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 <asm/uaccess.h> 37 #include <asm/system.h> 38 #include <asm/io.h> 39 #include <asm/mman.h> 40 #include <asm/atomic.h> 41 42 /* 43 * LOCKING: 44 * There are three level of locking required by epoll : 45 * 46 * 1) epmutex (mutex) 47 * 2) ep->mtx (mutex) 48 * 3) ep->lock (spinlock) 49 * 50 * The acquire order is the one listed above, from 1 to 3. 51 * We need a spinlock (ep->lock) because we manipulate objects 52 * from inside the poll callback, that might be triggered from 53 * a wake_up() that in turn might be called from IRQ context. 54 * So we can't sleep inside the poll callback and hence we need 55 * a spinlock. During the event transfer loop (from kernel to 56 * user space) we could end up sleeping due a copy_to_user(), so 57 * we need a lock that will allow us to sleep. This lock is a 58 * mutex (ep->mtx). It is acquired during the event transfer loop, 59 * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file(). 60 * Then we also need a global mutex to serialize eventpoll_release_file() 61 * and ep_free(). 62 * This mutex is acquired by ep_free() during the epoll file 63 * cleanup path and it is also acquired by eventpoll_release_file() 64 * if a file has been pushed inside an epoll set and it is then 65 * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL). 66 * It is possible to drop the "ep->mtx" and to use the global 67 * mutex "epmutex" (together with "ep->lock") to have it working, 68 * but having "ep->mtx" will make the interface more scalable. 69 * Events that require holding "epmutex" are very rare, while for 70 * normal operations the epoll private "ep->mtx" will guarantee 71 * a better scalability. 72 */ 73 74 /* Epoll private bits inside the event mask */ 75 #define EP_PRIVATE_BITS (EPOLLONESHOT | EPOLLET) 76 77 /* Maximum number of nesting allowed inside epoll sets */ 78 #define EP_MAX_NESTS 4 79 80 #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event)) 81 82 #define EP_UNACTIVE_PTR ((void *) -1L) 83 84 #define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry)) 85 86 struct epoll_filefd { 87 struct file *file; 88 int fd; 89 }; 90 91 /* 92 * Structure used to track possible nested calls, for too deep recursions 93 * and loop cycles. 94 */ 95 struct nested_call_node { 96 struct list_head llink; 97 void *cookie; 98 void *ctx; 99 }; 100 101 /* 102 * This structure is used as collector for nested calls, to check for 103 * maximum recursion dept and loop cycles. 104 */ 105 struct nested_calls { 106 struct list_head tasks_call_list; 107 spinlock_t lock; 108 }; 109 110 /* 111 * Each file descriptor added to the eventpoll interface will 112 * have an entry of this type linked to the "rbr" RB tree. 113 */ 114 struct epitem { 115 /* RB tree node used to link this structure to the eventpoll RB tree */ 116 struct rb_node rbn; 117 118 /* List header used to link this structure to the eventpoll ready list */ 119 struct list_head rdllink; 120 121 /* 122 * Works together "struct eventpoll"->ovflist in keeping the 123 * single linked chain of items. 124 */ 125 struct epitem *next; 126 127 /* The file descriptor information this item refers to */ 128 struct epoll_filefd ffd; 129 130 /* Number of active wait queue attached to poll operations */ 131 int nwait; 132 133 /* List containing poll wait queues */ 134 struct list_head pwqlist; 135 136 /* The "container" of this item */ 137 struct eventpoll *ep; 138 139 /* List header used to link this item to the "struct file" items list */ 140 struct list_head fllink; 141 142 /* The structure that describe the interested events and the source fd */ 143 struct epoll_event event; 144 }; 145 146 /* 147 * This structure is stored inside the "private_data" member of the file 148 * structure and rapresent the main data sructure for the eventpoll 149 * interface. 150 */ 151 struct eventpoll { 152 /* Protect the this structure access */ 153 spinlock_t lock; 154 155 /* 156 * This mutex is used to ensure that files are not removed 157 * while epoll is using them. This is held during the event 158 * collection loop, the file cleanup path, the epoll file exit 159 * code and the ctl operations. 160 */ 161 struct mutex mtx; 162 163 /* Wait queue used by sys_epoll_wait() */ 164 wait_queue_head_t wq; 165 166 /* Wait queue used by file->poll() */ 167 wait_queue_head_t poll_wait; 168 169 /* List of ready file descriptors */ 170 struct list_head rdllist; 171 172 /* RB tree root used to store monitored fd structs */ 173 struct rb_root rbr; 174 175 /* 176 * This is a single linked list that chains all the "struct epitem" that 177 * happened while transfering ready events to userspace w/out 178 * holding ->lock. 179 */ 180 struct epitem *ovflist; 181 182 /* The user that created the eventpoll descriptor */ 183 struct user_struct *user; 184 }; 185 186 /* Wait structure used by the poll hooks */ 187 struct eppoll_entry { 188 /* List header used to link this structure to the "struct epitem" */ 189 struct list_head llink; 190 191 /* The "base" pointer is set to the container "struct epitem" */ 192 struct epitem *base; 193 194 /* 195 * Wait queue item that will be linked to the target file wait 196 * queue head. 197 */ 198 wait_queue_t wait; 199 200 /* The wait queue head that linked the "wait" wait queue item */ 201 wait_queue_head_t *whead; 202 }; 203 204 /* Wrapper struct used by poll queueing */ 205 struct ep_pqueue { 206 poll_table pt; 207 struct epitem *epi; 208 }; 209 210 /* Used by the ep_send_events() function as callback private data */ 211 struct ep_send_events_data { 212 int maxevents; 213 struct epoll_event __user *events; 214 }; 215 216 /* 217 * Configuration options available inside /proc/sys/fs/epoll/ 218 */ 219 /* Maximum number of epoll watched descriptors, per user */ 220 static int max_user_watches __read_mostly; 221 222 /* 223 * This mutex is used to serialize ep_free() and eventpoll_release_file(). 