epitem *epi; 257 }; 258 259 /* Used by the ep_send_events() function as callback private data */ 260 struct ep_send_events_data { 261 int maxevents; 262 struct epoll_event __user *events; 263 int res; 264 }; 265 266 /* 267 * Configuration options available inside /proc/sys/fs/epoll/ 268 */ 269 /* Maximum number of epoll watched descriptors, per user */ 270 static long max_user_watches __read_mostly; 271 272 /* 273 * This mutex is used to serialize ep_free() and eventpoll_release_file(). 274 */ 275 static DEFINE_MUTEX(epmutex); 276 277 /* Used to check for epoll file descriptor inclusion loops */ 278 static struct nested_calls poll_loop_ncalls; 279 280 /* Slab cache used to allocate "struct epitem" */ 281 static struct kmem_cache *epi_cache __read_mostly; 282 283 /* Slab cache used to allocate "struct eppoll_entry" */ 284 static struct kmem_cache *pwq_cache __read_mostly; 285 286 /* Visited nodes during ep_loop_check(), so we can unset them when we finish */ 287 static LIST_HEAD(visited_list); 288 289 /* 290 * List of files with newly added links, where we may need to limit the number 291 * of emanating paths. Protected by the epmutex. 292 */ 293 static LIST_HEAD(tfile_check_list); 294 295 #ifdef CONFIG_SYSCTL 296 297 #include <linux/sysctl.h> 298 299 static long long_zero; 300 static long long_max = LONG_MAX; 301 302 struct ctl_table epoll_table[] = { 303 { 304 .procname = "max_user_watches", 305 .data = &max_user_watches, 306 .maxlen = sizeof(max_user_watches), 307 .mode = 0644, 308 .proc_handler = proc_doulongvec_minmax, 309 .extra1 = &long_zero, 310 .extra2 = &long_max, 311 }, 312 { } 313 }; 314 #endif /* CONFIG_SYSCTL */ 315 316 static const struct file_operations eventpoll_fops; 317 318 static inline int is_file_epoll(struct file *f) 319 { 320 return f->f_op == &eventpoll_fops; 321 } 322 323 /* Setup the structure that is used as key for the RB tree */ 324 static inline void ep_set_ffd(struct epoll_filefd *ffd, 325 struct file *file, int fd) 326 { 327 ffd->file = file; 328 ffd->fd = fd; 329 } 330 331 /* Compare RB tree keys */ 332 static inline int ep_cmp_ffd(struct epoll_filefd *p1, 333 struct epoll_filefd *p2) 334 { 335 return (p1->file > p2->file ? +1: 336 (p1->file < p2->file ? -1 : p1->fd - p2->fd)); 337 } 338 339 /* Tells us if the item is currently linked */ 340 static inline int ep_is_linked(struct epitem *epi) 341 { 342 return !list_empty(&epi->rdllink); 343 } 344 345 static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p) 346 { 347 return container_of(p, struct eppoll_entry, wait); 348 } 349 350 /* Get the "struct epitem" from a wait queue pointer */ 351 static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p) 352 { 353 return container_of(p, struct eppoll_entry, wait)->base; 354 } 355 356 /* Get the "struct epitem" from an epoll queue wrapper */ 357 static inline struct epitem *ep_item_from_epqueue(poll_table *p) 358 { 359 return container_of(p, struct ep_pqueue, pt)->epi; 360 } 361 362 /* Initialize the poll safe wake up structure */ 363 static void ep_nested_calls_init(struct nested_calls *ncalls) 364 { 365 INIT_LIST_HEAD(&ncalls->tasks_call_list); 366 spin_lock_init(&ncalls->lock); 367 } 368 369 /** 370 * ep_events_available - Checks if ready events might be available. 371 * 372 * @ep: Pointer to the eventpoll context. 373 * 374 * Returns: Returns a value different than zero if ready events are available, 375 * or zero otherwise. 376 */ 377 static inline int ep_events_available(struct eventpoll *ep) 378 { 379 return !list_empty_careful(&ep->rdllist) || 380 READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR; 381 } 382 383 #ifdef CONFIG_NET_RX_BUSY_POLL 384 static bool ep_busy_loop_end(void *p, unsigned long start_time) 385 { 386 struct eventpoll *ep = p; 387 388 return ep_events_available(ep) || busy_loop_timeout(start_time); 389 } 390 391 /* 392 * Busy poll if globally on and supporting sockets found && no events, 393 * busy loop will return if need_resched or ep_events_available. 394 * 395 * we must do our busy polling with irqs enabled 396 */ 397 static void ep_busy_loop(struct eventpoll *ep, int nonblock) 398 { 399 unsigned int napi_id = READ_ONCE(ep->napi_id); 400 401 if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on()) 402 napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep); 403 } 404 405 static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep) 406 { 407 if (ep->napi_id) 408 ep->napi_id = 0; 409 } 410 411 /* 412 * Set epoll busy poll NAPI ID from sk. 413 */ 414 static inline void ep_set_busy_poll_napi_id(struct epitem *epi) 415 { 416 struct eventpoll *ep; 417 unsigned int napi_id; 418 struct socket *sock; 419 struct sock *sk; 420 int err; 421 422 if (!net_busy_loop_on()) 423 return; 424 425 sock = sock_from_file(epi->ffd.file, &err); 426 if (!sock) 427 return; 428 429 sk = sock->sk; 430 if (!sk) 431 return; 432 433 napi_id = READ_ONCE(sk->sk_napi_id); 434 ep = epi->ep; 435 436 /* Non-NAPI IDs can be rejected 437 * or 438 * Nothing to do if we already have this ID 439 */ 440 if (napi_id < MIN_NAPI_ID || napi_id == ep->napi_id) 441 return; 442 443 /* record NAPI ID for use in next busy poll */ 444 ep->napi_id = napi_id; 445 } 446 447 #else 448 449 static inline void ep_busy_loop(struct eventpoll *ep, int nonblock) 450 { 451 } 452 453 static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep) 454 { 455 } 456 457 static inline void ep_set_busy_poll_napi_id(struct epitem *epi) 458 { 459 } 460 461 #endif /* CONFIG_NET_RX_BUSY_POLL */ 462 463 /** 464 * ep_call_nested - Perform a bound (possibly) nested call, by checking 465 * that the recursion limit is not exceeded, and that 466 * the same nested call (by the meaning of same cookie) is 467 * no re-entered. 468 * 469 * @ncalls: Pointer to the nested_calls structure to be used for this call. 470 * @nproc: Nested call core function pointer. 471 * @priv: Opaque data to be passed to the @nproc callback. 472 * @cookie: Cookie to be used to identify this nested call. 473 * @ctx: This instance context. 474 * 475 * Returns: Returns the code returned by the @nproc callback, or -1 if 476 * the maximum recursion limit has been exceeded. 477 */ 478 static int ep_call_nested(struct nested_calls *ncalls, 479 int (*nproc)(void *, void *, int), void *priv, 480 void *cookie, void *ctx) 481 { 482 int error, call_nests = 0; 483 unsigned long flags; 484 struct list_head *lsthead = &ncalls->tasks_call_list; 485 struct nested_call_node *tncur; 486 struct nested_call_node tnode; 487 488 spin_lock_irqsave(&ncalls->lock, flags); 489 490 /* 491 * Try to see if the current task is already inside this wakeup call. 492 * We use a list here, since the population inside this set is always 493 * very much limited. 494 */ 495 list_for_each_entry(tncur, lsthead, llink) { 496 if (tncur->ctx == ctx && 497 (tncur->cookie == cookie || ++call_nests > EP_MAX_NESTS)) { 498 /* 499 * Ops ... loop detected or maximum nest level reached. 500 * We abort this wake by breaking the cycle itself. 501 */ 502 error = -1; 503 goto out_unlock; 504 } 505 } 506 507 /* Add the current task and cookie to the list */ 508 tnode.ctx = ctx; 509 tnode.cookie = cookie; 510 list_add(&tnode.llink, lsthead); 511 512 spin_unlock_irqrestore(&ncalls->lock, flags); 513 514 /* Call the nested function */ 515 error = (*nproc)(priv, cookie, call_nests); 516 517 /* Remove the current task from the list */ 518 spin_lock_irqsave(&ncalls->lock, flags); 519 list_del(&tnode.llink); 520 out_unlock: 521 spin_unlock_irqrestore(&ncalls->lock, flags); 522 523 return error; 524 } 525 526 /* 527 * As described in commit 0ccf831cb lockdep: annotate epoll 528 * the use of wait queues used by epoll is done in a very controlled 529 * manner. Wake ups can nest inside each other, but are never done 530 * with the same locking. For example: 531 * 532 * dfd = socket(...); 533 * efd1 = epoll_create(); 534 * efd2 = epoll_create(); 535 * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...); 536 * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); 537 * 538 * When a packet arrives to the device underneath "dfd", the net code will 539 * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a 540 * callback wakeup entry on that queue, and the wake_up() performed by the 541 * "dfd" net code will end up in ep_poll_callback(). At this point epoll 542 * (efd1) notices that it may have some event ready, so it needs to wake up 543 * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake() 544 * that ends up in another wake_up(), after having checked about the 545 * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to 546 * avoid stack blasting. 