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 <linux/capability.h> 41 #include <net/busy_poll.h> 42 43 /* 44 * LOCKING: 45 * There are three level of locking required by epoll : 46 * 47 * 1) epnested_mutex (mutex) 48 * 2) ep->mtx (mutex) 49 * 3) ep->lock (rwlock) 50 * 51 * The acquire order is the one listed above, from 1 to 3. 52 * We need a rwlock (ep->lock) because we manipulate objects 53 * from inside the poll callback, that might be triggered from 54 * a wake_up() that in turn might be called from IRQ context. 55 * So we can't sleep inside the poll callback and hence we need 56 * a spinlock. During the event transfer loop (from kernel to 57 * user space) we could end up sleeping due a copy_to_user(), so 58 * we need a lock that will allow us to sleep. This lock is a 59 * mutex (ep->mtx). It is acquired during the event transfer loop, 60 * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file(). 61 * The epnested_mutex is acquired when inserting an epoll fd onto another 62 * epoll fd. We do this so that we walk the epoll tree and ensure that this 63 * insertion does not create a cycle of epoll file descriptors, which 64 * could lead to deadlock. We need a global mutex to prevent two 65 * simultaneous inserts (A into B and B into A) from racing and 66 * constructing a cycle without either insert observing that it is 67 * going to. 68 * It is necessary to acquire multiple "ep->mtx"es at once in the 69 * case when one epoll fd is added to another. In this case, we 70 * always acquire the locks in the order of nesting (i.e. after 71 * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired 72 * before e2->mtx). Since we disallow cycles of epoll file 73 * descriptors, this ensures that the mutexes are well-ordered. In 74 * order to communicate this nesting to lockdep, when walking a tree 75 * of epoll file descriptors, we use the current recursion depth as 76 * the lockdep subkey. 77 * It is possible to drop the "ep->mtx" and to use the global 78 * mutex "epnested_mutex" (together with "ep->lock") to have it working, 79 * but having "ep->mtx" will make the interface more scalable. 80 * Events that require holding "epnested_mutex" are very rare, while for 81 * normal operations the epoll private "ep->mtx" will guarantee 82 * a better scalability. 83 */ 84 85 /* Epoll private bits inside the event mask */ 86 #define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE) 87 88 #define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT) 89 90 #define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \ 91 EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE) 92 93 /* Maximum number of nesting allowed inside epoll sets */ 94 #define EP_MAX_NESTS 4 95 96 #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event)) 97 98 #define EP_UNACTIVE_PTR ((void *) -1L) 99 100 #define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry)) 101 102 struct epoll_filefd { 103 struct file *file; 104 int fd; 105 } __packed; 106 107 /* Wait structure used by the poll hooks */ 108 struct eppoll_entry { 109 /* List header used to link this structure to the "struct epitem" */ 110 struct eppoll_entry *next; 111 112 /* The "base" pointer is set to the container "struct epitem" */ 113 struct epitem *base; 114 115 /* 116 * Wait queue item that will be linked to the target file wait 117 * queue head. 118 */ 119 wait_queue_entry_t wait; 120 121 /* The wait queue head that linked the "wait" wait queue item */ 122 wait_queue_head_t *whead; 123 }; 124 125 /* 126 * Each file descriptor added to the eventpoll interface will 127 * have an entry of this type linked to the "rbr" RB tree. 128 * Avoid increasing the size of this struct, there can be many thousands 129 * of these on a server and we do not want this to take another cache line. 130 */ 131 struct epitem { 132 union { 133 /* RB tree node links this structure to the eventpoll RB tree */ 134 struct rb_node rbn; 135 /* Used to free the struct epitem */ 136 struct rcu_head rcu; 137 }; 138 139 /* List header used to link this structure to the eventpoll ready list */ 140 struct list_head rdllink; 141 142 /* 143 * Works together "struct eventpoll"->ovflist in keeping the 144 * single linked chain of items. 145 */ 146 struct epitem *next; 147 148 /* The file descriptor information this item refers to */ 149 struct epoll_filefd ffd; 150 151 /* 152 * Protected by file->f_lock, true for to-be-released epitem already 153 * removed from the "struct file" items list; together with 154 * eventpoll->refcount orchestrates "struct eventpoll" disposal 155 */ 156 bool dying; 157 158 /* List containing poll wait queues */ 159 struct eppoll_entry *pwqlist; 160 161 /* The "container" of this item */ 162 struct eventpoll *ep; 163 164 /* List header used to link this item to the "struct file" items list */ 165 struct hlist_node fllink; 166 167 /* wakeup_source used when EPOLLWAKEUP is set */ 168 struct wakeup_source __rcu *ws; 169 170 /* The structure that describe the interested events and the source fd */ 171 struct epoll_event event; 172 }; 173 174 /* 175 * This structure is stored inside the "private_data" member of the file 176 * structure and represents the main data structure for the eventpoll 177 * interface. 178 */ 179 struct eventpoll { 180 /* 181 * This mutex is used to ensure that files are not removed 182 * while epoll is using them. This is held during the event 183 * collection loop, the file cleanup path, the epoll file exit 184 * code and the ctl operations. 185 */ 186 struct mutex mtx; 187 188 /* Wait queue used by sys_epoll_wait() */ 189 wait_queue_head_t wq; 190 191 /* Wait queue used by file->poll() */ 192 wait_queue_head_t poll_wait; 193 194 /* List of ready file descriptors */ 195 struct list_head rdllist; 196 197 /* Lock which protects rdllist and ovflist */ 198 rwlock_t lock; 199 200 /* RB tree root used to store monitored fd structs */ 201 struct rb_root_cached rbr; 202 203 /* 204 * This is a single linked list that chains all the "struct epitem" that 205 * happened while transferring ready events to userspace w/out 206 * holding ->lock. 207 */ 208 struct epitem *ovflist; 209 210 /* wakeup_source used when ep_send_events or __ep_eventpoll_poll is running */ 211 struct wakeup_source *ws; 212 213 /* The user that created the eventpoll descriptor */ 214 struct user_struct *user; 215 216 struct file *file; 217 218 /* used to optimize loop detection check */ 219 u64 gen; 220 struct hlist_head refs; 221 222 /* 223 * usage count, used together with epitem->dying to 224 * orchestrate the disposal of this struct 225 */ 226 refcount_t refcount; 227 228 #ifdef CONFIG_NET_RX_BUSY_POLL 229 /* used to track busy poll napi_id */ 230 unsigned int napi_id; 231 /* busy poll timeout */ 232 u32 busy_poll_usecs; 233 /* busy poll packet budget */ 234 u16 busy_poll_budget; 235 bool prefer_busy_poll; 236 #endif 237 238 #ifdef CONFIG_DEBUG_LOCK_ALLOC 239 /* tracks wakeup nests for lockdep validation */ 240 u8 nests; 241 #endif 242 }; 243 244 /* Wrapper struct used by poll queueing */ 245 struct ep_pqueue { 246 poll_table pt; 247 struct epitem *epi; 248 }; 249 250 /* 251 * Configuration options available inside /proc/sys/fs/epoll/ 252 */ 253 /* Maximum number of epoll watched descriptors, per user */ 254 static long max_user_watches __read_mostly; 255 256 /* Used for cycles detection */ 257 static DEFINE_MUTEX(epnested_mutex); 258 259 static u64 loop_check_gen = 0; 260 261 /* Used to check for epoll file descriptor inclusion loops */ 262 static struct eventpoll *inserting_into; 263 264 /* Slab cache used to allocate "struct epitem" */ 265 static struct kmem_cache *epi_cache __ro_after_init; 266 267 /* Slab cache used to allocate "struct eppoll_entry" */ 268 static struct kmem_cache *pwq_cache __ro_after_init; 269 270 /* 271 * List of files with newly added links, where we may need to limit the number 272 * of emanating paths. Protected by the epnested_mutex. 273 */ 274 struct epitems_head { 275 struct hlist_head epitems; 276 struct epitems_head *next; 277 }; 278 static struct epitems_head *tfile_check_list = EP_UNACTIVE_PTR; 279 280 static struct kmem_cache *ephead_cache __ro_after_init; 281 282 static inline void free_ephead(struct epitems_head *head) 283 { 284 if (head) 285 kmem_cache_free(ephead_cache, head); 286 } 287 288 static void list_file(struct file *file) 289 { 290 struct epitems_head *head; 291 292 head = container_of(file->f_ep, struct epitems_head, epitems); 293 if (!head->next) { 294 head->next = tfile_check_list; 295 tfile_check_list = head; 296 } 297 } 298 299 static void unlist_file(struct epitems_head *head) 300 { 301 struct epitems_head *to_free = head; 302 struct hlist_node *p = rcu_dereference(hlist_first_rcu(&head->epitems)); 303 if (p) { 304 struct epitem *epi= container_of(p, struct epitem, fllink); 305 spin_lock(&epi->ffd.file->f_lock); 306 if (!hlist_empty(&head->epitems)) 307 to_free = NULL; 308 head->next = NULL; 309 spin_unlock(&epi->ffd.file->f_lock); 310 } 311 free_ephead(to_free); 312 } 313 314 #ifdef CONFIG_SYSCTL 315 316 #include <linux/sysctl.h> 317 318 static long long_zero; 319 static long long_max = LONG_MAX; 320 321 static struct ctl_table epoll_table[] = { 322 { 323 .procname = "max_user_watches", 324 .data = &max_user_watches, 325 .maxlen = sizeof(max_user_watches), 326 .mode = 0644, 327 .proc_handler = proc_doulongvec_minmax, 328 .extra1 = &long_zero, 329 .extra2 = &long_max, 330 }, 331 }; 332 333 static void __init epoll_sysctls_init(void) 334 { 335 register_sysctl("fs/epoll", epoll_table); 336 } 337 #else 338 #define epoll_sysctls_init() do { } while (0) 339 #endif /* CONFIG_SYSCTL */ 340 341 static const struct file_operations eventpoll_fops; 342 343 static inline int is_file_epoll(struct file *f) 344 { 345 return f->f_op == &eventpoll_fops; 346 } 347 348 /* Setup the structure that is used as key for the RB tree */ 349 static inline void ep_set_ffd(struct epoll_filefd *ffd, 350 struct file *file, int fd) 351 { 352 ffd->file = file; 353 ffd->fd = fd; 354 } 355 356 /* Compare RB tree keys */ 357 static inline int ep_cmp_ffd(struct epoll_filefd *p1, 358 struct epoll_filefd *p2) 359 { 360 return (p1->file > p2->file ? +1: 361 (p1->file < p2->file ? -1 : p1->fd - p2->fd)); 362 } 363 364 /* Tells us if the item is currently linked */ 365 static inline int ep_is_linked(struct epitem *epi) 366 { 367 return !list_empty(&epi->rdllink); 368 } 369 370 static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p) 371 { 372 return container_of(p, struct eppoll_entry, wait); 373 } 374 375 /* Get the "struct epitem" from a wait queue pointer */ 376 static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p) 377 { 378 return container_of(p, struct eppoll_entry, wait)->base; 379 } 380 381 /** 382 * ep_events_available - Checks if ready events might be available. 