224 */ 225 static DEFINE_MUTEX(epmutex); 226 227 /* Used for safe wake up implementation */ 228 static struct nested_calls poll_safewake_ncalls; 229 230 /* Used to call file's f_op->poll() under the nested calls boundaries */ 231 static struct nested_calls poll_readywalk_ncalls; 232 233 /* Slab cache used to allocate "struct epitem" */ 234 static struct kmem_cache *epi_cache __read_mostly; 235 236 /* Slab cache used to allocate "struct eppoll_entry" */ 237 static struct kmem_cache *pwq_cache __read_mostly; 238 239 #ifdef CONFIG_SYSCTL 240 241 #include <linux/sysctl.h> 242 243 static int zero; 244 245 ctl_table epoll_table[] = { 246 { 247 .procname = "max_user_watches", 248 .data = &max_user_watches, 249 .maxlen = sizeof(int), 250 .mode = 0644, 251 .proc_handler = proc_dointvec_minmax, 252 .extra1 = &zero, 253 }, 254 { } 255 }; 256 #endif /* CONFIG_SYSCTL */ 257 258 259 /* Setup the structure that is used as key for the RB tree */ 260 static inline void ep_set_ffd(struct epoll_filefd *ffd, 261 struct file *file, int fd) 262 { 263 ffd->file = file; 264 ffd->fd = fd; 265 } 266 267 /* Compare RB tree keys */ 268 static inline int ep_cmp_ffd(struct epoll_filefd *p1, 269 struct epoll_filefd *p2) 270 { 271 return (p1->file > p2->file ? +1: 272 (p1->file < p2->file ? -1 : p1->fd - p2->fd)); 273 } 274 275 /* Tells us if the item is currently linked */ 276 static inline int ep_is_linked(struct list_head *p) 277 { 278 return !list_empty(p); 279 } 280 281 /* Get the "struct epitem" from a wait queue pointer */ 282 static inline struct epitem *ep_item_from_wait(wait_queue_t *p) 283 { 284 return container_of(p, struct eppoll_entry, wait)->base; 285 } 286 287 /* Get the "struct epitem" from an epoll queue wrapper */ 288 static inline struct epitem *ep_item_from_epqueue(poll_table *p) 289 { 290 return container_of(p, struct ep_pqueue, pt)->epi; 291 } 292 293 /* Tells if the epoll_ctl(2) operation needs an event copy from userspace */ 294 static inline int ep_op_has_event(int op) 295 { 296 return op != EPOLL_CTL_DEL; 297 } 298 299 /* Initialize the poll safe wake up structure */ 300 static void ep_nested_calls_init(struct nested_calls *ncalls) 301 { 302 INIT_LIST_HEAD(&ncalls->tasks_call_list); 303 spin_lock_init(&ncalls->lock); 304 } 305 306 /** 307 * ep_call_nested - Perform a bound (possibly) nested call, by checking 308 * that the recursion limit is not exceeded, and that 309 * the same nested call (by the meaning of same cookie) is 310 * no re-entered. 311 * 312 * @ncalls: Pointer to the nested_calls structure to be used for this call. 313 * @max_nests: Maximum number of allowed nesting calls. 314 * @nproc: Nested call core function pointer. 315 * @priv: Opaque data to be passed to the @nproc callback. 316 * @cookie: Cookie to be used to identify this nested call. 317 * @ctx: This instance context. 318 * 319 * Returns: Returns the code returned by the @nproc callback, or -1 if 320 * the maximum recursion limit has been exceeded. 321 */ 322 static int ep_call_nested(struct nested_calls *ncalls, int max_nests, 323 int (*nproc)(void *, void *, int), void *priv, 324 void *cookie, void *ctx) 325 { 326 int error, call_nests = 0; 327 unsigned long flags; 328 struct list_head *lsthead = &ncalls->tasks_call_list; 329 struct nested_call_node *tncur; 330 struct nested_call_node tnode; 331 332 spin_lock_irqsave(&ncalls->lock, flags); 333 334 /* 335 * Try to see if the current task is already inside this wakeup call. 336 * We use a list here, since the population inside this set is always 337 * very much limited. 338 */ 339 list_for_each_entry(tncur, lsthead, llink) { 340 if (tncur->ctx == ctx && 341 (tncur->cookie == cookie || ++call_nests > max_nests)) { 342 /* 343 * Ops ... loop detected or maximum nest level reached. 344 * We abort this wake by breaking the cycle itself. 345 */ 346 error = -1; 347 goto out_unlock; 348 } 349 } 350 351 /* Add the current task and cookie to the list */ 352 tnode.ctx = ctx; 353 tnode.cookie = cookie; 354 list_add(&tnode.llink, lsthead); 355 356 spin_unlock_irqrestore(&ncalls->lock, flags); 357 358 /* Call the nested function */ 359 error = (*nproc)(priv, cookie, call_nests); 360 361 /* Remove the current task from the list */ 362 spin_lock_irqsave(&ncalls->lock, flags); 363 list_del(&tnode.llink); 364 out_unlock: 365 spin_unlock_irqrestore(&ncalls->lock, flags); 366 367 return error; 368 } 369 370 #ifdef CONFIG_DEBUG_LOCK_ALLOC 371 static inline void ep_wake_up_nested(wait_queue_head_t *wqueue, 372 unsigned long events, int subclass) 373 { 374 unsigned long flags; 375 376 spin_lock_irqsave_nested(&wqueue->lock, flags, subclass); 377 wake_up_locked_poll(wqueue, events); 378 spin_unlock_irqrestore(&wqueue->lock, flags); 