547 * 548 * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle 549 * this special case of epoll. 550 */ 551 #ifdef CONFIG_DEBUG_LOCK_ALLOC 552 553 static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi) 554 { 555 struct eventpoll *ep_src; 556 unsigned long flags; 557 u8 nests = 0; 558 559 /* 560 * To set the subclass or nesting level for spin_lock_irqsave_nested() 561 * it might be natural to create a per-cpu nest count. However, since 562 * we can recurse on ep->poll_wait.lock, and a non-raw spinlock can 563 * schedule() in the -rt kernel, the per-cpu variable are no longer 564 * protected. Thus, we are introducing a per eventpoll nest field. 565 * If we are not being call from ep_poll_callback(), epi is NULL and 566 * we are at the first level of nesting, 0. Otherwise, we are being 567 * called from ep_poll_callback() and if a previous wakeup source is 568 * not an epoll file itself, we are at depth 1 since the wakeup source 569 * is depth 0. If the wakeup source is a previous epoll file in the 570 * wakeup chain then we use its nests value and record ours as 571 * nests + 1. The previous epoll file nests value is stable since its 572 * already holding its own poll_wait.lock. 573 */ 574 if (epi) { 575 if ((is_file_epoll(epi->ffd.file))) { 576 ep_src = epi->ffd.file->private_data; 577 nests = ep_src->nests; 578 } else { 579 nests = 1; 580 } 581 } 582 spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests); 583 ep->nests = nests + 1; 584 wake_up_locked_poll(&ep->poll_wait, EPOLLIN); 585 ep->nests = 0; 586 spin_unlock_irqrestore(&ep->poll_wait.lock, flags); 587 } 588 589 #else 590 591 static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi) 592 { 593 wake_up_poll(&ep->poll_wait, EPOLLIN); 594 } 595 596 #endif 597 598 static void ep_remove_wait_queue(struct eppoll_entry *pwq) 599 { 600 wait_queue_head_t *whead; 601 602 rcu_read_lock(); 603 /* 604 * If it is cleared by POLLFREE, it should be rcu-safe. 605 * If we read NULL we need a barrier paired with 606 * smp_store_release() in ep_poll_callback(), otherwise 607 * we rely on whead->lock. 608 */ 609 whead = smp_load_acquire(&pwq->whead); 610 if (whead) 611 remove_wait_queue(whead, &pwq->wait); 612 rcu_read_unlock(); 613 } 614 615 /* 616 * This function unregisters poll callbacks from the associated file 617 * descriptor. Must be called with "mtx" held (or "epmutex" if called from 618 * ep_free). 619 */ 620 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) 621 { 622 struct list_head *lsthead = &epi->pwqlist; 623 struct eppoll_entry *pwq; 624 625 while (!list_empty(lsthead)) { 626 pwq = list_first_entry(lsthead, struct eppoll_entry, llink); 627 628 list_del(&pwq->llink); 629 ep_remove_wait_queue(pwq); 630 kmem_cache_free(pwq_cache, pwq); 631 } 632 } 633 634 /* call only when ep->mtx is held */ 635 static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi) 636 { 637 return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx)); 638 } 639 640 /* call only when ep->mtx is held */ 641 static inline void ep_pm_stay_awake(struct epitem *epi) 642 { 643 struct wakeup_source *ws = ep_wakeup_source(epi); 644 645 if (ws) 646 __pm_stay_awake(ws); 647 } 648 649 static inline bool ep_has_wakeup_source(struct epitem *epi) 650 { 651 return rcu_access_pointer(epi->ws) ? true : false; 652 } 653 654 /* call when ep->mtx cannot be held (ep_poll_callback) */ 655 static inline void ep_pm_stay_awake_rcu(struct epitem *epi) 656 { 657 struct wakeup_source *ws; 658 659 rcu_read_lock(); 660 ws = rcu_dereference(epi->ws); 661 if (ws) 662 __pm_stay_awake(ws); 663 rcu_read_unlock(); 664 } 665 666 /** 667 * ep_scan_ready_list - Scans the ready list in a way that makes possible for 668 * the scan code, to call f_op->poll(). Also allows for 669 * O(NumReady) performance. 670 * 671 * @ep: Pointer to the epoll private data structure. 672 * @sproc: Pointer to the scan callback. 673 * @priv: Private opaque data passed to the @sproc callback. 674 * @depth: The current depth of recursive f_op->poll calls. 675 * @ep_locked: caller already holds ep->mtx 676 * 677 * Returns: The same integer error code returned by the @sproc callback. 678 */ 679 static __poll_t ep_scan_ready_list(struct eventpoll *ep, 680 __poll_t (*sproc)(struct eventpoll *, 681 struct list_head *, void *), 682 void *priv, int depth, bool ep_locked) 683 { 684 __poll_t res; 685 struct epitem *epi, *nepi; 686 LIST_HEAD(txlist); 687 688 lockdep_assert_irqs_enabled(); 689 690 /* 691 * We need to lock this because we could be hit by 692 * eventpoll_release_file() and epoll_ctl(). 693 */ 694 695 if (!ep_locked) 696 mutex_lock_nested(&ep->mtx, depth); 697 698 /* 699 * Steal the ready list, and re-init the original one to the 700 * empty list. Also, set ep->ovflist to NULL so that events 701 * happening while looping w/out locks, are not lost. We cannot 702 * have the poll callback to queue directly on ep->rdllist, 703 * because we want the "sproc" callback to be able to do it 704 * in a lockless way. 705 */ 706 write_lock_irq(&ep->lock); 707 list_splice_init(&ep->rdllist, &txlist); 708 WRITE_ONCE(ep->ovflist, NULL); 709 write_unlock_irq(&ep->lock); 710 711 /* 712 * Now call the callback function. 713 */ 714 res = (*sproc)(ep, &txlist, priv); 715 716 write_lock_irq(&ep->lock); 717 /* 718 * During the time we spent inside the "sproc" callback, some 719 * other events might have been queued by the poll callback. 720 * We re-insert them inside the main ready-list here. 721 */ 722 for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL; 723 nepi = epi->next, epi->next = EP_UNACTIVE_PTR) { 724 /* 725 * We need to check if the item is already in the list. 726 * During the "sproc" callback execution time, items are 727 * queued into ->ovflist but the "txlist" might already 728 * contain them, and the list_splice() below takes care of them. 729 */ 730 if (!ep_is_linked(epi)) { 731 /* 732 * ->ovflist is LIFO, so we have to reverse it in order 733 * to keep in FIFO. 734 */ 735 list_add(&epi->rdllink, &ep->rdllist); 736 ep_pm_stay_awake(epi); 737 } 738 } 739 /* 740 * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after 741 * releasing the lock, events will be queued in the normal way inside 742 * ep->rdllist. 743 */ 744 WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR); 745 746 /* 747 * Quickly re-inject items left on "txlist". 748 */ 749 list_splice(&txlist, &ep->rdllist); 750 __pm_relax(ep->ws); 751 write_unlock_irq(&ep->lock); 752 753 if (!ep_locked) 754 mutex_unlock(&ep->mtx); 755 756 return res; 757 } 758 759 static void epi_rcu_free(struct rcu_head *head) 760 { 761 struct epitem *epi = container_of(head, struct epitem, rcu); 762 kmem_cache_free(epi_cache, epi); 763 } 764 765 /* 766 * Removes a "struct epitem" from the eventpoll RB tree and deallocates 767 * all the associated resources. Must be called with "mtx" held. 768 */ 769 static int ep_remove(struct eventpoll *ep, struct epitem *epi) 770 { 771 struct file *file = epi->ffd.file; 772 773 lockdep_assert_irqs_enabled(); 774 775 /* 776 * Removes poll wait queue hooks. 777 */ 778 ep_unregister_pollwait(ep, epi); 779 780 /* Remove the current item from the list of epoll hooks */ 781 spin_lock(&file->f_lock); 782 list_del_rcu(&epi->fllink); 783 spin_unlock(&file->f_lock); 784 785 rb_erase_cached(&epi->rbn, &ep->rbr); 786 787 write_lock_irq(&ep->lock); 788 if (ep_is_linked(epi)) 789 list_del_init(&epi->rdllink); 790 write_unlock_irq(&ep->lock); 791 792 wakeup_source_unregister(ep_wakeup_source(epi)); 793 /* 794 * At this point it is safe to free the eventpoll item. Use the union 795 * field epi->rcu, since we are trying to minimize the size of 796 * 'struct epitem'. The 'rbn' field is no longer in use. Protected by 797 * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make 798 * use of the rbn field. 