383 * 384 * @ep: Pointer to the eventpoll context. 385 * 386 * Return: a value different than %zero if ready events are available, 387 * or %zero otherwise. 388 */ 389 static inline int ep_events_available(struct eventpoll *ep) 390 { 391 return !list_empty_careful(&ep->rdllist) || 392 READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR; 393 } 394 395 #ifdef CONFIG_NET_RX_BUSY_POLL 396 /** 397 * busy_loop_ep_timeout - check if busy poll has timed out. The timeout value 398 * from the epoll instance ep is preferred, but if it is not set fallback to 399 * the system-wide global via busy_loop_timeout. 400 * 401 * @start_time: The start time used to compute the remaining time until timeout. 402 * @ep: Pointer to the eventpoll context. 403 * 404 * Return: true if the timeout has expired, false otherwise. 405 */ 406 static bool busy_loop_ep_timeout(unsigned long start_time, 407 struct eventpoll *ep) 408 { 409 unsigned long bp_usec = READ_ONCE(ep->busy_poll_usecs); 410 411 if (bp_usec) { 412 unsigned long end_time = start_time + bp_usec; 413 unsigned long now = busy_loop_current_time(); 414 415 return time_after(now, end_time); 416 } else { 417 return busy_loop_timeout(start_time); 418 } 419 } 420 421 static bool ep_busy_loop_on(struct eventpoll *ep) 422 { 423 return !!READ_ONCE(ep->busy_poll_usecs) || net_busy_loop_on(); 424 } 425 426 static bool ep_busy_loop_end(void *p, unsigned long start_time) 427 { 428 struct eventpoll *ep = p; 429 430 return ep_events_available(ep) || busy_loop_ep_timeout(start_time, ep); 431 } 432 433 /* 434 * Busy poll if globally on and supporting sockets found && no events, 435 * busy loop will return if need_resched or ep_events_available. 436 * 437 * we must do our busy polling with irqs enabled 438 */ 439 static bool ep_busy_loop(struct eventpoll *ep, int nonblock) 440 { 441 unsigned int napi_id = READ_ONCE(ep->napi_id); 442 u16 budget = READ_ONCE(ep->busy_poll_budget); 443 bool prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll); 444 445 if (!budget) 446 budget = BUSY_POLL_BUDGET; 447 448 if (napi_id >= MIN_NAPI_ID && ep_busy_loop_on(ep)) { 449 napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, 450 ep, prefer_busy_poll, budget); 451 if (ep_events_available(ep)) 452 return true; 453 /* 454 * Busy poll timed out. Drop NAPI ID for now, we can add 455 * it back in when we have moved a socket with a valid NAPI 456 * ID onto the ready list. 457 */ 458 ep->napi_id = 0; 459 return false; 460 } 461 return false; 462 } 463 464 /* 465 * Set epoll busy poll NAPI ID from sk. 466 */ 467 static inline void ep_set_busy_poll_napi_id(struct epitem *epi) 468 { 469 struct eventpoll *ep = epi->ep; 470 unsigned int napi_id; 471 struct socket *sock; 472 struct sock *sk; 473 474 if (!ep_busy_loop_on(ep)) 475 return; 476 477 sock = sock_from_file(epi->ffd.file); 478 if (!sock) 479 return; 480 481 sk = sock->sk; 482 if (!sk) 483 return; 484 485 napi_id = READ_ONCE(sk->sk_napi_id); 486 487 /* Non-NAPI IDs can be rejected 488 * or 489 * Nothing to do if we already have this ID 490 */ 491 if (napi_id < MIN_NAPI_ID || napi_id == ep->napi_id) 492 return; 493 494 /* record NAPI ID for use in next busy poll */ 495 ep->napi_id = napi_id; 496 } 497 498 static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd, 499 unsigned long arg) 500 { 501 struct eventpoll *ep = file->private_data; 502 void __user *uarg = (void __user *)arg; 503 struct epoll_params epoll_params; 504 505 switch (cmd) { 506 case EPIOCSPARAMS: 507 if (copy_from_user(&epoll_params, uarg, sizeof(epoll_params))) 508 return -EFAULT; 509 510 /* pad byte must be zero */ 511 if (epoll_params.__pad) 512 return -EINVAL; 513 514 if (epoll_params.busy_poll_usecs > S32_MAX) 515 return -EINVAL; 516 517 if (epoll_params.prefer_busy_poll > 1) 518 return -EINVAL; 519 520 if (epoll_params.busy_poll_budget > NAPI_POLL_WEIGHT && 521 !capable(CAP_NET_ADMIN)) 522 return -EPERM; 523 524 WRITE_ONCE(ep->busy_poll_usecs, epoll_params.busy_poll_usecs); 525 WRITE_ONCE(ep->busy_poll_budget, epoll_params.busy_poll_budget); 526 WRITE_ONCE(ep->prefer_busy_poll, epoll_params.prefer_busy_poll); 527 return 0; 528 case EPIOCGPARAMS: 529 memset(&epoll_params, 0, sizeof(epoll_params)); 530 epoll_params.busy_poll_usecs = READ_ONCE(ep->busy_poll_usecs); 531 epoll_params.busy_poll_budget = READ_ONCE(ep->busy_poll_budget); 532 epoll_params.prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll); 533 if (copy_to_user(uarg, &epoll_params, sizeof(epoll_params))) 534 return -EFAULT; 535 return 0; 536 default: 537 return -ENOIOCTLCMD; 538 } 539 } 540 541 #else 542 543 static inline bool ep_busy_loop(struct eventpoll *ep, int nonblock) 544 { 545 return false; 546 } 547 548 static inline void ep_set_busy_poll_napi_id(struct epitem *epi) 549 { 550 } 551 552 static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd, 553 unsigned long arg) 554 { 555 return -EOPNOTSUPP; 556 } 557 558 #endif /* CONFIG_NET_RX_BUSY_POLL */ 559 560 /* 561 * As described in commit 0ccf831cb lockdep: annotate epoll 562 * the use of wait queues used by epoll is done in a very controlled 563 * manner. Wake ups can nest inside each other, but are never done 564 * with the same locking. For example: 565 * 566 * dfd = socket(...); 567 * efd1 = epoll_create(); 568 * efd2 = epoll_create(); 569 * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...); 570 * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); 571 * 572 * When a packet arrives to the device underneath "dfd", the net code will 573 * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a 574 * callback wakeup entry on that queue, and the wake_up() performed by the 575 * "dfd" net code will end up in ep_poll_callback(). At this point epoll 576 * (efd1) notices that it may have some event ready, so it needs to wake up 577 * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake() 578 * that ends up in another wake_up(), after having checked about the 579 * recursion constraints. That are, no more than EP_MAX_NESTS, to avoid 580 * stack blasting. 581 * 582 * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle 583 * this special case of epoll. 584 */ 585 #ifdef CONFIG_DEBUG_LOCK_ALLOC 586 587 static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, 588 unsigned pollflags) 589 { 590 struct eventpoll *ep_src; 591 unsigned long flags; 592 u8 nests = 0; 593 594 /* 595 * To set the subclass or nesting level for spin_lock_irqsave_nested() 596 * it might be natural to create a per-cpu nest count. However, since 597 * we can recurse on ep->poll_wait.lock, and a non-raw spinlock can 598 * schedule() in the -rt kernel, the per-cpu variable are no longer 599 * protected. Thus, we are introducing a per eventpoll nest field. 600 * If we are not being call from ep_poll_callback(), epi is NULL and 601 * we are at the first level of nesting, 0. Otherwise, we are being 602 * called from ep_poll_callback() and if a previous wakeup source is 603 * not an epoll file itself, we are at depth 1 since the wakeup source 604 * is depth 0. If the wakeup source is a previous epoll file in the 605 * wakeup chain then we use its nests value and record ours as 606 * nests + 1. The previous epoll file nests value is stable since its 607 * already holding its own poll_wait.lock. 608 */ 609 if (epi) { 610 if ((is_file_epoll(epi->ffd.file))) { 611 ep_src = epi->ffd.file->private_data; 612 nests = ep_src->nests; 613 } else { 614 nests = 1; 615 } 616 } 617 spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests); 618 ep->nests = nests + 1; 619 wake_up_locked_poll(&ep->poll_wait, EPOLLIN | pollflags); 620 ep->nests = 0; 621 spin_unlock_irqrestore(&ep->poll_wait.lock, flags); 622 } 623 624 #else 625 626 static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, 627 __poll_t pollflags) 628 { 629 wake_up_poll(&ep->poll_wait, EPOLLIN | pollflags); 630 } 631 632 #endif 633 634 static void ep_remove_wait_queue(struct eppoll_entry *pwq) 635 { 636 wait_queue_head_t *whead; 637 638 rcu_read_lock(); 639 /* 640 * If it is cleared by POLLFREE, it should be rcu-safe. 641 * If we read NULL we need a barrier paired with 642 * smp_store_release() in ep_poll_callback(), otherwise 643 * we rely on whead->lock. 644 */ 645 whead = smp_load_acquire(&pwq->whead); 646 if (whead) 647 remove_wait_queue(whead, &pwq->wait); 648 rcu_read_unlock(); 649 } 650 651 /* 652 * This function unregisters poll callbacks from the associated file 653 * descriptor. Must be called with "mtx" held. 654 */ 655 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) 656 { 657 struct eppoll_entry **p = &epi->pwqlist; 658 struct eppoll_entry *pwq; 659 660 while ((pwq = *p) != NULL) { 661 *p = pwq->next; 662 ep_remove_wait_queue(pwq); 663 kmem_cache_free(pwq_cache, pwq); 664 } 665 } 666 667 /* call only when ep->mtx is held */ 668 static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi) 669 { 670 return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx)); 671 } 672 673 /* call only when ep->mtx is held */ 674 static inline void ep_pm_stay_awake(struct epitem *epi) 675 { 676 struct wakeup_source *ws = ep_wakeup_source(epi); 677 678 if (ws) 679 __pm_stay_awake(ws); 680 } 681 682 static inline bool ep_has_wakeup_source(struct epitem *epi) 683 { 684 return rcu_access_pointer(epi->ws) ? true : false; 685 } 686 687 /* call when ep->mtx cannot be held (ep_poll_callback) */ 688 static inline void ep_pm_stay_awake_rcu(struct epitem *epi) 689 { 690 struct wakeup_source *ws; 691 692 rcu_read_lock(); 693 ws = rcu_dereference(epi->ws); 694 if (ws) 695 __pm_stay_awake(ws); 696 rcu_read_unlock(); 697 } 698 699 700 /* 701 * ep->mutex needs to be held because we could be hit by 702 * eventpoll_release_file() and epoll_ctl(). 