379 } 380 #else 381 static inline void ep_wake_up_nested(wait_queue_head_t *wqueue, 382 unsigned long events, int subclass) 383 { 384 wake_up_poll(wqueue, events); 385 } 386 #endif 387 388 static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests) 389 { 390 ep_wake_up_nested((wait_queue_head_t *) cookie, POLLIN, 391 1 + call_nests); 392 return 0; 393 } 394 395 /* 396 * Perform a safe wake up of the poll wait list. The problem is that 397 * with the new callback'd wake up system, it is possible that the 398 * poll callback is reentered from inside the call to wake_up() done 399 * on the poll wait queue head. The rule is that we cannot reenter the 400 * wake up code from the same task more than EP_MAX_NESTS times, 401 * and we cannot reenter the same wait queue head at all. This will 402 * enable to have a hierarchy of epoll file descriptor of no more than 403 * EP_MAX_NESTS deep. 404 */ 405 static void ep_poll_safewake(wait_queue_head_t *wq) 406 { 407 int this_cpu = get_cpu(); 408 409 ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS, 410 ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu); 411 412 put_cpu(); 413 } 414 415 /* 416 * This function unregisters poll callbacks from the associated file 417 * descriptor. Must be called with "mtx" held (or "epmutex" if called from 418 * ep_free). 419 */ 420 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) 421 { 422 struct list_head *lsthead = &epi->pwqlist; 423 struct eppoll_entry *pwq; 424 425 while (!list_empty(lsthead)) { 426 pwq = list_first_entry(lsthead, struct eppoll_entry, llink); 427 428 list_del(&pwq->llink); 429 remove_wait_queue(pwq->whead, &pwq->wait); 430 kmem_cache_free(pwq_cache, pwq); 431 } 432 } 433 434 /** 435 * ep_scan_ready_list - Scans the ready list in a way that makes possible for 436 * the scan code, to call f_op->poll(). Also allows for 437 * O(NumReady) performance. 438 * 439 * @ep: Pointer to the epoll private data structure. 440 * @sproc: Pointer to the scan callback. 441 * @priv: Private opaque data passed to the @sproc callback. 442 * 443 * Returns: The same integer error code returned by the @sproc callback. 444 */ 445 static int ep_scan_ready_list(struct eventpoll *ep, 446 int (*sproc)(struct eventpoll *, 447 struct list_head *, void *), 448 void *priv) 449 { 450 int error, pwake = 0; 451 unsigned long flags; 452 struct epitem *epi, *nepi; 453 LIST_HEAD(txlist); 454 455 /* 456 * We need to lock this because we could be hit by 457 * eventpoll_release_file() and epoll_ctl(). 458 */ 459 mutex_lock(&ep->mtx); 460 461 /* 462 * Steal the ready list, and re-init the original one to the 463 * empty list. Also, set ep->ovflist to NULL so that events 464 * happening while looping w/out locks, are not lost. We cannot 465 * have the poll callback to queue directly on ep->rdllist, 466 * because we want the "sproc" callback to be able to do it 467 * in a lockless way. 468 */ 469 spin_lock_irqsave(&ep->lock, flags); 470 list_splice_init(&ep->rdllist, &txlist); 471 ep->ovflist = NULL; 472 spin_unlock_irqrestore(&ep->lock, flags); 473 474 /* 475 * Now call the callback function. 476 */ 477 error = (*sproc)(ep, &txlist, priv); 478 479 spin_lock_irqsave(&ep->lock, flags); 480 /* 481 * During the time we spent inside the "sproc" callback, some 482 * other events might have been queued by the poll callback. 483 * We re-insert them inside the main ready-list here. 484 */ 485 for (nepi = ep->ovflist; (epi = nepi) != NULL; 486 nepi = epi->next, epi->next = EP_UNACTIVE_PTR) { 487 /* 488 * We need to check if the item is already in the list. 489 * During the "sproc" callback execution time, items are 490 * queued into ->ovflist but the "txlist" might already 491 * contain them, and the list_splice() below takes care of them. 492 */ 493 if (!ep_is_linked(&epi->rdllink)) 494 list_add_tail(&epi->rdllink, &ep->rdllist); 495 } 496 /* 497 * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after 498 * releasing the lock, events will be queued in the normal way inside 499 * ep->rdllist. 500 */ 501 ep->ovflist = EP_UNACTIVE_PTR; 502 503 /* 504 * Quickly re-inject items left on "txlist". 505 */ 506 list_splice(&txlist, &ep->rdllist); 507 508 if (!list_empty(&ep->rdllist)) { 509 /* 510 * Wake up (if active) both the eventpoll wait list and 511 * the ->poll() wait list (delayed after we release the lock). 512 */ 513 if (waitqueue_active(&ep->wq)) 514 wake_up_locked(&ep->wq); 515 if (waitqueue_active(&ep->poll_wait)) 516 pwake++; 517 } 518 spin_unlock_irqrestore(&ep->lock, flags); 519 520 mutex_unlock(&ep->mtx); 521 522 /* We have to call this outside the lock */ 523 if (pwake) 524 ep_poll_safewake(&ep->poll_wait); 525 526 return error; 527 } 528 529 /* 530 * Removes a "struct epitem" from the eventpoll RB tree and deallocates 531 * all the associated resources. Must be called with "mtx" held. 532 */ 533 static int ep_remove(struct eventpoll *ep, struct epitem *epi) 534 { 535 unsigned long flags; 536 struct file *file = epi->ffd.file; 537 538 /* 539 * Removes poll wait queue hooks. We _have_ to do this without holding 540 * the "ep->lock" otherwise a deadlock might occur. This because of the 541 * sequence of the lock acquisition. Here we do "ep->lock" then the wait 542 * queue head lock when unregistering the wait queue. The wakeup callback 543 * will run by holding the wait queue head lock and will call our callback 544 * that will try to get "ep->lock". 