799 */ 800 call_rcu(&epi->rcu, epi_rcu_free); 801 802 atomic_long_dec(&ep->user->epoll_watches); 803 804 return 0; 805 } 806 807 static void ep_free(struct eventpoll *ep) 808 { 809 struct rb_node *rbp; 810 struct epitem *epi; 811 812 /* We need to release all tasks waiting for these file */ 813 if (waitqueue_active(&ep->poll_wait)) 814 ep_poll_safewake(ep, NULL); 815 816 /* 817 * We need to lock this because we could be hit by 818 * eventpoll_release_file() while we're freeing the "struct eventpoll". 819 * We do not need to hold "ep->mtx" here because the epoll file 820 * is on the way to be removed and no one has references to it 821 * anymore. The only hit might come from eventpoll_release_file() but 822 * holding "epmutex" is sufficient here. 823 */ 824 mutex_lock(&epmutex); 825 826 /* 827 * Walks through the whole tree by unregistering poll callbacks. 828 */ 829 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { 830 epi = rb_entry(rbp, struct epitem, rbn); 831 832 ep_unregister_pollwait(ep, epi); 833 cond_resched(); 834 } 835 836 /* 837 * Walks through the whole tree by freeing each "struct epitem". At this 838 * point we are sure no poll callbacks will be lingering around, and also by 839 * holding "epmutex" we can be sure that no file cleanup code will hit 840 * us during this operation. So we can avoid the lock on "ep->lock". 841 * We do not need to lock ep->mtx, either, we only do it to prevent 842 * a lockdep warning. 843 */ 844 mutex_lock(&ep->mtx); 845 while ((rbp = rb_first_cached(&ep->rbr)) != NULL) { 846 epi = rb_entry(rbp, struct epitem, rbn); 847 ep_remove(ep, epi); 848 cond_resched(); 849 } 850 mutex_unlock(&ep->mtx); 851 852 mutex_unlock(&epmutex); 853 mutex_destroy(&ep->mtx); 854 free_uid(ep->user); 855 wakeup_source_unregister(ep->ws); 856 kfree(ep); 857 } 858 859 static int ep_eventpoll_release(struct inode *inode, struct file *file) 860 { 861 struct eventpoll *ep = file->private_data; 862 863 if (ep) 864 ep_free(ep); 865 866 return 0; 867 } 868 869 static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head, 870 void *priv); 871 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, 872 poll_table *pt); 873 874 /* 875 * Differs from ep_eventpoll_poll() in that internal callers already have 876 * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested() 877 * is correctly annotated. 878 */ 879 static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, 880 int depth) 881 { 882 struct eventpoll *ep; 883 bool locked; 884 885 pt->_key = epi->event.events; 886 if (!is_file_epoll(epi->ffd.file)) 887 return vfs_poll(epi->ffd.file, pt) & epi->event.events; 888 889 ep = epi->ffd.file->private_data; 890 poll_wait(epi->ffd.file, &ep->poll_wait, pt); 891 locked = pt && (pt->_qproc == ep_ptable_queue_proc); 892 893 return ep_scan_ready_list(epi->ffd.file->private_data, 894 ep_read_events_proc, &depth, depth, 895 locked) & epi->event.events; 896 } 897 898 static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head, 899 void *priv) 900 { 901 struct epitem *epi, *tmp; 902 poll_table pt; 903 int depth = *(int *)priv; 904 905 init_poll_funcptr(&pt, NULL); 906 depth++; 907 908 list_for_each_entry_safe(epi, tmp, head, rdllink) { 909 if (ep_item_poll(epi, &pt, depth)) { 910 return EPOLLIN | EPOLLRDNORM; 911 } else { 912 /* 913 * Item has been dropped into the ready list by the poll 914 * callback, but it's not actually ready, as far as 915 * caller requested events goes. We can remove it here. 916 */ 917 __pm_relax(ep_wakeup_source(epi)); 918 list_del_init(&epi->rdllink); 919 } 920 } 921 922 return 0; 923 } 924 925 static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait) 926 { 927 struct eventpoll *ep = file->private_data; 928 int depth = 0; 929 930 /* Insert inside our poll wait queue */ 931 poll_wait(file, &ep->poll_wait, wait); 932 933 /* 934 * Proceed to find out if wanted events are really available inside 935 * the ready list. 936 */ 937 return ep_scan_ready_list(ep, ep_read_events_proc, 938 &depth, depth, false); 939 } 940 941 #ifdef CONFIG_PROC_FS 942 static void ep_show_fdinfo(struct seq_file *m, struct file *f) 943 { 944 struct eventpoll *ep = f->private_data; 945 struct rb_node *rbp; 946 947 mutex_lock(&ep->mtx); 948 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { 949 struct epitem *epi = rb_entry(rbp, struct epitem, rbn); 950 struct inode *inode = file_inode(epi->ffd.file); 951 952 seq_printf(m, "tfd: %8d events: %8x data: %16llx " 953 " pos:%lli ino:%lx sdev:%x\n", 954 epi->ffd.fd, epi->event.events, 955 (long long)epi->event.data, 956 (long long)epi->ffd.file->f_pos, 957 inode->i_ino, inode->i_sb->s_dev); 958 if (seq_has_overflowed(m)) 959 break; 960 } 961 mutex_unlock(&ep->mtx); 962 } 963 #endif 964 965 /* File callbacks that implement the eventpoll file behaviour */ 966 static const struct file_operations eventpoll_fops = { 967 #ifdef CONFIG_PROC_FS 968 .show_fdinfo = ep_show_fdinfo, 969 #endif 970 .release = ep_eventpoll_release, 971 .poll = ep_eventpoll_poll, 972 .llseek = noop_llseek, 973 }; 974 975 /* 976 * This is called from eventpoll_release() to unlink files from the eventpoll 977 * interface. We need to have this facility to cleanup correctly files that are 978 * closed without being removed from the eventpoll interface. 979 */ 980 void eventpoll_release_file(struct file *file) 981 { 982 struct eventpoll *ep; 983 struct epitem *epi, *next; 984 985 /* 986 * We don't want to get "file->f_lock" because it is not 987 * necessary. It is not necessary because we're in the "struct file" 988 * cleanup path, and this means that no one is using this file anymore. 989 * So, for example, epoll_ctl() cannot hit here since if we reach this 990 * point, the file counter already went to zero and fget() would fail. 991 * The only hit might come from ep_free() but by holding the mutex 992 * will correctly serialize the operation. We do need to acquire 993 * "ep->mtx" after "epmutex" because ep_remove() requires it when called 994 * from anywhere but ep_free(). 995 * 996 * Besides, ep_remove() acquires the lock, so we can't hold it here. 997 */ 998 mutex_lock(&epmutex); 999 list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) { 1000 ep = epi->ep; 1001 mutex_lock_nested(&ep->mtx, 0); 1002 ep_remove(ep, epi); 1003 mutex_unlock(&ep->mtx); 1004 } 1005 mutex_unlock(&epmutex); 1006 } 1007 1008 static int ep_alloc(struct eventpoll **pep) 1009 { 1010 int error; 1011 struct user_struct *user; 1012 struct eventpoll *ep; 1013 1014 user = get_current_user(); 1015 error = -ENOMEM; 1016 ep = kzalloc(sizeof(*ep), GFP_KERNEL); 1017 if (unlikely(!ep)) 1018 goto free_uid; 1019 1020 mutex_init(&ep->mtx); 1021 rwlock_init(&ep->lock); 1022 init_waitqueue_head(&ep->wq); 1023 init_waitqueue_head(&ep->poll_wait); 1024 INIT_LIST_HEAD(&ep->rdllist); 1025 ep->rbr = RB_ROOT_CACHED; 1026 ep->ovflist = EP_UNACTIVE_PTR; 1027 ep->user = user; 1028 1029 *pep = ep; 1030 1031 return 0; 1032 1033 free_uid: 1034 free_uid(user); 1035 return error; 1036 } 1037 1038 /* 1039 * Search the file inside the eventpoll tree. The RB tree operations 1040 * are protected by the "mtx" mutex, and ep_find() must be called with 1041 * "mtx" held. 1042 */ 1043 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) 1044 { 1045 int kcmp; 1046 struct rb_node *rbp; 1047 struct epitem *epi, *epir = NULL; 1048 struct epoll_filefd ffd; 1049 1050 ep_set_ffd(&ffd, file, fd); 1051 for (rbp = ep->rbr.rb_root.rb_node; rbp; ) { 1052 epi = rb_entry(rbp, struct epitem, rbn); 1053 kcmp = ep_cmp_ffd(&ffd, &epi->ffd); 1054 if (kcmp > 0) 1055 rbp = rbp->rb_right; 1056 else if (kcmp < 0) 1057 rbp = rbp->rb_left; 1058 else { 1059 epir = epi; 1060 break; 1061 } 1062 } 1063 1064 return epir; 1065 } 1066 1067 #ifdef CONFIG_CHECKPOINT_RESTORE 1068 static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff) 1069 { 1070 struct rb_node *rbp; 1071 struct epitem *epi; 1072 1073 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { 1074 epi = rb_entry(rbp, struct epitem, rbn); 1075 if (epi->ffd.fd == tfd) { 1076 if (toff == 0) 1077 return epi; 1078 else 1079 toff--; 1080 } 1081 cond_resched(); 1082 } 1083 1084 return NULL; 1085 } 1086 1087 struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, 1088 unsigned long toff) 1089 { 1090 struct file *file_raw; 1091 struct eventpoll *ep; 1092 struct epitem *epi; 1093 1094 if (!is_file_epoll(file)) 1095 return ERR_PTR(-EINVAL); 1096 1097 ep = file->private_data; 1098 1099 mutex_lock(&ep->mtx); 1100 epi = ep_find_tfd(ep, tfd, toff); 1101 if (epi) 1102 file_raw = epi->ffd.file; 1103 else 1104 file_raw = ERR_PTR(-ENOENT); 1105 mutex_unlock(&ep->mtx); 1106 1107 return file_raw; 1108 } 1109 #endif /* CONFIG_CHECKPOINT_RESTORE */ 1110 1111 /** 1112 * Adds a new entry to the tail of the list in a lockless way, i.e. 1113 * multiple CPUs are allowed to call this function concurrently. 