linux/fs/eventpoll.c
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   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 <linux/freezer.h>
  38#include <asm/uaccess.h>
  39#include <asm/io.h>
  40#include <asm/mman.h>
  41#include <linux/atomic.h>
  42#include <linux/proc_fs.h>
  43#include <linux/seq_file.h>
  44#include <linux/compat.h>
  45
  46/*
  47 * LOCKING:
  48 * There are three level of locking required by epoll :
  49 *
  50 * 1) epmutex (mutex)
  51 * 2) ep->mtx (mutex)
  52 * 3) ep->lock (spinlock)
  53 *
  54 * The acquire order is the one listed above, from 1 to 3.
  55 * We need a spinlock (ep->lock) because we manipulate objects
  56 * from inside the poll callback, that might be triggered from
  57 * a wake_up() that in turn might be called from IRQ context.
  58 * So we can't sleep inside the poll callback and hence we need
  59 * a spinlock. During the event transfer loop (from kernel to
  60 * user space) we could end up sleeping due a copy_to_user(), so
  61 * we need a lock that will allow us to sleep. This lock is a
  62 * mutex (ep->mtx). It is acquired during the event transfer loop,
  63 * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
  64 * Then we also need a global mutex to serialize eventpoll_release_file()
  65 * and ep_free().
  66 * This mutex is acquired by ep_free() during the epoll file
  67 * cleanup path and it is also acquired by eventpoll_release_file()
  68 * if a file has been pushed inside an epoll set and it is then
  69 * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
  70 * It is also acquired when inserting an epoll fd onto another epoll
  71 * fd. We do this so that we walk the epoll tree and ensure that this
  72 * insertion does not create a cycle of epoll file descriptors, which
  73 * could lead to deadlock. We need a global mutex to prevent two
  74 * simultaneous inserts (A into B and B into A) from racing and
  75 * constructing a cycle without either insert observing that it is
  76 * going to.
  77 * It is necessary to acquire multiple "ep->mtx"es at once in the
  78 * case when one epoll fd is added to another. In this case, we
  79 * always acquire the locks in the order of nesting (i.e. after
  80 * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
  81 * before e2->mtx). Since we disallow cycles of epoll file
  82 * descriptors, this ensures that the mutexes are well-ordered. In
  83 * order to communicate this nesting to lockdep, when walking a tree
  84 * of epoll file descriptors, we use the current recursion depth as
  85 * the lockdep subkey.
  86 * It is possible to drop the "ep->mtx" and to use the global
  87 * mutex "epmutex" (together with "ep->lock") to have it working,
  88 * but having "ep->mtx" will make the interface more scalable.
  89 * Events that require holding "epmutex" are very rare, while for
  90 * normal operations the epoll private "ep->mtx" will guarantee
  91 * a better scalability.
  92 */
  93
  94/* Epoll private bits inside the event mask */
  95#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET)
  96
  97/* Maximum number of nesting allowed inside epoll sets */
  98#define EP_MAX_NESTS 4
  99
 100#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
 101
 102#define EP_UNACTIVE_PTR ((void *) -1L)
 103
 104#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
 105
 106struct epoll_filefd {
 107        struct file *file;
 108        int fd;
 109} __packed;
 110
 111/*
 112 * Structure used to track possible nested calls, for too deep recursions
 113 * and loop cycles.
 114 */
 115struct nested_call_node {
 116        struct list_head llink;
 117        void *cookie;
 118        void *ctx;
 119};
 120
 121/*
 122 * This structure is used as collector for nested calls, to check for
 123 * maximum recursion dept and loop cycles.
 124 */
 125struct nested_calls {
 126        struct list_head tasks_call_list;
 127        spinlock_t lock;
 128};
 129
 130/*
 131 * Each file descriptor added to the eventpoll interface will
 132 * have an entry of this type linked to the "rbr" RB tree.
 133 * Avoid increasing the size of this struct, there can be many thousands
 134 * of these on a server and we do not want this to take another cache line.
 135 */
 136struct epitem {
 137        /* RB tree node used to link this structure to the eventpoll RB tree */
 138        struct rb_node rbn;
 139
 140        /* List header used to link this structure to the eventpoll ready list */
 141        struct list_head rdllink;
 142
 143        /*
 144         * Works together "struct eventpoll"->ovflist in keeping the
 145         * single linked chain of items.
 146         */
 147        struct epitem *next;
 148
 149        /* The file descriptor information this item refers to */
 150        struct epoll_filefd ffd;
 151
 152        /* Number of active wait queue attached to poll operations */
 153        int nwait;
 154
 155        /* List containing poll wait queues */
 156        struct list_head pwqlist;
 157
 158        /* The "container" of this item */
 159        struct eventpoll *ep;
 160
 161        /* List header used to link this item to the "struct file" items list */
 162        struct list_head fllink;
 163
 164        /* wakeup_source used when EPOLLWAKEUP is set */
 165        struct wakeup_source __rcu *ws;
 166
 167        /* The structure that describe the interested events and the source fd */
 168        struct epoll_event event;
 169};
 170
 171/*
 172 * This structure is stored inside the "private_data" member of the file
 173 * structure and represents the main data structure for the eventpoll
 174 * interface.
 175 */
 176struct eventpoll {
 177        /* Protect the access to this structure */
 178        spinlock_t lock;
 179
 180        /*
 181         * This mutex is used to ensure that files are not removed
 182         * while epoll is using them. This is held during the event
 183         * collection loop, the file cleanup path, the epoll file exit
 184         * code and the ctl operations.
 185         */
 186        struct mutex mtx;
 187
 188        /* Wait queue used by sys_epoll_wait() */
 189        wait_queue_head_t wq;
 190
 191        /* Wait queue used by file->poll() */
 192        wait_queue_head_t poll_wait;
 193
 194        /* List of ready file descriptors */
 195        struct list_head rdllist;
 196
 197        /* RB tree root used to store monitored fd structs */
 198        struct rb_root rbr;
 199
 200        /*
 201         * This is a single linked list that chains all the "struct epitem" that
 202         * happened while transferring ready events to userspace w/out
 203         * holding ->lock.
 204         */
 205        struct epitem *ovflist;
 206
 207        /* wakeup_source used when ep_scan_ready_list is running */
 208        struct wakeup_source *ws;
 209
 210        /* The user that created the eventpoll descriptor */
 211        struct user_struct *user;
 212
 213        struct file *file;
 214
 215        /* used to optimize loop detection check */
 216        int visited;
 217        struct list_head visited_list_link;
 218};
 219
 220/* Wait structure used by the poll hooks */
 221struct eppoll_entry {
 222        /* List header used to link this structure to the "struct epitem" */
 223        struct list_head llink;
 224
 225        /* The "base" pointer is set to the container "struct epitem" */
 226        struct epitem *base;
 227
 228        /*
 229         * Wait queue item that will be linked to the target file wait
 230         * queue head.
 231         */
 232        wait_queue_t wait;
 233
 234        /* The wait queue head that linked the "wait" wait queue item */
 235        wait_queue_head_t *whead;
 236};
 237
 238/* Wrapper struct used by poll queueing */
 239struct ep_pqueue {
 240        poll_table pt;
 241        struct epitem *epi;
 242};
 243
 244/* Used by the ep_send_events() function as callback private data */
 245struct ep_send_events_data {
 246        int maxevents;
 247        struct epoll_event __user *events;
 248};
 249
 250/*
 251 * Configuration options available inside /proc/sys/fs/epoll/
 252 */
 253/* Maximum number of epoll watched descriptors, per user */
 254static long max_user_watches __read_mostly;
 255
 256/*
 257 * This mutex is used to serialize ep_free() and eventpoll_release_file().
 258 */
 259static DEFINE_MUTEX(epmutex);
 260
 261/* Used to check for epoll file descriptor inclusion loops */
 262static struct nested_calls poll_loop_ncalls;
 263
 264/* Used for safe wake up implementation */
 265static struct nested_calls poll_safewake_ncalls;
 266
 267/* Used to call file's f_op->poll() under the nested calls boundaries */
 268static struct nested_calls poll_readywalk_ncalls;
 269
 270/* Slab cache used to allocate "struct epitem" */
 271static struct kmem_cache *epi_cache __read_mostly;
 272
 273/* Slab cache used to allocate "struct eppoll_entry" */
 274static struct kmem_cache *pwq_cache __read_mostly;
 275
 276/* Visited nodes during ep_loop_check(), so we can unset them when we finish */
 277static LIST_HEAD(visited_list);
 278
 279/*
 280 * List of files with newly added links, where we may need to limit the number
 281 * of emanating paths. Protected by the epmutex.
