Bootlin logo

Elixir Cross Referencer

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
/*
 *  fs/eventpoll.c (Efficent event polling implementation)
 *  Copyright (C) 2001,...,2007	 Davide Libenzi
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  Davide Libenzi <davidel@xmailserver.org>
 *
 */

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/string.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/spinlock.h>
#include <linux/syscalls.h>
#include <linux/rbtree.h>
#include <linux/wait.h>
#include <linux/eventpoll.h>
#include <linux/mount.h>
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <linux/anon_inodes.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/io.h>
#include <asm/mman.h>
#include <asm/atomic.h>

/*
 * LOCKING:
 * There are three level of locking required by epoll :
 *
 * 1) epmutex (mutex)
 * 2) ep->mtx (mutex)
 * 3) ep->lock (spinlock)
 *
 * The acquire order is the one listed above, from 1 to 3.
 * We need a spinlock (ep->lock) because we manipulate objects
 * from inside the poll callback, that might be triggered from
 * a wake_up() that in turn might be called from IRQ context.
 * So we can't sleep inside the poll callback and hence we need
 * a spinlock. During the event transfer loop (from kernel to
 * user space) we could end up sleeping due a copy_to_user(), so
 * we need a lock that will allow us to sleep. This lock is a
 * mutex (ep->mtx). It is acquired during the event transfer loop,
 * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
 * Then we also need a global mutex to serialize eventpoll_release_file()
 * and ep_free().
 * This mutex is acquired by ep_free() during the epoll file
 * cleanup path and it is also acquired by eventpoll_release_file()
 * if a file has been pushed inside an epoll set and it is then
 * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL).
 * It is possible to drop the "ep->mtx" and to use the global
 * mutex "epmutex" (together with "ep->lock") to have it working,
 * but having "ep->mtx" will make the interface more scalable.
 * Events that require holding "epmutex" are very rare, while for
 * normal operations the epoll private "ep->mtx" will guarantee
 * a better scalability.
 */

#define DEBUG_EPOLL 0

#if DEBUG_EPOLL > 0
#define DPRINTK(x) printk x
#define DNPRINTK(n, x) do { if ((n) <= DEBUG_EPOLL) printk x; } while (0)
#else /* #if DEBUG_EPOLL > 0 */
#define DPRINTK(x) (void) 0
#define DNPRINTK(n, x) (void) 0
#endif /* #if DEBUG_EPOLL > 0 */

#define DEBUG_EPI 0

#if DEBUG_EPI != 0
#define EPI_SLAB_DEBUG (SLAB_DEBUG_FREE | SLAB_RED_ZONE /* | SLAB_POISON */)
#else /* #if DEBUG_EPI != 0 */
#define EPI_SLAB_DEBUG 0
#endif /* #if DEBUG_EPI != 0 */

/* Epoll private bits inside the event mask */
#define EP_PRIVATE_BITS (EPOLLONESHOT | EPOLLET)

/* Maximum number of poll wake up nests we are allowing */
#define EP_MAX_POLLWAKE_NESTS 4

/* Maximum msec timeout value storeable in a long int */
#define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ)

#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))

#define EP_UNACTIVE_PTR ((void *) -1L)

struct epoll_filefd {
	struct file *file;
	int fd;
};

/*
 * Node that is linked into the "wake_task_list" member of the "struct poll_safewake".
 * It is used to keep track on all tasks that are currently inside the wake_up() code
 * to 1) short-circuit the one coming from the same task and same wait queue head
 * (loop) 2) allow a maximum number of epoll descriptors inclusion nesting
 * 3) let go the ones coming from other tasks.
 */
struct wake_task_node {
	struct list_head llink;
	struct task_struct *task;
	wait_queue_head_t *wq;
};

/*
 * This is used to implement the safe poll wake up avoiding to reenter
 * the poll callback from inside wake_up().
 */
struct poll_safewake {
	struct list_head wake_task_list;
	spinlock_t lock;
};

/*
 * Each file descriptor added to the eventpoll interface will
 * have an entry of this type linked to the "rbr" RB tree.
 */
struct epitem {
	/* RB tree node used to link this structure to the eventpoll RB tree */
	struct rb_node rbn;

	/* List header used to link this structure to the eventpoll ready list */
	struct list_head rdllink;

	/*
	 * Works together "struct eventpoll"->ovflist in keeping the
	 * single linked chain of items.
	 */
	struct epitem *next;

	/* The file descriptor information this item refers to */
	struct epoll_filefd ffd;

	/* Number of active wait queue attached to poll operations */
	int nwait;

	/* List containing poll wait queues */
	struct list_head pwqlist;

	/* The "container" of this item */
	struct eventpoll *ep;

	/* List header used to link this item to the "struct file" items list */
	struct list_head fllink;

	/* The structure that describe the interested events and the source fd */
	struct epoll_event event;
};