545 */ 546 ep_unregister_pollwait(ep, epi); 547 548 /* Remove the current item from the list of epoll hooks */ 549 spin_lock(&file->f_lock); 550 if (ep_is_linked(&epi->fllink)) 551 list_del_init(&epi->fllink); 552 spin_unlock(&file->f_lock); 553 554 rb_erase(&epi->rbn, &ep->rbr); 555 556 spin_lock_irqsave(&ep->lock, flags); 557 if (ep_is_linked(&epi->rdllink)) 558 list_del_init(&epi->rdllink); 559 spin_unlock_irqrestore(&ep->lock, flags); 560 561 /* At this point it is safe to free the eventpoll item */ 562 kmem_cache_free(epi_cache, epi); 563 564 atomic_dec(&ep->user->epoll_watches); 565 566 return 0; 567 } 568 569 static void ep_free(struct eventpoll *ep) 570 { 571 struct rb_node *rbp; 572 struct epitem *epi; 573 574 /* We need to release all tasks waiting for these file */ 575 if (waitqueue_active(&ep->poll_wait)) 576 ep_poll_safewake(&ep->poll_wait); 577 578 /* 579 * We need to lock this because we could be hit by 580 * eventpoll_release_file() while we're freeing the "struct eventpoll". 581 * We do not need to hold "ep->mtx" here because the epoll file 582 * is on the way to be removed and no one has references to it 583 * anymore. The only hit might come from eventpoll_release_file() but 584 * holding "epmutex" is sufficent here. 585 */ 586 mutex_lock(&epmutex); 587 588 /* 589 * Walks through the whole tree by unregistering poll callbacks. 590 */ 591 for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) { 592 epi = rb_entry(rbp, struct epitem, rbn); 593 594 ep_unregister_pollwait(ep, epi); 595 } 596 597 /* 598 * Walks through the whole tree by freeing each "struct epitem". At this 599 * point we are sure no poll callbacks will be lingering around, and also by 600 * holding "epmutex" we can be sure that no file cleanup code will hit 601 * us during this operation. So we can avoid the lock on "ep->lock". 602 */ 603 while ((rbp = rb_first(&ep->rbr)) != NULL) { 604 epi = rb_entry(rbp, struct epitem, rbn); 605 ep_remove(ep, epi); 606 } 607 608 mutex_unlock(&epmutex); 609 mutex_destroy(&ep->mtx); 610 free_uid(ep->user); 611 kfree(ep); 612 } 613 614 static int ep_eventpoll_release(struct inode *inode, struct file *file) 615 { 616 struct eventpoll *ep = file->private_data; 617 618 if (ep) 619 ep_free(ep); 620 621 return 0; 622 } 623 624 static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head, 625 void *priv) 626 { 627 struct epitem *epi, *tmp; 628 629 list_for_each_entry_safe(epi, tmp, head, rdllink) { 630 if (epi->ffd.file->f_op->poll(epi->ffd.file, NULL) & 631 epi->event.events) 632 return POLLIN | POLLRDNORM; 633 else { 634 /* 635 * Item has been dropped into the ready list by the poll 636 * callback, but it's not actually ready, as far as 637 * caller requested events goes. We can remove it here. 638 */ 639 list_del_init(&epi->rdllink); 640 } 641 } 642 643 return 0; 644 } 645 646 static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests) 647 { 648 return ep_scan_ready_list(priv, ep_read_events_proc, NULL); 649 } 650 651 static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait) 652 { 653 int pollflags; 654 struct eventpoll *ep = file->private_data; 655 656 /* Insert inside our poll wait queue */ 657 poll_wait(file, &ep->poll_wait, wait); 658 659 /* 660 * Proceed to find out if wanted events are really available inside 661 * the ready list. This need to be done under ep_call_nested() 662 * supervision, since the call to f_op->poll() done on listed files 663 * could re-enter here. 664 */ 665 pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS, 666 ep_poll_readyevents_proc, ep, ep, current); 667 668 return pollflags != -1 ? pollflags : 0; 669 } 670 671 /* File callbacks that implement the eventpoll file behaviour */ 672 static const struct file_operations eventpoll_fops = { 673 .release = ep_eventpoll_release, 674 .poll = ep_eventpoll_poll, 675 .llseek = noop_llseek, 676 }; 677 678 /* Fast test to see if the file is an evenpoll file */ 679 static inline int is_file_epoll(struct file *f) 680 { 681 return f->f_op == &eventpoll_fops; 682 } 683 684 /* 685 * This is called from eventpoll_release() to unlink files from the eventpoll 686 * interface. We need to have this facility to cleanup correctly files that are 687 * closed without being removed from the eventpoll interface. 688 */ 689 void eventpoll_release_file(struct file *file) 690 { 691 struct list_head *lsthead = &file->f_ep_links; 692 struct eventpoll *ep; 693 struct epitem *epi; 694 695 /* 696 * We don't want to get "file->f_lock" because it is not 697 * necessary. It is not necessary because we're in the "struct file" 698 * cleanup path, and this means that noone is using this file anymore. 699 * So, for example, epoll_ctl() cannot hit here since if we reach this 700 * point, the file counter already went to zero and fget() would fail. 701 * The only hit might come from ep_free() but by holding the mutex 702 * will correctly serialize the operation. We do need to acquire 703 * "ep->mtx" after "epmutex" because ep_remove() requires it when called 704 * from anywhere but ep_free(). 