 282 */
 283static LIST_HEAD(tfile_check_list);
 284
 285#ifdef CONFIG_SYSCTL
 286
 287#include <linux/sysctl.h>
 288
 289static long zero;
 290static long long_max = LONG_MAX;
 291
 292ctl_table epoll_table[] = {
 293        {
 294                .procname       = "max_user_watches",
 295                .data           = &max_user_watches,
 296                .maxlen         = sizeof(max_user_watches),
 297                .mode           = 0644,
 298                .proc_handler   = proc_doulongvec_minmax,
 299                .extra1         = &zero,
 300                .extra2         = &long_max,
 301        },
 302        { }
 303};
 304#endif /* CONFIG_SYSCTL */
 305
 306static const struct file_operations eventpoll_fops;
 307
 308static inline int is_file_epoll(struct file *f)
 309{
 310        return f->f_op == &eventpoll_fops;
 311}
 312
 313/* Setup the structure that is used as key for the RB tree */
 314static inline void ep_set_ffd(struct epoll_filefd *ffd,
 315                              struct file *file, int fd)
 316{
 317        ffd->file = file;
 318        ffd->fd = fd;
 319}
 320
 321/* Compare RB tree keys */
 322static inline int ep_cmp_ffd(struct epoll_filefd *p1,
 323                             struct epoll_filefd *p2)
 324{
 325        return (p1->file > p2->file ? +1:
 326                (p1->file < p2->file ? -1 : p1->fd - p2->fd));
 327}
 328
 329/* Tells us if the item is currently linked */
 330static inline int ep_is_linked(struct list_head *p)
 331{
 332        return !list_empty(p);
 333}
 334
 335static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_t *p)
 336{
 337        return container_of(p, struct eppoll_entry, wait);
 338}
 339
 340/* Get the "struct epitem" from a wait queue pointer */
 341static inline struct epitem *ep_item_from_wait(wait_queue_t *p)
 342{
 343        return container_of(p, struct eppoll_entry, wait)->base;
 344}
 345
 346/* Get the "struct epitem" from an epoll queue wrapper */
 347static inline struct epitem *ep_item_from_epqueue(poll_table *p)
 348{
 349        return container_of(p, struct ep_pqueue, pt)->epi;
 350}
 351
 352/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
 353static inline int ep_op_has_event(int op)
 354{
 355        return op != EPOLL_CTL_DEL;
 356}
 357
 358/* Initialize the poll safe wake up structure */
 359static void ep_nested_calls_init(struct nested_calls *ncalls)
 360{
 361        INIT_LIST_HEAD(&ncalls->tasks_call_list);
 362        spin_lock_init(&ncalls->lock);
 363}
 364
 365/**
 366 * ep_events_available - Checks if ready events might be available.
 367 *
 368 * @ep: Pointer to the eventpoll context.
 369 *
 370 * Returns: Returns a value different than zero if ready events are available,
 371 *          or zero otherwise.
 372 */
 373static inline int ep_events_available(struct eventpoll *ep)
 374{
 375        return !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
 376}
 377
 378/**
 379 * ep_call_nested - Perform a bound (possibly) nested call, by checking
 380 *                  that the recursion limit is not exceeded, and that
 381 *                  the same nested call (by the meaning of same cookie) is
 382 *                  no re-entered.
 383 *
 384 * @ncalls: Pointer to the nested_calls structure to be used for this call.
 385 * @max_nests: Maximum number of allowed nesting calls.
 386 * @nproc: Nested call core function pointer.
 387 * @priv: Opaque data to be passed to the @nproc callback.
 388 * @cookie: Cookie to be used to identify this nested call.
 389 * @ctx: This instance context.
 390 *
 391 * Returns: Returns the code returned by the @nproc callback, or -1 if
 392 *          the maximum recursion limit has been exceeded.
 393 */
 394static int ep_call_nested(struct nested_calls *ncalls, int max_nests,
 395                          int (*nproc)(void *, void *, int), void *priv,
 396                          void *cookie, void *ctx)
 397{
 398        int error, call_nests = 0;
 399        unsigned long flags;
 400        struct list_head *lsthead = &ncalls->tasks_call_list;
 401        struct nested_call_node *tncur;
 402        struct nested_call_node tnode;
 403
 404        spin_lock_irqsave(&ncalls->lock, flags);
 405
 406        /*
 407         * Try to see if the current task is already inside this wakeup call.
 408         * We use a list here, since the population inside this set is always
 409         * very much limited.
 410         */
 411        list_for_each_entry(tncur, lsthead, llink) {
 412                if (tncur->ctx == ctx &&
 413                    (tncur->cookie == cookie || ++call_nests > max_nests)) {
 414                        /*
 415                         * Ops ... loop detected or maximum nest level reached.
 416                         * We abort this wake by breaking the cycle itself.
 417                         */
 418                        error = -1;
 419                        goto out_unlock;
 420                }
 421        }
 422
 423        /* Add the current task and cookie to the list */
 424        tnode.ctx = ctx;
 425        tnode.cookie = cookie;
 426        list_add(&tnode.llink, lsthead);
 427
 428        spin_unlock_irqrestore(&ncalls->lock, flags);
 429
 430        /* Call the nested function */
 431        error = (*nproc)(priv, cookie, call_nests);
 432
 433        /* Remove the current task from the list */
 434        spin_lock_irqsave(&ncalls->lock, flags);
 435        list_del(&tnode.llink);
 436out_unlock:
 437        spin_unlock_irqrestore(&ncalls->lock, flags);
 438
 439        return error;
 440}
 441
 442/*
 443 * As described in commit 0ccf831cb lockdep: annotate epoll
 444 * the use of wait queues used by epoll is done in a very controlled
 445 * manner. Wake ups can nest inside each other, but are never done
 446 * with the same locking. For example:
 447 *
 448 *   dfd = socket(...);
 449 *   efd1 = epoll_create();
 450 *   efd2 = epoll_create();
 451 *   epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
 452 *   epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
 453 *
 454 * When a packet arrives to the device underneath "dfd", the net code will
 455 * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
 456 * callback wakeup entry on that queue, and the wake_up() performed by the
 457 * "dfd" net code will end up in ep_poll_callback(). At this point epoll
 458 * (efd1) notices that it may have some event ready, so it needs to wake up
 459 * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
 460 * that ends up in another wake_up(), after having checked about the
 461 * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
 462 * avoid stack blasting.
 463 *
 464 * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
 465 * this special case of epoll.
 466 */
 467#ifdef CONFIG_DEBUG_LOCK_ALLOC
 468static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
 469                                     unsigned long events, int subclass)
 470{
 471        unsigned long flags;
 472
 473        spin_lock_irqsave_nested(&wqueue->lock, flags, subclass);
 474        wake_up_locked_poll(wqueue, events);
 475        spin_unlock_irqrestore(&wqueue->lock, flags);
 476}
 477#else
 478static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
 479                                     unsigned long events, int subclass)
 480{
 481        wake_up_poll(wqueue, events);
 482}
 483#endif
 484
 485static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
 486{
 487        ep_wake_up_nested((wait_queue_head_t *) cookie, POLLIN,
 488                          1 + call_nests);
 489        return 0;
 490}
 491
 492/*
 493 * Perform a safe wake up of the poll wait list. The problem is that
 494 * with the new callback'd wake up system, it is possible that the
 495 * poll callback is reentered from inside the call to wake_up() done
 496 * on the poll wait queue head. The rule is that we cannot reenter the
 497 * wake up code from the same task more than EP_MAX_NESTS times,
 498 * and we cannot reenter the same wait queue head at all. This will
 499 * enable to have a hierarchy of epoll file descriptor of no more than
 500 * EP_MAX_NESTS deep.
 501 */
 502static void ep_poll_safewake(wait_queue_head_t *wq)
 503{
 504        int this_cpu = get_cpu();
 505
 506        ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS,
 507                       ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
 508
 509        put_cpu();
 510}
 511
 512static void ep_remove_wait_queue(struct eppoll_entry *pwq)
 513{
 514        wait_queue_head_t *whead;
 515
 516        rcu_read_lock();
 517        /* If it is cleared by POLLFREE, it should be rcu-safe */
 518        whead = rcu_dereference(pwq->whead);
 519        if (whead)
 520                remove_wait_queue(whead, &pwq->wait);
 521        rcu_read_unlock();
 522}
 523
 524/*
 525 * This function unregisters poll callbacks from the associated file
 526 * descriptor.  Must be called with "mtx" held (or "epmutex" if called from
 527 * ep_free).