/*
 * This structure is stored inside the "private_data" member of the file
 * structure and rapresent the main data sructure for the eventpoll
 * interface.
 */
struct eventpoll {
	/* Protect the this structure access */
	spinlock_t lock;

	/*
	 * This mutex is used to ensure that files are not removed
	 * while epoll is using them. This is held during the event
	 * collection loop, the file cleanup path, the epoll file exit
	 * code and the ctl operations.
	 */
	struct mutex mtx;

	/* Wait queue used by sys_epoll_wait() */
	wait_queue_head_t wq;

	/* Wait queue used by file->poll() */
	wait_queue_head_t poll_wait;

	/* List of ready file descriptors */
	struct list_head rdllist;

	/* RB tree root used to store monitored fd structs */
	struct rb_root rbr;

	/*
	 * This is a single linked list that chains all the "struct epitem" that
	 * happened while transfering ready events to userspace w/out
	 * holding ->lock.
	 */
	struct epitem *ovflist;
};

/* Wait structure used by the poll hooks */
struct eppoll_entry {
	/* List header used to link this structure to the "struct epitem" */
	struct list_head llink;

	/* The "base" pointer is set to the container "struct epitem" */
	void *base;

	/*
	 * Wait queue item that will be linked to the target file wait
	 * queue head.
	 */
	wait_queue_t wait;

	/* The wait queue head that linked the "wait" wait queue item */
	wait_queue_head_t *whead;
};

/* Wrapper struct used by poll queueing */
struct ep_pqueue {
	poll_table pt;
	struct epitem *epi;
};

/*
 * This mutex is used to serialize ep_free() and eventpoll_release_file().
 */
static struct mutex epmutex;

/* Safe wake up implementation */
static struct poll_safewake psw;

/* Slab cache used to allocate "struct epitem" */
static struct kmem_cache *epi_cache __read_mostly;

/* Slab cache used to allocate "struct eppoll_entry" */
static struct kmem_cache *pwq_cache __read_mostly;


/* Setup the structure that is used as key for the RB tree */
static inline void ep_set_ffd(struct epoll_filefd *ffd,
			      struct file *file, int fd)
{
	ffd->file = file;
	ffd->fd = fd;
}

/* Compare RB tree keys */
static inline int ep_cmp_ffd(struct epoll_filefd *p1,
			     struct epoll_filefd *p2)
{
	return (p1->file > p2->file ? +1:
	        (p1->file < p2->file ? -1 : p1->fd - p2->fd));
}

/* Special initialization for the RB tree node to detect linkage */
static inline void ep_rb_initnode(struct rb_node *n)
{
	rb_set_parent(n, n);
}

/* Removes a node from the RB tree and marks it for a fast is-linked check */
static inline void ep_rb_erase(struct rb_node *n, struct rb_root *r)
{
	rb_erase(n, r);
	rb_set_parent(n, n);
}

/* Fast check to verify that the item is linked to the main RB tree */
static inline int ep_rb_linked(struct rb_node *n)
{
	return rb_parent(n) != n;
}

/* Tells us if the item is currently linked */
static inline int ep_is_linked(struct list_head *p)
{
	return !list_empty(p);
}

/* Get the "struct epitem" from a wait queue pointer */
static inline struct epitem * ep_item_from_wait(wait_queue_t *p)
{
	return container_of(p, struct eppoll_entry, wait)->base;
}

/* Get the "struct epitem" from an epoll queue wrapper */
static inline struct epitem * ep_item_from_epqueue(poll_table *p)
{
	return container_of(p, struct ep_pqueue, pt)->epi;
}

/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
static inline int ep_op_has_event(int op)
{
	return op != EPOLL_CTL_DEL;
}

/* Initialize the poll safe wake up structure */
static void ep_poll_safewake_init(struct poll_safewake *psw)
{

	INIT_LIST_HEAD(&psw->wake_task_list);
	spin_lock_init(&psw->lock);
}

/*
 * Perform a safe wake up of the poll wait list. The problem is that
 * with the new callback'd wake up system, it is possible that the
 * poll callback is reentered from inside the call to wake_up() done
 * on the poll wait queue head. The rule is that we cannot reenter the
 * wake up code from the same task more than EP_MAX_POLLWAKE_NESTS times,
 * and we cannot reenter the same wait queue head at all. This will
 * enable to have a hierarchy of epoll file descriptor of no more than
 * EP_MAX_POLLWAKE_NESTS deep. We need the irq version of the spin lock
 * because this one gets called by the poll callback, that in turn is called
 * from inside a wake_up(), that might be called from irq context.
 */
static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq)
{
	int wake_nests = 0;
	unsigned long flags;
	struct task_struct *this_task = current;
	struct list_head *lsthead = &psw->wake_task_list, *lnk;
	struct wake_task_node *tncur;
	struct wake_task_node tnode;

	spin_lock_irqsave(&psw->lock, flags);

