Root/fs/eventpoll.c

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 to epoll_ctl(EPOLL_CTL_DEL).
66 * It is also acquired when inserting an epoll fd onto another epoll
67 * fd. We do this so that we walk the epoll tree and ensure that this
68 * insertion does not create a cycle of epoll file descriptors, which
69 * could lead to deadlock. We need a global mutex to prevent two
70 * simultaneous inserts (A into B and B into A) from racing and
71 * constructing a cycle without either insert observing that it is
72 * going to.
73 * It is possible to drop the "ep->mtx" and to use the global
74 * mutex "epmutex" (together with "ep->lock") to have it working,
75 * but having "ep->mtx" will make the interface more scalable.
76 * Events that require holding "epmutex" are very rare, while for
77 * normal operations the epoll private "ep->mtx" will guarantee
78 * a better scalability.
79 */
80
81/* Epoll private bits inside the event mask */
82#define EP_PRIVATE_BITS (EPOLLONESHOT | EPOLLET)
83
84/* Maximum number of nesting allowed inside epoll sets */
85#define EP_MAX_NESTS 4
86
87#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
88
89#define EP_UNACTIVE_PTR ((void *) -1L)
90
91#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
92
93struct epoll_filefd {
94    struct file *file;
95    int fd;
96};
97
98/*
99 * Structure used to track possible nested calls, for too deep recursions
100 * and loop cycles.
101 */
102struct nested_call_node {
103    struct list_head llink;
104    void *cookie;
105    void *ctx;
106};
107
108/*
109 * This structure is used as collector for nested calls, to check for
110 * maximum recursion dept and loop cycles.
111 */
112struct nested_calls {
113    struct list_head tasks_call_list;
114    spinlock_t lock;
115};
116
117/*
118 * Each file descriptor added to the eventpoll interface will
119 * have an entry of this type linked to the "rbr" RB tree.
120 */
121struct epitem {
122    /* RB tree node used to link this structure to the eventpoll RB tree */
123    struct rb_node rbn;
124
125    /* List header used to link this structure to the eventpoll ready list */
126    struct list_head rdllink;
127
128    /*
129     * Works together "struct eventpoll"->ovflist in keeping the
130     * single linked chain of items.
131     */
132    struct epitem *next;
133
134    /* The file descriptor information this item refers to */
135    struct epoll_filefd ffd;
136
137    /* Number of active wait queue attached to poll operations */
138    int nwait;
139
140    /* List containing poll wait queues */
141    struct list_head pwqlist;
142
143    /* The "container" of this item */
144    struct eventpoll *ep;
145
146    /* List header used to link this item to the "struct file" items list */
147    struct list_head fllink;
148
149    /* The structure that describe the interested events and the source fd */
150    struct epoll_event event;
151};
152
153/*
154 * This structure is stored inside the "private_data" member of the file
155 * structure and represents the main data structure for the eventpoll
156 * interface.
157 */
158struct eventpoll {
159    /* Protect the access to this structure */
160    spinlock_t lock;
161
162    /*
163     * This mutex is used to ensure that files are not removed
164     * while epoll is using them. This is held during the event
165     * collection loop, the file cleanup path, the epoll file exit
166     * code and the ctl operations.
167     */
168    struct mutex mtx;
169
170    /* Wait queue used by sys_epoll_wait() */
171    wait_queue_head_t wq;
172
173    /* Wait queue used by file->poll() */
174    wait_queue_head_t poll_wait;
175
176    /* List of ready file descriptors */
177    struct list_head rdllist;
178
179    /* RB tree root used to store monitored fd structs */
180    struct rb_root rbr;
181
182    /*
183     * This is a single linked list that chains all the "struct epitem" that
184     * happened while transferring ready events to userspace w/out
185     * holding ->lock.
186     */
187    struct epitem *ovflist;
188
189    /* The user that created the eventpoll descriptor */
190    struct user_struct *user;
191};
192
193/* Wait structure used by the poll hooks */
194struct eppoll_entry {
195    /* List header used to link this structure to the "struct epitem" */
196    struct list_head llink;
197
198    /* The "base" pointer is set to the container "struct epitem" */
199    struct epitem *base;
200
201    /*
202     * Wait queue item that will be linked to the target file wait
203     * queue head.
204     */
205    wait_queue_t wait;
206
207    /* The wait queue head that linked the "wait" wait queue item */
208    wait_queue_head_t *whead;
209};
210
211/* Wrapper struct used by poll queueing */
212struct ep_pqueue {
213    poll_table pt;
214    struct epitem *epi;
215};
216
217/* Used by the ep_send_events() function as callback private data */
218struct ep_send_events_data {
219    int maxevents;
220    struct epoll_event __user *events;
221};
222
223/*
224 * Configuration options available inside /proc/sys/fs/epoll/
225 */
226/* Maximum number of epoll watched descriptors, per user */
227static long max_user_watches __read_mostly;
228
229/*
230 * This mutex is used to serialize ep_free() and eventpoll_release_file().