 528 */
 529static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
 530{
 531        struct list_head *lsthead = &epi->pwqlist;
 532        struct eppoll_entry *pwq;
 533
 534        while (!list_empty(lsthead)) {
 535                pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
 536
 537                list_del(&pwq->llink);
 538                ep_remove_wait_queue(pwq);
 539                kmem_cache_free(pwq_cache, pwq);
 540        }
 541}
 542
 543/* call only when ep->mtx is held */
 544static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
 545{
 546        return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
 547}
 548
 549/* call only when ep->mtx is held */
 550static inline void ep_pm_stay_awake(struct epitem *epi)
 551{
 552        struct wakeup_source *ws = ep_wakeup_source(epi);
 553
 554        if (ws)
 555                __pm_stay_awake(ws);
 556}
 557
 558static inline bool ep_has_wakeup_source(struct epitem *epi)
 559{
 560        return rcu_access_pointer(epi->ws) ? true : false;
 561}
 562
 563/* call when ep->mtx cannot be held (ep_poll_callback) */
 564static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
 565{
 566        struct wakeup_source *ws;
 567
 568        rcu_read_lock();
 569        ws = rcu_dereference(epi->ws);
 570        if (ws)
 571                __pm_stay_awake(ws);
 572        rcu_read_unlock();
 573}
 574
 575/**
 576 * ep_scan_ready_list - Scans the ready list in a way that makes possible for
 577 *                      the scan code, to call f_op->poll(). Also allows for
 578 *                      O(NumReady) performance.
 579 *
 580 * @ep: Pointer to the epoll private data structure.
 581 * @sproc: Pointer to the scan callback.
 582 * @priv: Private opaque data passed to the @sproc callback.
 583 * @depth: The current depth of recursive f_op->poll calls.
 584 *
 585 * Returns: The same integer error code returned by the @sproc callback.
 586 */
 587static int ep_scan_ready_list(struct eventpoll *ep,
 588                              int (*sproc)(struct eventpoll *,
 589                                           struct list_head *, void *),
 590                              void *priv,
 591                              int depth)
 592{
 593        int error, pwake = 0;
 594        unsigned long flags;
 595        struct epitem *epi, *nepi;
 596        LIST_HEAD(txlist);
 597
 598        /*
 599         * We need to lock this because we could be hit by
 600         * eventpoll_release_file() and epoll_ctl().
 601         */
 602        mutex_lock_nested(&ep->mtx, depth);
 603
 604        /*
 605         * Steal the ready list, and re-init the original one to the
 606         * empty list. Also, set ep->ovflist to NULL so that events
 607         * happening while looping w/out locks, are not lost. We cannot
 608         * have the poll callback to queue directly on ep->rdllist,
 609         * because we want the "sproc" callback to be able to do it
 610         * in a lockless way.
 611         */
 612        spin_lock_irqsave(&ep->lock, flags);
 613        list_splice_init(&ep->rdllist, &txlist);
 614        ep->ovflist = NULL;
 615        spin_unlock_irqrestore(&ep->lock, flags);
 616
 617        /*
 618         * Now call the callback function.
 619         */
 620        error = (*sproc)(ep, &txlist, priv);
 621
 622        spin_lock_irqsave(&ep->lock, flags);
 623        /*
 624         * During the time we spent inside the "sproc" callback, some
 625         * other events might have been queued by the poll callback.
 626         * We re-insert them inside the main ready-list here.
 627         */
 628        for (nepi = ep->ovflist; (epi = nepi) != NULL;
 629             nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
 630                /*
 631                 * We need to check if the item is already in the list.
 632                 * During the "sproc" callback execution time, items are
 633                 * queued into ->ovflist but the "txlist" might already
 634                 * contain them, and the list_splice() below takes care of them.
 635                 */
 636                if (!ep_is_linked(&epi->rdllink)) {
 637                        list_add_tail(&epi->rdllink, &ep->rdllist);
 638                        ep_pm_stay_awake(epi);
 639                }
 640        }
 641        /*
 642         * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
 643         * releasing the lock, events will be queued in the normal way inside
 644         * ep->rdllist.
 645         */
 646        ep->ovflist = EP_UNACTIVE_PTR;
 647
 648        /*
 649         * Quickly re-inject items left on "txlist".
 650         */
 651        list_splice(&txlist, &ep->rdllist);
 652        __pm_relax(ep->ws);
 653
 654        if (!list_empty(&ep->rdllist)) {
 655                /*
 656                 * Wake up (if active) both the eventpoll wait list and
 657                 * the ->poll() wait list (delayed after we release the lock).
 658                 */
 659                if (waitqueue_active(&ep->wq))
 660                        wake_up_locked(&ep->wq);
 661                if (waitqueue_active(&ep->poll_wait))
 662                        pwake++;
 663        }
 664        spin_unlock_irqrestore(&ep->lock, flags);
 665
 666        mutex_unlock(&ep->mtx);
 667
 668        /* We have to call this outside the lock */
 669        if (pwake)
 670                ep_poll_safewake(&ep->poll_wait);
 671
 672        return error;
 673}
 674
 675/*
 676 * Removes a "struct epitem" from the eventpoll RB tree and deallocates
 677 * all the associated resources. Must be called with "mtx" held.
 678 */
 679static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 680{
 681        unsigned long flags;
 682        struct file *file = epi->ffd.file;
 683
 684        /*
 685         * Removes poll wait queue hooks. We _have_ to do this without holding
 686         * the "ep->lock" otherwise a deadlock might occur. This because of the
 687         * sequence of the lock acquisition. Here we do "ep->lock" then the wait
 688         * queue head lock when unregistering the wait queue. The wakeup callback
 689         * will run by holding the wait queue head lock and will call our callback
 690         * that will try to get "ep->lock".
 691         */
 692        ep_unregister_pollwait(ep, epi);
 693
 694        /* Remove the current item from the list of epoll hooks */
 695        spin_lock(&file->f_lock);
 696        if (ep_is_linked(&epi->fllink))
 697                list_del_init(&epi->fllink);
 698        spin_unlock(&file->f_lock);
 699
 700        rb_erase(&epi->rbn, &ep->rbr);
 701
 702        spin_lock_irqsave(&ep->lock, flags);
 703        if (ep_is_linked(&epi->rdllink))
 704                list_del_init(&epi->rdllink);
 705        spin_unlock_irqrestore(&ep->lock, flags);
 706
 707        wakeup_source_unregister(ep_wakeup_source(epi));
 708
 709        /* At this point it is safe to free the eventpoll item */
 710        kmem_cache_free(epi_cache, epi);
 711
 712        atomic_long_dec(&ep->user->epoll_watches);
 713
 714        return 0;
 715}
 716
 717static void ep_free(struct eventpoll *ep)
 718{
 719        struct rb_node *rbp;
 720        struct epitem *epi;
 721
 722        /* We need to release all tasks waiting for these file */
 723        if (waitqueue_active(&ep->poll_wait))
 724                ep_poll_safewake(&ep->poll_wait);
 725
 726        /*
 727         * We need to lock this because we could be hit by
 728         * eventpoll_release_file() while we're freeing the "struct eventpoll".
 729         * We do not need to hold "ep->mtx" here because the epoll file
 730         * is on the way to be removed and no one has references to it
 731         * anymore. The only hit might come from eventpoll_release_file() but
 732         * holding "epmutex" is sufficient here.
 733         */
 734        mutex_lock(&epmutex);
 735
 736        /*
 737         * Walks through the whole tree by unregistering poll callbacks.
 738         */
 739        for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
 740                epi = rb_entry(rbp, struct epitem, rbn);
 741
 742                ep_unregister_pollwait(ep, epi);
 743        }
 744
 745        /*
 746         * Walks through the whole tree by freeing each "struct epitem". At this
 747         * point we are sure no poll callbacks will be lingering around, and also by
 748         * holding "epmutex" we can be sure that no file cleanup code will hit
 749         * us during this operation. So we can avoid the lock on "ep->lock".
 750         * We do not need to lock ep->mtx, either, we only do it to prevent
 751         * a lockdep warning.
 752         */
 753        mutex_lock(&ep->mtx);
 754        while ((rbp = rb_first(&ep->rbr)) != NULL) {
 755                epi = rb_entry(rbp, struct epitem, rbn);
 756                ep_remove(ep, epi);
 757        }
 758        mutex_unlock(&ep->mtx);
 759
 760        mutex_unlock(&epmutex);
 761        mutex_destroy(&ep->mtx);
 762        free_uid(ep->user);
 763        wakeup_source_unregister(ep->ws);
 764        kfree(ep);
 765}
 766
 767static int ep_eventpoll_release(struct inode *inode, struct file *file)
 768{
 769        struct eventpoll *ep = file->private_data;
 770
 771        if (ep)
 772                ep_free(ep);
 773
 774        return 0;
 775}
 776
 777static inline unsigned int ep_item_poll(struct epitem *epi, poll_table *pt)
 778{
 779        pt->_key = epi->event.events;
 780
 781        return epi->ffd.file->f_op->poll(epi->ffd.file, pt) & epi->event.events;
 782}
 783
 784static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
 785                               void *priv)
 786{
 787        struct epitem *epi, *tmp;
 788        poll_table pt;
 789
 790        init_poll_funcptr(&pt, NULL);
 791
 792        list_for_each_entry_safe(epi, tmp, head, rdllink) {
 793                if (ep_item_poll(epi, &pt))
 794                        return POLLIN | POLLRDNORM;
 795                else {
 796                        /*
 797                         * Item has been dropped into the ready list by the poll
 798                         * callback, but it's not actually ready, as far as
 799                         * caller requested events goes. We can remove it here.
