aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/mtd/ubi/wl.c
blob: 05d70937b54322d8ecd878d05cc69e084ef4a5ed (plain)
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
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
/*
 * Copyright (c) International Business Machines Corp., 2006
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
 * the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * Authors: Artem Bityutskiy (Битюцкий Артём), Thomas Gleixner
 */

/*
 * UBI wear-leveling sub-system.
 *
 * This sub-system is responsible for wear-leveling. It works in terms of
 * physical* eraseblocks and erase counters and knows nothing about logical
 * eraseblocks, volumes, etc. From this sub-system's perspective all physical
 * eraseblocks are of two types - used and free. Used physical eraseblocks are
 * those that were "get" by the 'ubi_wl_get_peb()' function, and free physical
 * eraseblocks are those that were put by the 'ubi_wl_put_peb()' function.
 *
 * Physical eraseblocks returned by 'ubi_wl_get_peb()' have only erase counter
 * header. The rest of the physical eraseblock contains only %0xFF bytes.
 *
 * When physical eraseblocks are returned to the WL sub-system by means of the
 * 'ubi_wl_put_peb()' function, they are scheduled for erasure. The erasure is
 * done asynchronously in context of the per-UBI device background thread,
 * which is also managed by the WL sub-system.
 *
 * The wear-leveling is ensured by means of moving the contents of used
 * physical eraseblocks with low erase counter to free physical eraseblocks
 * with high erase counter.
 *
 * The 'ubi_wl_get_peb()' function accepts data type hints which help to pick
 * an "optimal" physical eraseblock. For example, when it is known that the
 * physical eraseblock will be "put" soon because it contains short-term data,
 * the WL sub-system may pick a free physical eraseblock with low erase
 * counter, and so forth.
 *
 * If the WL sub-system fails to erase a physical eraseblock, it marks it as
 * bad.
 *
 * This sub-system is also responsible for scrubbing. If a bit-flip is detected
 * in a physical eraseblock, it has to be moved. Technically this is the same
 * as moving it for wear-leveling reasons.
 *
 * As it was said, for the UBI sub-system all physical eraseblocks are either
 * "free" or "used". Free eraseblock are kept in the @wl->free RB-tree, while
 * used eraseblocks are kept in a set of different RB-trees: @wl->used,
 * @wl->prot.pnum, @wl->prot.aec, and @wl->scrub.
 *
 * Note, in this implementation, we keep a small in-RAM object for each physical
 * eraseblock. This is surely not a scalable solution. But it appears to be good
 * enough for moderately large flashes and it is simple. In future, one may
 * re-work this sub-system and make it more scalable.
 *
 * At the moment this sub-system does not utilize the sequence number, which
 * was introduced relatively recently. But it would be wise to do this because
 * the sequence number of a logical eraseblock characterizes how old is it. For
 * example, when we move a PEB with low erase counter, and we need to pick the
 * target PEB, we pick a PEB with the highest EC if our PEB is "old" and we
 * pick target PEB with an average EC if our PEB is not very "old". This is a
 * room for future re-works of the WL sub-system.
 *
 * Note: the stuff with protection trees looks too complex and is difficult to
 * understand. Should be fixed.
 */

#include <linux/slab.h>
#include <linux/crc32.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include "ubi.h"

/* Number of physical eraseblocks reserved for wear-leveling purposes */
#define WL_RESERVED_PEBS 1

/*
 * How many erase cycles are short term, unknown, and long term physical
 * eraseblocks protected.
 */
#define ST_PROTECTION 16
#define U_PROTECTION  10
#define LT_PROTECTION 4

/*
 * Maximum difference between two erase counters. If this threshold is
 * exceeded, the WL sub-system starts moving data from used physical
 * eraseblocks with low erase counter to free physical eraseblocks with high
 * erase counter.
 */
#define UBI_WL_THRESHOLD CONFIG_MTD_UBI_WL_THRESHOLD

/*
 * When a physical eraseblock is moved, the WL sub-system has to pick the target
 * physical eraseblock to move to. The simplest way would be just to pick the
 * one with the highest erase counter. But in certain workloads this could lead
 * to an unlimited wear of one or few physical eraseblock. Indeed, imagine a
 * situation when the picked physical eraseblock is constantly erased after the
 * data is written to it. So, we have a constant which limits the highest erase
 * counter of the free physical eraseblock to pick. Namely, the WL sub-system
 * does not pick eraseblocks with erase counter greater then the lowest erase
 * counter plus %WL_FREE_MAX_DIFF.
 */
#define WL_FREE_MAX_DIFF (2*UBI_WL_THRESHOLD)