231 */
232static DEFINE_MUTEX(epmutex);
233
234/* Used to check for epoll file descriptor inclusion loops */
235static struct nested_calls poll_loop_ncalls;
236
237/* Used for safe wake up implementation */
238static struct nested_calls poll_safewake_ncalls;
239
240/* Used to call file's f_op->poll() under the nested calls boundaries */
241static struct nested_calls poll_readywalk_ncalls;
242
243/* Slab cache used to allocate "struct epitem" */
244static struct kmem_cache *epi_cache __read_mostly;
245
246/* Slab cache used to allocate "struct eppoll_entry" */
247static struct kmem_cache *pwq_cache __read_mostly;
248
249#ifdef CONFIG_SYSCTL
250
251#include <linux/sysctl.h>
252
253static long zero;
254static long long_max = LONG_MAX;
255
256ctl_table epoll_table[] = {
257    {
258        .procname = "max_user_watches",
259        .data = &max_user_watches,
260        .maxlen = sizeof(max_user_watches),
261        .mode = 0644,
262        .proc_handler = proc_doulongvec_minmax,
263        .extra1 = &zero,
264        .extra2 = &long_max,
265    },
266    { }
267};
268#endif /* CONFIG_SYSCTL */
269
270
271/* Setup the structure that is used as key for the RB tree */
272static inline void ep_set_ffd(struct epoll_filefd *ffd,
273                  struct file *file, int fd)
274{
275    ffd->file = file;
276    ffd->fd = fd;
277}
278
279/* Compare RB tree keys */
280static inline int ep_cmp_ffd(struct epoll_filefd *p1,
281                 struct epoll_filefd *p2)
282{
283    return (p1->file > p2->file ? +1:
284            (p1->file < p2->file ? -1 : p1->fd - p2->fd));
285}
286
287/* Tells us if the item is currently linked */
288static inline int ep_is_linked(struct list_head *p)
289{
290    return !list_empty(p);
291}
292
293/* Get the "struct epitem" from a wait queue pointer */
294static inline struct epitem *ep_item_from_wait(wait_queue_t *p)
295{
296    return container_of(p, struct eppoll_entry, wait)->base;
297}
298
299/* Get the "struct epitem" from an epoll queue wrapper */
300static inline struct epitem *ep_item_from_epqueue(poll_table *p)
301{
302    return container_of(p, struct ep_pqueue, pt)->epi;
303}
304
305/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
306static inline int ep_op_has_event(int op)
307{
308    return op != EPOLL_CTL_DEL;
309}
310
311/* Initialize the poll safe wake up structure */
312static void ep_nested_calls_init(struct nested_calls *ncalls)
313{
314    INIT_LIST_HEAD(&ncalls->tasks_call_list);
315    spin_lock_init(&ncalls->lock);
316}
317
318/**
319 * ep_events_available - Checks if ready events might be available.
320 *
321 * @ep: Pointer to the eventpoll context.
322 *
323 * Returns: Returns a value different than zero if ready events are available,
324 * or zero otherwise.
325 */
326static inline int ep_events_available(struct eventpoll *ep)
327{
328    return !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
329}
330
331/**
332 * ep_call_nested - Perform a bound (possibly) nested call, by checking
333 * that the recursion limit is not exceeded, and that
334 * the same nested call (by the meaning of same cookie) is
335 * no re-entered.
336 *
337 * @ncalls: Pointer to the nested_calls structure to be used for this call.
338 * @max_nests: Maximum number of allowed nesting calls.
339 * @nproc: Nested call core function pointer.
340 * @priv: Opaque data to be passed to the @nproc callback.
341 * @cookie: Cookie to be used to identify this nested call.
342 * @ctx: This instance context.
343 *
344 * Returns: Returns the code returned by the @nproc callback, or -1 if
345 * the maximum recursion limit has been exceeded.
346 */
347static int ep_call_nested(struct nested_calls *ncalls, int max_nests,
348              int (*nproc)(void *, void *, int), void *priv,
349              void *cookie, void *ctx)
350{
351    int error, call_nests = 0;
352    unsigned long flags;
353    struct list_head *lsthead = &ncalls->tasks_call_list;
354    struct nested_call_node *tncur;
355    struct nested_call_node tnode;
356
357    spin_lock_irqsave(&ncalls->lock, flags);
358
359    /*
360     * Try to see if the current task is already inside this wakeup call.
361     * We use a list here, since the population inside this set is always
362     * very much limited.
363     */
364    list_for_each_entry(tncur, lsthead, llink) {
365        if (tncur->ctx == ctx &&
366            (tncur->cookie == cookie || ++call_nests > max_nests)) {
367            /*
368             * Ops ... loop detected or maximum nest level reached.
369             * We abort this wake by breaking the cycle itself.
370             */
371            error = -1;
372            goto out_unlock;
373        }
374    }
375
376    /* Add the current task and cookie to the list */
377    tnode.ctx = ctx;
378    tnode.cookie = cookie;
379    list_add(&tnode.llink, lsthead);
380
381    spin_unlock_irqrestore(&ncalls->lock, flags);
382
383    /* Call the nested function */
384    error = (*nproc)(priv, cookie, call_nests);
385
386    /* Remove the current task from the list */
387    spin_lock_irqsave(&ncalls->lock, flags);
388    list_del(&tnode.llink);
389out_unlock:
390    spin_unlock_irqrestore(&ncalls->lock, flags);
391
392    return error;
393}
394
395#ifdef CONFIG_DEBUG_LOCK_ALLOC
396static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
397                     unsigned long events, int subclass)
398{
399    unsigned long flags;
400
401    spin_lock_irqsave_nested(&wqueue->lock, flags, subclass);
402    wake_up_locked_poll(wqueue, events);
403    spin_unlock_irqrestore(&wqueue->lock, flags);
404}
405#else
406static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
407                     unsigned long events, int subclass)
408{
409    wake_up_poll(wqueue, events);
410}
411#endif
412
413static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
414{
415    ep_wake_up_nested((wait_queue_head_t *) cookie, POLLIN,
416              1 + call_nests);
417    return 0;
418}
419
420/*
421 * Perform a safe wake up of the poll wait list. The problem is that
422 * with the new callback'd wake up system, it is possible that the
423 * poll callback is reentered from inside the call to wake_up() done
424 * on the poll wait queue head. The rule is that we cannot reenter the
425 * wake up code from the same task more than EP_MAX_NESTS times,
426 * and we cannot reenter the same wait queue head at all. This will
427 * enable to have a hierarchy of epoll file descriptor of no more than
428 * EP_MAX_NESTS deep.
429 */
430static void ep_poll_safewake(wait_queue_head_t *wq)
431{
432    int this_cpu = get_cpu();
433
434    ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS,
435               ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
436
437    put_cpu();
438}
439
440/*
441 * This function unregisters poll callbacks from the associated file
442 * descriptor. Must be called with "mtx" held (or "epmutex" if called from
443 * ep_free).
444 */
445static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
446{
447    struct list_head *lsthead = &epi->pwqlist;
448    struct eppoll_entry *pwq;
449
450    while (!list_empty(lsthead)) {
451        pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
452
453        list_del(&pwq->llink);
454        remove_wait_queue(pwq->whead, &pwq->wait);
455        kmem_cache_free(pwq_cache, pwq);
456    }
457}
458
459/**
460 * ep_scan_ready_list - Scans the ready list in a way that makes possible for
461 * the scan code, to call f_op->poll(). Also allows for
462 * O(NumReady) performance.