 800                         */
 801                        __pm_relax(ep_wakeup_source(epi));
 802                        list_del_init(&epi->rdllink);
 803                }
 804        }
 805
 806        return 0;
 807}
 808
 809static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
 810{
 811        return ep_scan_ready_list(priv, ep_read_events_proc, NULL, call_nests + 1);
 812}
 813
 814static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
 815{
 816        int pollflags;
 817        struct eventpoll *ep = file->private_data;
 818
 819        /* Insert inside our poll wait queue */
 820        poll_wait(file, &ep->poll_wait, wait);
 821
 822        /*
 823         * Proceed to find out if wanted events are really available inside
 824         * the ready list. This need to be done under ep_call_nested()
 825         * supervision, since the call to f_op->poll() done on listed files
 826         * could re-enter here.
 827         */
 828        pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS,
 829                                   ep_poll_readyevents_proc, ep, ep, current);
 830
 831        return pollflags != -1 ? pollflags : 0;
 832}
 833
 834#ifdef CONFIG_PROC_FS
 835static int ep_show_fdinfo(struct seq_file *m, struct file *f)
 836{
 837        struct eventpoll *ep = f->private_data;
 838        struct rb_node *rbp;
 839        int ret = 0;
 840
 841        mutex_lock(&ep->mtx);
 842        for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
 843                struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
 844
 845                ret = seq_printf(m, "tfd: %8d events: %8x data: %16llx\n",
 846                                 epi->ffd.fd, epi->event.events,
 847                                 (long long)epi->event.data);
 848                if (ret)
 849                        break;
 850        }
 851        mutex_unlock(&ep->mtx);
 852
 853        return ret;
 854}
 855#endif
 856
 857/* File callbacks that implement the eventpoll file behaviour */
 858static const struct file_operations eventpoll_fops = {
 859#ifdef CONFIG_PROC_FS
 860        .show_fdinfo    = ep_show_fdinfo,
 861#endif
 862        .release        = ep_eventpoll_release,
 863        .poll           = ep_eventpoll_poll,
 864        .llseek         = noop_llseek,
 865};
 866
 867/*
 868 * This is called from eventpoll_release() to unlink files from the eventpoll
 869 * interface. We need to have this facility to cleanup correctly files that are
 870 * closed without being removed from the eventpoll interface.
 871 */
 872void eventpoll_release_file(struct file *file)
 873{
 874        struct list_head *lsthead = &file->f_ep_links;
 875        struct eventpoll *ep;
 876        struct epitem *epi;
 877
 878        /*
 879         * We don't want to get "file->f_lock" because it is not
 880         * necessary. It is not necessary because we're in the "struct file"
 881         * cleanup path, and this means that no one is using this file anymore.
 882         * So, for example, epoll_ctl() cannot hit here since if we reach this
 883         * point, the file counter already went to zero and fget() would fail.
 884         * The only hit might come from ep_free() but by holding the mutex
 885         * will correctly serialize the operation. We do need to acquire
 886         * "ep->mtx" after "epmutex" because ep_remove() requires it when called
 887         * from anywhere but ep_free().
 888         *
 889         * Besides, ep_remove() acquires the lock, so we can't hold it here.
 890         */
 891        mutex_lock(&epmutex);
 892
 893        while (!list_empty(lsthead)) {
 894                epi = list_first_entry(lsthead, struct epitem, fllink);
 895
 896                ep = epi->ep;
 897                list_del_init(&epi->fllink);
 898                mutex_lock_nested(&ep->mtx, 0);
 899                ep_remove(ep, epi);
 900                mutex_unlock(&ep->mtx);
 901        }
 902
 903        mutex_unlock(&epmutex);
 904}
 905
 906static int ep_alloc(struct eventpoll **pep)
 907{
 908        int error;
 909        struct user_struct *user;
 910        struct eventpoll *ep;
 911
 912        user = get_current_user();
 913        error = -ENOMEM;
 914        ep = kzalloc(sizeof(*ep), GFP_KERNEL);
 915        if (unlikely(!ep))
 916                goto free_uid;
 917
 918        spin_lock_init(&ep->lock);
 919        mutex_init(&ep->mtx);
 920        init_waitqueue_head(&ep->wq);
 921        init_waitqueue_head(&ep->poll_wait);
 922        INIT_LIST_HEAD(&ep->rdllist);
 923        ep->rbr = RB_ROOT;
 924        ep->ovflist = EP_UNACTIVE_PTR;
 925        ep->user = user;
 926
 927        *pep = ep;
 928
 929        return 0;
 930
 931free_uid:
 932        free_uid(user);
 933        return error;
 934}
 935
 936/*
 937 * Search the file inside the eventpoll tree. The RB tree operations
 938 * are protected by the "mtx" mutex, and ep_find() must be called with
 939 * "mtx" held.
 940 */
 941static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
 942{
 943        int kcmp;
 944        struct rb_node *rbp;
 945        struct epitem *epi, *epir = NULL;
 946        struct epoll_filefd ffd;
 947
 948        ep_set_ffd(&ffd, file, fd);
 949        for (rbp = ep->rbr.rb_node; rbp; ) {
 950                epi = rb_entry(rbp, struct epitem, rbn);
 951                kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
 952                if (kcmp > 0)
 953                        rbp = rbp->rb_right;
 954                else if (kcmp < 0)
 955                        rbp = rbp->rb_left;
 956                else {
 957                        epir = epi;
 958                        break;
 959                }
 960        }
 961
 962        return epir;
 963}
 964
 965/*
 966 * This is the callback that is passed to the wait queue wakeup
 967 * mechanism. It is called by the stored file descriptors when they
 968 * have events to report.
 969 */
 970static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
 971{
 972        int pwake = 0;
 973        unsigned long flags;
 974        struct epitem *epi = ep_item_from_wait(wait);
 975        struct eventpoll *ep = epi->ep;
 976
 977        if ((unsigned long)key & POLLFREE) {
 978                ep_pwq_from_wait(wait)->whead = NULL;
 979                /*
 980                 * whead = NULL above can race with ep_remove_wait_queue()
 981                 * which can do another remove_wait_queue() after us, so we
 982                 * can't use __remove_wait_queue(). whead->lock is held by
 983                 * the caller.
 984                 */
 985                list_del_init(&wait->task_list);
 986        }
 987
 988        spin_lock_irqsave(&ep->lock, flags);
 989
 990        /*
 991         * If the event mask does not contain any poll(2) event, we consider the
 992         * descriptor to be disabled. This condition is likely the effect of the
 993         * EPOLLONESHOT bit that disables the descriptor when an event is received,
 994         * until the next EPOLL_CTL_MOD will be issued.
 995         */
 996        if (!(epi->event.events & ~EP_PRIVATE_BITS))
 997                goto out_unlock;
 998
 999        /*
1000         * Check the events coming with the callback. At this stage, not
1001         * every device reports the events in the "key" parameter of the
1002         * callback. We need to be able to handle both cases here, hence the
1003         * test for "key" != NULL before the event match test.
1004         */
1005        if (key && !((unsigned long) key & epi->event.events))
1006                goto out_unlock;
1007
1008        /*
1009         * If we are transferring events to userspace, we can hold no locks
1010         * (because we're accessing user memory, and because of linux f_op->poll()
1011         * semantics). All the events that happen during that period of time are
1012         * chained in ep->ovflist and requeued later on.
1013         */
1014        if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
1015                if (epi->next == EP_UNACTIVE_PTR) {
1016                        epi->next = ep->ovflist;
1017                        ep->ovflist = epi;
1018                        if (epi->ws) {
1019                                /*
1020                                 * Activate ep->ws since epi->ws may get
1021                                 * deactivated at any time.
1022                                 */
1023                                __pm_stay_awake(ep->ws);
1024                        }
1025
1026                }
1027                goto out_unlock;
1028        }
1029
1030        /* If this file is already in the ready list we exit soon */
1031        if (!ep_is_linked(&epi->rdllink)) {
1032                list_add_tail(&epi->rdllink, &ep->rdllist);
1033                ep_pm_stay_awake_rcu(epi);
1034        }
1035
1036        /*
1037         * Wake up ( if active ) both the eventpoll wait list and the ->poll()
1038         * wait list.