1114 * 1115 * Beware: it is necessary to prevent any other modifications of the 1116 * existing list until all changes are completed, in other words 1117 * concurrent list_add_tail_lockless() calls should be protected 1118 * with a read lock, where write lock acts as a barrier which 1119 * makes sure all list_add_tail_lockless() calls are fully 1120 * completed. 1121 * 1122 * Also an element can be locklessly added to the list only in one 1123 * direction i.e. either to the tail either to the head, otherwise 1124 * concurrent access will corrupt the list. 1125 * 1126 * Returns %false if element has been already added to the list, %true 1127 * otherwise. 1128 */ 1129 static inline bool list_add_tail_lockless(struct list_head *new, 1130 struct list_head *head) 1131 { 1132 struct list_head *prev; 1133 1134 /* 1135 * This is simple 'new->next = head' operation, but cmpxchg() 1136 * is used in order to detect that same element has been just 1137 * added to the list from another CPU: the winner observes 1138 * new->next == new. 1139 */ 1140 if (cmpxchg(&new->next, new, head) != new) 1141 return false; 1142 1143 /* 1144 * Initially ->next of a new element must be updated with the head 1145 * (we are inserting to the tail) and only then pointers are atomically 1146 * exchanged. XCHG guarantees memory ordering, thus ->next should be 1147 * updated before pointers are actually swapped and pointers are 1148 * swapped before prev->next is updated. 1149 */ 1150 1151 prev = xchg(&head->prev, new); 1152 1153 /* 1154 * It is safe to modify prev->next and new->prev, because a new element 1155 * is added only to the tail and new->next is updated before XCHG. 1156 */ 1157 1158 prev->next = new; 1159 new->prev = prev; 1160 1161 return true; 1162 } 1163 1164 /** 1165 * Chains a new epi entry to the tail of the ep->ovflist in a lockless way, 1166 * i.e. multiple CPUs are allowed to call this function concurrently. 1167 * 1168 * Returns %false if epi element has been already chained, %true otherwise. 1169 */ 1170 static inline bool chain_epi_lockless(struct epitem *epi) 1171 { 1172 struct eventpoll *ep = epi->ep; 1173 1174 /* Fast preliminary check */ 1175 if (epi->next != EP_UNACTIVE_PTR) 1176 return false; 1177 1178 /* Check that the same epi has not been just chained from another CPU */ 1179 if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR) 1180 return false; 1181 1182 /* Atomically exchange tail */ 1183 epi->next = xchg(&ep->ovflist, epi); 1184 1185 return true; 1186 } 1187 1188 /* 1189 * This is the callback that is passed to the wait queue wakeup 1190 * mechanism. It is called by the stored file descriptors when they 1191 * have events to report. 1192 * 1193 * This callback takes a read lock in order not to content with concurrent 1194 * events from another file descriptors, thus all modifications to ->rdllist 1195 * or ->ovflist are lockless. Read lock is paired with the write lock from 1196 * ep_scan_ready_list(), which stops all list modifications and guarantees 1197 * that lists state is seen correctly. 1198 * 1199 * Another thing worth to mention is that ep_poll_callback() can be called 1200 * concurrently for the same @epi from different CPUs if poll table was inited 1201 * with several wait queues entries. Plural wakeup from different CPUs of a 1202 * single wait queue is serialized by wq.lock, but the case when multiple wait 1203 * queues are used should be detected accordingly. This is detected using 1204 * cmpxchg() operation. 1205 */ 1206 static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key) 1207 { 1208 int pwake = 0; 1209 struct epitem *epi = ep_item_from_wait(wait); 1210 struct eventpoll *ep = epi->ep; 1211 __poll_t pollflags = key_to_poll(key); 1212 unsigned long flags; 1213 int ewake = 0; 1214 1215 read_lock_irqsave(&ep->lock, flags); 1216 1217 ep_set_busy_poll_napi_id(epi); 1218 1219 /* 1220 * If the event mask does not contain any poll(2) event, we consider the 1221 * descriptor to be disabled. This condition is likely the effect of the 1222 * EPOLLONESHOT bit that disables the descriptor when an event is received, 1223 * until the next EPOLL_CTL_MOD will be issued. 1224 */ 1225 if (!(epi->event.events & ~EP_PRIVATE_BITS)) 1226 goto out_unlock; 1227 1228 /* 1229 * Check the events coming with the callback. At this stage, not 1230 * every device reports the events in the "key" parameter of the 1231 * callback. We need to be able to handle both cases here, hence the 1232 * test for "key" != NULL before the event match test. 1233 */ 1234 if (pollflags && !(pollflags & epi->event.events)) 1235 goto out_unlock; 1236 1237 /* 1238 * If we are transferring events to userspace, we can hold no locks 1239 * (because we're accessing user memory, and because of linux f_op->poll() 1240 * semantics). All the events that happen during that period of time are 1241 * chained in ep->ovflist and requeued later on. 1242 */ 1243 if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) { 1244 if (chain_epi_lockless(epi)) 1245 ep_pm_stay_awake_rcu(epi); 1246 } else if (!ep_is_linked(epi)) { 1247 /* In the usual case, add event to ready list. */ 1248 if (list_add_tail_lockless(&epi->rdllink, &ep->rdllist)) 1249 ep_pm_stay_awake_rcu(epi); 1250 } 1251 1252 /* 1253 * Wake up ( if active ) both the eventpoll wait list and the ->poll() 1254 * wait list. 1255 */ 1256 if (waitqueue_active(&ep->wq)) { 1257 if ((epi->event.events & EPOLLEXCLUSIVE) && 1258 !(pollflags & POLLFREE)) { 1259 switch (pollflags & EPOLLINOUT_BITS) { 1260 case EPOLLIN: 1261 if (epi->event.events & EPOLLIN) 1262 ewake = 1; 1263 break; 1264 case EPOLLOUT: 1265 if (epi->event.events & EPOLLOUT) 1266 ewake = 1; 1267 break; 1268 case 0: 1269 ewake = 1; 1270 break; 1271 } 1272 } 1273 wake_up(&ep->wq); 1274 } 1275 if (waitqueue_active(&ep->poll_wait)) 1276 pwake++; 1277 1278 out_unlock: 1279 read_unlock_irqrestore(&ep->lock, flags); 1280 1281 /* We have to call this outside the lock */ 1282 if (pwake) 1283 ep_poll_safewake(ep, epi); 1284 1285 if (!(epi->event.events & EPOLLEXCLUSIVE)) 1286 ewake = 1; 1287 1288 if (pollflags & POLLFREE) { 1289 /* 1290 * If we race with ep_remove_wait_queue() it can miss 1291 * ->whead = NULL and do another remove_wait_queue() after 1292 * us, so we can't use __remove_wait_queue(). 1293 */ 1294 list_del_init(&wait->entry); 1295 /* 1296 * ->whead != NULL protects us from the race with ep_free() 1297 * or ep_remove(), ep_remove_wait_queue() takes whead->lock 1298 * held by the caller. Once we nullify it, nothing protects 1299 * ep/epi or even wait. 1300 */ 1301 smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL); 1302 } 1303 1304 return ewake; 1305 } 1306 1307 /* 1308 * This is the callback that is used to add our wait queue to the 1309 * target file wakeup lists. 