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