463 *
464 * @ep: Pointer to the epoll private data structure.
465 * @sproc: Pointer to the scan callback.
466 * @priv: Private opaque data passed to the @sproc callback.
467 *
468 * Returns: The same integer error code returned by the @sproc callback.
469 */
470static int ep_scan_ready_list(struct eventpoll *ep,
471                  int (*sproc)(struct eventpoll *,
472                       struct list_head *, void *),
473                  void *priv)
474{
475    int error, pwake = 0;
476    unsigned long flags;
477    struct epitem *epi, *nepi;
478    LIST_HEAD(txlist);
479
480    /*
481     * We need to lock this because we could be hit by
482     * eventpoll_release_file() and epoll_ctl().
483     */
484    mutex_lock(&ep->mtx);
485
486    /*
487     * Steal the ready list, and re-init the original one to the
488     * empty list. Also, set ep->ovflist to NULL so that events
489     * happening while looping w/out locks, are not lost. We cannot
490     * have the poll callback to queue directly on ep->rdllist,
491     * because we want the "sproc" callback to be able to do it
492     * in a lockless way.
493     */
494    spin_lock_irqsave(&ep->lock, flags);
495    list_splice_init(&ep->rdllist, &txlist);
496    ep->ovflist = NULL;
497    spin_unlock_irqrestore(&ep->lock, flags);
498
499    /*
500     * Now call the callback function.
501     */
502    error = (*sproc)(ep, &txlist, priv);
503
504    spin_lock_irqsave(&ep->lock, flags);
505    /*
506     * During the time we spent inside the "sproc" callback, some
507     * other events might have been queued by the poll callback.
508     * We re-insert them inside the main ready-list here.
509     */
510    for (nepi = ep->ovflist; (epi = nepi) != NULL;
511         nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
512        /*
513         * We need to check if the item is already in the list.
514         * During the "sproc" callback execution time, items are
515         * queued into ->ovflist but the "txlist" might already
516         * contain them, and the list_splice() below takes care of them.
517         */
518        if (!ep_is_linked(&epi->rdllink))
519            list_add_tail(&epi->rdllink, &ep->rdllist);
520    }
521    /*
522     * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
523     * releasing the lock, events will be queued in the normal way inside
524     * ep->rdllist.
525     */
526    ep->ovflist = EP_UNACTIVE_PTR;
527
528    /*
529     * Quickly re-inject items left on "txlist".
530     */
531    list_splice(&txlist, &ep->rdllist);
532
533    if (!list_empty(&ep->rdllist)) {
534        /*
535         * Wake up (if active) both the eventpoll wait list and
536         * the ->poll() wait list (delayed after we release the lock).
537         */
538        if (waitqueue_active(&ep->wq))
539            wake_up_locked(&ep->wq);
540        if (waitqueue_active(&ep->poll_wait))
541            pwake++;
542    }
543    spin_unlock_irqrestore(&ep->lock, flags);
544
545    mutex_unlock(&ep->mtx);
546
547    /* We have to call this outside the lock */
548    if (pwake)
549        ep_poll_safewake(&ep->poll_wait);
550
551    return error;
552}
553
554/*
555 * Removes a "struct epitem" from the eventpoll RB tree and deallocates
556 * all the associated resources. Must be called with "mtx" held.
557 */
558static int ep_remove(struct eventpoll *ep, struct epitem *epi)
559{
560    unsigned long flags;
561    struct file *file = epi->ffd.file;
562
563    /*
564     * Removes poll wait queue hooks. We _have_ to do this without holding
565     * the "ep->lock" otherwise a deadlock might occur. This because of the
566     * sequence of the lock acquisition. Here we do "ep->lock" then the wait
567     * queue head lock when unregistering the wait queue. The wakeup callback
568     * will run by holding the wait queue head lock and will call our callback
569     * that will try to get "ep->lock".
570     */
571    ep_unregister_pollwait(ep, epi);
572
573    /* Remove the current item from the list of epoll hooks */
574    spin_lock(&file->f_lock);
575    if (ep_is_linked(&epi->fllink))
576        list_del_init(&epi->fllink);
577    spin_unlock(&file->f_lock);
578
579    rb_erase(&epi->rbn, &ep->rbr);
580
581    spin_lock_irqsave(&ep->lock, flags);
582    if (ep_is_linked(&epi->rdllink))
583        list_del_init(&epi->rdllink);
584    spin_unlock_irqrestore(&ep->lock, flags);
585
586    /* At this point it is safe to free the eventpoll item */
587    kmem_cache_free(epi_cache, epi);
588
589    atomic_long_dec(&ep->user->epoll_watches);
590
591    return 0;
592}
593
594static void ep_free(struct eventpoll *ep)
595{
596    struct rb_node *rbp;
597    struct epitem *epi;
598
599    /* We need to release all tasks waiting for these file */
600    if (waitqueue_active(&ep->poll_wait))
601        ep_poll_safewake(&ep->poll_wait);
602
603    /*
604     * We need to lock this because we could be hit by
605     * eventpoll_release_file() while we're freeing the "struct eventpoll".
606     * We do not need to hold "ep->mtx" here because the epoll file
607     * is on the way to be removed and no one has references to it
608     * anymore. The only hit might come from eventpoll_release_file() but
609     * holding "epmutex" is sufficient here.
610     */
611    mutex_lock(&epmutex);
612
613    /*
614     * Walks through the whole tree by unregistering poll callbacks.
615     */
616    for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
617        epi = rb_entry(rbp, struct epitem, rbn);
618
619        ep_unregister_pollwait(ep, epi);
620    }
621
622    /*
623     * Walks through the whole tree by freeing each "struct epitem". At this
624     * point we are sure no poll callbacks will be lingering around, and also by
625     * holding "epmutex" we can be sure that no file cleanup code will hit
626     * us during this operation. So we can avoid the lock on "ep->lock".