705 * 706 * Besides, ep_remove() acquires the lock, so we can't hold it here. 707 */ 708 mutex_lock(&epmutex); 709 710 while (!list_empty(lsthead)) { 711 epi = list_first_entry(lsthead, struct epitem, fllink); 712 713 ep = epi->ep; 714 list_del_init(&epi->fllink); 715 mutex_lock(&ep->mtx); 716 ep_remove(ep, epi); 717 mutex_unlock(&ep->mtx); 718 } 719 720 mutex_unlock(&epmutex); 721 } 722 723 static int ep_alloc(struct eventpoll **pep) 724 { 725 int error; 726 struct user_struct *user; 727 struct eventpoll *ep; 728 729 user = get_current_user(); 730 error = -ENOMEM; 731 ep = kzalloc(sizeof(*ep), GFP_KERNEL); 732 if (unlikely(!ep)) 733 goto free_uid; 734 735 spin_lock_init(&ep->lock); 736 mutex_init(&ep->mtx); 737 init_waitqueue_head(&ep->wq); 738 init_waitqueue_head(&ep->poll_wait); 739 INIT_LIST_HEAD(&ep->rdllist); 740 ep->rbr = RB_ROOT; 741 ep->ovflist = EP_UNACTIVE_PTR; 742 ep->user = user; 743 744 *pep = ep; 745 746 return 0; 747 748 free_uid: 749 free_uid(user); 750 return error; 751 } 752 753 /* 754 * Search the file inside the eventpoll tree. The RB tree operations 755 * are protected by the "mtx" mutex, and ep_find() must be called with 756 * "mtx" held. 757 */ 758 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) 759 { 760 int kcmp; 761 struct rb_node *rbp; 762 struct epitem *epi, *epir = NULL; 763 struct epoll_filefd ffd; 764 765 ep_set_ffd(&ffd, file, fd); 766 for (rbp = ep->rbr.rb_node; rbp; ) { 767 epi = rb_entry(rbp, struct epitem, rbn); 768 kcmp = ep_cmp_ffd(&ffd, &epi->ffd); 769 if (kcmp > 0) 770 rbp = rbp->rb_right; 771 else if (kcmp < 0) 772 rbp = rbp->rb_left; 773 else { 774 epir = epi; 775 break; 776 } 777 } 778 779 return epir; 780 } 781 782 /* 783 * This is the callback that is passed to the wait queue wakeup 784 * machanism. It is called by the stored file descriptors when they 785 * have events to report. 786 */ 787 static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key) 788 { 789 int pwake = 0; 790 unsigned long flags; 791 struct epitem *epi = ep_item_from_wait(wait); 792 struct eventpoll *ep = epi->ep; 793 794 spin_lock_irqsave(&ep->lock, flags); 795 796 /* 797 * If the event mask does not contain any poll(2) event, we consider the 798 * descriptor to be disabled. This condition is likely the effect of the 799 * EPOLLONESHOT bit that disables the descriptor when an event is received, 800 * until the next EPOLL_CTL_MOD will be issued. 801 */ 802 if (!(epi->event.events & ~EP_PRIVATE_BITS)) 803 goto out_unlock; 804 805 /* 806 * Check the events coming with the callback. At this stage, not 807 * every device reports the events in the "key" parameter of the 808 * callback. We need to be able to handle both cases here, hence the 809 * test for "key" != NULL before the event match test. 810 */ 811 if (key && !((unsigned long) key & epi->event.events)) 812 goto out_unlock; 813 814 /* 815 * If we are trasfering events to userspace, we can hold no locks 816 * (because we're accessing user memory, and because of linux f_op->poll() 817 * semantics). All the events that happens during that period of time are 818 * chained in ep->ovflist and requeued later on. 819 */ 820 if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) { 821 if (epi->next == EP_UNACTIVE_PTR) { 822 epi->next = ep->ovflist; 823 ep->ovflist = epi; 824 } 825 goto out_unlock; 826 } 827 828 /* If this file is already in the ready list we exit soon */ 829 if (!ep_is_linked(&epi->rdllink)) 830 list_add_tail(&epi->rdllink, &ep->rdllist); 831 832 /* 833 * Wake up ( if active ) both the eventpoll wait list and the ->poll() 834 * wait list. 835 */ 836 if (waitqueue_active(&ep->wq)) 837 wake_up_locked(&ep->wq); 838 if (waitqueue_active(&ep->poll_wait)) 839 pwake++; 840 841 out_unlock: 842 spin_unlock_irqrestore(&ep->lock, flags); 843 844 /* We have to call this outside the lock */ 845 if (pwake) 846 ep_poll_safewake(&ep->poll_wait); 847 848 return 1; 849 } 850 851 /* 852 * This is the callback that is used to add our wait queue to the 853 * target file wakeup lists. 854 */ 855 static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, 856 poll_table *pt) 857 { 858 struct epitem *epi = ep_item_from_epqueue(pt); 859 struct eppoll_entry *pwq; 860 861 if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) { 862 init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); 863 pwq->whead = whead; 864 pwq->base = epi; 865 add_wait_queue(whead, &pwq->wait); 866 list_add_tail(&pwq->llink, &epi->pwqlist); 867 epi->nwait++; 868 } else { 869 /* We have to signal that an error occurred */ 870 epi->nwait = -1; 871 } 872 } 873 874 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi) 875 { 876 int kcmp; 877 struct rb_node **p = &ep->rbr.rb_node, *parent = NULL; 878 struct epitem *epic; 879 880 while (*p) { 881 parent = *p; 882 epic = rb_entry(parent, struct epitem, rbn); 883 kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd); 884 if (kcmp > 0) 885 p = &parent->rb_right; 886 else 887 p = &parent->rb_left; 888 } 889 rb_link_node(&epi->rbn, parent, p); 890 rb_insert_color(&epi->rbn, &ep->rbr); 891 } 892 893 /* 894 * Must be called with "mtx" held. 895 */ 896 static int ep_insert(struct eventpoll *ep, struct epoll_event *event, 897 struct file *tfile, int fd) 898 { 899 int error, revents, pwake = 0; 900 unsigned long flags; 901 struct epitem *epi; 902 struct ep_pqueue epq; 903 904 if (unlikely(atomic_read(&ep->user->epoll_watches) >= 905 max_user_watches)) 906 return -ENOSPC; 907 