	/* Try to see if the current task is already inside this wakeup call */
	list_for_each(lnk, lsthead) {
		tncur = list_entry(lnk, struct wake_task_node, llink);

		if (tncur->wq == wq ||
		    (tncur->task == this_task && ++wake_nests > EP_MAX_POLLWAKE_NESTS)) {
			/*
			 * Ops ... loop detected or maximum nest level reached.
			 * We abort this wake by breaking the cycle itself.
			 */
			spin_unlock_irqrestore(&psw->lock, flags);
			return;
		}
	}

	/* Add the current task to the list */
	tnode.task = this_task;
	tnode.wq = wq;
	list_add(&tnode.llink, lsthead);

	spin_unlock_irqrestore(&psw->lock, flags);

	/* Do really wake up now */
	wake_up(wq);

	/* Remove the current task from the list */
	spin_lock_irqsave(&psw->lock, flags);
	list_del(&tnode.llink);
	spin_unlock_irqrestore(&psw->lock, flags);
}

/*
 * This function unregister poll callbacks from the associated file descriptor.
 * Since this must be called without holding "ep->lock" the atomic exchange trick
 * will protect us from multiple unregister.
 */
static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
{
	int nwait;
	struct list_head *lsthead = &epi->pwqlist;
	struct eppoll_entry *pwq;

	/* This is called without locks, so we need the atomic exchange */
	nwait = xchg(&epi->nwait, 0);

	if (nwait) {
		while (!list_empty(lsthead)) {
			pwq = list_first_entry(lsthead, struct eppoll_entry, llink);

			list_del_init(&pwq->llink);
			remove_wait_queue(pwq->whead, &pwq->wait);
			kmem_cache_free(pwq_cache, pwq);
		}
	}
}

/*
 * Removes a "struct epitem" from the eventpoll RB tree and deallocates
 * all the associated resources. Must be called with "mtx" held.
 */
static int ep_remove(struct eventpoll *ep, struct epitem *epi)
{
	unsigned long flags;
	struct file *file = epi->ffd.file;

	/*
	 * Removes poll wait queue hooks. We _have_ to do this without holding
	 * the "ep->lock" otherwise a deadlock might occur. This because of the
	 * sequence of the lock acquisition. Here we do "ep->lock" then the wait
	 * queue head lock when unregistering the wait queue. The wakeup callback
	 * will run by holding the wait queue head lock and will call our callback
	 * that will try to get "ep->lock".
	 */
	ep_unregister_pollwait(ep, epi);

	/* Remove the current item from the list of epoll hooks */
	spin_lock(&file->f_ep_lock);
	if (ep_is_linked(&epi->fllink))
		list_del_init(&epi->fllink);
	spin_unlock(&file->f_ep_lock);

	if (ep_rb_linked(&epi->rbn))
		ep_rb_erase(&epi->rbn, &ep->rbr);

	spin_lock_irqsave(&ep->lock, flags);
	if (ep_is_linked(&epi->rdllink))
		list_del_init(&epi->rdllink);
	spin_unlock_irqrestore(&ep->lock, flags);

	/* At this point it is safe to free the eventpoll item */
	kmem_cache_free(epi_cache, epi);

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_remove(%p, %p)\n",
		     current, ep, file));

	return 0;
}

static void ep_free(struct eventpoll *ep)
{
	struct rb_node *rbp;
	struct epitem *epi;

	/* We need to release all tasks waiting for these file */
	if (waitqueue_active(&ep->poll_wait))
		ep_poll_safewake(&psw, &ep->poll_wait);

	/*
	 * We need to lock this because we could be hit by
	 * eventpoll_release_file() while we're freeing the "struct eventpoll".
	 * We do not need to hold "ep->mtx" here because the epoll file
	 * is on the way to be removed and no one has references to it
	 * anymore. The only hit might come from eventpoll_release_file() but
	 * holding "epmutex" is sufficent here.
	 */
	mutex_lock(&epmutex);

	/*
	 * Walks through the whole tree by unregistering poll callbacks.
	 */
	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
		epi = rb_entry(rbp, struct epitem, rbn);

		ep_unregister_pollwait(ep, epi);
	}

	/*
	 * Walks through the whole tree by freeing each "struct epitem". At this
	 * point we are sure no poll callbacks will be lingering around, and also by
	 * holding "epmutex" we can be sure that no file cleanup code will hit
	 * us during this operation. So we can avoid the lock on "ep->lock".
	 */
	while ((rbp = rb_first(&ep->rbr)) != 0) {
		epi = rb_entry(rbp, struct epitem, rbn);
		ep_remove(ep, epi);
	}

	mutex_unlock(&epmutex);
	mutex_destroy(&ep->mtx);
	kfree(ep);
}

static int ep_eventpoll_release(struct inode *inode, struct file *file)
{
	struct eventpoll *ep = file->private_data;

	if (ep)
		ep_free(ep);

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: close() ep=%p\n", current, ep));
	return 0;
}

static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
{
	unsigned int pollflags = 0;
	unsigned long flags;
	struct eventpoll *ep = file->private_data;