627     */
628    while ((rbp = rb_first(&ep->rbr)) != NULL) {
629        epi = rb_entry(rbp, struct epitem, rbn);
630        ep_remove(ep, epi);
631    }
632
633    mutex_unlock(&epmutex);
634    mutex_destroy(&ep->mtx);
635    free_uid(ep->user);
636    kfree(ep);
637}
638
639static int ep_eventpoll_release(struct inode *inode, struct file *file)
640{
641    struct eventpoll *ep = file->private_data;
642
643    if (ep)
644        ep_free(ep);
645
646    return 0;
647}
648
649static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
650                   void *priv)
651{
652    struct epitem *epi, *tmp;
653
654    list_for_each_entry_safe(epi, tmp, head, rdllink) {
655        if (epi->ffd.file->f_op->poll(epi->ffd.file, NULL) &
656            epi->event.events)
657            return POLLIN | POLLRDNORM;
658        else {
659            /*
660             * Item has been dropped into the ready list by the poll
661             * callback, but it's not actually ready, as far as
662             * caller requested events goes. We can remove it here.
663             */
664            list_del_init(&epi->rdllink);
665        }
666    }
667
668    return 0;
669}
670
671static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
672{
673    return ep_scan_ready_list(priv, ep_read_events_proc, NULL);
674}
675
676static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
677{
678    int pollflags;
679    struct eventpoll *ep = file->private_data;
680
681    /* Insert inside our poll wait queue */
682    poll_wait(file, &ep->poll_wait, wait);
683
684    /*
685     * Proceed to find out if wanted events are really available inside
686     * the ready list. This need to be done under ep_call_nested()
687     * supervision, since the call to f_op->poll() done on listed files
688     * could re-enter here.
689     */
690    pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS,
691                   ep_poll_readyevents_proc, ep, ep, current);
692
693    return pollflags != -1 ? pollflags : 0;
694}
695
696/* File callbacks that implement the eventpoll file behaviour */
697static const struct file_operations eventpoll_fops = {
698    .release = ep_eventpoll_release,
699    .poll = ep_eventpoll_poll,
700    .llseek = noop_llseek,
701};
702
703/* Fast test to see if the file is an evenpoll file */
704static inline int is_file_epoll(struct file *f)
705{
706    return f->f_op == &eventpoll_fops;
707}
708
709/*
710 * This is called from eventpoll_release() to unlink files from the eventpoll
711 * interface. We need to have this facility to cleanup correctly files that are
712 * closed without being removed from the eventpoll interface.
713 */
714void eventpoll_release_file(struct file *file)
715{
716    struct list_head *lsthead = &file->f_ep_links;
717    struct eventpoll *ep;
718    struct epitem *epi;
719
720    /*
721     * We don't want to get "file->f_lock" because it is not
722     * necessary. It is not necessary because we're in the "struct file"
723     * cleanup path, and this means that no one is using this file anymore.
724     * So, for example, epoll_ctl() cannot hit here since if we reach this
725     * point, the file counter already went to zero and fget() would fail.
726     * The only hit might come from ep_free() but by holding the mutex
727     * will correctly serialize the operation. We do need to acquire
728     * "ep->mtx" after "epmutex" because ep_remove() requires it when called
729     * from anywhere but ep_free().
730     *
731     * Besides, ep_remove() acquires the lock, so we can't hold it here.
732     */
733    mutex_lock(&epmutex);
734
735    while (!list_empty(lsthead)) {
736        epi = list_first_entry(lsthead, struct epitem, fllink);
737
738        ep = epi->ep;
739        list_del_init(&epi->fllink);
740        mutex_lock(&ep->mtx);
741        ep_remove(ep, epi);
742        mutex_unlock(&ep->mtx);
743    }
744
745    mutex_unlock(&epmutex);
746}
747
748static int ep_alloc(struct eventpoll **pep)
749{
750    int error;
751    struct user_struct *user;
752    struct eventpoll *ep;
753
754    user = get_current_user();
755    error = -ENOMEM;
756    ep = kzalloc(sizeof(*ep), GFP_KERNEL);
757    if (unlikely(!ep))
758        goto free_uid;
759
760    spin_lock_init(&ep->lock);
761    mutex_init(&ep->mtx);
762    init_waitqueue_head(&ep->wq);
763    init_waitqueue_head(&ep->poll_wait);
764    INIT_LIST_HEAD(&ep->rdllist);
765    ep->rbr = RB_ROOT;
766    ep->ovflist = EP_UNACTIVE_PTR;
767    ep->user = user;
768
769    *pep = ep;
770
771    return 0;
772
773free_uid:
774    free_uid(user);
775    return error;
776}
777
778/*
779 * Search the file inside the eventpoll tree. The RB tree operations
780 * are protected by the "mtx" mutex, and ep_find() must be called with
781 * "mtx" held.
782 */
783static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
784{
785    int kcmp;
786    struct rb_node *rbp;
787    struct epitem *epi, *epir = NULL;
788    struct epoll_filefd ffd;
789
790    ep_set_ffd(&ffd, file, fd);
791    for (rbp = ep->rbr.rb_node; rbp; ) {
792        epi = rb_entry(rbp, struct epitem, rbn);
793        kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
794        if (kcmp > 0)
795            rbp = rbp->rb_right;
796        else if (kcmp < 0)
797            rbp = rbp->rb_left;
798        else {
799            epir = epi;
800            break;
801        }
802    }
803
804    return epir;
805}
806
807/*
808 * This is the callback that is passed to the wait queue wakeup
809 * mechanism. It is called by the stored file descriptors when they
810 * have events to report.
811 */
812static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
813{
814    int pwake = 0;
815    unsigned long flags;
816    struct epitem *epi = ep_item_from_wait(wait);
817    struct eventpoll *ep = epi->ep;
818
819    spin_lock_irqsave(&ep->lock, flags);
820
821    /*
822     * If the event mask does not contain any poll(2) event, we consider the
823     * descriptor to be disabled. This condition is likely the effect of the
824     * EPOLLONESHOT bit that disables the descriptor when an event is received,
825     * until the next EPOLL_CTL_MOD will be issued.
826     */
827    if (!(epi->event.events & ~EP_PRIVATE_BITS))
828        goto out_unlock;
829
830    /*
831     * Check the events coming with the callback. At this stage, not
832     * every device reports the events in the "key" parameter of the
833     * callback. We need to be able to handle both cases here, hence the
834     * test for "key" != NULL before the event match test.