if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL))) 908 return -ENOMEM; 909 910 /* Item initialization follow here ... */ 911 INIT_LIST_HEAD(&epi->rdllink); 912 INIT_LIST_HEAD(&epi->fllink); 913 INIT_LIST_HEAD(&epi->pwqlist); 914 epi->ep = ep; 915 ep_set_ffd(&epi->ffd, tfile, fd); 916 epi->event = *event; 917 epi->nwait = 0; 918 epi->next = EP_UNACTIVE_PTR; 919 920 /* Initialize the poll table using the queue callback */ 921 epq.epi = epi; 922 init_poll_funcptr(&epq.pt, ep_ptable_queue_proc); 923 924 /* 925 * Attach the item to the poll hooks and get current event bits. 926 * We can safely use the file* here because its usage count has 927 * been increased by the caller of this function. Note that after 928 * this operation completes, the poll callback can start hitting 929 * the new item. 930 */ 931 revents = tfile->f_op->poll(tfile, &epq.pt); 932 933 /* 934 * We have to check if something went wrong during the poll wait queue 935 * install process. Namely an allocation for a wait queue failed due 936 * high memory pressure. 937 */ 938 error = -ENOMEM; 939 if (epi->nwait < 0) 940 goto error_unregister; 941 942 /* Add the current item to the list of active epoll hook for this file */ 943 spin_lock(&tfile->f_lock); 944 list_add_tail(&epi->fllink, &tfile->f_ep_links); 945 spin_unlock(&tfile->f_lock); 946 947 /* 948 * Add the current item to the RB tree. All RB tree operations are 949 * protected by "mtx", and ep_insert() is called with "mtx" held. 950 */ 951 ep_rbtree_insert(ep, epi); 952 953 /* We have to drop the new item inside our item list to keep track of it */ 954 spin_lock_irqsave(&ep->lock, flags); 955 956 /* If the file is already "ready" we drop it inside the ready list */ 957 if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) { 958 list_add_tail(&epi->rdllink, &ep->rdllist); 959 960 /* Notify waiting tasks that events are available */ 961 if (waitqueue_active(&ep->wq)) 962 wake_up_locked(&ep->wq); 963 if (waitqueue_active(&ep->poll_wait)) 964 pwake++; 965 } 966 967 spin_unlock_irqrestore(&ep->lock, flags); 968 969 atomic_inc(&ep->user->epoll_watches); 970 971 /* We have to call this outside the lock */ 972 if (pwake) 973 ep_poll_safewake(&ep->poll_wait); 974 975 return 0; 976 977 error_unregister: 978 ep_unregister_pollwait(ep, epi); 979 980 /* 981 * We need to do this because an event could have been arrived on some 982 * allocated wait queue. Note that we don't care about the ep->ovflist 983 * list, since that is used/cleaned only inside a section bound by "mtx". 984 * And ep_insert() is called with "mtx" held. 985 */ 986 spin_lock_irqsave(&ep->lock, flags); 987 if (ep_is_linked(&epi->rdllink)) 988 list_del_init(&epi->rdllink); 989 spin_unlock_irqrestore(&ep->lock, flags); 990 991 kmem_cache_free(epi_cache, epi); 992 993 return error; 994 } 995 996 /* 997 * Modify the interest event mask by dropping an event if the new mask 998 * has a match in the current file status. Must be called with "mtx" held. 999 */ 1000 static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event) 1001 { 1002 int pwake = 0; 1003 unsigned int revents; 1004 1005 /* 1006 * Set the new event interest mask before calling f_op->poll(); 1007 * otherwise we might miss an event that happens between the 1008 * f_op->poll() call and the new event set registering. 1009 */ 1010 epi->event.events = event->events; 1011 epi->event.data = event->data; /* protected by mtx */ 1012 1013 /* 1014 * Get current event bits. We can safely use the file* here because 1015 * its usage count has been increased by the caller of this function. 1016 */ 1017 revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL); 1018 1019 /* 1020 * If the item is "hot" and it is not registered inside the ready 1021 * list, push it inside. 1022 */ 1023 if (revents & event->events) { 1024 spin_lock_irq(&ep->lock); 1025 if (!ep_is_linked(&epi->rdllink)) { 1026 list_add_tail(&epi->rdllink, &ep->rdllist); 1027 1028 /* Notify waiting tasks that events are available */ 1029 if (waitqueue_active(&ep->wq)) 1030 wake_up_locked(&ep->wq); 1031 if (waitqueue_active(&ep->poll_wait)) 1032 pwake++; 1033 } 1034 spin_unlock_irq(&ep->lock); 1035 } 1036 1037 /* We have to call this outside the lock */ 1038 if (pwake) 1039 ep_poll_safewake(&ep->poll_wait); 1040 1041 return 0; 1042 } 1043 1044 static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head, 1045 void *priv) 1046 { 1047 struct ep_send_events_data *esed = priv; 1048 int eventcnt; 1049 unsigned int revents; 1050 struct epitem *epi; 1051 struct epoll_event __user *uevent; 1052 1053 /* 1054 * We can loop without lock because we are passed a task private list. 1055 * Items cannot vanish during the loop because ep_scan_ready_list() is 1056 * holding "mtx" during this call. 1057 */ 1058 for (eventcnt = 0, uevent = esed->events; 1059 !list_empty(head) && eventcnt < esed->maxevents;) { 1060 epi = list_first_entry(head, struct epitem, rdllink); 1061 1062 list_del_init(&epi->rdllink); 1063 1064 revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL) & 1065 epi->event.events; 1066 1067 /* 1068 * If the event mask intersect the caller-requested one, 1069 * deliver the event to userspace. Again, ep_scan_ready_list() 1070 * is holding "mtx", so no operations coming from userspace 1071 * can change the item. 1072 */ 1073 if (revents) { 1074 if (__put_user(revents, &uevent->events) || 1075 __put_user(epi->event.data, &uevent->data)) { 1076 list_add(&epi->rdllink, head); 1077 return eventcnt ? eventcnt : -EFAULT; 1078 } 1079 eventcnt++; 1080 uevent++; 1081 if (epi->event.events & EPOLLONESHOT) 1082 epi->event.events &= EP_PRIVATE_BITS; 1083 else if (!