1039         */
1040        if (waitqueue_active(&ep->wq))
1041                wake_up_locked(&ep->wq);
1042        if (waitqueue_active(&ep->poll_wait))
1043                pwake++;
1044
1045out_unlock:
1046        spin_unlock_irqrestore(&ep->lock, flags);
1047
1048        /* We have to call this outside the lock */
1049        if (pwake)
1050                ep_poll_safewake(&ep->poll_wait);
1051
1052        return 1;
1053}
1054
1055/*
1056 * This is the callback that is used to add our wait queue to the
1057 * target file wakeup lists.
1058 */
1059static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
1060                                 poll_table *pt)
1061{
1062        struct epitem *epi = ep_item_from_epqueue(pt);
1063        struct eppoll_entry *pwq;
1064
1065        if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
1066                init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
1067                pwq->whead = whead;
1068                pwq->base = epi;
1069                add_wait_queue(whead, &pwq->wait);
1070                list_add_tail(&pwq->llink, &epi->pwqlist);
1071                epi->nwait++;
1072        } else {
1073                /* We have to signal that an error occurred */
1074                epi->nwait = -1;
1075        }
1076}
1077
1078static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
1079{
1080        int kcmp;
1081        struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
1082        struct epitem *epic;
1083
1084        while (*p) {
1085                parent = *p;
1086                epic = rb_entry(parent, struct epitem, rbn);
1087                kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
1088                if (kcmp > 0)
1089                        p = &parent->rb_right;
1090                else
1091                        p = &parent->rb_left;
1092        }
1093        rb_link_node(&epi->rbn, parent, p);
1094        rb_insert_color(&epi->rbn, &ep->rbr);
1095}
1096
1097
1098
1099#define PATH_ARR_SIZE 5
1100/*
1101 * These are the number paths of length 1 to 5, that we are allowing to emanate
1102 * from a single file of interest. For example, we allow 1000 paths of length
1103 * 1, to emanate from each file of interest. This essentially represents the
1104 * potential wakeup paths, which need to be limited in order to avoid massive
1105 * uncontrolled wakeup storms. The common use case should be a single ep which
1106 * is connected to n file sources. In this case each file source has 1 path
1107 * of length 1. Thus, the numbers below should be more than sufficient. These
1108 * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
1109 * and delete can't add additional paths. Protected by the epmutex.
1110 */
1111static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
1112static int path_count[PATH_ARR_SIZE];
1113
1114static int path_count_inc(int nests)
1115{
1116        /* Allow an arbitrary number of depth 1 paths */
1117        if (nests == 0)
1118                return 0;
1119
1120        if (++path_count[nests] > path_limits[nests])
1121                return -1;
1122        return 0;
1123}
1124
1125static void path_count_init(void)
1126{
1127        int i;
1128
1129        for (i = 0; i < PATH_ARR_SIZE; i++)
1130                path_count[i] = 0;
1131}
1132
1133static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
1134{
1135        int error = 0;
1136        struct file *file = priv;
1137        struct file *child_file;
1138        struct epitem *epi;
1139
1140        list_for_each_entry(epi, &file->f_ep_links, fllink) {
1141                child_file = epi->ep->file;
1142                if (is_file_epoll(child_file)) {
1143                        if (list_empty(&child_file->f_ep_links)) {
1144                                if (path_count_inc(call_nests)) {
1145                                        error = -1;
1146                                        break;
1147                                }
1148                        } else {
1149                                error = ep_call_nested(&poll_loop_ncalls,
1150                                                        EP_MAX_NESTS,
1151                                                        reverse_path_check_proc,
1152                                                        child_file, child_file,
1153                                                        current);
1154                        }
1155                        if (error != 0)
1156                                break;
1157                } else {
1158                        printk(KERN_ERR "reverse_path_check_proc: "
1159                                "file is not an ep!\n");
1160                }
1161        }
1162        return error;
1163}
1164
1165/**
1166 * reverse_path_check - The tfile_check_list is list of file *, which have
1167 *                      links that are proposed to be newly added. We need to
1168 *                      make sure that those added links don't add too many
1169 *                      paths such that we will spend all our time waking up
1170 *                      eventpoll objects.
1171 *
1172 * Returns: Returns zero if the proposed links don't create too many paths,
1173 *          -1 otherwise.
1174 */
1175static int reverse_path_check(void)
1176{
1177        int error = 0;
1178        struct file *current_file;
1179
1180        /* let's call this for all tfiles */
1181        list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
1182                path_count_init();
1183                error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1184                                        reverse_path_check_proc, current_file,
1185                                        current_file, current);
1186                if (error)
1187                        break;
1188        }
1189        return error;
1190}
1191
1192static int ep_create_wakeup_source(struct epitem *epi)
1193{
1194        const char *name;
1195        struct wakeup_source *ws;
1196
1197        if (!epi->ep->ws) {
1198                epi->ep->ws = wakeup_source_register("eventpoll");
1199                if (!epi->ep->ws)
1200                        return -ENOMEM;
1201        }
1202
1203        name = epi->ffd.file->f_path.dentry->d_name.name;
1204        ws = wakeup_source_register(name);
1205
1206        if (!ws)
1207                return -ENOMEM;
1208        rcu_assign_pointer(epi->ws, ws);
1209
1210        return 0;
1211}
1212
1213/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
1214static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1215{
1216        struct wakeup_source *ws = ep_wakeup_source(epi);
1217
1218        RCU_INIT_POINTER(epi->ws, NULL);
1219
1220        /*
1221         * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
1222         * used internally by wakeup_source_remove, too (called by
1223         * wakeup_source_unregister), so we cannot use call_rcu
1224         */
1225        synchronize_rcu();
1226        wakeup_source_unregister(ws);
1227}
1228
1229/*
1230 * Must be called with "mtx" held.
1231 */
1232static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
1233                     struct file *tfile, int fd)
1234{
1235        int error, revents, pwake = 0;
1236        unsigned long flags;
1237        long user_watches;
1238        struct epitem *epi;
1239        struct ep_pqueue epq;
1240
1241        user_watches = atomic_long_read(&ep->user->epoll_watches);
1242        if (unlikely(user_watches >= max_user_watches))
1243                return -ENOSPC;
1244        if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
1245                return -ENOMEM;
1246
1247        /* Item initialization follow here ... */
1248        INIT_LIST_HEAD(&epi->rdllink);
1249        INIT_LIST_HEAD(&epi->fllink);
1250        INIT_LIST_HEAD(&epi->pwqlist);
1251        epi->ep = ep;
1252        ep_set_ffd(&epi->ffd, tfile, fd);
1253        epi->event = *event;
1254        epi->nwait = 0;
1255        epi->next = EP_UNACTIVE_PTR;
1256        if (epi->event.events & EPOLLWAKEUP) {
1257                error = ep_create_wakeup_source(epi);
1258                if (error)
1259                        goto error_create_wakeup_source;
1260        } else {
1261                RCU_INIT_POINTER(epi->ws, NULL);
1262        }
1263
1264        /* Initialize the poll table using the queue callback */
1265        epq.epi = epi;
1266        init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
1267
1268        /*
1269         * Attach the item to the poll hooks and get current event bits.
1270         * We can safely use the file* here because its usage count has
1271         * been increased by the caller of this function. Note that after
1272         * this operation completes, the poll callback can start hitting
1273         * the new item.
1274         */
1275        revents = ep_item_poll(epi, &epq.pt);
1276
1277        /*
1278         * We have to check if something went wrong during the poll wait queue
1279         * install process. Namely an allocation for a wait queue failed due
1280         * high memory pressure.
1281         */
1282        error = -ENOMEM;
1283        if (epi->nwait < 0)
1284                goto error_unregister;
1285
1286        /* Add the current item to the list of active epoll hook for this file */
1287        spin_lock(&tfile->f_lock);
1288        list_add_tail(&epi->fllink, &tfile->f_ep_links);
1289        spin_unlock(&tfile->f_lock);
1290
1291        /*
1292         * Add the current item to the RB tree. All RB tree operations are
1293         * protected by "mtx", and ep_insert() is called with "mtx" held.
1294         */
1295        ep_rbtree_insert(ep, epi);
1296
1297        /* now check if we've created too many backpaths */
1298        error = -EINVAL;
1299        if (reverse_path_check())
1300                goto error_remove_epi;
1301
1302        /* We have to drop the new item inside our item list to keep track of it */
1303        spin_lock_irqsave(&ep->lock, flags);
1304
1305        /* If the file is already "ready" we drop it inside the ready list */
1306        if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
1307                list_add_tail(&epi->rdllink, &ep->rdllist);
1308                ep_pm_stay_awake(epi);
1309
1310                /* Notify waiting tasks that events are available */
1311                if (waitqueue_active(&ep->wq))
1312                        wake_up_locked(&ep->wq);
1313                if (waitqueue_active(&ep->poll_wait))
1314                        pwake++;
1315        }
1316
1317        spin_unlock_irqrestore(&ep->lock, flags);
1318
1319        atomic_long_inc(&ep->user->epoll_watches);
1320
1321        /* We have to call this outside the lock */
1322        if (pwake)
1323                ep_poll_safewake(&ep->poll_wait);
1324
1325        return 0;
1326
1327error_remove_epi:
1328        spin_lock(&tfile->f_lock);
1329        if (ep_is_linked(&epi->fllink))
1330                list_del_init(&epi->fllink);
1331        spin_unlock(&tfile->f_lock);
1332
1333        rb_erase(&epi->rbn, &ep->rbr);
1334
1335error_unregister:
1336        ep_unregister_pollwait(ep, epi);
1337
1338        /*
1339         * We need to do this because an event could have been arrived on some
1340         * allocated wait queue. Note that we don't care about the ep->ovflist
1341         * list, since that is used/cleaned only inside a section bound by "mtx".