835     */
836    if (key && !((unsigned long) key & epi->event.events))
837        goto out_unlock;
838
839    /*
840     * If we are transferring events to userspace, we can hold no locks
841     * (because we're accessing user memory, and because of linux f_op->poll()
842     * semantics). All the events that happen during that period of time are
843     * chained in ep->ovflist and requeued later on.
844     */
845    if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
846        if (epi->next == EP_UNACTIVE_PTR) {
847            epi->next = ep->ovflist;
848            ep->ovflist = epi;
849        }
850        goto out_unlock;
851    }
852
853    /* If this file is already in the ready list we exit soon */
854    if (!ep_is_linked(&epi->rdllink))
855        list_add_tail(&epi->rdllink, &ep->rdllist);
856
857    /*
858     * Wake up ( if active ) both the eventpoll wait list and the ->poll()
859     * wait list.
860     */
861    if (waitqueue_active(&ep->wq))
862        wake_up_locked(&ep->wq);
863    if (waitqueue_active(&ep->poll_wait))
864        pwake++;
865
866out_unlock:
867    spin_unlock_irqrestore(&ep->lock, flags);
868
869    /* We have to call this outside the lock */
870    if (pwake)
871        ep_poll_safewake(&ep->poll_wait);
872
873    return 1;
874}
875
876/*
877 * This is the callback that is used to add our wait queue to the
878 * target file wakeup lists.
879 */
880static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
881                 poll_table *pt)
882{
883    struct epitem *epi = ep_item_from_epqueue(pt);
884    struct eppoll_entry *pwq;
885
886    if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
887        init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
888        pwq->whead = whead;
889        pwq->base = epi;
890        add_wait_queue(whead, &pwq->wait);
891        list_add_tail(&pwq->llink, &epi->pwqlist);
892        epi->nwait++;
893    } else {
894        /* We have to signal that an error occurred */
895        epi->nwait = -1;
896    }
897}
898
899static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
900{
901    int kcmp;
902    struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
903    struct epitem *epic;
904
905    while (*p) {
906        parent = *p;
907        epic = rb_entry(parent, struct epitem, rbn);
908        kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
909        if (kcmp > 0)
910            p = &parent->rb_right;
911        else
912            p = &parent->rb_left;
913    }
914    rb_link_node(&epi->rbn, parent, p);
915    rb_insert_color(&epi->rbn, &ep->rbr);
916}
917
918/*
919 * Must be called with "mtx" held.
920 */
921static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
922             struct file *tfile, int fd)
923{
924    int error, revents, pwake = 0;
925    unsigned long flags;
926    long user_watches;
927    struct epitem *epi;
928    struct ep_pqueue epq;
929
930    user_watches = atomic_long_read(&ep->user->epoll_watches);
931    if (unlikely(user_watches >= max_user_watches))
932        return -ENOSPC;
933    if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
934        return -ENOMEM;
935
936    /* Item initialization follow here ... */
937    INIT_LIST_HEAD(&epi->rdllink);
938    INIT_LIST_HEAD(&epi->fllink);
939    INIT_LIST_HEAD(&epi->pwqlist);
940    epi->ep = ep;
941    ep_set_ffd(&epi->ffd, tfile, fd);
942    epi->event = *event;
943    epi->nwait = 0;
944    epi->next = EP_UNACTIVE_PTR;
945
946    /* Initialize the poll table using the queue callback */
947    epq.epi = epi;
948    init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
949
950    /*
951     * Attach the item to the poll hooks and get current event bits.
952     * We can safely use the file* here because its usage count has
953     * been increased by the caller of this function. Note that after
954     * this operation completes, the poll callback can start hitting
955     * the new item.
956     */
957    revents = tfile->f_op->poll(tfile, &epq.pt);
958
959    /*
960     * We have to check if something went wrong during the poll wait queue
961     * install process. Namely an allocation for a wait queue failed due
962     * high memory pressure.
963     */
964    error = -ENOMEM;
965    if (epi->nwait < 0)
966        goto error_unregister;
967
968    /* Add the current item to the list of active epoll hook for this file */
969    spin_lock(&tfile->f_lock);
970    list_add_tail(&epi->fllink, &tfile->f_ep_links);
971    spin_unlock(&tfile->f_lock);
972
973    /*
974     * Add the current item to the RB tree. All RB tree operations are
975     * protected by "mtx", and ep_insert() is called with "mtx" held.
976     */
977    ep_rbtree_insert(ep, epi);
978
979    /* We have to drop the new item inside our item list to keep track of it */
980    spin_lock_irqsave(&ep->lock, flags);
981
982    /* If the file is already "ready" we drop it inside the ready list */
983    if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
984        list_add_tail(&epi->rdllink, &ep->rdllist);
985
986        /* Notify waiting tasks that events are available */
987        if (waitqueue_active(&ep->wq))
988            wake_up_locked(&ep->wq);
989        if (waitqueue_active(&ep->poll_wait))
990            pwake++;
991    }
992
993    spin_unlock_irqrestore(&ep->lock, flags);
994
995    atomic_long_inc(&ep->user->epoll_watches);
996
997    /* We have to call this outside the lock */
998    if (pwake)
999        ep_poll_safewake(&ep->poll_wait);
1000
1001    return 0;
1002
1003error_unregister:
1004    ep_unregister_pollwait(ep, epi);
1005
1006    /*
1007     * We need to do this because an event could have been arrived on some
1008     * allocated wait queue. Note that we don't care about the ep->ovflist
1009     * list, since that is used/cleaned only inside a section bound by "mtx".
1010     * And ep_insert() is called with "mtx" held.
1011     */
1012    spin_lock_irqsave(&ep->lock, flags);
1013    if (ep_is_linked(&epi->rdllink))
1014        list_del_init(&epi->rdllink);
1015    spin_unlock_irqrestore(&ep->lock, flags);
1016
1017    kmem_cache_free(epi_cache, epi);
1018
1019    return error;
1020}
1021
1022/*
1023 * Modify the interest event mask by dropping an event if the new mask
1024 * has a match in the current file status. Must be called with "mtx" held.