1310 */ 1311 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, 1312 poll_table *pt) 1313 { 1314 struct epitem *epi = ep_item_from_epqueue(pt); 1315 struct eppoll_entry *pwq; 1316 1317 if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) { 1318 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); 1319 pwq->whead = whead; 1320 pwq->base = epi; 1321 if (epi->event.events & EPOLLEXCLUSIVE) 1322 add_wait_queue_exclusive(whead, &pwq->wait); 1323 else 1324 add_wait_queue(whead, &pwq->wait); 1325 list_add_tail(&pwq->llink, &epi->pwqlist); 1326 epi->nwait++; 1327 } else { 1328 /* We have to signal that an error occurred */ 1329 epi->nwait = -1; 1330 } 1331 } 1332 1333 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi) 1334 { 1335 int kcmp; 1336 struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL; 1337 struct epitem *epic; 1338 bool leftmost = true; 1339 1340 while (*p) { 1341 parent = *p; 1342 epic = rb_entry(parent, struct epitem, rbn); 1343 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd); 1344 if (kcmp > 0) { 1345 p = &parent->rb_right; 1346 leftmost = false; 1347 } else 1348 p = &parent->rb_left; 1349 } 1350 rb_link_node(&epi->rbn, parent, p); 1351 rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost); 1352 } 1353 1354 1355 1356 #define PATH_ARR_SIZE 5 1357 /* 1358 * These are the number paths of length 1 to 5, that we are allowing to emanate 1359 * from a single file of interest. For example, we allow 1000 paths of length 1360 * 1, to emanate from each file of interest. This essentially represents the 1361 * potential wakeup paths, which need to be limited in order to avoid massive 1362 * uncontrolled wakeup storms. The common use case should be a single ep which 1363 * is connected to n file sources. In this case each file source has 1 path 1364 * of length 1. Thus, the numbers below should be more than sufficient. These 1365 * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify 1366 * and delete can't add additional paths. Protected by the epmutex. 1367 */ 1368 static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 }; 1369 static int path_count[PATH_ARR_SIZE]; 1370 1371 static int path_count_inc(int nests) 1372 { 1373 /* Allow an arbitrary number of depth 1 paths */ 1374 if (nests == 0) 1375 return 0; 1376 1377 if (++path_count[nests] > path_limits[nests]) 1378 return -1; 1379 return 0; 1380 } 1381 1382 static void path_count_init(void) 1383 { 1384 int i; 1385 1386 for (i = 0; i < PATH_ARR_SIZE; i++) 1387 path_count[i] = 0; 1388 } 1389 1390 static int reverse_path_check_proc(void *priv, void *cookie, int call_nests) 1391 { 1392 int error = 0; 1393 struct file *file = priv; 1394 struct file *child_file; 1395 struct epitem *epi; 1396 1397 /* CTL_DEL can remove links here, but that can't increase our count */ 1398 rcu_read_lock(); 1399 list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) { 1400 child_file = epi->ep->file; 1401 if (is_file_epoll(child_file)) { 1402 if (list_empty(&child_file->f_ep_links)) { 1403 if (path_count_inc(call_nests)) { 1404 error = -1; 1405 break; 1406 } 1407 } else { 1408 error = ep_call_nested(&poll_loop_ncalls, 1409 reverse_path_check_proc, 1410 child_file, child_file, 1411 current); 1412 } 1413 if (error != 0) 1414 break; 1415 } else { 1416 printk(KERN_ERR "reverse_path_check_proc: " 1417 "file is not an ep!\n"); 1418 } 1419 } 1420 rcu_read_unlock(); 1421 return error; 1422 } 1423 1424 /** 1425 * reverse_path_check - The tfile_check_list is list of file *, which have 1426 * links that are proposed to be newly added. We need to 1427 * make sure that those added links don't add too many 1428 * paths such that we will spend all our time waking up 1429 * eventpoll objects. 1430 * 1431 * Returns: Returns zero if the proposed links don't create too many paths, 1432 * -1 otherwise. 1433 */ 1434 static int reverse_path_check(void) 1435 { 1436 int error = 0; 1437 struct file *current_file; 1438 1439 /* let's call this for all tfiles */ 1440 list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) { 1441 path_count_init(); 1442 error = ep_call_nested(&poll_loop_ncalls, 1443 reverse_path_check_proc, current_file, 1444 current_file, current); 1445 if (error) 1446 break; 1447 } 1448 return error; 1449 } 1450 1451 static int ep_create_wakeup_source(struct epitem *epi) 1452 { 1453 const char *name; 1454 struct wakeup_source *ws; 1455 1456 if (!epi->ep->ws) { 1457 epi->ep->ws = wakeup_source_register(NULL, "eventpoll"); 1458 if (!epi->ep->ws) 1459 return -ENOMEM; 1460 } 1461 1462 name = epi->ffd.file->f_path.dentry->d_name.name; 1463 ws = wakeup_source_register(NULL, name); 1464 1465 if (!ws) 1466 return -ENOMEM; 1467 rcu_assign_pointer(epi->ws, ws); 1468 1469 return 0; 1470 } 1471 1472 /* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */ 1473 static noinline void ep_destroy_wakeup_source(struct epitem *epi) 1474 { 1475 struct wakeup_source *ws = ep_wakeup_source(epi); 1476 1477 RCU_INIT_POINTER(epi->ws, NULL); 1478 1479 /* 1480 * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is 1481 * used internally by wakeup_source_remove, too (called by 1482 * wakeup_source_unregister), so we cannot use call_rcu 1483 */ 1484 synchronize_rcu(); 1485 wakeup_source_unregister(ws); 1486 } 1487 1488 /* 1489 * Must be called with "mtx" held. 1490 */ 1491 static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, 1492 struct file *tfile, int fd, int full_check) 1493 { 1494 int error, pwake = 0; 1495 __poll_t revents; 1496 long user_watches; 1497 struct epitem *epi; 1498 struct ep_pqueue epq; 1499 1500 lockdep_assert_irqs_enabled(); 1501 1502 user_watches = atomic_long_read(&ep->user->epoll_watches); 1503 if (unlikely(user_watches >= max_user_watches)) 1504 return -ENOSPC; 1505 if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL))) 1506 return -ENOMEM; 1507 1508 /* Item initialization follow here ... */ 1509 INIT_LIST_HEAD(&epi->rdllink); 1510 INIT_LIST_HEAD(&epi->fllink); 1511 INIT_LIST_HEAD(&epi->pwqlist); 1512 epi->ep = ep; 1513 ep_set_ffd(&epi->ffd, tfile, fd); 1514 epi->event = *event; 1515 epi->nwait = 0; 1516 epi->next = EP_UNACTIVE_PTR; 1517 if (epi->event.events & EPOLLWAKEUP) { 1518 error = ep_create_wakeup_source(epi); 1519 if (error) 1520 goto error_create_wakeup_source; 1521 } else { 1522 RCU_INIT_POINTER(epi->ws, NULL); 1523 } 1524 1525 /* Initialize the poll table using the queue callback */ 1526 epq.epi = epi; 1527 init_poll_funcptr(&epq.pt, ep_ptable_queue_proc); 1528 1529 /* 1530 * Attach the item to the poll hooks and get current event bits. 1531 * We can safely use the file* here because its usage count has 1532 * been increased by the caller of this function. Note that after 1533 * this operation completes, the poll callback can start hitting 1534 * the new item. 1535 */ 1536 revents = ep_item_poll(epi, &epq.pt, 1); 1537 1538 /* 1539 * We have to check if something went wrong during the poll wait queue 1540 * install process. Namely an allocation for a wait queue failed due 1541 * high memory pressure. 1542 */ 1543 error = -ENOMEM; 1544 if (epi->nwait < 0) 1545 goto error_unregister; 1546 1547 /* Add the current item to the list of active epoll hook for this file */ 1548 spin_lock(&tfile->f_lock); 1549 list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links); 1550 spin_unlock(&tfile->f_lock); 1551 1552 /* 1553 * Add the current item to the RB tree. All RB tree operations are 1554 * protected by "mtx", and ep_insert() is called with "mtx" held. 1555 */ 1556 ep_rbtree_insert(ep, epi); 1557 1558 /* now check if we've created too many backpaths */ 1559 error = -EINVAL; 1560 if (full_check && reverse_path_check()) 1561 goto error_remove_epi; 1562 1563 /* We have to drop the new item inside our item list to keep track of it */ 1564 write_lock_irq(&ep->lock); 1565 1566 /* record NAPI ID of new item if present */ 1567 ep_set_busy_poll_napi_id(epi); 1568 1569 /* If the file is already "ready" we drop it inside the ready list */ 1570 if (revents && !ep_is_linked(epi)) { 1571 list_add_tail(&epi->rdllink, &ep->rdllist); 1572 ep_pm_stay_awake(epi); 1573 1574 /* Notify waiting tasks that events are available */ 1575 if (waitqueue_active(&ep->wq)) 1576 wake_up(&ep->wq); 1577 if (waitqueue_active(&ep->poll_wait)) 1578 pwake++; 1579 } 1580 1581 write_unlock_irq(&ep->lock); 1582 1583 atomic_long_inc(&ep->user->epoll_watches); 1584 1585 /* We have to call this outside the lock */ 1586 if (pwake) 1587 ep_poll_safewake(ep, NULL); 1588 1589 return 0; 1590 1591 error_remove_epi: 1592 spin_lock(&tfile->f_lock); 1593 list_del_rcu(&epi->fllink); 1594 spin_unlock(&tfile->f_lock); 1595 1596 rb_erase_cached(&epi->rbn, &ep->rbr); 1597 1598 error_unregister: 1599 ep_unregister_pollwait(ep, epi); 1600 1601 /* 1602 * We need to do this because an event could have been arrived on some 1603 * allocated wait queue. Note that we don't care about the ep->ovflist 1604 * list, since that is used/cleaned only inside a section bound by "mtx". 