	/* Insert inside our poll wait queue */
	poll_wait(file, &ep->poll_wait, wait);

	/* Check our condition */
	spin_lock_irqsave(&ep->lock, flags);
	if (!list_empty(&ep->rdllist))
		pollflags = POLLIN | POLLRDNORM;
	spin_unlock_irqrestore(&ep->lock, flags);

	return pollflags;
}

/* File callbacks that implement the eventpoll file behaviour */
static const struct file_operations eventpoll_fops = {
	.release	= ep_eventpoll_release,
	.poll		= ep_eventpoll_poll
};

/* Fast test to see if the file is an evenpoll file */
static inline int is_file_epoll(struct file *f)
{
	return f->f_op == &eventpoll_fops;
}

/*
 * This is called from eventpoll_release() to unlink files from the eventpoll
 * interface. We need to have this facility to cleanup correctly files that are
 * closed without being removed from the eventpoll interface.
 */
void eventpoll_release_file(struct file *file)
{
	struct list_head *lsthead = &file->f_ep_links;
	struct eventpoll *ep;
	struct epitem *epi;

	/*
	 * We don't want to get "file->f_ep_lock" because it is not
	 * necessary. It is not necessary because we're in the "struct file"
	 * cleanup path, and this means that noone is using this file anymore.
	 * So, for example, epoll_ctl() cannot hit here sicne if we reach this
	 * point, the file counter already went to zero and fget() would fail.
	 * The only hit might come from ep_free() but by holding the mutex
	 * will correctly serialize the operation. We do need to acquire
	 * "ep->mtx" after "epmutex" because ep_remove() requires it when called
	 * from anywhere but ep_free().
	 */
	mutex_lock(&epmutex);

	while (!list_empty(lsthead)) {
		epi = list_first_entry(lsthead, struct epitem, fllink);

		ep = epi->ep;
		list_del_init(&epi->fllink);
		mutex_lock(&ep->mtx);
		ep_remove(ep, epi);
		mutex_unlock(&ep->mtx);
	}

	mutex_unlock(&epmutex);
}

static int ep_alloc(struct eventpoll **pep)
{
	struct eventpoll *ep = kzalloc(sizeof(*ep), GFP_KERNEL);

	if (!ep)
		return -ENOMEM;

	spin_lock_init(&ep->lock);
	mutex_init(&ep->mtx);
	init_waitqueue_head(&ep->wq);
	init_waitqueue_head(&ep->poll_wait);
	INIT_LIST_HEAD(&ep->rdllist);
	ep->rbr = RB_ROOT;
	ep->ovflist = EP_UNACTIVE_PTR;

	*pep = ep;

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_alloc() ep=%p\n",
		     current, ep));
	return 0;
}

/*
 * Search the file inside the eventpoll tree. The RB tree operations
 * are protected by the "mtx" mutex, and ep_find() must be called with
 * "mtx" held.
 */
static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
{
	int kcmp;
	struct rb_node *rbp;
	struct epitem *epi, *epir = NULL;
	struct epoll_filefd ffd;

	ep_set_ffd(&ffd, file, fd);
	for (rbp = ep->rbr.rb_node; rbp; ) {
		epi = rb_entry(rbp, struct epitem, rbn);
		kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
		if (kcmp > 0)
			rbp = rbp->rb_right;
		else if (kcmp < 0)
			rbp = rbp->rb_left;
		else {
			epir = epi;
			break;
		}
	}

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_find(%p) -> %p\n",
		     current, file, epir));

	return epir;
}

/*
 * This is the callback that is passed to the wait queue wakeup
 * machanism. It is called by the stored file descriptors when they
 * have events to report.
 */
static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
	int pwake = 0;
	unsigned long flags;
	struct epitem *epi = ep_item_from_wait(wait);
	struct eventpoll *ep = epi->ep;

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: poll_callback(%p) epi=%p ep=%p\n",
		     current, epi->ffd.file, epi, ep));

	spin_lock_irqsave(&ep->lock, flags);

	/*
	 * If the event mask does not contain any poll(2) event, we consider the
	 * descriptor to be disabled. This condition is likely the effect of the
	 * EPOLLONESHOT bit that disables the descriptor when an event is received,
	 * until the next EPOLL_CTL_MOD will be issued.
	 */
	if (!(epi->event.events & ~EP_PRIVATE_BITS))
		goto out_unlock;

	/*
	 * If we are trasfering events to userspace, we can hold no locks
	 * (because we're accessing user memory, and because of linux f_op->poll()
	 * semantics). All the events that happens during that period of time are
	 * chained in ep->ovflist and requeued later on.
	 */
	if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
		if (epi->next == EP_UNACTIVE_PTR) {
			epi->next = ep->ovflist;
			ep->ovflist = epi;
		}
		goto out_unlock;
	}