1025 */
1026static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
1027{
1028    int pwake = 0;
1029    unsigned int revents;
1030
1031    /*
1032     * Set the new event interest mask before calling f_op->poll();
1033     * otherwise we might miss an event that happens between the
1034     * f_op->poll() call and the new event set registering.
1035     */
1036    epi->event.events = event->events;
1037    epi->event.data = event->data; /* protected by mtx */
1038
1039    /*
1040     * Get current event bits. We can safely use the file* here because
1041     * its usage count has been increased by the caller of this function.
1042     */
1043    revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
1044
1045    /*
1046     * If the item is "hot" and it is not registered inside the ready
1047     * list, push it inside.
1048     */
1049    if (revents & event->events) {
1050        spin_lock_irq(&ep->lock);
1051        if (!ep_is_linked(&epi->rdllink)) {
1052            list_add_tail(&epi->rdllink, &ep->rdllist);
1053
1054            /* Notify waiting tasks that events are available */
1055            if (waitqueue_active(&ep->wq))
1056                wake_up_locked(&ep->wq);
1057            if (waitqueue_active(&ep->poll_wait))
1058                pwake++;
1059        }
1060        spin_unlock_irq(&ep->lock);
1061    }
1062
1063    /* We have to call this outside the lock */
1064    if (pwake)
1065        ep_poll_safewake(&ep->poll_wait);
1066
1067    return 0;
1068}
1069
1070static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
1071                   void *priv)
1072{
1073    struct ep_send_events_data *esed = priv;
1074    int eventcnt;
1075    unsigned int revents;
1076    struct epitem *epi;
1077    struct epoll_event __user *uevent;
1078
1079    /*
1080     * We can loop without lock because we are passed a task private list.
1081     * Items cannot vanish during the loop because ep_scan_ready_list() is
1082     * holding "mtx" during this call.
1083     */
1084    for (eventcnt = 0, uevent = esed->events;
1085         !list_empty(head) && eventcnt < esed->maxevents;) {
1086        epi = list_first_entry(head, struct epitem, rdllink);
1087
1088        list_del_init(&epi->rdllink);
1089
1090        revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL) &
1091            epi->event.events;
1092
1093        /*
1094         * If the event mask intersect the caller-requested one,
1095         * deliver the event to userspace. Again, ep_scan_ready_list()
1096         * is holding "mtx", so no operations coming from userspace
1097         * can change the item.
1098         */
1099        if (revents) {
1100            if (__put_user(revents, &uevent->events) ||
1101                __put_user(epi->event.data, &uevent->data)) {
1102                list_add(&epi->rdllink, head);
1103                return eventcnt ? eventcnt : -EFAULT;
1104            }
1105            eventcnt++;
1106            uevent++;
1107            if (epi->event.events & EPOLLONESHOT)
1108                epi->event.events &= EP_PRIVATE_BITS;
1109            else if (!(epi->event.events & EPOLLET)) {
1110                /*
1111                 * If this file has been added with Level
1112                 * Trigger mode, we need to insert back inside
1113                 * the ready list, so that the next call to
1114                 * epoll_wait() will check again the events
1115                 * availability. At this point, no one can insert
1116                 * into ep->rdllist besides us. The epoll_ctl()
1117                 * callers are locked out by
1118                 * ep_scan_ready_list() holding "mtx" and the
1119                 * poll callback will queue them in ep->ovflist.
1120                 */
1121                list_add_tail(&epi->rdllink, &ep->rdllist);
1122            }
1123        }
1124    }
1125
1126    return eventcnt;
1127}
1128
1129static int ep_send_events(struct eventpoll *ep,
1130              struct epoll_event __user *events, int maxevents)
1131{
1132    struct ep_send_events_data esed;
1133
1134    esed.maxevents = maxevents;
1135    esed.events = events;
1136
1137    return ep_scan_ready_list(ep, ep_send_events_proc, &esed);
1138}
1139
1140static inline struct timespec ep_set_mstimeout(long ms)
1141{
1142    struct timespec now, ts = {
1143        .tv_sec = ms / MSEC_PER_SEC,
1144        .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
1145    };
1146
1147    ktime_get_ts(&now);
1148    return timespec_add_safe(now, ts);
1149}
1150
1151/**
1152 * ep_poll - Retrieves ready events, and delivers them to the caller supplied
1153 * event buffer.
1154 *
1155 * @ep: Pointer to the eventpoll context.
1156 * @events: Pointer to the userspace buffer where the ready events should be
1157 * stored.
1158 * @maxevents: Size (in terms of number of events) of the caller event buffer.
1159 * @timeout: Maximum timeout for the ready events fetch operation, in
1160 * milliseconds. If the @timeout is zero, the function will not block,
1161 * while if the @timeout is less than zero, the function will block
1162 * until at least one event has been retrieved (or an error
1163 * occurred).
1164 *
1165 * Returns: Returns the number of ready events which have been fetched, or an
1166 * error code, in case of error.
1167 */
1168static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
1169           int maxevents, long timeout)
1170{
1171    int res = 0, eavail, timed_out = 0;
1172    unsigned long flags;
1173    long slack = 0;
1174    wait_queue_t wait;
1175    ktime_t expires, *to = NULL;
1176
1177    if (timeout > 0) {
1178        struct timespec end_time = ep_set_mstimeout(timeout);
1179
1180        slack = select_estimate_accuracy(&end_time);
1181        to = &expires;
1182        *to = timespec_to_ktime(end_time);
1183    } else if (timeout == 0) {
1184        /*
1185         * Avoid the unnecessary trip to the wait queue loop, if the
1186         * caller specified a non blocking operation.
1187         */
1188        timed_out = 1;
1189        spin_lock_irqsave(&ep->lock, flags);
1190        goto check_events;
1191    }
1192
1193fetch_events:
1194    spin_lock_irqsave(&ep->lock, flags);
1195
1196    if (!ep_events_available(ep)) {
1197        /*
1198         * We don't have any available event to return to the caller.
1199         * We need to sleep here, and we will be wake up by
1200         * ep_poll_callback() when events will become available.
1201         */
1202        init_waitqueue_entry(&wait, current);
1203        __add_wait_queue_exclusive(&ep->wq, &wait);
1204
1205        for (;;) {
1206            /*
1207             * We don't want to sleep if the ep_poll_callback() sends us
1208             * a wakeup in between. That's why we set the task state
1209             * to TASK_INTERRUPTIBLE before doing the checks.