1605 * And ep_insert() is called with "mtx" held. 1606 */ 1607 write_lock_irq(&ep->lock); 1608 if (ep_is_linked(epi)) 1609 list_del_init(&epi->rdllink); 1610 write_unlock_irq(&ep->lock); 1611 1612 wakeup_source_unregister(ep_wakeup_source(epi)); 1613 1614 error_create_wakeup_source: 1615 kmem_cache_free(epi_cache, epi); 1616 1617 return error; 1618 } 1619 1620 /* 1621 * Modify the interest event mask by dropping an event if the new mask 1622 * has a match in the current file status. Must be called with "mtx" held. 1623 */ 1624 static int ep_modify(struct eventpoll *ep, struct epitem *epi, 1625 const struct epoll_event *event) 1626 { 1627 int pwake = 0; 1628 poll_table pt; 1629 1630 lockdep_assert_irqs_enabled(); 1631 1632 init_poll_funcptr(&pt, NULL); 1633 1634 /* 1635 * Set the new event interest mask before calling f_op->poll(); 1636 * otherwise we might miss an event that happens between the 1637 * f_op->poll() call and the new event set registering. 1638 */ 1639 epi->event.events = event->events; /* need barrier below */ 1640 epi->event.data = event->data; /* protected by mtx */ 1641 if (epi->event.events & EPOLLWAKEUP) { 1642 if (!ep_has_wakeup_source(epi)) 1643 ep_create_wakeup_source(epi); 1644 } else if (ep_has_wakeup_source(epi)) { 1645 ep_destroy_wakeup_source(epi); 1646 } 1647 1648 /* 1649 * The following barrier has two effects: 1650 * 1651 * 1) Flush epi changes above to other CPUs. This ensures 1652 * we do not miss events from ep_poll_callback if an 1653 * event occurs immediately after we call f_op->poll(). 1654 * We need this because we did not take ep->lock while 1655 * changing epi above (but ep_poll_callback does take 1656 * ep->lock). 1657 * 1658 * 2) We also need to ensure we do not miss _past_ events 1659 * when calling f_op->poll(). This barrier also 1660 * pairs with the barrier in wq_has_sleeper (see 1661 * comments for wq_has_sleeper). 1662 * 1663 * This barrier will now guarantee ep_poll_callback or f_op->poll 1664 * (or both) will notice the readiness of an item. 1665 */ 1666 smp_mb(); 1667 1668 /* 1669 * Get current event bits. We can safely use the file* here because 1670 * its usage count has been increased by the caller of this function. 1671 * If the item is "hot" and it is not registered inside the ready 1672 * list, push it inside. 1673 */ 1674 if (ep_item_poll(epi, &pt, 1)) { 1675 write_lock_irq(&ep->lock); 1676 if (!ep_is_linked(epi)) { 1677 list_add_tail(&epi->rdllink, &ep->rdllist); 1678 ep_pm_stay_awake(epi); 1679 1680 /* Notify waiting tasks that events are available */ 1681 if (waitqueue_active(&ep->wq)) 1682 wake_up(&ep->wq); 1683 if (waitqueue_active(&ep->poll_wait)) 1684 pwake++; 1685 } 1686 write_unlock_irq(&ep->lock); 1687 } 1688 1689 /* We have to call this outside the lock */ 1690 if (pwake) 1691 ep_poll_safewake(ep, NULL); 1692 1693 return 0; 1694 } 1695 1696 static __poll_t ep_send_events_proc(struct eventpoll *ep, struct list_head *head, 1697 void *priv) 1698 { 1699 struct ep_send_events_data *esed = priv; 1700 __poll_t revents; 1701 struct epitem *epi, *tmp; 1702 struct epoll_event __user *uevent = esed->events; 1703 struct wakeup_source *ws; 1704 poll_table pt; 1705 1706 init_poll_funcptr(&pt, NULL); 1707 esed->res = 0; 1708 1709 /* 1710 * We can loop without lock because we are passed a task private list. 1711 * Items cannot vanish during the loop because ep_scan_ready_list() is 1712 * holding "mtx" during this call. 1713 */ 1714 lockdep_assert_held(&ep->mtx); 1715 1716 list_for_each_entry_safe(epi, tmp, head, rdllink) { 1717 if (esed->res >= esed->maxevents) 1718 break; 1719 1720 /* 1721 * Activate ep->ws before deactivating epi->ws to prevent 1722 * triggering auto-suspend here (in case we reactive epi->ws 1723 * below). 1724 * 1725 * This could be rearranged to delay the deactivation of epi->ws 1726 * instead, but then epi->ws would temporarily be out of sync 1727 * with ep_is_linked(). 1728 */ 1729 ws = ep_wakeup_source(epi); 1730 if (ws) { 1731 if (ws->active) 1732 __pm_stay_awake(ep->ws); 1733 __pm_relax(ws); 1734 } 1735 1736 list_del_init(&epi->rdllink); 1737 1738 /* 1739 * If the event mask intersect the caller-requested one, 1740 * deliver the event to userspace. Again, ep_scan_ready_list() 1741 * is holding ep->mtx, so no operations coming from userspace 1742 * can change the item. 1743 */ 1744 revents = ep_item_poll(epi, &pt, 1); 1745 if (!revents) 1746 continue; 1747 1748 if (__put_user(revents, &uevent->events) || 1749 __put_user(epi->event.data, &uevent->data)) { 1750 list_add(&epi->rdllink, head); 1751 ep_pm_stay_awake(epi); 1752 if (!esed->res) 1753 esed->res = -EFAULT; 1754 return 0; 1755 } 1756 esed->res++; 1757 uevent++; 1758 if (epi->event.events & EPOLLONESHOT) 1759 epi->event.events &= EP_PRIVATE_BITS; 1760 else if (!(epi->event.events & EPOLLET)) { 1761 /* 1762 * If this file has been added with Level 1763 * Trigger mode, we need to insert back inside 1764 * the ready list, so that the next call to 1765 * epoll_wait() will check again the events 1766 * availability. At this point, no one can insert 1767 * into ep->rdllist besides us. The epoll_ctl() 1768 * callers are locked out by 1769 * ep_scan_ready_list() holding "mtx" and the 1770 * poll callback will queue them in ep->ovflist. 1771 */ 1772 list_add_tail(&epi->rdllink, &ep->rdllist); 1773 ep_pm_stay_awake(epi); 1774 } 1775 } 1776 1777 return 0; 1778 } 1779 1780 static int ep_send_events(struct eventpoll *ep, 1781 struct epoll_event __user *events, int maxevents) 1782 { 1783 struct ep_send_events_data esed; 1784 1785 esed.maxevents = maxevents; 1786 esed.events = events; 1787 1788 ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false); 1789 return esed.res; 1790 } 1791 1792 static inline struct timespec64 ep_set_mstimeout(long ms) 1793 { 1794 struct timespec64 now, ts = { 1795 .tv_sec = ms / MSEC_PER_SEC, 1796 .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC), 1797 }; 1798 1799 ktime_get_ts64(&now); 1800 return timespec64_add_safe(now, ts); 1801 } 1802 1803 /** 1804 * ep_poll - Retrieves ready events, and delivers them to the caller supplied 1805 * event buffer. 1806 * 1807 * @ep: Pointer to the eventpoll context. 1808 * @events: Pointer to the userspace buffer where the ready events should be 1809 * stored. 1810 * @maxevents: Size (in terms of number of events) of the caller event buffer. 1811 * @timeout: Maximum timeout for the ready events fetch operation, in 1812 * milliseconds. If the @timeout is zero, the function will not block, 1813 * while if the @timeout is less than zero, the function will block 1814 * until at least one event has been retrieved (or an error 1815 * occurred). 1816 * 1817 * Returns: Returns the number of ready events which have been fetched, or an 1818 * error code, in case of error. 1819 */ 1820 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 1821 int maxevents, long timeout) 1822 { 1823 int res = 0, eavail, timed_out = 0; 1824 u64 slack = 0; 1825 wait_queue_entry_t wait; 1826 ktime_t expires, *to = NULL; 1827 1828 lockdep_assert_irqs_enabled(); 1829 1830 if (timeout > 0) { 1831 struct timespec64 end_time = ep_set_mstimeout(timeout); 1832 1833 slack = select_estimate_accuracy(&end_time); 1834 to = &expires; 1835 *to = timespec64_to_ktime(end_time); 1836 } else if (timeout == 0) { 1837 /* 1838 * Avoid the unnecessary trip to the wait queue loop, if the 1839 * caller specified a non blocking operation. We still need 1840 * lock because we could race and not see an epi being added 1841 * to the ready list while in irq callback. Thus incorrectly 1842 * returning 0 back to userspace. 1843 */ 1844 timed_out = 1; 1845 1846 write_lock_irq(&ep->lock); 1847 eavail = ep_events_available(ep); 1848 write_unlock_irq(&ep->lock); 1849 1850 goto send_events; 1851 } 1852 1853 fetch_events: 1854 1855 if (!ep_events_available(ep)) 1856 ep_busy_loop(ep, timed_out); 1857 1858 eavail = ep_events_available(ep); 1859 if (eavail) 1860 goto send_events; 1861 1862 /* 1863 * Busy poll timed out. Drop NAPI ID for now, we can add 1864 * it back in when we have moved a socket with a valid NAPI 1865 * ID onto the ready list. 1866 */ 1867 ep_reset_busy_poll_napi_id(ep); 1868 1869 do { 1870 /* 1871 * Internally init_wait() uses autoremove_wake_function(), 1872 * thus wait entry is removed from the wait queue on each 1873 * wakeup. Why it is important? In case of several waiters 1874 * each new wakeup will hit the next waiter, giving it the 1875 * chance to harvest new event. Otherwise wakeup can be 1876 * lost. This is also good performance-wise, because on 1877 * normal wakeup path no need to call __remove_wait_queue() 1878 * explicitly, thus ep->lock is not taken, which halts the 1879 * event delivery. 