1342         * And ep_insert() is called with "mtx" held.
1343         */
1344        spin_lock_irqsave(&ep->lock, flags);
1345        if (ep_is_linked(&epi->rdllink))
1346                list_del_init(&epi->rdllink);
1347        spin_unlock_irqrestore(&ep->lock, flags);
1348
1349        wakeup_source_unregister(ep_wakeup_source(epi));
1350
1351error_create_wakeup_source:
1352        kmem_cache_free(epi_cache, epi);
1353
1354        return error;
1355}
1356
1357/*
1358 * Modify the interest event mask by dropping an event if the new mask
1359 * has a match in the current file status. Must be called with "mtx" held.
1360 */
1361static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
1362{
1363        int pwake = 0;
1364        unsigned int revents;
1365        poll_table pt;
1366
1367        init_poll_funcptr(&pt, NULL);
1368
1369        /*
1370         * Set the new event interest mask before calling f_op->poll();
1371         * otherwise we might miss an event that happens between the
1372         * f_op->poll() call and the new event set registering.
1373         */
1374        epi->event.events = event->events; /* need barrier below */
1375        epi->event.data = event->data; /* protected by mtx */
1376        if (epi->event.events & EPOLLWAKEUP) {
1377                if (!ep_has_wakeup_source(epi))
1378                        ep_create_wakeup_source(epi);
1379        } else if (ep_has_wakeup_source(epi)) {
1380                ep_destroy_wakeup_source(epi);
1381        }
1382
1383        /*
1384         * The following barrier has two effects:
1385         *
1386         * 1) Flush epi changes above to other CPUs.  This ensures
1387         *    we do not miss events from ep_poll_callback if an
1388         *    event occurs immediately after we call f_op->poll().
1389         *    We need this because we did not take ep->lock while
1390         *    changing epi above (but ep_poll_callback does take
1391         *    ep->lock).
1392         *
1393         * 2) We also need to ensure we do not miss _past_ events
1394         *    when calling f_op->poll().  This barrier also
1395         *    pairs with the barrier in wq_has_sleeper (see
1396         *    comments for wq_has_sleeper).
1397         *
1398         * This barrier will now guarantee ep_poll_callback or f_op->poll
1399         * (or both) will notice the readiness of an item.
1400         */
1401        smp_mb();
1402
1403        /*
1404         * Get current event bits. We can safely use the file* here because
1405         * its usage count has been increased by the caller of this function.
1406         */
1407        revents = ep_item_poll(epi, &pt);
1408
1409        /*
1410         * If the item is "hot" and it is not registered inside the ready
1411         * list, push it inside.
1412         */
1413        if (revents & event->events) {
1414                spin_lock_irq(&ep->lock);
1415                if (!ep_is_linked(&epi->rdllink)) {
1416                        list_add_tail(&epi->rdllink, &ep->rdllist);
1417                        ep_pm_stay_awake(epi);
1418
1419                        /* Notify waiting tasks that events are available */
1420                        if (waitqueue_active(&ep->wq))
1421                                wake_up_locked(&ep->wq);
1422                        if (waitqueue_active(&ep->poll_wait))
1423                                pwake++;
1424                }
1425                spin_unlock_irq(&ep->lock);
1426        }
1427
1428        /* We have to call this outside the lock */
1429        if (pwake)
1430                ep_poll_safewake(&ep->poll_wait);
1431
1432        return 0;
1433}
1434
1435static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
1436                               void *priv)
1437{
1438        struct ep_send_events_data *esed = priv;
1439        int eventcnt;
1440        unsigned int revents;
1441        struct epitem *epi;
1442        struct epoll_event __user *uevent;
1443        struct wakeup_source *ws;
1444        poll_table pt;
1445
1446        init_poll_funcptr(&pt, NULL);
1447
1448        /*
1449         * We can loop without lock because we are passed a task private list.
1450         * Items cannot vanish during the loop because ep_scan_ready_list() is
1451         * holding "mtx" during this call.
1452         */
1453        for (eventcnt = 0, uevent = esed->events;
1454             !list_empty(head) && eventcnt < esed->maxevents;) {
1455                epi = list_first_entry(head, struct epitem, rdllink);
1456
1457                /*
1458                 * Activate ep->ws before deactivating epi->ws to prevent
1459                 * triggering auto-suspend here (in case we reactive epi->ws
1460                 * below).
1461                 *
1462                 * This could be rearranged to delay the deactivation of epi->ws
1463                 * instead, but then epi->ws would temporarily be out of sync
1464                 * with ep_is_linked().
1465                 */
1466                ws = ep_wakeup_source(epi);
1467                if (ws) {
1468                        if (ws->active)
1469                                __pm_stay_awake(ep->ws);
1470                        __pm_relax(ws);
1471                }
1472
1473                list_del_init(&epi->rdllink);
1474
1475                revents = ep_item_poll(epi, &pt);
1476
1477                /*
1478                 * If the event mask intersect the caller-requested one,
1479                 * deliver the event to userspace. Again, ep_scan_ready_list()
1480                 * is holding "mtx", so no operations coming from userspace
1481                 * can change the item.
1482                 */
1483                if (revents) {
1484                        if (__put_user(revents, &uevent->events) ||
1485                            __put_user(epi->event.data, &uevent->data)) {
1486                                list_add(&epi->rdllink, head);
1487                                ep_pm_stay_awake(epi);
1488                                return eventcnt ? eventcnt : -EFAULT;
1489                        }
1490                        eventcnt++;
1491                        uevent++;
1492                        if (epi->event.events & EPOLLONESHOT)
1493                                epi->event.events &= EP_PRIVATE_BITS;
1494                        else if (!(epi->event.events & EPOLLET)) {
1495                                /*
1496                                 * If this file has been added with Level
1497                                 * Trigger mode, we need to insert back inside
1498                                 * the ready list, so that the next call to
1499                                 * epoll_wait() will check again the events
1500                                 * availability. At this point, no one can insert
1501                                 * into ep->rdllist besides us. The epoll_ctl()
1502                                 * callers are locked out by
1503                                 * ep_scan_ready_list() holding "mtx" and the
1504                                 * poll callback will queue them in ep->ovflist.
1505                                 */
1506                                list_add_tail(&epi->rdllink, &ep->rdllist);
1507                                ep_pm_stay_awake(epi);
1508                        }
1509                }
1510        }
1511
1512        return eventcnt;
1513}
1514
1515static int ep_send_events(struct eventpoll *ep,
1516                          struct epoll_event __user *events, int maxevents)
1517{
1518        struct ep_send_events_data esed;
1519
1520        esed.maxevents = maxevents;
1521        esed.events = events;
1522
1523        return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0);
1524}
1525
1526static inline struct timespec ep_set_mstimeout(long ms)
1527{
1528        struct timespec now, ts = {
1529                .tv_sec = ms / MSEC_PER_SEC,
1530                .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
1531        };
1532
1533        ktime_get_ts(&now);
1534        return timespec_add_safe(now, ts);
1535}
1536
1537/**
1538 * ep_poll - Retrieves ready events, and delivers them to the caller supplied
1539 *           event buffer.
1540 *
1541 * @ep: Pointer to the eventpoll context.
1542 * @events: Pointer to the userspace buffer where the ready events should be
1543 *          stored.
1544 * @maxevents: Size (in terms of number of events) of the caller event buffer.
1545 * @timeout: Maximum timeout for the ready events fetch operation, in
1546 *           milliseconds. If the @timeout is zero, the function will not block,
1547 *           while if the @timeout is less than zero, the function will block
1548 *           until at least one event has been retrieved (or an error
1549 *           occurred).
1550 *
1551 * Returns: Returns the number of ready events which have been fetched, or an
1552 *          error code, in case of error.
1553 */
1554static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1555                   int maxevents, long timeout)
1556{
1557        int res = 0, eavail, timed_out = 0;
1558        unsigned long flags;
1559        long slack = 0;
1560        wait_queue_t wait;
1561        ktime_t expires, *to = NULL;
1562
1563        if (timeout > 0) {
1564                struct timespec end_time = ep_set_mstimeout(timeout);
1565
1566                slack = select_estimate_accuracy(&end_time);
1567                to = &expires;
1568                *to = timespec_to_ktime(end_time);
1569        } else if (timeout == 0) {
1570                /*
1571                 * Avoid the unnecessary trip to the wait queue loop, if the
1572                 * caller specified a non blocking operation.