703 */ 704 static void ep_start_scan(struct eventpoll *ep, struct list_head *txlist) 705 { 706 /* 707 * Steal the ready list, and re-init the original one to the 708 * empty list. Also, set ep->ovflist to NULL so that events 709 * happening while looping w/out locks, are not lost. We cannot 710 * have the poll callback to queue directly on ep->rdllist, 711 * because we want the "sproc" callback to be able to do it 712 * in a lockless way. 713 */ 714 lockdep_assert_irqs_enabled(); 715 write_lock_irq(&ep->lock); 716 list_splice_init(&ep->rdllist, txlist); 717 WRITE_ONCE(ep->ovflist, NULL); 718 write_unlock_irq(&ep->lock); 719 } 720 721 static void ep_done_scan(struct eventpoll *ep, 722 struct list_head *txlist) 723 { 724 struct epitem *epi, *nepi; 725 726 write_lock_irq(&ep->lock); 727 /* 728 * During the time we spent inside the "sproc" callback, some 729 * other events might have been queued by the poll callback. 730 * We re-insert them inside the main ready-list here. 731 */ 732 for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL; 733 nepi = epi->next, epi->next = EP_UNACTIVE_PTR) { 734 /* 735 * We need to check if the item is already in the list. 736 * During the "sproc" callback execution time, items are 737 * queued into ->ovflist but the "txlist" might already 738 * contain them, and the list_splice() below takes care of them. 739 */ 740 if (!ep_is_linked(epi)) { 741 /* 742 * ->ovflist is LIFO, so we have to reverse it in order 743 * to keep in FIFO. 744 */ 745 list_add(&epi->rdllink, &ep->rdllist); 746 ep_pm_stay_awake(epi); 747 } 748 } 749 /* 750 * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after 751 * releasing the lock, events will be queued in the normal way inside 752 * ep->rdllist. 753 */ 754 WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR); 755 756 /* 757 * Quickly re-inject items left on "txlist". 758 */ 759 list_splice(txlist, &ep->rdllist); 760 __pm_relax(ep->ws); 761 762 if (!list_empty(&ep->rdllist)) { 763 if (waitqueue_active(&ep->wq)) 764 wake_up(&ep->wq); 765 } 766 767 write_unlock_irq(&ep->lock); 768 } 769 770 static void ep_get(struct eventpoll *ep) 771 { 772 refcount_inc(&ep->refcount); 773 } 774 775 /* 776 * Returns true if the event poll can be disposed 777 */ 778 static bool ep_refcount_dec_and_test(struct eventpoll *ep) 779 { 780 if (!refcount_dec_and_test(&ep->refcount)) 781 return false; 782 783 WARN_ON_ONCE(!RB_EMPTY_ROOT(&ep->rbr.rb_root)); 784 return true; 785 } 786 787 static void ep_free(struct eventpoll *ep) 788 { 789 mutex_destroy(&ep->mtx); 790 free_uid(ep->user); 791 wakeup_source_unregister(ep->ws); 792 kfree(ep); 793 } 794 795 /* 796 * Removes a "struct epitem" from the eventpoll RB tree and deallocates 797 * all the associated resources. Must be called with "mtx" held. 798 * If the dying flag is set, do the removal only if force is true. 799 * This prevents ep_clear_and_put() from dropping all the ep references 800 * while running concurrently with eventpoll_release_file(). 801 * Returns true if the eventpoll can be disposed. 802 */ 803 static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force) 804 { 805 struct file *file = epi->ffd.file; 806 struct epitems_head *to_free; 807 struct hlist_head *head; 808 809 lockdep_assert_irqs_enabled(); 810 811 /* 812 * Removes poll wait queue hooks. 813 */ 814 ep_unregister_pollwait(ep, epi); 815 816 /* Remove the current item from the list of epoll hooks */ 817 spin_lock(&file->f_lock); 818 if (epi->dying && !force) { 819 spin_unlock(&file->f_lock); 820 return false; 821 } 822 823 to_free = NULL; 824 head = file->f_ep; 825 if (head->first == &epi->fllink && !epi->fllink.next) { 826 /* See eventpoll_release() for details. */ 827 WRITE_ONCE(file->f_ep, NULL); 828 if (!is_file_epoll(file)) { 829 struct epitems_head *v; 830 v = container_of(head, struct epitems_head, epitems); 831 if (!smp_load_acquire(&v->next)) 832 to_free = v; 833 } 834 } 835 hlist_del_rcu(&epi->fllink); 836 spin_unlock(&file->f_lock); 837 free_ephead(to_free); 838 839 rb_erase_cached(&epi->rbn, &ep->rbr); 840 841 write_lock_irq(&ep->lock); 842 if (ep_is_linked(epi)) 843 list_del_init(&epi->rdllink); 844 write_unlock_irq(&ep->lock); 845 846 wakeup_source_unregister(ep_wakeup_source(epi)); 847 /* 848 * At this point it is safe to free the eventpoll item. Use the union 849 * field epi->rcu, since we are trying to minimize the size of 850 * 'struct epitem'. The 'rbn' field is no longer in use. Protected by 851 * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make 852 * use of the rbn field. 853 */ 854 kfree_rcu(epi, rcu); 855 856 percpu_counter_dec(&ep->user->epoll_watches); 857 return ep_refcount_dec_and_test(ep); 858 } 859 860 /* 861 * ep_remove variant for callers owing an additional reference to the ep 862 */ 863 static void ep_remove_safe(struct eventpoll *ep, struct epitem *epi) 864 { 865 WARN_ON_ONCE(__ep_remove(ep, epi, false)); 866 } 867 868 static void ep_clear_and_put(struct eventpoll *ep) 869 { 870 struct rb_node *rbp, *next; 871 struct epitem *epi; 872 bool dispose; 873 874 /* We need to release all tasks waiting for these file */ 875 if (waitqueue_active(&ep->poll_wait)) 876 ep_poll_safewake(ep, NULL, 0); 877 878 mutex_lock(&ep->mtx); 879 880 /* 881 * Walks through the whole tree by unregistering poll callbacks. 882 */ 883 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { 884 epi = rb_entry(rbp, struct epitem, rbn); 885 886 ep_unregister_pollwait(ep, epi); 887 cond_resched(); 888 } 889 890 /* 891 * Walks through the whole tree and try to free each "struct epitem". 892 * Note that ep_remove_safe() will not remove the epitem in case of a 893 * racing eventpoll_release_file(); the latter will do the removal. 894 * At this point we are sure no poll callbacks will be lingering around. 895 * Since we still own a reference to the eventpoll struct, the loop can't 896 * dispose it. 897 */ 898 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = next) { 899 next = rb_next(rbp); 900 epi = rb_entry(rbp, struct epitem, rbn); 901 ep_remove_safe(ep, epi); 902 cond_resched(); 903 } 904 905 dispose = ep_refcount_dec_and_test(ep); 906 mutex_unlock(&ep->mtx); 907 908 if (dispose) 909 ep_free(ep); 910 } 911 912 static long ep_eventpoll_ioctl(struct file *file, unsigned int cmd, 913 unsigned long arg) 914 { 915 int ret; 916 917 if (!is_file_epoll(file)) 918 return -EINVAL; 919 920 switch (cmd) { 921 case EPIOCSPARAMS: 922 case EPIOCGPARAMS: 923 ret = ep_eventpoll_bp_ioctl(file, cmd, arg); 924 break; 925 default: 926 ret = -EINVAL; 927 break; 928 } 929 930 return ret; 931 } 932 933 static int ep_eventpoll_release(struct inode *inode, struct file *file) 934 { 935 struct eventpoll *ep = file->private_data; 936 937 if (ep) 938 ep_clear_and_put(ep); 939 940 return 0; 941 } 942 943 static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, int depth); 944 945 static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int depth) 946 { 947 struct eventpoll *ep = file->private_data; 948 LIST_HEAD(txlist); 949 struct epitem *epi, *tmp; 950 poll_table pt; 951 __poll_t res = 0; 952 953 init_poll_funcptr(&pt, NULL); 954 955 /* Insert inside our poll wait queue */ 956 poll_wait(file, &ep->poll_wait, wait); 957 958 /* 959 * Proceed to find out if wanted events are really available inside 960 * the ready list. 961 */ 962 mutex_lock_nested(&ep->mtx, depth); 963 ep_start_scan(ep, &txlist); 964 list_for_each_entry_safe(epi, tmp, &txlist, rdllink) { 965 if (ep_item_poll(epi, &pt, depth + 1)) { 966 res = EPOLLIN | EPOLLRDNORM; 967 break; 968 } else { 969 /* 970 * Item has been dropped into the ready list by the poll 971 * callback, but it's not actually ready, as far as 972 * caller requested events goes. We can remove it here. 973 */ 974 __pm_relax(ep_wakeup_source(epi)); 975 list_del_init(&epi->rdllink); 976 } 977 } 978 ep_done_scan(ep, &txlist); 979 mutex_unlock(&ep->mtx); 980 return res; 981 } 982 983 /* 984 * The ffd.file pointer may be in the process of being torn down due to 985 * being closed, but we may not have finished eventpoll_release() yet. 986 * 987 * Normally, even with the atomic_long_inc_not_zero, the file may have 988 * been free'd and then gotten re-allocated to something else (since 989 * files are not RCU-delayed, they are SLAB_TYPESAFE_BY_RCU). 990 * 991 * But for epoll, users hold the ep->mtx mutex, and as such any file in 992 * the process of being free'd will block in eventpoll_release_file() 993 * and thus the underlying file allocation will not be free'd, and the 994 * file re-use cannot happen. 995 * 996 * For the same reason we can avoid a rcu_read_lock() around the 997 * operation - 'ffd.file' cannot go away even if the refcount has 998 * reached zero (but we must still not call out to ->poll() functions 999 * etc). 