1880 */ 1881 init_wait(&wait); 1882 1883 write_lock_irq(&ep->lock); 1884 /* 1885 * Barrierless variant, waitqueue_active() is called under 1886 * the same lock on wakeup ep_poll_callback() side, so it 1887 * is safe to avoid an explicit barrier. 1888 */ 1889 __set_current_state(TASK_INTERRUPTIBLE); 1890 1891 /* 1892 * Do the final check under the lock. ep_scan_ready_list() 1893 * plays with two lists (->rdllist and ->ovflist) and there 1894 * is always a race when both lists are empty for short 1895 * period of time although events are pending, so lock is 1896 * important. 1897 */ 1898 eavail = ep_events_available(ep); 1899 if (!eavail) { 1900 if (signal_pending(current)) 1901 res = -EINTR; 1902 else 1903 __add_wait_queue_exclusive(&ep->wq, &wait); 1904 } 1905 write_unlock_irq(&ep->lock); 1906 1907 if (eavail || res) 1908 break; 1909 1910 if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) { 1911 timed_out = 1; 1912 break; 1913 } 1914 1915 /* We were woken up, thus go and try to harvest some events */ 1916 eavail = 1; 1917 1918 } while (0); 1919 1920 __set_current_state(TASK_RUNNING); 1921 1922 if (!list_empty_careful(&wait.entry)) { 1923 write_lock_irq(&ep->lock); 1924 __remove_wait_queue(&ep->wq, &wait); 1925 write_unlock_irq(&ep->lock); 1926 } 1927 1928 send_events: 1929 if (fatal_signal_pending(current)) { 1930 /* 1931 * Always short-circuit for fatal signals to allow 1932 * threads to make a timely exit without the chance of 1933 * finding more events available and fetching 1934 * repeatedly. 1935 */ 1936 res = -EINTR; 1937 } 1938 /* 1939 * Try to transfer events to user space. In case we get 0 events and 1940 * there's still timeout left over, we go trying again in search of 1941 * more luck. 1942 */ 1943 if (!res && eavail && 1944 !(res = ep_send_events(ep, events, maxevents)) && !timed_out) 1945 goto fetch_events; 1946 1947 return res; 1948 } 1949 1950 /** 1951 * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested() 1952 * API, to verify that adding an epoll file inside another 1953 * epoll structure, does not violate the constraints, in 1954 * terms of closed loops, or too deep chains (which can 1955 * result in excessive stack usage). 1956 * 1957 * @priv: Pointer to the epoll file to be currently checked. 1958 * @cookie: Original cookie for this call. This is the top-of-the-chain epoll 1959 * data structure pointer. 1960 * @call_nests: Current dept of the @ep_call_nested() call stack. 1961 * 1962 * Returns: Returns zero if adding the epoll @file inside current epoll 1963 * structure @ep does not violate the constraints, or -1 otherwise. 1964 */ 1965 static int ep_loop_check_proc(void *priv, void *cookie, int call_nests) 1966 { 1967 int error = 0; 1968 struct file *file = priv; 1969 struct eventpoll *ep = file->private_data; 1970 struct eventpoll *ep_tovisit; 1971 struct rb_node *rbp; 1972 struct epitem *epi; 1973 1974 mutex_lock_nested(&ep->mtx, call_nests + 1); 1975 ep->visited = 1; 1976 list_add(&ep->visited_list_link, &visited_list); 1977 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { 1978 epi = rb_entry(rbp, struct epitem, rbn); 1979 if (unlikely(is_file_epoll(epi->ffd.file))) { 1980 ep_tovisit = epi->ffd.file->private_data; 1981 if (ep_tovisit->visited) 1982 continue; 1983 error = ep_call_nested(&poll_loop_ncalls, 1984 ep_loop_check_proc, epi->ffd.file, 1985 ep_tovisit, current); 1986 if (error != 0) 1987 break; 1988 } else { 1989 /* 1990 * If we've reached a file that is not associated with 1991 * an ep, then we need to check if the newly added 1992 * links are going to add too many wakeup paths. We do 1993 * this by adding it to the tfile_check_list, if it's 1994 * not already there, and calling reverse_path_check() 1995 * during ep_insert(). 1996 */ 1997 if (list_empty(&epi->ffd.file->f_tfile_llink)) 1998 list_add(&epi->ffd.file->f_tfile_llink, 1999 &tfile_check_list); 2000 } 2001 } 2002 mutex_unlock(&ep->mtx); 2003 2004 return error; 2005 } 2006 2007 /** 2008 * ep_loop_check - Performs a check to verify that adding an epoll file (@file) 2009 * another epoll file (represented by @ep) does not create 2010 * closed loops or too deep chains. 2011 * 2012 * @ep: Pointer to the epoll private data structure. 2013 * @file: Pointer to the epoll file to be checked. 2014 * 2015 * Returns: Returns zero if adding the epoll @file inside current epoll 2016 * structure @ep does not violate the constraints, or -1 otherwise. 2017 */ 2018 static int ep_loop_check(struct eventpoll *ep, struct file *file) 2019 { 2020 int ret; 2021 struct eventpoll *ep_cur, *ep_next; 2022 2023 ret = ep_call_nested(&poll_loop_ncalls, 2024 ep_loop_check_proc, file, ep, current); 2025 /* clear visited list */ 2026 list_for_each_entry_safe(ep_cur, ep_next, &visited_list, 2027 visited_list_link) { 2028 ep_cur->visited = 0; 2029 list_del(&ep_cur->visited_list_link); 2030 } 2031 return ret; 2032 } 2033 2034 static void clear_tfile_check_list(void) 2035 { 2036 struct file *file; 2037 2038 /* first clear the tfile_check_list */ 2039 while (!list_empty(&tfile_check_list)) { 2040 file = list_first_entry(&tfile_check_list, struct file, 2041 f_tfile_llink); 2042 list_del_init(&file->f_tfile_llink); 2043 } 2044 INIT_LIST_HEAD(&tfile_check_list); 2045 } 2046 2047 /* 2048 * Open an eventpoll file descriptor. 2049 */ 2050 static int do_epoll_create(int flags) 2051 { 2052 int error, fd; 2053 struct eventpoll *ep = NULL; 2054 struct file *file; 2055 2056 /* Check the EPOLL_* constant for consistency. */ 2057 BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC); 2058 2059 if (flags & ~EPOLL_CLOEXEC) 2060 return -EINVAL; 2061 /* 2062 * Create the internal data structure ("struct eventpoll"). 2063 */ 2064 error = ep_alloc(&ep); 2065 if (error < 0) 2066 return error; 2067 /* 2068 * Creates all the items needed to setup an eventpoll file. That is, 2069 * a file structure and a free file descriptor. 2070 */ 2071 fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC)); 2072 if (fd < 0) { 2073 error = fd; 2074 goto out_free_ep; 2075 } 2076 file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep, 2077 O_RDWR | (flags & O_CLOEXEC)); 2078 if (IS_ERR(file)) { 2079 error = PTR_ERR(file); 2080 goto out_free_fd; 2081 } 2082 ep->file = file; 2083 fd_install(fd, file); 2084 return fd; 2085 2086 out_free_fd: 2087 put_unused_fd(fd); 2088 out_free_ep: 2089 ep_free(ep); 2090 return error; 2091 } 2092 2093 SYSCALL_DEFINE1(epoll_create1, int, flags) 2094 { 2095 return do_epoll_create(flags); 2096 } 2097 2098 SYSCALL_DEFINE1(epoll_create, int, size) 2099 { 2100 if (size <= 0) 2101 return -EINVAL; 2102 2103 return do_epoll_create(0); 2104 } 2105 2106 static inline int epoll_mutex_lock(struct mutex *mutex, int depth, 2107 bool nonblock) 2108 { 2109 if (!nonblock) { 2110 mutex_lock_nested(mutex, depth); 2111 return 0; 2112 } 2113 if (mutex_trylock(mutex)) 2114 return 0; 2115 return -EAGAIN; 2116 } 2117 2118 int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, 2119 bool nonblock) 2120 { 2121 int error; 2122 int full_check = 0; 2123 struct fd f, tf; 2124 struct eventpoll *ep; 2125 struct epitem *epi; 2126 struct eventpoll *tep = NULL; 2127 2128 error = -EBADF; 2129 f = fdget(epfd); 2130 if (!f.file) 2131 goto error_return; 2132 2133 /* Get the "struct file *" for the target file */ 2134 tf = fdget(fd); 2135 if (!tf.file) 2136 goto error_fput; 2137 2138 /* The target file descriptor must support poll */ 2139 error = -EPERM; 2140 if (!file_can_poll(tf.file)) 2141 goto error_tgt_fput; 2142 2143 /* Check if EPOLLWAKEUP is allowed */ 2144 if (ep_op_has_event(op)) 2145 ep_take_care_of_epollwakeup(epds); 2146 2147 /* 2148 * We have to check that the file structure underneath the file descriptor 2149 * the user passed to us _is_ an eventpoll file. And also we do not permit 2150 * adding an epoll file descriptor inside itself. 