	/* If this file is already in the ready list we exit soon */
	if (ep_is_linked(&epi->rdllink))
		goto is_linked;

	list_add_tail(&epi->rdllink, &ep->rdllist);

is_linked:
	/*
	 * Wake up ( if active ) both the eventpoll wait list and the ->poll()
	 * wait list.
	 */
	if (waitqueue_active(&ep->wq))
		__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
				 TASK_INTERRUPTIBLE);
	if (waitqueue_active(&ep->poll_wait))
		pwake++;

out_unlock:
	spin_unlock_irqrestore(&ep->lock, flags);

	/* We have to call this outside the lock */
	if (pwake)
		ep_poll_safewake(&psw, &ep->poll_wait);

	return 1;
}

/*
 * This is the callback that is used to add our wait queue to the
 * target file wakeup lists.
 */
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
				 poll_table *pt)
{
	struct epitem *epi = ep_item_from_epqueue(pt);
	struct eppoll_entry *pwq;

	if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
		init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
		pwq->whead = whead;
		pwq->base = epi;
		add_wait_queue(whead, &pwq->wait);
		list_add_tail(&pwq->llink, &epi->pwqlist);
		epi->nwait++;
	} else {
		/* We have to signal that an error occurred */
		epi->nwait = -1;
	}
}

static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
{
	int kcmp;
	struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
	struct epitem *epic;

	while (*p) {
		parent = *p;
		epic = rb_entry(parent, struct epitem, rbn);
		kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
		if (kcmp > 0)
			p = &parent->rb_right;
		else
			p = &parent->rb_left;
	}
	rb_link_node(&epi->rbn, parent, p);
	rb_insert_color(&epi->rbn, &ep->rbr);
}

/*
 * Must be called with "mtx" held.
 */
static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
		     struct file *tfile, int fd)
{
	int error, revents, pwake = 0;
	unsigned long flags;
	struct epitem *epi;
	struct ep_pqueue epq;

	error = -ENOMEM;
	if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
		goto error_return;

	/* Item initialization follow here ... */
	ep_rb_initnode(&epi->rbn);
	INIT_LIST_HEAD(&epi->rdllink);
	INIT_LIST_HEAD(&epi->fllink);
	INIT_LIST_HEAD(&epi->pwqlist);
	epi->ep = ep;
	ep_set_ffd(&epi->ffd, tfile, fd);
	epi->event = *event;
	epi->nwait = 0;
	epi->next = EP_UNACTIVE_PTR;

	/* Initialize the poll table using the queue callback */
	epq.epi = epi;
	init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);

	/*
	 * Attach the item to the poll hooks and get current event bits.
	 * We can safely use the file* here because its usage count has
	 * been increased by the caller of this function. Note that after
	 * this operation completes, the poll callback can start hitting
	 * the new item.
	 */
	revents = tfile->f_op->poll(tfile, &epq.pt);

	/*
	 * We have to check if something went wrong during the poll wait queue
	 * install process. Namely an allocation for a wait queue failed due
	 * high memory pressure.
	 */
	if (epi->nwait < 0)
		goto error_unregister;

	/* Add the current item to the list of active epoll hook for this file */
	spin_lock(&tfile->f_ep_lock);
	list_add_tail(&epi->fllink, &tfile->f_ep_links);
	spin_unlock(&tfile->f_ep_lock);

	/*
	 * Add the current item to the RB tree. All RB tree operations are
	 * protected by "mtx", and ep_insert() is called with "mtx" held.
	 */
	ep_rbtree_insert(ep, epi);

	/* We have to drop the new item inside our item list to keep track of it */
	spin_lock_irqsave(&ep->lock, flags);

	/* If the file is already "ready" we drop it inside the ready list */
	if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
		list_add_tail(&epi->rdllink, &ep->rdllist);

		/* Notify waiting tasks that events are available */
		if (waitqueue_active(&ep->wq))
			__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE);
		if (waitqueue_active(&ep->poll_wait))
			pwake++;
	}

	spin_unlock_irqrestore(&ep->lock, flags);

	/* We have to call this outside the lock */
	if (pwake)
		ep_poll_safewake(&psw, &ep->poll_wait);

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_insert(%p, %p, %d)\n",
		     current, ep, tfile, fd));

	return 0;

error_unregister:
	ep_unregister_pollwait(ep, epi);

	/*
	 * We need to do this because an event could have been arrived on some
	 * allocated wait queue. Note that we don't care about the ep->ovflist
	 * list, since that is used/cleaned only inside a section bound by "mtx".
	 * And ep_insert() is called with "mtx" held.
	 */
	spin_lock_irqsave(&ep->lock, flags);
	if (ep_is_linked(&epi->rdllink))
		list_del_init(&epi->rdllink);
	spin_unlock_irqrestore(&ep->lock, flags);

	kmem_cache_free(epi_cache, epi);
error_return:
	return error;
}

/*
 * Modify the interest event mask by dropping an event if the new mask
 * has a match in the current file status. Must be called with "mtx" held.
 */
static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
{
	int pwake = 0;
	unsigned int revents;
	unsigned long flags;