1000 */ 1001 static struct file *epi_fget(const struct epitem *epi) 1002 { 1003 struct file *file; 1004 1005 file = epi->ffd.file; 1006 if (!file_ref_get(&file->f_ref)) 1007 file = NULL; 1008 return file; 1009 } 1010 1011 /* 1012 * Differs from ep_eventpoll_poll() in that internal callers already have 1013 * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested() 1014 * is correctly annotated. 1015 */ 1016 static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, 1017 int depth) 1018 { 1019 struct file *file = epi_fget(epi); 1020 __poll_t res; 1021 1022 /* 1023 * We could return EPOLLERR | EPOLLHUP or something, but let's 1024 * treat this more as "file doesn't exist, poll didn't happen". 1025 */ 1026 if (!file) 1027 return 0; 1028 1029 pt->_key = epi->event.events; 1030 if (!is_file_epoll(file)) 1031 res = vfs_poll(file, pt); 1032 else 1033 res = __ep_eventpoll_poll(file, pt, depth); 1034 fput(file); 1035 return res & epi->event.events; 1036 } 1037 1038 static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait) 1039 { 1040 return __ep_eventpoll_poll(file, wait, 0); 1041 } 1042 1043 #ifdef CONFIG_PROC_FS 1044 static void ep_show_fdinfo(struct seq_file *m, struct file *f) 1045 { 1046 struct eventpoll *ep = f->private_data; 1047 struct rb_node *rbp; 1048 1049 mutex_lock(&ep->mtx); 1050 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { 1051 struct epitem *epi = rb_entry(rbp, struct epitem, rbn); 1052 struct inode *inode = file_inode(epi->ffd.file); 1053 1054 seq_printf(m, "tfd: %8d events: %8x data: %16llx " 1055 " pos:%lli ino:%lx sdev:%x\n", 1056 epi->ffd.fd, epi->event.events, 1057 (long long)epi->event.data, 1058 (long long)epi->ffd.file->f_pos, 1059 inode->i_ino, inode->i_sb->s_dev); 1060 if (seq_has_overflowed(m)) 1061 break; 1062 } 1063 mutex_unlock(&ep->mtx); 1064 } 1065 #endif 1066 1067 /* File callbacks that implement the eventpoll file behaviour */ 1068 static const struct file_operations eventpoll_fops = { 1069 #ifdef CONFIG_PROC_FS 1070 .show_fdinfo = ep_show_fdinfo, 1071 #endif 1072 .release = ep_eventpoll_release, 1073 .poll = ep_eventpoll_poll, 1074 .llseek = noop_llseek, 1075 .unlocked_ioctl = ep_eventpoll_ioctl, 1076 .compat_ioctl = compat_ptr_ioctl, 1077 }; 1078 1079 /* 1080 * This is called from eventpoll_release() to unlink files from the eventpoll 1081 * interface. We need to have this facility to cleanup correctly files that are 1082 * closed without being removed from the eventpoll interface. 1083 */ 1084 void eventpoll_release_file(struct file *file) 1085 { 1086 struct eventpoll *ep; 1087 struct epitem *epi; 1088 bool dispose; 1089 1090 /* 1091 * Use the 'dying' flag to prevent a concurrent ep_clear_and_put() from 1092 * touching the epitems list before eventpoll_release_file() can access 1093 * the ep->mtx. 1094 */ 1095 again: 1096 spin_lock(&file->f_lock); 1097 if (file->f_ep && file->f_ep->first) { 1098 epi = hlist_entry(file->f_ep->first, struct epitem, fllink); 1099 epi->dying = true; 1100 spin_unlock(&file->f_lock); 1101 1102 /* 1103 * ep access is safe as we still own a reference to the ep 1104 * struct 1105 */ 1106 ep = epi->ep; 1107 mutex_lock(&ep->mtx); 1108 dispose = __ep_remove(ep, epi, true); 1109 mutex_unlock(&ep->mtx); 1110 1111 if (dispose) 1112 ep_free(ep); 1113 goto again; 1114 } 1115 spin_unlock(&file->f_lock); 1116 } 1117 1118 static int ep_alloc(struct eventpoll **pep) 1119 { 1120 struct eventpoll *ep; 1121 1122 ep = kzalloc(sizeof(*ep), GFP_KERNEL); 1123 if (unlikely(!ep)) 1124 return -ENOMEM; 1125 1126 mutex_init(&ep->mtx); 1127 rwlock_init(&ep->lock); 1128 init_waitqueue_head(&ep->wq); 1129 init_waitqueue_head(&ep->poll_wait); 1130 INIT_LIST_HEAD(&ep->rdllist); 1131 ep->rbr = RB_ROOT_CACHED; 1132 ep->ovflist = EP_UNACTIVE_PTR; 1133 ep->user = get_current_user(); 1134 refcount_set(&ep->refcount, 1); 1135 1136 *pep = ep; 1137 1138 return 0; 1139 } 1140 1141 /* 1142 * Search the file inside the eventpoll tree. The RB tree operations 1143 * are protected by the "mtx" mutex, and ep_find() must be called with 1144 * "mtx" held. 1145 */ 1146 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) 1147 { 1148 int kcmp; 1149 struct rb_node *rbp; 1150 struct epitem *epi, *epir = NULL; 1151 struct epoll_filefd ffd; 1152 1153 ep_set_ffd(&ffd, file, fd); 1154 for (rbp = ep->rbr.rb_root.rb_node; rbp; ) { 1155 epi = rb_entry(rbp, struct epitem, rbn); 1156 kcmp = ep_cmp_ffd(&ffd, &epi->ffd); 1157 if (kcmp > 0) 1158 rbp = rbp->rb_right; 1159 else if (kcmp < 0) 1160 rbp = rbp->rb_left; 1161 else { 1162 epir = epi; 1163 break; 1164 } 1165 } 1166 1167 return epir; 1168 } 1169 1170 #ifdef CONFIG_KCMP 1171 static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff) 1172 { 1173 struct rb_node *rbp; 1174 struct epitem *epi; 1175 1176 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { 1177 epi = rb_entry(rbp, struct epitem, rbn); 1178 if (epi->ffd.fd == tfd) { 1179 if (toff == 0) 1180 return epi; 1181 else 1182 toff--; 1183 } 1184 cond_resched(); 1185 } 1186 1187 return NULL; 1188 } 1189 1190 struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, 1191 unsigned long toff) 1192 { 1193 struct file *file_raw; 1194 struct eventpoll *ep; 1195 struct epitem *epi; 1196 1197 if (!is_file_epoll(file)) 1198 return ERR_PTR(-EINVAL); 1199 1200 ep = file->private_data; 1201 1202 mutex_lock(&ep->mtx); 1203 epi = ep_find_tfd(ep, tfd, toff); 1204 if (epi) 1205 file_raw = epi->ffd.file; 1206 else 1207 file_raw = ERR_PTR(-ENOENT); 1208 mutex_unlock(&ep->mtx); 1209 1210 return file_raw; 1211 } 1212 #endif /* CONFIG_KCMP */ 1213 1214 /* 1215 * Adds a new entry to the tail of the list in a lockless way, i.e. 1216 * multiple CPUs are allowed to call this function concurrently. 1217 * 1218 * Beware: it is necessary to prevent any other modifications of the 1219 * existing list until all changes are completed, in other words 1220 * concurrent list_add_tail_lockless() calls should be protected 1221 * with a read lock, where write lock acts as a barrier which 1222 * makes sure all list_add_tail_lockless() calls are fully 1223 * completed. 1224 * 1225 * Also an element can be locklessly added to the list only in one 1226 * direction i.e. either to the tail or to the head, otherwise 1227 * concurrent access will corrupt the list. 1228 * 1229 * Return: %false if element has been already added to the list, %true 1230 * otherwise. 1231 */ 1232 static inline bool list_add_tail_lockless(struct list_head *new, 1233 struct list_head *head) 1234 { 1235 struct list_head *prev; 1236 1237 /* 1238 * This is simple 'new->next = head' operation, but cmpxchg() 1239 * is used in order to detect that same element has been just 1240 * added to the list from another CPU: the winner observes 1241 * new->next == new. 1242 */ 1243 if (!try_cmpxchg(&new->next, &new, head)) 1244 return false; 1245 1246 /* 1247 * Initially ->next of a new element must be updated with the head 1248 * (we are inserting to the tail) and only then pointers are atomically 1249 * exchanged. XCHG guarantees memory ordering, thus ->next should be 1250 * updated before pointers are actually swapped and pointers are 1251 * swapped before prev->next is updated. 1252 */ 1253 1254 prev = xchg(&head->prev, new); 1255 1256 /* 1257 * It is safe to modify prev->next and new->prev, because a new element 1258 * is added only to the tail and new->next is updated before XCHG. 1259 */ 1260 1261 prev->next = new; 1262 new->prev = prev; 1263 1264 return true; 1265 } 1266 1267 /* 1268 * Chains a new epi entry to the tail of the ep->ovflist in a lockless way, 1269 * i.e. multiple CPUs are allowed to call this function concurrently. 1270 * 1271 * Return: %false if epi element has been already chained, %true otherwise. 1272 */ 1273 static inline bool chain_epi_lockless(struct epitem *epi) 1274 { 1275 struct eventpoll *ep = epi->ep; 1276 1277 /* Fast preliminary check */ 1278 if (epi->next != EP_UNACTIVE_PTR) 1279 return false; 1280 1281 /* Check that the same epi has not been just chained from another CPU */ 1282 if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR) 1283 return false; 1284 1285 /* Atomically exchange tail */ 1286 epi->next = xchg(&ep->ovflist, epi); 1287 1288 return true; 1289 } 1290 1291 /* 1292 * This is the callback that is passed to the wait queue wakeup 1293 * mechanism. It is called by the stored file descriptors when they 1294 * have events to report. 1295 * 1296 * This callback takes a read lock in order not to contend with concurrent 1297 * events from another file descriptor, thus all modifications to ->rdllist 1298 * or ->ovflist are lockless. Read lock is paired with the write lock from 1299 * ep_start/done_scan(), which stops all list modifications and guarantees 1300 * that lists state is seen correctly. 1301 * 1302 * Another thing worth to mention is that ep_poll_callback() can be called 1303 * concurrently for the same @epi from different CPUs if poll table was inited 1304 * with several wait queues entries. Plural wakeup from different CPUs of a 1305 * single wait queue is serialized by wq.lock, but the case when multiple wait 1306 * queues are used should be detected accordingly. This is detected using 1307 * cmpxchg() operation. 1308 */ 1309 static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key) 1310 { 1311 int pwake = 0; 1312 struct epitem *epi = ep_item_from_wait(wait); 1313 struct eventpoll *ep = epi->ep; 1314 __poll_t pollflags = key_to_poll(key); 1315 unsigned long flags; 1316 int ewake = 0; 1317 1318 read_lock_irqsave(&ep->lock, flags); 1319 1320 ep_set_busy_poll_napi_id(epi); 1321 1322 /* 1323 * If the event mask does not contain any poll(2) event, we consider the 1324 * descriptor to be disabled. This condition is likely the effect of the 1325 * EPOLLONESHOT bit that disables the descriptor when an event is received, 1326 * until the next EPOLL_CTL_MOD will be issued. 