1210             */
1211            set_current_state(TASK_INTERRUPTIBLE);
1212            if (ep_events_available(ep) || timed_out)
1213                break;
1214            if (signal_pending(current)) {
1215                res = -EINTR;
1216                break;
1217            }
1218
1219            spin_unlock_irqrestore(&ep->lock, flags);
1220            if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
1221                timed_out = 1;
1222
1223            spin_lock_irqsave(&ep->lock, flags);
1224        }
1225        __remove_wait_queue(&ep->wq, &wait);
1226
1227        set_current_state(TASK_RUNNING);
1228    }
1229check_events:
1230    /* Is it worth to try to dig for events ? */
1231    eavail = ep_events_available(ep);
1232
1233    spin_unlock_irqrestore(&ep->lock, flags);
1234
1235    /*
1236     * Try to transfer events to user space. In case we get 0 events and
1237     * there's still timeout left over, we go trying again in search of
1238     * more luck.
1239     */
1240    if (!res && eavail &&
1241        !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
1242        goto fetch_events;
1243
1244    return res;
1245}
1246
1247/**
1248 * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
1249 * API, to verify that adding an epoll file inside another
1250 * epoll structure, does not violate the constraints, in
1251 * terms of closed loops, or too deep chains (which can
1252 * result in excessive stack usage).
1253 *
1254 * @priv: Pointer to the epoll file to be currently checked.
1255 * @cookie: Original cookie for this call. This is the top-of-the-chain epoll
1256 * data structure pointer.
1257 * @call_nests: Current dept of the @ep_call_nested() call stack.
1258 *
1259 * Returns: Returns zero if adding the epoll @file inside current epoll
1260 * structure @ep does not violate the constraints, or -1 otherwise.
1261 */
1262static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
1263{
1264    int error = 0;
1265    struct file *file = priv;
1266    struct eventpoll *ep = file->private_data;
1267    struct rb_node *rbp;
1268    struct epitem *epi;
1269
1270    mutex_lock(&ep->mtx);
1271    for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
1272        epi = rb_entry(rbp, struct epitem, rbn);
1273        if (unlikely(is_file_epoll(epi->ffd.file))) {
1274            error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1275                           ep_loop_check_proc, epi->ffd.file,
1276                           epi->ffd.file->private_data, current);
1277            if (error != 0)
1278                break;
1279        }
1280    }
1281    mutex_unlock(&ep->mtx);
1282
1283    return error;
1284}
1285
1286/**
1287 * ep_loop_check - Performs a check to verify that adding an epoll file (@file)
1288 * another epoll file (represented by @ep) does not create
1289 * closed loops or too deep chains.
1290 *
1291 * @ep: Pointer to the epoll private data structure.
1292 * @file: Pointer to the epoll file to be checked.
1293 *
1294 * Returns: Returns zero if adding the epoll @file inside current epoll
1295 * structure @ep does not violate the constraints, or -1 otherwise.
1296 */
1297static int ep_loop_check(struct eventpoll *ep, struct file *file)
1298{
1299    return ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1300                  ep_loop_check_proc, file, ep, current);
1301}
1302
1303/*
1304 * Open an eventpoll file descriptor.
1305 */
1306SYSCALL_DEFINE1(epoll_create1, int, flags)
1307{
1308    int error;
1309    struct eventpoll *ep = NULL;
1310
1311    /* Check the EPOLL_* constant for consistency. */
1312    BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
1313
1314    if (flags & ~EPOLL_CLOEXEC)
1315        return -EINVAL;
1316    /*
1317     * Create the internal data structure ("struct eventpoll").
1318     */
1319    error = ep_alloc(&ep);
1320    if (error < 0)
1321        return error;
1322    /*
1323     * Creates all the items needed to setup an eventpoll file. That is,
1324     * a file structure and a free file descriptor.
1325     */
1326    error = anon_inode_getfd("[eventpoll]", &eventpoll_fops, ep,
1327                 O_RDWR | (flags & O_CLOEXEC));
1328    if (error < 0)
1329        ep_free(ep);
1330
1331    return error;
1332}
1333
1334SYSCALL_DEFINE1(epoll_create, int, size)
1335{
1336    if (size <= 0)
1337        return -EINVAL;
1338
1339    return sys_epoll_create1(0);
1340}
1341
1342/*
1343 * The following function implements the controller interface for
1344 * the eventpoll file that enables the insertion/removal/change of
1345 * file descriptors inside the interest set.
1346 */
1347SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
1348        struct epoll_event __user *, event)
1349{
1350    int error;
1351    int did_lock_epmutex = 0;
1352    struct file *file, *tfile;
1353    struct eventpoll *ep;
1354    struct epitem *epi;
1355    struct epoll_event epds;
1356
1357    error = -EFAULT;
1358    if (ep_op_has_event(op) &&
1359        copy_from_user(&epds, event, sizeof(struct epoll_event)))
1360        goto error_return;
1361
1362    /* Get the "struct file *" for the eventpoll file */
1363    error = -EBADF;
1364    file = fget(epfd);
1365    if (!file)
1366        goto error_return;
1367
1368    /* Get the "struct file *" for the target file */
1369    tfile = fget(fd);
1370    if (!tfile)
1371        goto error_fput;
1372
1373    /* The target file descriptor must support poll */
1374    error = -EPERM;
1375    if (!tfile->f_op || !tfile->f_op->poll)
1376        goto error_tgt_fput;
1377
1378    /*
1379     * We have to check that the file structure underneath the file descriptor
1380     * the user passed to us _is_ an eventpoll file. And also we do not permit
1381     * adding an epoll file descriptor inside itself.
1382     */
1383    error = -EINVAL;
1384    if (file == tfile || !is_file_epoll(file))
1385        goto error_tgt_fput;
1386
1387    /*
1388     * At this point it is safe to assume that the "private_data" contains
1389     * our own data structure.
1390     */
1391    ep = file->private_data;
1392
1393    /*
1394     * When we insert an epoll file descriptor, inside another epoll file
1395     * descriptor, there is the change of creating closed loops, which are
1396     * better be handled here, than in more critical paths.