1573                 */
1574                timed_out = 1;
1575                spin_lock_irqsave(&ep->lock, flags);
1576                goto check_events;
1577        }
1578
1579fetch_events:
1580        spin_lock_irqsave(&ep->lock, flags);
1581
1582        if (!ep_events_available(ep)) {
1583                /*
1584                 * We don't have any available event to return to the caller.
1585                 * We need to sleep here, and we will be wake up by
1586                 * ep_poll_callback() when events will become available.
1587                 */
1588                init_waitqueue_entry(&wait, current);
1589                __add_wait_queue_exclusive(&ep->wq, &wait);
1590
1591                for (;;) {
1592                        /*
1593                         * We don't want to sleep if the ep_poll_callback() sends us
1594                         * a wakeup in between. That's why we set the task state
1595                         * to TASK_INTERRUPTIBLE before doing the checks.
1596                         */
1597                        set_current_state(TASK_INTERRUPTIBLE);
1598                        if (ep_events_available(ep) || timed_out)
1599                                break;
1600                        if (signal_pending(current)) {
1601                                res = -EINTR;
1602                                break;
1603                        }
1604
1605                        spin_unlock_irqrestore(&ep->lock, flags);
1606                        if (!freezable_schedule_hrtimeout_range(to, slack,
1607                                                                HRTIMER_MODE_ABS))
1608                                timed_out = 1;
1609
1610                        spin_lock_irqsave(&ep->lock, flags);
1611                }
1612                __remove_wait_queue(&ep->wq, &wait);
1613
1614                set_current_state(TASK_RUNNING);
1615        }
1616check_events:
1617        /* Is it worth to try to dig for events ? */
1618        eavail = ep_events_available(ep);
1619
1620        spin_unlock_irqrestore(&ep->lock, flags);
1621
1622        /*
1623         * Try to transfer events to user space. In case we get 0 events and
1624         * there's still timeout left over, we go trying again in search of
1625         * more luck.
1626         */
1627        if (!res && eavail &&
1628            !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
1629                goto fetch_events;
1630
1631        return res;
1632}
1633
1634/**
1635 * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
1636 *                      API, to verify that adding an epoll file inside another
1637 *                      epoll structure, does not violate the constraints, in
1638 *                      terms of closed loops, or too deep chains (which can
1639 *                      result in excessive stack usage).
1640 *
1641 * @priv: Pointer to the epoll file to be currently checked.
1642 * @cookie: Original cookie for this call. This is the top-of-the-chain epoll
1643 *          data structure pointer.
1644 * @call_nests: Current dept of the @ep_call_nested() call stack.
1645 *
1646 * Returns: Returns zero if adding the epoll @file inside current epoll
1647 *          structure @ep does not violate the constraints, or -1 otherwise.
1648 */
1649static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
1650{
1651        int error = 0;
1652        struct file *file = priv;
1653        struct eventpoll *ep = file->private_data;
1654        struct eventpoll *ep_tovisit;
1655        struct rb_node *rbp;
1656        struct epitem *epi;
1657
1658        mutex_lock_nested(&ep->mtx, call_nests + 1);
1659        ep->visited = 1;
1660        list_add(&ep->visited_list_link, &visited_list);
1661        for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1662                epi = rb_entry(rbp, struct epitem, rbn);
1663                if (unlikely(is_file_epoll(epi->ffd.file))) {
1664                        ep_tovisit = epi->ffd.file->private_data;
1665                        if (ep_tovisit->visited)
1666                                continue;
1667                        error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1668                                        ep_loop_check_proc, epi->ffd.file,
1669                                        ep_tovisit, current);
1670                        if (error != 0)
1671                                break;
1672                } else {
1673                        /*
1674                         * If we've reached a file that is not associated with
1675                         * an ep, then we need to check if the newly added
1676                         * links are going to add too many wakeup paths. We do
1677                         * this by adding it to the tfile_check_list, if it's
1678                         * not already there, and calling reverse_path_check()
1679                         * during ep_insert().
1680                         */
1681                        if (list_empty(&epi->ffd.file->f_tfile_llink))
1682                                list_add(&epi->ffd.file->f_tfile_llink,
1683                                         &tfile_check_list);
1684                }
1685        }
1686        mutex_unlock(&ep->mtx);
1687
1688        return error;
1689}
1690
1691/**
1692 * ep_loop_check - Performs a check to verify that adding an epoll file (@file)
1693 *                 another epoll file (represented by @ep) does not create
1694 *                 closed loops or too deep chains.
1695 *
1696 * @ep: Pointer to the epoll private data structure.
1697 * @file: Pointer to the epoll file to be checked.
1698 *
1699 * Returns: Returns zero if adding the epoll @file inside current epoll
1700 *          structure @ep does not violate the constraints, or -1 otherwise.
1701 */
1702static int ep_loop_check(struct eventpoll *ep, struct file *file)
1703{
1704        int ret;
1705        struct eventpoll *ep_cur, *ep_next;
1706
1707        ret = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1708                              ep_loop_check_proc, file, ep, current);
1709        /* clear visited list */
1710        list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
1711                                                        visited_list_link) {
1712                ep_cur->visited = 0;
1713                list_del(&ep_cur->visited_list_link);
1714        }
1715        return ret;
1716}
1717
1718static void clear_tfile_check_list(void)
1719{
1720        struct file *file;
1721
1722        /* first clear the tfile_check_list */
1723        while (!list_empty(&tfile_check_list)) {
1724                file = list_first_entry(&tfile_check_list, struct file,
1725                                        f_tfile_llink);
1726                list_del_init(&file->f_tfile_llink);
1727        }
1728        INIT_LIST_HEAD(&tfile_check_list);
1729}
1730
1731/*
1732 * Open an eventpoll file descriptor.
1733 */
1734SYSCALL_DEFINE1(epoll_create1, int, flags)
1735{
1736        int error, fd;
1737        struct eventpoll *ep = NULL;
1738        struct file *file;
1739
1740        /* Check the EPOLL_* constant for consistency.  */
1741        BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
1742
1743        if (flags & ~EPOLL_CLOEXEC)
1744                return -EINVAL;
1745        /*
1746         * Create the internal data structure ("struct eventpoll").
1747         */
1748        error = ep_alloc(&ep);
1749        if (error < 0)
1750                return error;
1751        /*
1752         * Creates all the items needed to setup an eventpoll file. That is,
1753         * a file structure and a free file descriptor.
1754         */
1755        fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
1756        if (fd < 0) {
1757                error = fd;
1758                goto out_free_ep;
1759        }
1760        file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
1761                                 O_RDWR | (flags & O_CLOEXEC));
1762        if (IS_ERR(file)) {
1763                error = PTR_ERR(file);
1764                goto out_free_fd;
1765        }
1766        ep->file = file;
1767        fd_install(fd, file);
1768        return fd;
1769
1770out_free_fd:
1771        put_unused_fd(fd);
1772out_free_ep:
1773        ep_free(ep);
1774        return error;
1775}
1776
1777SYSCALL_DEFINE1(epoll_create, int, size)
1778{
1779        if (size <= 0)
1780                return -EINVAL;
1781
1782        return sys_epoll_create1(0);
1783}
1784
1785/*
1786 * The following function implements the controller interface for
1787 * the eventpoll file that enables the insertion/removal/change of
1788 * file descriptors inside the interest set.
1789 */
1790SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
1791                struct epoll_event __user *, event)
1792{
1793        int error;
1794        int did_lock_epmutex = 0;
1795        struct file *file, *tfile;
1796        struct eventpoll *ep;
1797        struct epitem *epi;
1798        struct epoll_event epds;
1799
1800        error = -EFAULT;
1801        if (ep_op_has_event(op) &&
1802            copy_from_user(&epds, event, sizeof(struct epoll_event)))
1803                goto error_return;
1804
1805        /* Get the "struct file *" for the eventpoll file */
1806        error = -EBADF;
1807        file = fget(epfd);
1808        if (!file)
1809                goto error_return;
1810
1811        /* Get the "struct file *" for the target file */
1812        tfile = fget(fd);
1813        if (!tfile)
1814                goto error_fput;
1815
1816        /* The target file descriptor must support poll */
1817        error = -EPERM;
1818        if (!tfile->f_op || !tfile->f_op->poll)
1819                goto error_tgt_fput;
1820
1821        /* Check if EPOLLWAKEUP is allowed */
1822        if ((epds.events & EPOLLWAKEUP) && !capable(CAP_BLOCK_SUSPEND))
1823                epds.events &= ~EPOLLWAKEUP;
1824
1825        /*
1826         * We have to check that the file structure underneath the file descriptor
1827         * the user passed to us _is_ an eventpoll file. And also we do not permit
1828         * adding an epoll file descriptor inside itself.