1327 */ 1328 if (!(epi->event.events & ~EP_PRIVATE_BITS)) 1329 goto out_unlock; 1330 1331 /* 1332 * Check the events coming with the callback. At this stage, not 1333 * every device reports the events in the "key" parameter of the 1334 * callback. We need to be able to handle both cases here, hence the 1335 * test for "key" != NULL before the event match test. 1336 */ 1337 if (pollflags && !(pollflags & epi->event.events)) 1338 goto out_unlock; 1339 1340 /* 1341 * If we are transferring events to userspace, we can hold no locks 1342 * (because we're accessing user memory, and because of linux f_op->poll() 1343 * semantics). All the events that happen during that period of time are 1344 * chained in ep->ovflist and requeued later on. 1345 */ 1346 if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) { 1347 if (chain_epi_lockless(epi)) 1348 ep_pm_stay_awake_rcu(epi); 1349 } else if (!ep_is_linked(epi)) { 1350 /* In the usual case, add event to ready list. */ 1351 if (list_add_tail_lockless(&epi->rdllink, &ep->rdllist)) 1352 ep_pm_stay_awake_rcu(epi); 1353 } 1354 1355 /* 1356 * Wake up ( if active ) both the eventpoll wait list and the ->poll() 1357 * wait list. 1358 */ 1359 if (waitqueue_active(&ep->wq)) { 1360 if ((epi->event.events & EPOLLEXCLUSIVE) && 1361 !(pollflags & POLLFREE)) { 1362 switch (pollflags & EPOLLINOUT_BITS) { 1363 case EPOLLIN: 1364 if (epi->event.events & EPOLLIN) 1365 ewake = 1; 1366 break; 1367 case EPOLLOUT: 1368 if (epi->event.events & EPOLLOUT) 1369 ewake = 1; 1370 break; 1371 case 0: 1372 ewake = 1; 1373 break; 1374 } 1375 } 1376 if (sync) 1377 wake_up_sync(&ep->wq); 1378 else 1379 wake_up(&ep->wq); 1380 } 1381 if (waitqueue_active(&ep->poll_wait)) 1382 pwake++; 1383 1384 out_unlock: 1385 read_unlock_irqrestore(&ep->lock, flags); 1386 1387 /* We have to call this outside the lock */ 1388 if (pwake) 1389 ep_poll_safewake(ep, epi, pollflags & EPOLL_URING_WAKE); 1390 1391 if (!(epi->event.events & EPOLLEXCLUSIVE)) 1392 ewake = 1; 1393 1394 if (pollflags & POLLFREE) { 1395 /* 1396 * If we race with ep_remove_wait_queue() it can miss 1397 * ->whead = NULL and do another remove_wait_queue() after 1398 * us, so we can't use __remove_wait_queue(). 1399 */ 1400 list_del_init(&wait->entry); 1401 /* 1402 * ->whead != NULL protects us from the race with 1403 * ep_clear_and_put() or ep_remove(), ep_remove_wait_queue() 1404 * takes whead->lock held by the caller. Once we nullify it, 1405 * nothing protects ep/epi or even wait. 1406 */ 1407 smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL); 1408 } 1409 1410 return ewake; 1411 } 1412 1413 /* 1414 * This is the callback that is used to add our wait queue to the 1415 * target file wakeup lists. 1416 */ 1417 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, 1418 poll_table *pt) 1419 { 1420 struct ep_pqueue *epq = container_of(pt, struct ep_pqueue, pt); 1421 struct epitem *epi = epq->epi; 1422 struct eppoll_entry *pwq; 1423 1424 if (unlikely(!epi)) // an earlier allocation has failed 1425 return; 1426 1427 pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL); 1428 if (unlikely(!pwq)) { 1429 epq->epi = NULL; 1430 return; 1431 } 1432 1433 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); 1434 pwq->whead = whead; 1435 pwq->base = epi; 1436 if (epi->event.events & EPOLLEXCLUSIVE) 1437 add_wait_queue_exclusive(whead, &pwq->wait); 1438 else 1439 add_wait_queue(whead, &pwq->wait); 1440 pwq->next = epi->pwqlist; 1441 epi->pwqlist = pwq; 1442 } 1443 1444 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi) 1445 { 1446 int kcmp; 1447 struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL; 1448 struct epitem *epic; 1449 bool leftmost = true; 1450 1451 while (*p) { 1452 parent = *p; 1453 epic = rb_entry(parent, struct epitem, rbn); 1454 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd); 1455 if (kcmp > 0) { 1456 p = &parent->rb_right; 1457 leftmost = false; 1458 } else 1459 p = &parent->rb_left; 1460 } 1461 rb_link_node(&epi->rbn, parent, p); 1462 rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost); 1463 } 1464 1465 1466 1467 #define PATH_ARR_SIZE 5 1468 /* 1469 * These are the number paths of length 1 to 5, that we are allowing to emanate 1470 * from a single file of interest. For example, we allow 1000 paths of length 1471 * 1, to emanate from each file of interest. This essentially represents the 1472 * potential wakeup paths, which need to be limited in order to avoid massive 1473 * uncontrolled wakeup storms. The common use case should be a single ep which 1474 * is connected to n file sources. In this case each file source has 1 path 1475 * of length 1. Thus, the numbers below should be more than sufficient. These 1476 * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify 1477 * and delete can't add additional paths. Protected by the epnested_mutex. 1478 */ 1479 static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 }; 1480 static int path_count[PATH_ARR_SIZE]; 1481 1482 static int path_count_inc(int nests) 1483 { 1484 /* Allow an arbitrary number of depth 1 paths */ 1485 if (nests == 0) 1486 return 0; 1487 1488 if (++path_count[nests] > path_limits[nests]) 1489 return -1; 1490 return 0; 1491 } 1492 1493 static void path_count_init(void) 1494 { 1495 int i; 1496 1497 for (i = 0; i < PATH_ARR_SIZE; i++) 1498 path_count[i] = 0; 1499 } 1500 1501 static int reverse_path_check_proc(struct hlist_head *refs, int depth) 1502 { 1503 int error = 0; 1504 struct epitem *epi; 1505 1506 if (depth > EP_MAX_NESTS) /* too deep nesting */ 1507 return -1; 1508 1509 /* CTL_DEL can remove links here, but that can't increase our count */ 1510 hlist_for_each_entry_rcu(epi, refs, fllink) { 1511 struct hlist_head *refs = &epi->ep->refs; 1512 if (hlist_empty(refs)) 1513 error = path_count_inc(depth); 1514 else 1515 error = reverse_path_check_proc(refs, depth + 1); 1516 if (error != 0) 1517 break; 1518 } 1519 return error; 1520 } 1521 1522 /** 1523 * reverse_path_check - The tfile_check_list is list of epitem_head, which have 1524 * links that are proposed to be newly added. We need to 1525 * make sure that those added links don't add too many 1526 * paths such that we will spend all our time waking up 1527 * eventpoll objects. 1528 * 1529 * Return: %zero if the proposed links don't create too many paths, 1530 * %-1 otherwise. 1531 */ 1532 static int reverse_path_check(void) 1533 { 1534 struct epitems_head *p; 1535 1536 for (p = tfile_check_list; p != EP_UNACTIVE_PTR; p = p->next) { 1537 int error; 1538 path_count_init(); 1539 rcu_read_lock(); 1540 error = reverse_path_check_proc(&p->epitems, 0); 1541 rcu_read_unlock(); 1542 if (error) 1543 return error; 1544 } 1545 return 0; 1546 } 1547 1548 static int ep_create_wakeup_source(struct epitem *epi) 1549 { 1550 struct name_snapshot n; 1551 struct wakeup_source *ws; 1552 1553 if (!epi->ep->ws) { 1554 epi->ep->ws = wakeup_source_register(NULL, "eventpoll"); 1555 if (!epi->ep->ws) 1556 return -ENOMEM; 1557 } 1558 1559 take_dentry_name_snapshot(&n, epi->ffd.file->f_path.dentry); 1560 ws = wakeup_source_register(NULL, n.name.name); 1561 release_dentry_name_snapshot(&n); 1562 1563 if (!ws) 1564 return -ENOMEM; 1565 rcu_assign_pointer(epi->ws, ws); 1566 1567 return 0; 1568 } 1569 1570 /* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */ 1571 static noinline void ep_destroy_wakeup_source(struct epitem *epi) 1572 { 1573 struct wakeup_source *ws = ep_wakeup_source(epi); 1574 1575 RCU_INIT_POINTER(epi->ws, NULL); 1576 1577 /* 1578 * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is 1579 * used internally by wakeup_source_remove, too (called by 1580 * wakeup_source_unregister), so we cannot use call_rcu 1581 */ 1582 synchronize_rcu(); 1583 wakeup_source_unregister(ws); 1584 } 1585 1586 static int attach_epitem(struct file *file, struct epitem *epi) 1587 { 1588 struct epitems_head *to_free = NULL; 1589 struct hlist_head *head = NULL; 1590 struct eventpoll *ep = NULL; 1591 1592 if (is_file_epoll(file)) 1593 ep = file->private_data; 1594 1595 if (ep) { 1596 head = &ep->refs; 1597 } else if (!READ_ONCE(file->f_ep)) { 1598 allocate: 1599 to_free = kmem_cache_zalloc(ephead_cache, GFP_KERNEL); 1600 if (!to_free) 1601 return -ENOMEM; 1602 head = &to_free->epitems; 1603 } 1604 spin_lock(&file->f_lock); 1605 if (!file->f_ep) { 1606 if (unlikely(!head)) { 1607 spin_unlock(&file->f_lock); 1608 goto allocate; 1609 } 1610 /* See eventpoll_release() for details. */ 1611 WRITE_ONCE(file->f_ep, head); 1612 to_free = NULL; 1613 } 1614 hlist_add_head_rcu(&epi->fllink, file->f_ep); 1615 spin_unlock(&file->f_lock); 1616 free_ephead(to_free); 1617 return 0; 1618 } 1619 1620 /* 1621 * Must be called with "mtx" held. 1622 */ 1623 static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, 1624 struct file *tfile, int fd, int full_check) 1625 { 1626 int error, pwake = 0; 1627 __poll_t revents; 1628 struct epitem *epi; 1629 struct ep_pqueue epq; 1630 struct eventpoll *tep = NULL; 1631 1632 if (is_file_epoll(tfile)) 1633 tep = tfile->private_data; 1634 1635 lockdep_assert_irqs_enabled(); 1636 1637 if (unlikely(percpu_counter_compare(&ep->user->epoll_watches, 1638 max_user_watches) >= 0)) 1639 return -ENOSPC; 1640 percpu_counter_inc(&ep->user->epoll_watches); 1641 1642 if (!(epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL))) { 1643 percpu_counter_dec(&ep->user->epoll_watches); 1644 return -ENOMEM; 1645 } 1646 1647 /* Item initialization follow here ... */ 1648 INIT_LIST_HEAD(&epi->rdllink); 1649 epi->ep = ep; 1650 ep_set_ffd(&epi->ffd, tfile, fd); 1651 epi->event = *event; 1652 epi->next = EP_UNACTIVE_PTR; 1653 1654 if (tep) 1655 mutex_lock_nested(&tep->mtx, 1); 1656 /* Add the current item to the list of active epoll hook for this file */ 1657 if (unlikely(attach_epitem(tfile, epi) < 0)) { 1658 if (tep) 1659 mutex_unlock(&tep->mtx); 1660 kmem_cache_free(epi_cache, epi); 1661 percpu_counter_dec(&ep->user->epoll_watches); 1662 return -ENOMEM; 1663 } 1664 1665 if (full_check && !tep) 1666 list_file(tfile); 1667 1668 /* 1669 * Add the current item to the RB tree. All RB tree operations are 1670 * protected by "mtx", and ep_insert() is called with "mtx" held. 1671 */ 1672 ep_rbtree_insert(ep, epi); 1673 if (tep) 1674 mutex_unlock(&tep->mtx); 1675 1676 /* 1677 * ep_remove_safe() calls in the later error paths can't lead to 1678 * ep_free() as the ep file itself still holds an ep reference. 1679 */ 1680 ep_get(ep); 1681 1682 /* now check if we've created too many backpaths */ 1683 if (unlikely(full_check && reverse_path_check())) { 1684 ep_remove_safe(ep, epi); 1685 return -EINVAL; 1686 } 1687 1688 if (epi->event.events & EPOLLWAKEUP) { 1689 error = ep_create_wakeup_source(epi); 1690 if (error) { 1691 ep_remove_safe(ep, epi); 1692 return error; 1693 } 1694 } 1695 1696 /* Initialize the poll table using the queue callback */ 1697 epq.epi = epi; 1698 init_poll_funcptr(&epq.pt, ep_ptable_queue_proc); 1699 1700 /* 1701 * Attach the item to the poll hooks and get current event bits. 1702 * We can safely use the file* here because its usage count has 1703 * been increased by the caller of this function. Note that after 1704 * this operation completes, the poll callback can start hitting 1705 * the new item. 1706 */ 1707 revents = ep_item_poll(epi, &epq.pt, 1); 1708 1709 /* 1710 * We have to check if something went wrong during the poll wait queue 1711 * install process. Namely an allocation for a wait queue failed due 1712 * high memory pressure. 1713 */ 1714 if (unlikely(!epq.epi)) { 1715 ep_remove_safe(ep, epi); 1716 return -ENOMEM; 1717 } 1718 1719 /* We have to drop the new item inside our item list to keep track of it */ 1720 write_lock_irq(&ep->lock); 1721 1722 /* record NAPI ID of new item if present */ 1723 ep_set_busy_poll_napi_id(epi); 1724 1725 /* If the file is already "ready" we drop it inside the ready list */ 1726 if (revents && !ep_is_linked(epi)) { 1727 list_add_tail(&epi->rdllink, &ep->rdllist); 1728 ep_pm_stay_awake(epi); 1729 1730 /* Notify waiting tasks that events are available */ 1731 if (waitqueue_active(&ep->wq)) 1732 wake_up(&ep->wq); 1733 if (waitqueue_active(&ep->poll_wait)) 1734 pwake++; 1735 } 1736 1737 write_unlock_irq(&ep->lock); 1738 1739 /* We have to call this outside the lock */ 1740 if (pwake) 1741 ep_poll_safewake(ep, NULL, 0); 1742 1743 return 0; 1744 } 1745 1746 /* 1747 * Modify the interest event mask by dropping an event if the new mask 1748 * has a match in the current file status. Must be called with "mtx" held. 1749 */ 1750 static int ep_modify(struct eventpoll *ep, struct epitem *epi, 1751 const struct epoll_event *event) 1752 { 1753 int pwake = 0; 1754 poll_table pt; 1755 1756 lockdep_assert_irqs_enabled(); 1757 1758 init_poll_funcptr(&pt, NULL); 1759 1760 /* 1761 * Set the new event interest mask before calling f_op->poll(); 1762 * otherwise we might miss an event that happens between the 1763 * f_op->poll() call and the new event set registering. 1764 */ 1765 epi->event.events = event->events; /* need barrier below */ 1766 epi->event.data = event->data; /* protected by mtx */ 1767 if (epi->event.events & EPOLLWAKEUP) { 1768 if (!ep_has_wakeup_source(epi)) 1769 ep_create_wakeup_source(epi); 1770 } else if (ep_has_wakeup_source(epi)) { 1771 ep_destroy_wakeup_source(epi); 1772 } 1773 1774 /* 1775 * The following barrier has two effects: 1776 * 1777 * 1) Flush epi changes above to other CPUs. This ensures 1778 * we do not miss events from ep_poll_callback if an 1779 * event occurs immediately after we call f_op->poll(). 1780 * We need this because we did not take ep->lock while 1781 * changing epi above (but ep_poll_callback does take 1782 * ep->lock). 1783 * 1784 * 2) We also need to ensure we do not miss _past_ events 1785 * when calling f_op->poll(). This barrier also 1786 * pairs with the barrier in wq_has_sleeper (see 1787 * comments for wq_has_sleeper). 1788 * 1789 * This barrier will now guarantee ep_poll_callback or f_op->poll 1790 * (or both) will notice the readiness of an item. 1791 */ 1792 smp_mb(); 1793 1794 /* 1795 * Get current event bits. We can safely use the file* here because 1796 * its usage count has been increased by the caller of this function. 1797 * If the item is "hot" and it is not registered inside the ready 1798 * list, push it inside. 1799 */ 1800 if (ep_item_poll(epi, &pt, 1)) { 1801 write_lock_irq(&ep->lock); 1802 if (!ep_is_linked(epi)) { 1803 list_add_tail(&epi->rdllink, &ep->rdllist); 1804 ep_pm_stay_awake(epi); 1805 1806 /* Notify waiting tasks that events are available */ 1807 if (waitqueue_active(&ep->wq)) 1808 wake_up(&ep->wq); 1809 if (waitqueue_active(&ep->poll_wait)) 1810 pwake++; 1811 } 1812 write_unlock_irq(&ep->lock); 1813 } 1814 1815 /* We have to call this outside the lock */ 1816 if (pwake) 1817 ep_poll_safewake(ep, NULL, 0); 1818 1819 return 0; 1820 } 1821 1822 static int ep_send_events(struct eventpoll *ep, 1823 struct epoll_event __user *events, int maxevents) 1824 { 1825 struct epitem *epi, *tmp; 1826 LIST_HEAD(txlist); 1827 poll_table pt; 1828 int res = 0; 1829 1830 /* 1831 * Always short-circuit for fatal signals to allow threads to make a 1832 * timely exit without the chance of finding more events available and 1833 * fetching repeatedly. 1834 */ 1835 if (fatal_signal_pending(current)) 1836 return -EINTR; 1837 1838 init_poll_funcptr(&pt, NULL); 1839 1840 mutex_lock(&ep->mtx); 1841 ep_start_scan(ep, &txlist); 1842 1843 /* 1844 * We can loop without lock because we are passed a task private list. 1845 * Items cannot vanish during the loop we are holding ep->mtx. 1846 */ 1847 list_for_each_entry_safe(epi, tmp, &txlist, rdllink) { 1848 struct wakeup_source *ws; 1849 __poll_t revents; 1850 1851 if (res >= maxevents) 1852 break; 1853 1854 /* 1855 * Activate ep->ws before deactivating epi->ws to prevent 1856 * triggering auto-suspend here (in case we reactive epi->ws 1857 * below). 1858 * 1859 * This could be rearranged to delay the deactivation of epi->ws 1860 * instead, but then epi->ws would temporarily be out of sync 1861 * with ep_is_linked(). 1862 */ 1863 ws = ep_wakeup_source(epi); 1864 if (ws) { 1865 if (ws->active) 1866 __pm_stay_awake(ep->ws); 1867 __pm_relax(ws); 1868 } 1869 1870 list_del_init(&epi->rdllink); 1871 1872 /* 1873 * If the event mask intersect the caller-requested one, 1874 * deliver the event to userspace. Again, we are holding ep->mtx, 1875 * so no operations coming from userspace can change the item. 1876 */ 1877 revents = ep_item_poll(epi, &pt, 1); 1878 if (!revents) 1879 continue; 1880 1881 events = epoll_put_uevent(revents, epi->event.data, events); 1882 if (!events) { 1883 list_add(&epi->rdllink, &txlist); 1884 ep_pm_stay_awake(epi); 1885 if (!res) 1886 res = -EFAULT; 1887 break; 1888 } 1889 res++; 1890 if (epi->event.events & EPOLLONESHOT) 1891 epi->event.events &= EP_PRIVATE_BITS; 1892 else if (!(epi->event.events & EPOLLET)) { 1893 /* 1894 * If this file has been added with Level 1895 * Trigger mode, we need to insert back inside 1896 * the ready list, so that the next call to 1897 * epoll_wait() will check again the events 1898 * availability. At this point, no one can insert 1899 * into ep->rdllist besides us. The epoll_ctl() 1900 * callers are locked out by 1901 * ep_send_events() holding "mtx" and the 1902 * poll callback will queue them in ep->ovflist. 1903 */ 1904 list_add_tail(&epi->rdllink, &ep->rdllist); 1905 ep_pm_stay_awake(epi); 1906 } 1907 } 1908 ep_done_scan(ep, &txlist); 1909 mutex_unlock(&ep->mtx); 1910 1911 return res; 1912 } 1913 1914 static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms) 1915 { 1916 struct timespec64 now; 1917 1918 if (ms < 0) 1919 return NULL; 1920 1921 if (!ms) { 1922 to->tv_sec = 0; 1923 to->tv_nsec = 0; 1924 return to; 1925 } 1926 1927 to->tv_sec = ms / MSEC_PER_SEC; 1928 to->tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC); 1929 1930 ktime_get_ts64(&now); 1931 *to = timespec64_add_safe(now, *to); 1932 return to; 1933 } 1934 1935 /* 1936 * autoremove_wake_function, but remove even on failure to wake up, because we 1937 * know that default_wake_function/ttwu will only fail if the thread is already 1938 * woken, and in that case the ep_poll loop will remove the entry anyways, not 1939 * try to reuse it. 1940 */ 1941 static int ep_autoremove_wake_function(struct wait_queue_entry *wq_entry, 1942 unsigned int mode, int sync, void *key) 1943 { 1944 int ret = default_wake_function(wq_entry, mode, sync, key); 1945 1946 /* 1947 * Pairs with list_empty_careful in ep_poll, and ensures future loop 1948 * iterations see the cause of this wakeup. 1949 */ 1950 list_del_init_careful(&wq_entry->entry); 1951 return ret; 1952 } 1953 1954 /** 1955 * ep_poll - Retrieves ready events, and delivers them to the caller-supplied 1956 * event buffer. 1957 * 1958 * @ep: Pointer to the eventpoll context. 1959 * @events: Pointer to the userspace buffer where the ready events should be 1960 * stored. 1961 * @maxevents: Size (in terms of number of events) of the caller event buffer. 1962 * @timeout: Maximum timeout for the ready events fetch operation, in 1963 * timespec. If the timeout is zero, the function will not block, 1964 * while if the @timeout ptr is NULL, the function will block 1965 * until at least one event has been retrieved (or an error 1966 * occurred). 