(epi->event.events & EPOLLET)) { 1084 /* 1085 * If this file has been added with Level 1086 * Trigger mode, we need to insert back inside 1087 * the ready list, so that the next call to 1088 * epoll_wait() will check again the events 1089 * availability. At this point, noone can insert 1090 * into ep->rdllist besides us. The epoll_ctl() 1091 * callers are locked out by 1092 * ep_scan_ready_list() holding "mtx" and the 1093 * poll callback will queue them in ep->ovflist. 1094 */ 1095 list_add_tail(&epi->rdllink, &ep->rdllist); 1096 } 1097 } 1098 } 1099 1100 return eventcnt; 1101 } 1102 1103 static int ep_send_events(struct eventpoll *ep, 1104 struct epoll_event __user *events, int maxevents) 1105 { 1106 struct ep_send_events_data esed; 1107 1108 esed.maxevents = maxevents; 1109 esed.events = events; 1110 1111 return ep_scan_ready_list(ep, ep_send_events_proc, &esed); 1112 } 1113 1114 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 1115 int maxevents, long timeout) 1116 { 1117 int res, eavail, timed_out = 0; 1118 unsigned long flags; 1119 long slack; 1120 wait_queue_t wait; 1121 struct timespec end_time; 1122 ktime_t expires, *to = NULL; 1123 1124 if (timeout > 0) { 1125 ktime_get_ts(&end_time); 1126 timespec_add_ns(&end_time, (u64)timeout * NSEC_PER_MSEC); 1127 slack = select_estimate_accuracy(&end_time); 1128 to = &expires; 1129 *to = timespec_to_ktime(end_time); 1130 } else if (timeout == 0) { 1131 timed_out = 1; 1132 } 1133 1134 retry: 1135 spin_lock_irqsave(&ep->lock, flags); 1136 1137 res = 0; 1138 if (list_empty(&ep->rdllist)) { 1139 /* 1140 * We don't have any available event to return to the caller. 1141 * We need to sleep here, and we will be wake up by 1142 * ep_poll_callback() when events will become available. 1143 */ 1144 init_waitqueue_entry(&wait, current); 1145 __add_wait_queue_exclusive(&ep->wq, &wait); 1146 1147 for (;;) { 1148 /* 1149 * We don't want to sleep if the ep_poll_callback() sends us 1150 * a wakeup in between. That's why we set the task state 1151 * to TASK_INTERRUPTIBLE before doing the checks. 1152 */ 1153 set_current_state(TASK_INTERRUPTIBLE); 1154 if (!list_empty(&ep->rdllist) || timed_out) 1155 break; 1156 if (signal_pending(current)) { 1157 res = -EINTR; 1158 break; 1159 } 1160 1161 spin_unlock_irqrestore(&ep->lock, flags); 1162 if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) 1163 timed_out = 1; 1164 1165 spin_lock_irqsave(&ep->lock, flags); 1166 } 1167 __remove_wait_queue(&ep->wq, &wait); 1168 1169 set_current_state(TASK_RUNNING); 1170 } 1171 /* Is it worth to try to dig for events ? */ 1172 eavail = !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR; 1173 1174 spin_unlock_irqrestore(&ep->lock, flags); 1175 1176 /* 1177 * Try to transfer events to user space. In case we get 0 events and 1178 * there's still timeout left over, we go trying again in search of 1179 * more luck. 1180 */ 1181 if (!res && eavail && 1182 !(res = ep_send_events(ep, events, maxevents)) && !timed_out) 1183 goto retry; 1184 1185 return res; 1186 } 1187 1188 /* 1189 * Open an eventpoll file descriptor. 1190 */ 1191 SYSCALL_DEFINE1(epoll_create1, int, flags) 1192 { 1193 int error; 1194 struct eventpoll *ep = NULL; 1195 1196 /* Check the EPOLL_* constant for consistency. */ 1197 BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC); 1198 1199 if (flags & ~EPOLL_CLOEXEC) 1200 return -EINVAL; 1201 /* 1202 * Create the internal data structure ("struct eventpoll"). 1203 */ 1204 error = ep_alloc(&ep); 1205 if (error < 0) 1206 return error; 1207 /* 1208 * Creates all the items needed to setup an eventpoll file. That is, 1209 * a file structure and a free file descriptor. 1210 */ 1211 error = anon_inode_getfd("[eventpoll]", &eventpoll_fops, ep, 1212 O_RDWR | (flags & O_CLOEXEC)); 1213 if (error < 0) 1214 ep_free(ep); 1215 1216 return error; 1217 } 1218 1219 SYSCALL_DEFINE1(epoll_create, int, size) 1220 { 1221 if (size <= 0) 1222 return -EINVAL; 1223 1224 return sys_epoll_create1(0); 1225 } 1226 1227 /* 1228 * The following function implements the controller interface for 1229 * the eventpoll file that enables the insertion/removal/change of 1230 * file descriptors inside the interest set. 1231 */ 1232 SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, 1233 struct epoll_event __user *, event) 1234 { 1235 int error; 1236 struct file *file, *tfile; 1237 struct eventpoll *ep; 1238 struct epitem *epi; 1239 struct epoll_event epds; 1240 1241 error = -EFAULT; 1242 if (ep_op_has_event(op) && 1243 copy_from_user(&epds, event, sizeof(struct epoll_event))) 1244 goto error_return; 1245 1246 /* Get the "struct file *" for the eventpoll file */ 1247 error = -EBADF; 1248 file = fget(epfd); 1249 if (!file) 1250 goto error_return; 1251 1252 /* Get the "struct file *" for the target file */ 1253 tfile = fget(fd); 1254 if (!tfile) 1255 goto error_fput; 1256 1257 /* The target file descriptor must support poll */ 1258 error = -EPERM; 1259 if (!tfile->f_op || !tfile->f_op->poll) 1260 goto error_tgt_fput; 1261 1262 /* 1263 * We have to check that the file structure underneath the file descriptor 1264 * the user passed to us _is_ an eventpoll file. And also we do not permit 1265 * adding an epoll file descriptor inside itself. 