	/*
	 * Set the new event interest mask before calling f_op->poll(), otherwise
	 * a potential race might occur. In fact if we do this operation inside
	 * the lock, an event might happen between the f_op->poll() call and the
	 * new event set registering.
	 */
	epi->event.events = event->events;

	/*
	 * Get current event bits. We can safely use the file* here because
	 * its usage count has been increased by the caller of this function.
	 */
	revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);

	spin_lock_irqsave(&ep->lock, flags);

	/* Copy the data member from inside the lock */
	epi->event.data = event->data;

	/*
	 * If the item is "hot" and it is not registered inside the ready
	 * list, push it inside.
	 */
	if (revents & event->events) {
		if (!ep_is_linked(&epi->rdllink)) {
			list_add_tail(&epi->rdllink, &ep->rdllist);

			/* Notify waiting tasks that events are available */
			if (waitqueue_active(&ep->wq))
				__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
						 TASK_INTERRUPTIBLE);
			if (waitqueue_active(&ep->poll_wait))
				pwake++;
		}
	}
	spin_unlock_irqrestore(&ep->lock, flags);

	/* We have to call this outside the lock */
	if (pwake)
		ep_poll_safewake(&psw, &ep->poll_wait);

	return 0;
}

static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *events,
			  int maxevents)
{
	int eventcnt, error = -EFAULT, pwake = 0;
	unsigned int revents;
	unsigned long flags;
	struct epitem *epi, *nepi;
	struct list_head txlist;

	INIT_LIST_HEAD(&txlist);

	/*
	 * We need to lock this because we could be hit by
	 * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL).
	 */
	mutex_lock(&ep->mtx);

	/*
	 * Steal the ready list, and re-init the original one to the
	 * empty list. Also, set ep->ovflist to NULL so that events
	 * happening while looping w/out locks, are not lost. We cannot
	 * have the poll callback to queue directly on ep->rdllist,
	 * because we are doing it in the loop below, in a lockless way.
	 */
	spin_lock_irqsave(&ep->lock, flags);
	list_splice(&ep->rdllist, &txlist);
	INIT_LIST_HEAD(&ep->rdllist);
	ep->ovflist = NULL;
	spin_unlock_irqrestore(&ep->lock, flags);

	/*
	 * We can loop without lock because this is a task private list.
	 * We just splice'd out the ep->rdllist in ep_collect_ready_items().
	 * Items cannot vanish during the loop because we are holding "mtx".
	 */
	for (eventcnt = 0; !list_empty(&txlist) && eventcnt < maxevents;) {
		epi = list_first_entry(&txlist, struct epitem, rdllink);

		list_del_init(&epi->rdllink);

		/*
		 * Get the ready file event set. We can safely use the file
		 * because we are holding the "mtx" and this will guarantee
		 * that both the file and the item will not vanish.
		 */
		revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
		revents &= epi->event.events;

		/*
		 * Is the event mask intersect the caller-requested one,
		 * deliver the event to userspace. Again, we are holding
		 * "mtx", so no operations coming from userspace can change
		 * the item.
		 */
		if (revents) {
			if (__put_user(revents,
				       &events[eventcnt].events) ||
			    __put_user(epi->event.data,
				       &events[eventcnt].data))
				goto errxit;
			if (epi->event.events & EPOLLONESHOT)
				epi->event.events &= EP_PRIVATE_BITS;
			eventcnt++;
		}
		/*
		 * At this point, noone can insert into ep->rdllist besides
		 * us. The epoll_ctl() callers are locked out by us holding
		 * "mtx" and the poll callback will queue them in ep->ovflist.
		 */
		if (!(epi->event.events & EPOLLET) &&
		    (revents & epi->event.events))
			list_add_tail(&epi->rdllink, &ep->rdllist);
	}
	error = 0;

errxit:

	spin_lock_irqsave(&ep->lock, flags);
	/*
	 * During the time we spent in the loop above, some other events
	 * might have been queued by the poll callback. We re-insert them
	 * here (in case they are not already queued, or they're one-shot).
	 */
	for (nepi = ep->ovflist; (epi = nepi) != NULL;
	     nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
		if (!ep_is_linked(&epi->rdllink) &&
		    (epi->event.events & ~EP_PRIVATE_BITS))
			list_add_tail(&epi->rdllink, &ep->rdllist);
	}
	/*
	 * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
	 * releasing the lock, events will be queued in the normal way inside
	 * ep->rdllist.
	 */
	ep->ovflist = EP_UNACTIVE_PTR;