1967 * 1968 * Return: the number of ready events which have been fetched, or an 1969 * error code, in case of error. 1970 */ 1971 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 1972 int maxevents, struct timespec64 *timeout) 1973 { 1974 int res, eavail, timed_out = 0; 1975 u64 slack = 0; 1976 wait_queue_entry_t wait; 1977 ktime_t expires, *to = NULL; 1978 1979 lockdep_assert_irqs_enabled(); 1980 1981 if (timeout && (timeout->tv_sec | timeout->tv_nsec)) { 1982 slack = select_estimate_accuracy(timeout); 1983 to = &expires; 1984 *to = timespec64_to_ktime(*timeout); 1985 } else if (timeout) { 1986 /* 1987 * Avoid the unnecessary trip to the wait queue loop, if the 1988 * caller specified a non blocking operation. 1989 */ 1990 timed_out = 1; 1991 } 1992 1993 /* 1994 * This call is racy: We may or may not see events that are being added 1995 * to the ready list under the lock (e.g., in IRQ callbacks). For cases 1996 * with a non-zero timeout, this thread will check the ready list under 1997 * lock and will add to the wait queue. For cases with a zero 1998 * timeout, the user by definition should not care and will have to 1999 * recheck again. 2000 */ 2001 eavail = ep_events_available(ep); 2002 2003 while (1) { 2004 if (eavail) { 2005 /* 2006 * Try to transfer events to user space. In case we get 2007 * 0 events and there's still timeout left over, we go 2008 * trying again in search of more luck. 2009 */ 2010 res = ep_send_events(ep, events, maxevents); 2011 if (res) 2012 return res; 2013 } 2014 2015 if (timed_out) 2016 return 0; 2017 2018 eavail = ep_busy_loop(ep, timed_out); 2019 if (eavail) 2020 continue; 2021 2022 if (signal_pending(current)) 2023 return -EINTR; 2024 2025 /* 2026 * Internally init_wait() uses autoremove_wake_function(), 2027 * thus wait entry is removed from the wait queue on each 2028 * wakeup. Why it is important? In case of several waiters 2029 * each new wakeup will hit the next waiter, giving it the 2030 * chance to harvest new event. Otherwise wakeup can be 2031 * lost. This is also good performance-wise, because on 2032 * normal wakeup path no need to call __remove_wait_queue() 2033 * explicitly, thus ep->lock is not taken, which halts the 2034 * event delivery. 2035 * 2036 * In fact, we now use an even more aggressive function that 2037 * unconditionally removes, because we don't reuse the wait 2038 * entry between loop iterations. This lets us also avoid the 2039 * performance issue if a process is killed, causing all of its 2040 * threads to wake up without being removed normally. 2041 */ 2042 init_wait(&wait); 2043 wait.func = ep_autoremove_wake_function; 2044 2045 write_lock_irq(&ep->lock); 2046 /* 2047 * Barrierless variant, waitqueue_active() is called under 2048 * the same lock on wakeup ep_poll_callback() side, so it 2049 * is safe to avoid an explicit barrier. 2050 */ 2051 __set_current_state(TASK_INTERRUPTIBLE); 2052 2053 /* 2054 * Do the final check under the lock. ep_start/done_scan() 2055 * plays with two lists (->rdllist and ->ovflist) and there 2056 * is always a race when both lists are empty for short 2057 * period of time although events are pending, so lock is 2058 * important. 2059 */ 2060 eavail = ep_events_available(ep); 2061 if (!eavail) 2062 __add_wait_queue_exclusive(&ep->wq, &wait); 2063 2064 write_unlock_irq(&ep->lock); 2065 2066 if (!eavail) 2067 timed_out = !schedule_hrtimeout_range(to, slack, 2068 HRTIMER_MODE_ABS); 2069 __set_current_state(TASK_RUNNING); 2070 2071 /* 2072 * We were woken up, thus go and try to harvest some events. 2073 * If timed out and still on the wait queue, recheck eavail 2074 * carefully under lock, below. 2075 */ 2076 eavail = 1; 2077 2078 if (!list_empty_careful(&wait.entry)) { 2079 write_lock_irq(&ep->lock); 2080 /* 2081 * If the thread timed out and is not on the wait queue, 2082 * it means that the thread was woken up after its 2083 * timeout expired before it could reacquire the lock. 2084 * Thus, when wait.entry is empty, it needs to harvest 2085 * events. 2086 */ 2087 if (timed_out) 2088 eavail = list_empty(&wait.entry); 2089 __remove_wait_queue(&ep->wq, &wait); 2090 write_unlock_irq(&ep->lock); 2091 } 2092 } 2093 } 2094 2095 /** 2096 * ep_loop_check_proc - verify that adding an epoll file inside another 2097 * epoll structure does not violate the constraints, in 2098 * terms of closed loops, or too deep chains (which can 2099 * result in excessive stack usage). 2100 * 2101 * @ep: the &struct eventpoll to be currently checked. 2102 * @depth: Current depth of the path being checked. 2103 * 2104 * Return: %zero if adding the epoll @file inside current epoll 2105 * structure @ep does not violate the constraints, or %-1 otherwise. 2106 */ 2107 static int ep_loop_check_proc(struct eventpoll *ep, int depth) 2108 { 2109 int error = 0; 2110 struct rb_node *rbp; 2111 struct epitem *epi; 2112 2113 mutex_lock_nested(&ep->mtx, depth + 1); 2114 ep->gen = loop_check_gen; 2115 for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { 2116 epi = rb_entry(rbp, struct epitem, rbn); 2117 if (unlikely(is_file_epoll(epi->ffd.file))) { 2118 struct eventpoll *ep_tovisit; 2119 ep_tovisit = epi->ffd.file->private_data; 2120 if (ep_tovisit->gen == loop_check_gen) 2121 continue; 2122 if (ep_tovisit == inserting_into || depth > EP_MAX_NESTS) 2123 error = -1; 2124 else 2125 error = ep_loop_check_proc(ep_tovisit, depth + 1); 2126 if (error != 0) 2127 break; 2128 } else { 2129 /* 2130 * If we've reached a file that is not associated with 2131 * an ep, then we need to check if the newly added 2132 * links are going to add too many wakeup paths. We do 2133 * this by adding it to the tfile_check_list, if it's 2134 * not already there, and calling reverse_path_check() 2135 * during ep_insert(). 2136 */ 2137 list_file(epi->ffd.file); 2138 } 2139 } 2140 mutex_unlock(&ep->mtx); 2141 2142 return error; 2143 } 2144 2145 /** 2146 * ep_loop_check - Performs a check to verify that adding an epoll file (@to) 2147 * into another epoll file (represented by @ep) does not create 2148 * closed loops or too deep chains. 2149 * 2150 * @ep: Pointer to the epoll we are inserting into. 2151 * @to: Pointer to the epoll to be inserted. 2152 * 2153 * Return: %zero if adding the epoll @to inside the epoll @from 2154 * does not violate the constraints, or %-1 otherwise. 2155 */ 2156 static int ep_loop_check(struct eventpoll *ep, struct eventpoll *to) 2157 { 2158 inserting_into = ep; 2159 return ep_loop_check_proc(to, 0); 2160 } 2161 2162 static void clear_tfile_check_list(void) 2163 { 2164 rcu_read_lock(); 2165 while (tfile_check_list != EP_UNACTIVE_PTR) { 2166 struct epitems_head *head = tfile_check_list; 2167 tfile_check_list = head->next; 2168 unlist_file(head); 2169 } 2170 rcu_read_unlock(); 2171 } 2172 2173 /* 2174 * Open an eventpoll file descriptor. 2175 */ 2176 static int do_epoll_create(int flags) 2177 { 2178 int error, fd; 2179 struct eventpoll *ep = NULL; 2180 struct file *file; 2181 2182 /* Check the EPOLL_* constant for consistency. */ 2183 BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC); 2184 2185 if (flags & ~EPOLL_CLOEXEC) 2186 return -EINVAL; 2187 /* 2188 * Create the internal data structure ("struct eventpoll"). 2189 */ 2190 error = ep_alloc(&ep); 2191 if (error < 0) 2192 return error; 2193 /* 2194 * Creates all the items needed to setup an eventpoll file. That is, 2195 * a file structure and a free file descriptor. 2196 */ 2197 fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC)); 2198 if (fd < 0) { 2199 error = fd; 2200 goto out_free_ep; 2201 } 2202 file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep, 2203 O_RDWR | (flags & O_CLOEXEC)); 2204 if (IS_ERR(file)) { 2205 error = PTR_ERR(file); 2206 goto out_free_fd; 2207 } 2208 ep->file = file; 2209 fd_install(fd, file); 2210 return fd; 2211 2212 out_free_fd: 2213 put_unused_fd(fd); 2214 out_free_ep: 2215 ep_clear_and_put(ep); 2216 return error; 2217 } 2218 2219 SYSCALL_DEFINE1(epoll_create1, int, flags) 2220 { 2221 return do_epoll_create(flags); 2222 } 2223 2224 SYSCALL_DEFINE1(epoll_create, int, size) 2225 { 2226 if (size <= 0) 2227 return -EINVAL; 2228 2229 return do_epoll_create(0); 2230 } 2231 2232 #ifdef CONFIG_PM_SLEEP 2233 static inline void ep_take_care_of_epollwakeup(struct epoll_event *epev) 2234 { 2235 if ((epev->events & EPOLLWAKEUP) && !capable(CAP_BLOCK_SUSPEND)) 2236 epev->events &= ~EPOLLWAKEUP; 2237 } 2238 #else 2239 static inline void ep_take_care_of_epollwakeup(struct epoll_event *epev) 2240 { 2241 epev->events &= ~EPOLLWAKEUP; 2242 } 2243 #endif 2244 2245 static inline int epoll_mutex_lock(struct mutex *mutex, int depth, 2246 bool nonblock) 2247 { 2248 if (!nonblock) { 2249 mutex_lock_nested(mutex, depth); 2250 return 0; 2251 } 2252 if (mutex_trylock(mutex)) 2253 return 0; 2254 return -EAGAIN; 2255 } 2256 2257 int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, 2258 bool nonblock) 2259 { 2260 int error; 2261 int full_check = 0; 2262 struct eventpoll *ep; 2263 struct epitem *epi; 2264 struct eventpoll *tep = NULL; 2265 2266 CLASS(fd, f)(epfd); 2267 if (fd_empty(f)) 2268 return -EBADF; 2269 2270 /* Get the "struct file *" for the target file */ 2271 CLASS(fd, tf)(fd); 2272 if (fd_empty(tf)) 2273 return -EBADF; 2274 2275 /* The target file descriptor must support poll */ 2276 if (!file_can_poll(fd_file(tf))) 2277 return -EPERM; 2278 2279 /* Check if EPOLLWAKEUP is allowed */ 2280 if (ep_op_has_event(op)) 2281 ep_take_care_of_epollwakeup(epds); 2282 2283 /* 2284 * We have to check that the file structure underneath the file descriptor 2285 * the user passed to us _is_ an eventpoll file. And also we do not permit 2286 * adding an epoll file descriptor inside itself. 