1266 */ 1267 error = -EINVAL; 1268 if (file == tfile || !is_file_epoll(file)) 1269 goto error_tgt_fput; 1270 1271 /* 1272 * At this point it is safe to assume that the "private_data" contains 1273 * our own data structure. 1274 */ 1275 ep = file->private_data; 1276 1277 mutex_lock(&ep->mtx); 1278 1279 /* 1280 * Try to lookup the file inside our RB tree, Since we grabbed "mtx" 1281 * above, we can be sure to be able to use the item looked up by 1282 * ep_find() till we release the mutex. 1283 */ 1284 epi = ep_find(ep, tfile, fd); 1285 1286 error = -EINVAL; 1287 switch (op) { 1288 case EPOLL_CTL_ADD: 1289 if (!epi) { 1290 epds.events |= POLLERR | POLLHUP; 1291 error = ep_insert(ep, &epds, tfile, fd); 1292 } else 1293 error = -EEXIST; 1294 break; 1295 case EPOLL_CTL_DEL: 1296 if (epi) 1297 error = ep_remove(ep, epi); 1298 else 1299 error = -ENOENT; 1300 break; 1301 case EPOLL_CTL_MOD: 1302 if (epi) { 1303 epds.events |= POLLERR | POLLHUP; 1304 error = ep_modify(ep, epi, &epds); 1305 } else 1306 error = -ENOENT; 1307 break; 1308 } 1309 mutex_unlock(&ep->mtx); 1310 1311 error_tgt_fput: 1312 fput(tfile); 1313 error_fput: 1314 fput(file); 1315 error_return: 1316 1317 return error; 1318 } 1319 1320 /* 1321 * Implement the event wait interface for the eventpoll file. It is the kernel 1322 * part of the user space epoll_wait(2). 1323 */ 1324 SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, 1325 int, maxevents, int, timeout) 1326 { 1327 int error; 1328 struct file *file; 1329 struct eventpoll *ep; 1330 1331 /* The maximum number of event must be greater than zero */ 1332 if (maxevents <= 0 || maxevents > EP_MAX_EVENTS) 1333 return -EINVAL; 1334 1335 /* Verify that the area passed by the user is writeable */ 1336 if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event))) { 1337 error = -EFAULT; 1338 goto error_return; 1339 } 1340 1341 /* Get the "struct file *" for the eventpoll file */ 1342 error = -EBADF; 1343 file = fget(epfd); 1344 if (!file) 1345 goto error_return; 1346 1347 /* 1348 * We have to check that the file structure underneath the fd 1349 * the user passed to us _is_ an eventpoll file. 1350 */ 1351 error = -EINVAL; 1352 if (!is_file_epoll(file)) 1353 goto error_fput; 1354 1355 /* 1356 * At this point it is safe to assume that the "private_data" contains 1357 * our own data structure. 1358 */ 1359 ep = file->private_data; 1360 1361 /* Time to fish for events ... */ 1362 error = ep_poll(ep, events, maxevents, timeout); 1363 1364 error_fput: 1365 fput(file); 1366 error_return: 1367 1368 return error; 1369 } 1370 1371 #ifdef HAVE_SET_RESTORE_SIGMASK 1372 1373 /* 1374 * Implement the event wait interface for the eventpoll file. It is the kernel 1375 * part of the user space epoll_pwait(2). 1376 */ 1377 SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events, 1378 int, maxevents, int, timeout, const sigset_t __user *, sigmask, 1379 size_t, sigsetsize) 1380 { 1381 int error; 1382 sigset_t ksigmask, sigsaved; 1383 1384 /* 1385 * If the caller wants a certain signal mask to be set during the wait, 1386 * we apply it here. 1387 */ 1388 if (sigmask) { 1389 if (sigsetsize != sizeof(sigset_t)) 1390 return -EINVAL; 1391 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask))) 1392 return -EFAULT; 1393 sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP)); 1394 sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved); 1395 } 1396 1397 error = sys_epoll_wait(epfd, events, maxevents, timeout); 1398 1399 /* 1400 * If we changed the signal mask, we need to restore the original one. 1401 * In case we've got a signal while waiting, we do not restore the 1402 * signal mask yet, and we allow do_signal() to deliver the signal on 1403 * the way back to userspace, before the signal mask is restored. 1404 */ 1405 if (sigmask) { 1406 if (error == -EINTR) { 1407 memcpy(¤t->saved_sigmask, &sigsaved, 1408 sizeof(sigsaved)); 1409 set_restore_sigmask(); 1410 } else 1411 sigprocmask(SIG_SETMASK, &sigsaved, NULL); 1412 } 1413 1414 return error; 1415 } 1416 1417 #endif /* HAVE_SET_RESTORE_SIGMASK */ 1418 1419 static int __init eventpoll_init(void) 1420 { 1421 struct sysinfo si; 1422 1423 si_meminfo(&si); 1424 /* 1425 * Allows top 4% of lomem to be allocated for epoll watches (per user). 1426 */ 1427 max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) / 1428 EP_ITEM_COST; 1429 1430 /* Initialize the structure used to perform safe poll wait head wake ups */ 1431 ep_nested_calls_init(&poll_safewake_ncalls); 1432 1433 /* Initialize the structure used to perform file's f_op->poll() calls */ 1434 ep_nested_calls_init(&poll_readywalk_ncalls); 1435 1436 /* Allocates slab cache used to allocate "struct epitem" items */ 1437 epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), 1438 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); 1439 1440 /* Allocates slab cache used to allocate "struct eppoll_entry" */ 1441 pwq_cache = kmem_cache_create("eventpoll_pwq", 1442 sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL); 1443 1444 return 0; 1445 } 1446 fs_initcall(eventpoll_init); 1447