	/*
	 * In case of error in the event-send loop, or in case the number of
	 * ready events exceeds the userspace limit, we need to splice the
	 * "txlist" back inside ep->rdllist.
	 */
	list_splice(&txlist, &ep->rdllist);

	if (!list_empty(&ep->rdllist)) {
		/*
		 * Wake up (if active) both the eventpoll wait list and the ->poll()
		 * wait list (delayed after we release the lock).
		 */
		if (waitqueue_active(&ep->wq))
			__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
					 TASK_INTERRUPTIBLE);
		if (waitqueue_active(&ep->poll_wait))
			pwake++;
	}
	spin_unlock_irqrestore(&ep->lock, flags);

	mutex_unlock(&ep->mtx);

	/* We have to call this outside the lock */
	if (pwake)
		ep_poll_safewake(&psw, &ep->poll_wait);

	return eventcnt == 0 ? error: eventcnt;
}

static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
		   int maxevents, long timeout)
{
	int res, eavail;
	unsigned long flags;
	long jtimeout;
	wait_queue_t wait;

	/*
	 * Calculate the timeout by checking for the "infinite" value ( -1 )
	 * and the overflow condition. The passed timeout is in milliseconds,
	 * that why (t * HZ) / 1000.
	 */
	jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ?
		MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000;

retry:
	spin_lock_irqsave(&ep->lock, flags);

	res = 0;
	if (list_empty(&ep->rdllist)) {
		/*
		 * We don't have any available event to return to the caller.
		 * We need to sleep here, and we will be wake up by
		 * ep_poll_callback() when events will become available.
		 */
		init_waitqueue_entry(&wait, current);
		wait.flags |= WQ_FLAG_EXCLUSIVE;
		__add_wait_queue(&ep->wq, &wait);

		for (;;) {
			/*
			 * We don't want to sleep if the ep_poll_callback() sends us
			 * a wakeup in between. That's why we set the task state
			 * to TASK_INTERRUPTIBLE before doing the checks.
			 */
			set_current_state(TASK_INTERRUPTIBLE);
			if (!list_empty(&ep->rdllist) || !jtimeout)
				break;
			if (signal_pending(current)) {
				res = -EINTR;
				break;
			}

			spin_unlock_irqrestore(&ep->lock, flags);
			jtimeout = schedule_timeout(jtimeout);
			spin_lock_irqsave(&ep->lock, flags);
		}
		__remove_wait_queue(&ep->wq, &wait);

		set_current_state(TASK_RUNNING);
	}

	/* Is it worth to try to dig for events ? */
	eavail = !list_empty(&ep->rdllist);

	spin_unlock_irqrestore(&ep->lock, flags);

	/*
	 * Try to transfer events to user space. In case we get 0 events and
	 * there's still timeout left over, we go trying again in search of
	 * more luck.
	 */
	if (!res && eavail &&
	    !(res = ep_send_events(ep, events, maxevents)) && jtimeout)
		goto retry;

	return res;
}

/*
 * It opens an eventpoll file descriptor. The "size" parameter is there
 * for historical reasons, when epoll was using an hash instead of an
 * RB tree. With the current implementation, the "size" parameter is ignored
 * (besides sanity checks).
 */
asmlinkage long sys_epoll_create(int size)
{
	int error, fd = -1;
	struct eventpoll *ep;
	struct inode *inode;
	struct file *file;

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n",
		     current, size));

	/*
	 * Sanity check on the size parameter, and create the internal data
	 * structure ( "struct eventpoll" ).
	 */
	error = -EINVAL;
	if (size <= 0 || (error = ep_alloc(&ep)) != 0)
		goto error_return;

	/*
	 * Creates all the items needed to setup an eventpoll file. That is,
	 * a file structure, and inode and a free file descriptor.
	 */
	error = anon_inode_getfd(&fd, &inode, &file, "[eventpoll]",
				 &eventpoll_fops, ep);
	if (error)
		goto error_free;

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
		     current, size, fd));

	return fd;

error_free:
	ep_free(ep);
error_return:
	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
		     current, size, error));
	return error;
}

/*
 * The following function implements the controller interface for
 * the eventpoll file that enables the insertion/removal/change of
 * file descriptors inside the interest set.
 */
asmlinkage long sys_epoll_ctl(int epfd, int op, int fd,
			      struct epoll_event __user *event)
{
	int error;
	struct file *file, *tfile;
	struct eventpoll *ep;
	struct epitem *epi;
	struct epoll_event epds;

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p)\n",
		     current, epfd, op, fd, event));

	error = -EFAULT;
	if (ep_op_has_event(op) &&
	    copy_from_user(&epds, event, sizeof(struct epoll_event)))
		goto error_return;

	/* Get the "struct file *" for the eventpoll file */
	error = -EBADF;
	file = fget(epfd);
	if (!file)
		goto error_return;

	/* Get the "struct file *" for the target file */
	tfile = fget(fd);
	if (!tfile)
		goto error_fput;

	/* The target file descriptor must support poll */
	error = -EPERM;
	if (!tfile->f_op || !tfile->f_op->poll)
		goto error_tgt_fput;