1397     *
1398     * We hold epmutex across the loop check and the insert in this case, in
1399     * order to prevent two separate inserts from racing and each doing the
1400     * insert "at the same time" such that ep_loop_check passes on both
1401     * before either one does the insert, thereby creating a cycle.
1402     */
1403    if (unlikely(is_file_epoll(tfile) && op == EPOLL_CTL_ADD)) {
1404        mutex_lock(&epmutex);
1405        did_lock_epmutex = 1;
1406        error = -ELOOP;
1407        if (ep_loop_check(ep, tfile) != 0)
1408            goto error_tgt_fput;
1409    }
1410
1411
1412    mutex_lock(&ep->mtx);
1413
1414    /*
1415     * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
1416     * above, we can be sure to be able to use the item looked up by
1417     * ep_find() till we release the mutex.
1418     */
1419    epi = ep_find(ep, tfile, fd);
1420
1421    error = -EINVAL;
1422    switch (op) {
1423    case EPOLL_CTL_ADD:
1424        if (!epi) {
1425            epds.events |= POLLERR | POLLHUP;
1426            error = ep_insert(ep, &epds, tfile, fd);
1427        } else
1428            error = -EEXIST;
1429        break;
1430    case EPOLL_CTL_DEL:
1431        if (epi)
1432            error = ep_remove(ep, epi);
1433        else
1434            error = -ENOENT;
1435        break;
1436    case EPOLL_CTL_MOD:
1437        if (epi) {
1438            epds.events |= POLLERR | POLLHUP;
1439            error = ep_modify(ep, epi, &epds);
1440        } else
1441            error = -ENOENT;
1442        break;
1443    }
1444    mutex_unlock(&ep->mtx);
1445
1446error_tgt_fput:
1447    if (unlikely(did_lock_epmutex))
1448        mutex_unlock(&epmutex);
1449
1450    fput(tfile);
1451error_fput:
1452    fput(file);
1453error_return:
1454
1455    return error;
1456}
1457
1458/*
1459 * Implement the event wait interface for the eventpoll file. It is the kernel
1460 * part of the user space epoll_wait(2).
1461 */
1462SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
1463        int, maxevents, int, timeout)
1464{
1465    int error;
1466    struct file *file;
1467    struct eventpoll *ep;
1468
1469    /* The maximum number of event must be greater than zero */
1470    if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
1471        return -EINVAL;
1472
1473    /* Verify that the area passed by the user is writeable */
1474    if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event))) {
1475        error = -EFAULT;
1476        goto error_return;
1477    }
1478
1479    /* Get the "struct file *" for the eventpoll file */
1480    error = -EBADF;
1481    file = fget(epfd);
1482    if (!file)
1483        goto error_return;
1484
1485    /*
1486     * We have to check that the file structure underneath the fd
1487     * the user passed to us _is_ an eventpoll file.
1488     */
1489    error = -EINVAL;
1490    if (!is_file_epoll(file))
1491        goto error_fput;
1492
1493    /*
1494     * At this point it is safe to assume that the "private_data" contains
1495     * our own data structure.
1496     */
1497    ep = file->private_data;
1498
1499    /* Time to fish for events ... */
1500    error = ep_poll(ep, events, maxevents, timeout);
1501
1502error_fput:
1503    fput(file);
1504error_return:
1505
1506    return error;
1507}
1508
1509#ifdef HAVE_SET_RESTORE_SIGMASK
1510
1511/*
1512 * Implement the event wait interface for the eventpoll file. It is the kernel
1513 * part of the user space epoll_pwait(2).
1514 */
1515SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
1516        int, maxevents, int, timeout, const sigset_t __user *, sigmask,
1517        size_t, sigsetsize)
1518{
1519    int error;
1520    sigset_t ksigmask, sigsaved;
1521
1522    /*
1523     * If the caller wants a certain signal mask to be set during the wait,
1524     * we apply it here.
1525     */
1526    if (sigmask) {
1527        if (sigsetsize != sizeof(sigset_t))
1528            return -EINVAL;
1529        if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
1530            return -EFAULT;
1531        sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
1532        sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
1533    }
1534
1535    error = sys_epoll_wait(epfd, events, maxevents, timeout);
1536
1537    /*
1538     * If we changed the signal mask, we need to restore the original one.
1539     * In case we've got a signal while waiting, we do not restore the
1540     * signal mask yet, and we allow do_signal() to deliver the signal on
1541     * the way back to userspace, before the signal mask is restored.
1542     */
1543    if (sigmask) {
1544        if (error == -EINTR) {
1545            memcpy(&current->saved_sigmask, &sigsaved,
1546                   sizeof(sigsaved));
1547            set_restore_sigmask();
1548        } else
1549            sigprocmask(SIG_SETMASK, &sigsaved, NULL);
1550    }
1551
1552    return error;
1553}
1554
1555#endif /* HAVE_SET_RESTORE_SIGMASK */
1556
1557static int __init eventpoll_init(void)
1558{
1559    struct sysinfo si;
1560
1561    si_meminfo(&si);
1562    /*
1563     * Allows top 4% of lomem to be allocated for epoll watches (per user).
1564     */
1565    max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
1566        EP_ITEM_COST;
1567    BUG_ON(max_user_watches < 0);
1568
1569    /*
1570     * Initialize the structure used to perform epoll file descriptor
1571     * inclusion loops checks.
1572     */
1573    ep_nested_calls_init(&poll_loop_ncalls);
1574
1575    /* Initialize the structure used to perform safe poll wait head wake ups */
1576    ep_nested_calls_init(&poll_safewake_ncalls);
1577
1578    /* Initialize the structure used to perform file's f_op->poll() calls */
1579    ep_nested_calls_init(&poll_readywalk_ncalls);
1580
1581    /* Allocates slab cache used to allocate "struct epitem" items */
1582    epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
1583            0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
1584
1585    /* Allocates slab cache used to allocate "struct eppoll_entry" */
1586    pwq_cache = kmem_cache_create("eventpoll_pwq",
1587            sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL);
1588
1589    return 0;
1590}
1591fs_initcall(eventpoll_init);
1592

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