2287 */ 2288 error = -EINVAL; 2289 if (fd_file(f) == fd_file(tf) || !is_file_epoll(fd_file(f))) 2290 goto error_tgt_fput; 2291 2292 /* 2293 * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only, 2294 * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation. 2295 * Also, we do not currently supported nested exclusive wakeups. 2296 */ 2297 if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) { 2298 if (op == EPOLL_CTL_MOD) 2299 goto error_tgt_fput; 2300 if (op == EPOLL_CTL_ADD && (is_file_epoll(fd_file(tf)) || 2301 (epds->events & ~EPOLLEXCLUSIVE_OK_BITS))) 2302 goto error_tgt_fput; 2303 } 2304 2305 /* 2306 * At this point it is safe to assume that the "private_data" contains 2307 * our own data structure. 2308 */ 2309 ep = fd_file(f)->private_data; 2310 2311 /* 2312 * When we insert an epoll file descriptor inside another epoll file 2313 * descriptor, there is the chance of creating closed loops, which are 2314 * better be handled here, than in more critical paths. While we are 2315 * checking for loops we also determine the list of files reachable 2316 * and hang them on the tfile_check_list, so we can check that we 2317 * haven't created too many possible wakeup paths. 2318 * 2319 * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when 2320 * the epoll file descriptor is attaching directly to a wakeup source, 2321 * unless the epoll file descriptor is nested. The purpose of taking the 2322 * 'epnested_mutex' on add is to prevent complex toplogies such as loops and 2323 * deep wakeup paths from forming in parallel through multiple 2324 * EPOLL_CTL_ADD operations. 2325 */ 2326 error = epoll_mutex_lock(&ep->mtx, 0, nonblock); 2327 if (error) 2328 goto error_tgt_fput; 2329 if (op == EPOLL_CTL_ADD) { 2330 if (READ_ONCE(fd_file(f)->f_ep) || ep->gen == loop_check_gen || 2331 is_file_epoll(fd_file(tf))) { 2332 mutex_unlock(&ep->mtx); 2333 error = epoll_mutex_lock(&epnested_mutex, 0, nonblock); 2334 if (error) 2335 goto error_tgt_fput; 2336 loop_check_gen++; 2337 full_check = 1; 2338 if (is_file_epoll(fd_file(tf))) { 2339 tep = fd_file(tf)->private_data; 2340 error = -ELOOP; 2341 if (ep_loop_check(ep, tep) != 0) 2342 goto error_tgt_fput; 2343 } 2344 error = epoll_mutex_lock(&ep->mtx, 0, nonblock); 2345 if (error) 2346 goto error_tgt_fput; 2347 } 2348 } 2349 2350 /* 2351 * Try to lookup the file inside our RB tree. Since we grabbed "mtx" 2352 * above, we can be sure to be able to use the item looked up by 2353 * ep_find() till we release the mutex. 2354 */ 2355 epi = ep_find(ep, fd_file(tf), fd); 2356 2357 error = -EINVAL; 2358 switch (op) { 2359 case EPOLL_CTL_ADD: 2360 if (!epi) { 2361 epds->events |= EPOLLERR | EPOLLHUP; 2362 error = ep_insert(ep, epds, fd_file(tf), fd, full_check); 2363 } else 2364 error = -EEXIST; 2365 break; 2366 case EPOLL_CTL_DEL: 2367 if (epi) { 2368 /* 2369 * The eventpoll itself is still alive: the refcount 2370 * can't go to zero here. 2371 */ 2372 ep_remove_safe(ep, epi); 2373 error = 0; 2374 } else { 2375 error = -ENOENT; 2376 } 2377 break; 2378 case EPOLL_CTL_MOD: 2379 if (epi) { 2380 if (!(epi->event.events & EPOLLEXCLUSIVE)) { 2381 epds->events |= EPOLLERR | EPOLLHUP; 2382 error = ep_modify(ep, epi, epds); 2383 } 2384 } else 2385 error = -ENOENT; 2386 break; 2387 } 2388 mutex_unlock(&ep->mtx); 2389 2390 error_tgt_fput: 2391 if (full_check) { 2392 clear_tfile_check_list(); 2393 loop_check_gen++; 2394 mutex_unlock(&epnested_mutex); 2395 } 2396 return error; 2397 } 2398 2399 /* 2400 * The following function implements the controller interface for 2401 * the eventpoll file that enables the insertion/removal/change of 2402 * file descriptors inside the interest set. 2403 */ 2404 SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, 2405 struct epoll_event __user *, event) 2406 { 2407 struct epoll_event epds; 2408 2409 if (ep_op_has_event(op) && 2410 copy_from_user(&epds, event, sizeof(struct epoll_event))) 2411 return -EFAULT; 2412 2413 return do_epoll_ctl(epfd, op, fd, &epds, false); 2414 } 2415 2416 /* 2417 * Implement the event wait interface for the eventpoll file. It is the kernel 2418 * part of the user space epoll_wait(2). 2419 */ 2420 static int do_epoll_wait(int epfd, struct epoll_event __user *events, 2421 int maxevents, struct timespec64 *to) 2422 { 2423 struct eventpoll *ep; 2424 2425 /* The maximum number of event must be greater than zero */ 2426 if (maxevents <= 0 || maxevents > EP_MAX_EVENTS) 2427 return -EINVAL; 2428 2429 /* Verify that the area passed by the user is writeable */ 2430 if (!access_ok(events, maxevents * sizeof(struct epoll_event))) 2431 return -EFAULT; 2432 2433 /* Get the "struct file *" for the eventpoll file */ 2434 CLASS(fd, f)(epfd); 2435 if (fd_empty(f)) 2436 return -EBADF; 2437 2438 /* 2439 * We have to check that the file structure underneath the fd 2440 * the user passed to us _is_ an eventpoll file. 2441 */ 2442 if (!is_file_epoll(fd_file(f))) 2443 return -EINVAL; 2444 2445 /* 2446 * At this point it is safe to assume that the "private_data" contains 2447 * our own data structure. 2448 */ 2449 ep = fd_file(f)->private_data; 2450 2451 /* Time to fish for events ... */ 2452 return ep_poll(ep, events, maxevents, to); 2453 } 2454 2455 SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, 2456 int, maxevents, int, timeout) 2457 { 2458 struct timespec64 to; 2459 2460 return do_epoll_wait(epfd, events, maxevents, 2461 ep_timeout_to_timespec(&to, timeout)); 2462 } 2463 2464 /* 2465 * Implement the event wait interface for the eventpoll file. It is the kernel 2466 * part of the user space epoll_pwait(2). 2467 */ 2468 static int do_epoll_pwait(int epfd, struct epoll_event __user *events, 2469 int maxevents, struct timespec64 *to, 2470 const sigset_t __user *sigmask, size_t sigsetsize) 2471 { 2472 int error; 2473 2474 /* 2475 * If the caller wants a certain signal mask to be set during the wait, 2476 * we apply it here. 2477 */ 2478 error = set_user_sigmask(sigmask, sigsetsize); 2479 if (error) 2480 return error; 2481 2482 error = do_epoll_wait(epfd, events, maxevents, to); 2483 2484 restore_saved_sigmask_unless(error == -EINTR); 2485 2486 return error; 2487 } 2488 2489 SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events, 2490 int, maxevents, int, timeout, const sigset_t __user *, sigmask, 2491 size_t, sigsetsize) 2492 { 2493 struct timespec64 to; 2494 2495 return do_epoll_pwait(epfd, events, maxevents, 2496 ep_timeout_to_timespec(&to, timeout), 2497 sigmask, sigsetsize); 2498 } 2499 2500 SYSCALL_DEFINE6(epoll_pwait2, int, epfd, struct epoll_event __user *, events, 2501 int, maxevents, const struct __kernel_timespec __user *, timeout, 2502 const sigset_t __user *, sigmask, size_t, sigsetsize) 2503 { 2504 struct timespec64 ts, *to = NULL; 2505 2506 if (timeout) { 2507 if (get_timespec64(&ts, timeout)) 2508 return -EFAULT; 2509 to = &ts; 2510 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) 2511 return -EINVAL; 2512 } 2513 2514 return do_epoll_pwait(epfd, events, maxevents, to, 2515 sigmask, sigsetsize); 2516 } 2517 2518 #ifdef CONFIG_COMPAT 2519 static int do_compat_epoll_pwait(int epfd, struct epoll_event __user *events, 2520 int maxevents, struct timespec64 *timeout, 2521 const compat_sigset_t __user *sigmask, 2522 compat_size_t sigsetsize) 2523 { 2524 long err; 2525 2526 /* 2527 * If the caller wants a certain signal mask to be set during the wait, 2528 * we apply it here. 2529 */ 2530 err = set_compat_user_sigmask(sigmask, sigsetsize); 2531 if (err) 2532 return err; 2533 2534 err = do_epoll_wait(epfd, events, maxevents, timeout); 2535 2536 restore_saved_sigmask_unless(err == -EINTR); 2537 2538 return err; 2539 } 2540 2541 COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd, 2542 struct epoll_event __user *, events, 2543 int, maxevents, int, timeout, 2544 const compat_sigset_t __user *, sigmask, 2545 compat_size_t, sigsetsize) 2546 { 2547 struct timespec64 to; 2548 2549 return do_compat_epoll_pwait(epfd, events, maxevents, 2550 ep_timeout_to_timespec(&to, timeout), 2551 sigmask, sigsetsize); 2552 } 2553 2554 COMPAT_SYSCALL_DEFINE6(epoll_pwait2, int, epfd, 2555 struct epoll_event __user *, events, 2556 int, maxevents, 2557 const struct __kernel_timespec __user *, timeout, 2558 const compat_sigset_t __user *, sigmask, 2559 compat_size_t, sigsetsize) 2560 { 2561 struct timespec64 ts, *to = NULL; 2562 2563 if (timeout) { 2564 if (get_timespec64(&ts, timeout)) 2565 return -EFAULT; 2566 to = &ts; 2567 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) 2568 return -EINVAL; 2569 } 2570 2571 return do_compat_epoll_pwait(epfd, events, maxevents, to, 2572 sigmask, sigsetsize); 2573 } 2574 2575 #endif 2576 2577 static int __init eventpoll_init(void) 2578 { 2579 struct sysinfo si; 2580 2581 si_meminfo(&si); 2582 /* 2583 * Allows top 4% of lomem to be allocated for epoll watches (per user). 2584 */ 2585 max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) / 2586 EP_ITEM_COST; 2587 BUG_ON(max_user_watches < 0); 2588 2589 /* 2590 * We can have many thousands of epitems, so prevent this from 2591 * using an extra cache line on 64-bit (and smaller) CPUs 2592 */ 2593 BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128); 2594 2595 /* Allocates slab cache used to allocate "struct epitem" items */ 2596 epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), 2597 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL); 2598 2599 /* Allocates slab cache used to allocate "struct eppoll_entry" */ 2600 pwq_cache = kmem_cache_create("eventpoll_pwq", 2601 sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL); 2602 epoll_sysctls_init(); 2603 2604 ephead_cache = kmem_cache_create("ep_head", 2605 sizeof(struct epitems_head), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL); 2606 2607 return 0; 2608 } 2609 fs_initcall(eventpoll_init); 2610