	/*
	 * We have to check that the file structure underneath the file descriptor
	 * the user passed to us _is_ an eventpoll file. And also we do not permit
	 * adding an epoll file descriptor inside itself.
	 */
	error = -EINVAL;
	if (file == tfile || !is_file_epoll(file))
		goto error_tgt_fput;

	/*
	 * At this point it is safe to assume that the "private_data" contains
	 * our own data structure.
	 */
	ep = file->private_data;

	mutex_lock(&ep->mtx);

	/*
	 * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
	 * above, we can be sure to be able to use the item looked up by
	 * ep_find() till we release the mutex.
	 */
	epi = ep_find(ep, tfile, fd);

	error = -EINVAL;
	switch (op) {
	case EPOLL_CTL_ADD:
		if (!epi) {
			epds.events |= POLLERR | POLLHUP;

			error = ep_insert(ep, &epds, tfile, fd);
		} else
			error = -EEXIST;
		break;
	case EPOLL_CTL_DEL:
		if (epi)
			error = ep_remove(ep, epi);
		else
			error = -ENOENT;
		break;
	case EPOLL_CTL_MOD:
		if (epi) {
			epds.events |= POLLERR | POLLHUP;
			error = ep_modify(ep, epi, &epds);
		} else
			error = -ENOENT;
		break;
	}
	mutex_unlock(&ep->mtx);

error_tgt_fput:
	fput(tfile);
error_fput:
	fput(file);
error_return:
	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p) = %d\n",
		     current, epfd, op, fd, event, error));

	return error;
}

/*
 * Implement the event wait interface for the eventpoll file. It is the kernel
 * part of the user space epoll_wait(2).
 */
asmlinkage long sys_epoll_wait(int epfd, struct epoll_event __user *events,
			       int maxevents, int timeout)
{
	int error;
	struct file *file;
	struct eventpoll *ep;

	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d)\n",
		     current, epfd, events, maxevents, timeout));

	/* The maximum number of event must be greater than zero */
	if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
		return -EINVAL;

	/* Verify that the area passed by the user is writeable */
	if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event))) {
		error = -EFAULT;
		goto error_return;
	}

	/* Get the "struct file *" for the eventpoll file */
	error = -EBADF;
	file = fget(epfd);
	if (!file)
		goto error_return;

	/*
	 * We have to check that the file structure underneath the fd
	 * the user passed to us _is_ an eventpoll file.
	 */
	error = -EINVAL;
	if (!is_file_epoll(file))
		goto error_fput;

	/*
	 * At this point it is safe to assume that the "private_data" contains
	 * our own data structure.
	 */
	ep = file->private_data;

	/* Time to fish for events ... */
	error = ep_poll(ep, events, maxevents, timeout);

error_fput:
	fput(file);
error_return:
	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d) = %d\n",
		     current, epfd, events, maxevents, timeout, error));

	return error;
}

#ifdef TIF_RESTORE_SIGMASK

/*
 * Implement the event wait interface for the eventpoll file. It is the kernel
 * part of the user space epoll_pwait(2).
 */
asmlinkage long sys_epoll_pwait(int epfd, struct epoll_event __user *events,
		int maxevents, int timeout, const sigset_t __user *sigmask,
		size_t sigsetsize)
{
	int error;
	sigset_t ksigmask, sigsaved;

	/*
	 * If the caller wants a certain signal mask to be set during the wait,
	 * we apply it here.
	 */
	if (sigmask) {
		if (sigsetsize != sizeof(sigset_t))
			return -EINVAL;
		if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
			return -EFAULT;
		sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
		sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
	}

	error = sys_epoll_wait(epfd, events, maxevents, timeout);

	/*
	 * If we changed the signal mask, we need to restore the original one.
	 * In case we've got a signal while waiting, we do not restore the
	 * signal mask yet, and we allow do_signal() to deliver the signal on
	 * the way back to userspace, before the signal mask is restored.
	 */
	if (sigmask) {
		if (error == -EINTR) {
			memcpy(&current->saved_sigmask, &sigsaved,
			       sizeof(sigsaved));
			set_thread_flag(TIF_RESTORE_SIGMASK);
		} else
			sigprocmask(SIG_SETMASK, &sigsaved, NULL);
	}

	return error;
}

#endif /* #ifdef TIF_RESTORE_SIGMASK */

static int __init eventpoll_init(void)
{
	mutex_init(&epmutex);

	/* Initialize the structure used to perform safe poll wait head wake ups */
	ep_poll_safewake_init(&psw);

	/* Allocates slab cache used to allocate "struct epitem" items */
	epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
			0, SLAB_HWCACHE_ALIGN|EPI_SLAB_DEBUG|SLAB_PANIC,
			NULL, NULL);

	/* Allocates slab cache used to allocate "struct eppoll_entry" */
	pwq_cache = kmem_cache_create("eventpoll_pwq",
			sizeof(struct eppoll_entry), 0,
			EPI_SLAB_DEBUG|SLAB_PANIC, NULL, NULL);

	return 0;
}
fs_initcall(eventpoll_init);