1829         */
1830        error = -EINVAL;
1831        if (file == tfile || !is_file_epoll(file))
1832                goto error_tgt_fput;
1833
1834        /*
1835         * At this point it is safe to assume that the "private_data" contains
1836         * our own data structure.
1837         */
1838        ep = file->private_data;
1839
1840        /*
1841         * When we insert an epoll file descriptor, inside another epoll file
1842         * descriptor, there is the change of creating closed loops, which are
1843         * better be handled here, than in more critical paths. While we are
1844         * checking for loops we also determine the list of files reachable
1845         * and hang them on the tfile_check_list, so we can check that we
1846         * haven't created too many possible wakeup paths.
1847         *
1848         * We need to hold the epmutex across both ep_insert and ep_remove
1849         * b/c we want to make sure we are looking at a coherent view of
1850         * epoll network.
1851         */
1852        if (op == EPOLL_CTL_ADD || op == EPOLL_CTL_DEL) {
1853                mutex_lock(&epmutex);
1854                did_lock_epmutex = 1;
1855        }
1856        if (op == EPOLL_CTL_ADD) {
1857                if (is_file_epoll(tfile)) {
1858                        error = -ELOOP;
1859                        if (ep_loop_check(ep, tfile) != 0) {
1860                                clear_tfile_check_list();
1861                                goto error_tgt_fput;
1862                        }
1863                } else
1864                        list_add(&tfile->f_tfile_llink, &tfile_check_list);
1865        }
1866
1867        mutex_lock_nested(&ep->mtx, 0);
1868
1869        /*
1870         * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
1871         * above, we can be sure to be able to use the item looked up by
1872         * ep_find() till we release the mutex.
1873         */
1874        epi = ep_find(ep, tfile, fd);
1875
1876        error = -EINVAL;
1877        switch (op) {
1878        case EPOLL_CTL_ADD:
1879                if (!epi) {
1880                        epds.events |= POLLERR | POLLHUP;
1881                        error = ep_insert(ep, &epds, tfile, fd);
1882                } else
1883                        error = -EEXIST;
1884                clear_tfile_check_list();
1885                break;
1886        case EPOLL_CTL_DEL:
1887                if (epi)
1888                        error = ep_remove(ep, epi);
1889                else
1890                        error = -ENOENT;
1891                break;
1892        case EPOLL_CTL_MOD:
1893                if (epi) {
1894                        epds.events |= POLLERR | POLLHUP;
1895                        error = ep_modify(ep, epi, &epds);
1896                } else
1897                        error = -ENOENT;
1898                break;
1899        }
1900        mutex_unlock(&ep->mtx);
1901
1902error_tgt_fput:
1903        if (did_lock_epmutex)
1904                mutex_unlock(&epmutex);
1905
1906        fput(tfile);
1907error_fput:
1908        fput(file);
1909error_return:
1910
1911        return error;
1912}
1913
1914/*
1915 * Implement the event wait interface for the eventpoll file. It is the kernel
1916 * part of the user space epoll_wait(2).
1917 */
1918SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
1919                int, maxevents, int, timeout)
1920{
1921        int error;
1922        struct fd f;
1923        struct eventpoll *ep;
1924
1925        /* The maximum number of event must be greater than zero */
1926        if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
1927                return -EINVAL;
1928
1929        /* Verify that the area passed by the user is writeable */
1930        if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event)))
1931                return -EFAULT;
1932
1933        /* Get the "struct file *" for the eventpoll file */
1934        f = fdget(epfd);
1935        if (!f.file)
1936                return -EBADF;
1937
1938        /*
1939         * We have to check that the file structure underneath the fd
1940         * the user passed to us _is_ an eventpoll file.
1941         */
1942        error = -EINVAL;
1943        if (!is_file_epoll(f.file))
1944                goto error_fput;
1945
1946        /*
1947         * At this point it is safe to assume that the "private_data" contains
1948         * our own data structure.
1949         */
1950        ep = f.file->private_data;
1951
1952        /* Time to fish for events ... */
1953        error = ep_poll(ep, events, maxevents, timeout);
1954
1955error_fput:
1956        fdput(f);
1957        return error;
1958}
1959
1960/*
1961 * Implement the event wait interface for the eventpoll file. It is the kernel
1962 * part of the user space epoll_pwait(2).
1963 */
1964SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
1965                int, maxevents, int, timeout, const sigset_t __user *, sigmask,
1966                size_t, sigsetsize)
1967{
1968        int error;
1969        sigset_t ksigmask, sigsaved;
1970
1971        /*
1972         * If the caller wants a certain signal mask to be set during the wait,
1973         * we apply it here.
1974         */
1975        if (sigmask) {
1976                if (sigsetsize != sizeof(sigset_t))
1977                        return -EINVAL;
1978                if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
1979                        return -EFAULT;
1980                sigsaved = current->blocked;
1981                set_current_blocked(&ksigmask);
1982        }
1983
1984        error = sys_epoll_wait(epfd, events, maxevents, timeout);
1985
1986        /*
1987         * If we changed the signal mask, we need to restore the original one.
1988         * In case we've got a signal while waiting, we do not restore the
1989         * signal mask yet, and we allow do_signal() to deliver the signal on
1990         * the way back to userspace, before the signal mask is restored.
1991         */
1992        if (sigmask) {
1993                if (error == -EINTR) {
1994                        memcpy(&current->saved_sigmask, &sigsaved,
1995                               sizeof(sigsaved));
1996                        set_restore_sigmask();
1997                } else
1998                        set_current_blocked(&sigsaved);
1999        }
2000
2001        return error;
2002}
2003
2004#ifdef CONFIG_COMPAT
2005COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
2006                        struct epoll_event __user *, events,
2007                        int, maxevents, int, timeout,
2008                        const compat_sigset_t __user *, sigmask,
2009                        compat_size_t, sigsetsize)
2010{
2011        long err;
2012        compat_sigset_t csigmask;
2013        sigset_t ksigmask, sigsaved;
2014
2015        /*
2016         * If the caller wants a certain signal mask to be set during the wait,
2017         * we apply it here.
2018         */
2019        if (sigmask) {
2020                if (sigsetsize != sizeof(compat_sigset_t))
2021                        return -EINVAL;
2022                if (copy_from_user(&csigmask, sigmask, sizeof(csigmask)))
2023                        return -EFAULT;
2024                sigset_from_compat(&ksigmask, &csigmask);
2025                sigsaved = current->blocked;
2026                set_current_blocked(&ksigmask);
2027        }
2028
2029        err = sys_epoll_wait(epfd, events, maxevents, timeout);
2030
2031        /*
2032         * If we changed the signal mask, we need to restore the original one.
2033         * In case we've got a signal while waiting, we do not restore the
2034         * signal mask yet, and we allow do_signal() to deliver the signal on
2035         * the way back to userspace, before the signal mask is restored.
2036         */
2037        if (sigmask) {
2038                if (err == -EINTR) {
2039                        memcpy(&current->saved_sigmask, &sigsaved,
2040                               sizeof(sigsaved));
2041                        set_restore_sigmask();
2042                } else
2043                        set_current_blocked(&sigsaved);
2044        }
2045
2046        return err;
2047}
2048#endif
2049
2050static int __init eventpoll_init(void)
2051{
2052        struct sysinfo si;
2053
2054        si_meminfo(&si);
2055        /*
2056         * Allows top 4% of lomem to be allocated for epoll watches (per user).
2057         */
2058        max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2059                EP_ITEM_COST;
2060        BUG_ON(max_user_watches < 0);
2061
2062        /*
2063         * Initialize the structure used to perform epoll file descriptor
2064         * inclusion loops checks.
2065         */
2066        ep_nested_calls_init(&poll_loop_ncalls);
2067
2068        /* Initialize the structure used to perform safe poll wait head wake ups */
2069        ep_nested_calls_init(&poll_safewake_ncalls);
2070
2071        /* Initialize the structure used to perform file's f_op->poll() calls */
2072        ep_nested_calls_init(&poll_readywalk_ncalls);
2073
2074        /*
2075         * We can have many thousands of epitems, so prevent this from
2076         * using an extra cache line on 64-bit (and smaller) CPUs
2077         */
2078        BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
2079
2080        /* Allocates slab cache used to allocate "struct epitem" items */
2081        epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
2082                        0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
2083
2084        /* Allocates slab cache used to allocate "struct eppoll_entry" */
2085        pwq_cache = kmem_cache_create("eventpoll_pwq",
2086                        sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL);
2087
2088        return 0;
2089}
2090fs_initcall(eventpoll_init);
2091
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