2151 */ 2152 error = -EINVAL; 2153 if (f.file == tf.file || !is_file_epoll(f.file)) 2154 goto error_tgt_fput; 2155 2156 /* 2157 * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only, 2158 * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation. 2159 * Also, we do not currently supported nested exclusive wakeups. 2160 */ 2161 if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) { 2162 if (op == EPOLL_CTL_MOD) 2163 goto error_tgt_fput; 2164 if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) || 2165 (epds->events & ~EPOLLEXCLUSIVE_OK_BITS))) 2166 goto error_tgt_fput; 2167 } 2168 2169 /* 2170 * At this point it is safe to assume that the "private_data" contains 2171 * our own data structure. 2172 */ 2173 ep = f.file->private_data; 2174 2175 /* 2176 * When we insert an epoll file descriptor, inside another epoll file 2177 * descriptor, there is the change of creating closed loops, which are 2178 * better be handled here, than in more critical paths. While we are 2179 * checking for loops we also determine the list of files reachable 2180 * and hang them on the tfile_check_list, so we can check that we 2181 * haven't created too many possible wakeup paths. 2182 * 2183 * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when 2184 * the epoll file descriptor is attaching directly to a wakeup source, 2185 * unless the epoll file descriptor is nested. The purpose of taking the 2186 * 'epmutex' on add is to prevent complex toplogies such as loops and 2187 * deep wakeup paths from forming in parallel through multiple 2188 * EPOLL_CTL_ADD operations. 2189 */ 2190 error = epoll_mutex_lock(&ep->mtx, 0, nonblock); 2191 if (error) 2192 goto error_tgt_fput; 2193 if (op == EPOLL_CTL_ADD) { 2194 if (!list_empty(&f.file->f_ep_links) || 2195 is_file_epoll(tf.file)) { 2196 mutex_unlock(&ep->mtx); 2197 error = epoll_mutex_lock(&epmutex, 0, nonblock); 2198 if (error) 2199 goto error_tgt_fput; 2200 full_check = 1; 2201 if (is_file_epoll(tf.file)) { 2202 error = -ELOOP; 2203 if (ep_loop_check(ep, tf.file) != 0) { 2204 clear_tfile_check_list(); 2205 goto error_tgt_fput; 2206 } 2207 } else 2208 list_add(&tf.file->f_tfile_llink, 2209 &tfile_check_list); 2210 error = epoll_mutex_lock(&ep->mtx, 0, nonblock); 2211 if (error) { 2212 out_del: 2213 list_del(&tf.file->f_tfile_llink); 2214 goto error_tgt_fput; 2215 } 2216 if (is_file_epoll(tf.file)) { 2217 tep = tf.file->private_data; 2218 error = epoll_mutex_lock(&tep->mtx, 1, nonblock); 2219 if (error) { 2220 mutex_unlock(&ep->mtx); 2221 goto out_del; 2222 } 2223 } 2224 } 2225 } 2226 2227 /* 2228 * Try to lookup the file inside our RB tree, Since we grabbed "mtx" 2229 * above, we can be sure to be able to use the item looked up by 2230 * ep_find() till we release the mutex. 2231 */ 2232 epi = ep_find(ep, tf.file, fd); 2233 2234 error = -EINVAL; 2235 switch (op) { 2236 case EPOLL_CTL_ADD: 2237 if (!epi) { 2238 epds->events |= EPOLLERR | EPOLLHUP; 2239 error = ep_insert(ep, epds, tf.file, fd, full_check); 2240 } else 2241 error = -EEXIST; 2242 if (full_check) 2243 clear_tfile_check_list(); 2244 break; 2245 case EPOLL_CTL_DEL: 2246 if (epi) 2247 error = ep_remove(ep, epi); 2248 else 2249 error = -ENOENT; 2250 break; 2251 case EPOLL_CTL_MOD: 2252 if (epi) { 2253 if (!(epi->event.events & EPOLLEXCLUSIVE)) { 2254 epds->events |= EPOLLERR | EPOLLHUP; 2255 error = ep_modify(ep, epi, epds); 2256 } 2257 } else 2258 error = -ENOENT; 2259 break; 2260 } 2261 if (tep != NULL) 2262 mutex_unlock(&tep->mtx); 2263 mutex_unlock(&ep->mtx); 2264 2265 error_tgt_fput: 2266 if (full_check) 2267 mutex_unlock(&epmutex); 2268 2269 fdput(tf); 2270 error_fput: 2271 fdput(f); 2272 error_return: 2273 2274 return error; 2275 } 2276 2277 /* 2278 * The following function implements the controller interface for 2279 * the eventpoll file that enables the insertion/removal/change of 2280 * file descriptors inside the interest set. 2281 */ 2282 SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, 2283 struct epoll_event __user *, event) 2284 { 2285 struct epoll_event epds; 2286 2287 if (ep_op_has_event(op) && 2288 copy_from_user(&epds, event, sizeof(struct epoll_event))) 2289 return -EFAULT; 2290 2291 return do_epoll_ctl(epfd, op, fd, &epds, false); 2292 } 2293 2294 /* 2295 * Implement the event wait interface for the eventpoll file. It is the kernel 2296 * part of the user space epoll_wait(2). 2297 */ 2298 static int do_epoll_wait(int epfd, struct epoll_event __user *events, 2299 int maxevents, int timeout) 2300 { 2301 int error; 2302 struct fd f; 2303 struct eventpoll *ep; 2304 2305 /* The maximum number of event must be greater than zero */ 2306 if (maxevents <= 0 || maxevents > EP_MAX_EVENTS) 2307 return -EINVAL; 2308 2309 /* Verify that the area passed by the user is writeable */ 2310 if (!access_ok(events, maxevents * sizeof(struct epoll_event))) 2311 return -EFAULT; 2312 2313 /* Get the "struct file *" for the eventpoll file */ 2314 f = fdget(epfd); 2315 if (!f.file) 2316 return -EBADF; 2317 2318 /* 2319 * We have to check that the file structure underneath the fd 2320 * the user passed to us _is_ an eventpoll file. 2321 */ 2322 error = -EINVAL; 2323 if (!is_file_epoll(f.file)) 2324 goto error_fput; 2325 2326 /* 2327 * At this point it is safe to assume that the "private_data" contains 2328 * our own data structure. 2329 */ 2330 ep = f.file->private_data; 2331 2332 /* Time to fish for events ... */ 2333 error = ep_poll(ep, events, maxevents, timeout); 2334 2335 error_fput: 2336 fdput(f); 2337 return error; 2338 } 2339 2340 SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, 2341 int, maxevents, int, timeout) 2342 { 2343 return do_epoll_wait(epfd, events, maxevents, timeout); 2344 } 2345 2346 /* 2347 * Implement the event wait interface for the eventpoll file. It is the kernel 2348 * part of the user space epoll_pwait(2). 2349 */ 2350 SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events, 2351 int, maxevents, int, timeout, const sigset_t __user *, sigmask, 2352 size_t, sigsetsize) 2353 { 2354 int error; 2355 2356 /* 2357 * If the caller wants a certain signal mask to be set during the wait, 2358 * we apply it here. 2359 */ 2360 error = set_user_sigmask(sigmask, sigsetsize); 2361 if (error) 2362 return error; 2363 2364 error = do_epoll_wait(epfd, events, maxevents, timeout); 2365 restore_saved_sigmask_unless(error == -EINTR); 2366 2367 return error; 2368 } 2369 2370 #ifdef CONFIG_COMPAT 2371 COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd, 2372 struct epoll_event __user *, events, 2373 int, maxevents, int, timeout, 2374 const compat_sigset_t __user *, sigmask, 2375 compat_size_t, sigsetsize) 2376 { 2377 long err; 2378 2379 /* 2380 * If the caller wants a certain signal mask to be set during the wait, 2381 * we apply it here. 2382 */ 2383 err = set_compat_user_sigmask(sigmask, sigsetsize); 2384 if (err) 2385 return err; 2386 2387 err = do_epoll_wait(epfd, events, maxevents, timeout); 2388 restore_saved_sigmask_unless(err == -EINTR); 2389 2390 return err; 2391 } 2392 #endif 2393 2394 static int __init eventpoll_init(void) 2395 { 2396 struct sysinfo si; 2397 2398 si_meminfo(&si); 2399 /* 2400 * Allows top 4% of lomem to be allocated for epoll watches (per user). 2401 */ 2402 max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) / 2403 EP_ITEM_COST; 2404 BUG_ON(max_user_watches < 0); 2405 2406 /* 2407 * Initialize the structure used to perform epoll file descriptor 2408 * inclusion loops checks. 2409 */ 2410 ep_nested_calls_init(&poll_loop_ncalls); 2411 2412 /* 2413 * We can have many thousands of epitems, so prevent this from 2414 * using an extra cache line on 64-bit (and smaller) CPUs 2415 */ 2416 BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128); 2417 2418 /* Allocates slab cache used to allocate "struct epitem" items */ 2419 epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), 2420 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL); 2421 2422 /* Allocates slab cache used to allocate "struct eppoll_entry" */ 2423 pwq_cache = kmem_cache_create("eventpoll_pwq", 2424 sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL); 2425 2426 return 0; 2427 } 2428 fs_initcall(eventpoll_init); 2429