/*
 * Maximum number of consecutive background thread failures which is enough to
 * switch to read-only mode.
 */
#define WL_MAX_FAILURES 32

/**
 * struct ubi_wl_prot_entry - PEB protection entry.
 * @rb_pnum: link in the @wl->prot.pnum RB-tree
 * @rb_aec: link in the @wl->prot.aec RB-tree
 * @abs_ec: the absolute erase counter value when the protection ends
 * @e: the wear-leveling entry of the physical eraseblock under protection
 *
 * When the WL sub-system returns a physical eraseblock, the physical
 * eraseblock is protected from being moved for some "time". For this reason,
 * the physical eraseblock is not directly moved from the @wl->free tree to the
 * @wl->used tree. There is one more tree in between where this physical
 * eraseblock is temporarily stored (@wl->prot).
 *
 * All this protection stuff is needed because:
 *  o we don't want to move physical eraseblocks just after we have given them
 *    to the user; instead, we first want to let users fill them up with data;
 *
 *  o there is a chance that the user will put the physical eraseblock very
 *    soon, so it makes sense not to move it for some time, but wait; this is
 *    especially important in case of "short term" physical eraseblocks.
 *
 * Physical eraseblocks stay protected only for limited time. But the "time" is
 * measured in erase cycles in this case. This is implemented with help of the
 * absolute erase counter (@wl->abs_ec). When it reaches certain value, the
 * physical eraseblocks are moved from the protection trees (@wl->prot.*) to
 * the @wl->used tree.
 *
 * Protected physical eraseblocks are searched by physical eraseblock number
 * (when they are put) and by the absolute erase counter (to check if it is
 * time to move them to the @wl->used tree). So there are actually 2 RB-trees
 * storing the protected physical eraseblocks: @wl->prot.pnum and
 * @wl->prot.aec. They are referred to as the "protection" trees. The
 * first one is indexed by the physical eraseblock number. The second one is
 * indexed by the absolute erase counter. Both trees store
 * &struct ubi_wl_prot_entry objects.
 *
 * Each physical eraseblock has 2 main states: free and used. The former state
 * corresponds to the @wl->free tree. The latter state is split up on several
 * sub-states:
 * o the WL movement is allowed (@wl->used tree);
 * o the WL movement is temporarily prohibited (@wl->prot.pnum and
 * @wl->prot.aec trees);
 * o scrubbing is needed (@wl->scrub tree).
 *
 * Depending on the sub-state, wear-leveling entries of the used physical
 * eraseblocks may be kept in one of those trees.
 */
struct ubi_wl_prot_entry {
	struct rb_node rb_pnum;
	struct rb_node rb_aec;
	unsigned long long abs_ec;
	struct ubi_wl_entry *e;
};

/**
 * struct ubi_work - UBI work description data structure.
 * @list: a link in the list of pending works
 * @func: worker function
 * @priv: private data of the worker function
 * @e: physical eraseblock to erase
 * @torture: if the physical eraseblock has to be tortured
 *
 * The @func pointer points to the worker function. If the @cancel argument is
 * not zero, the worker has to free the resources and exit immediately. The
 * worker has to return zero in case of success and a negative error code in
 * case of failure.
 */
struct ubi_work {
	struct list_head list;
	int (*func)(struct ubi_device *ubi, struct ubi_work *wrk, int cancel);
	/* The below fields are only relevant to erasure works */
	struct ubi_wl_entry *e;
	int torture;
};

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID
static int paranoid_check_ec(struct ubi_device *ubi, int pnum, int ec);
static int paranoid_check_in_wl_tree(struct ubi_wl_entry *e,
				     struct rb_root *root);
#else
#define paranoid_check_ec(ubi, pnum, ec) 0
#define paranoid_check_in_wl_tree(e, root)
#endif

/**
 * wl_tree_add - add a wear-leveling entry to a WL RB-tree.
 * @e: the wear-leveling entry to add
 * @root: the root of the tree
 *
 * Note, we use (erase counter, physical eraseblock number) pairs as keys in
 * the @ubi->used and @ubi->free RB-trees.
 */
static void wl_tree_add(struct ubi_wl_entry *e, struct rb_root *root)
{
	struct rb_node **p, *parent = NULL;

	p = &root->rb_node;
	while (*p) {
		struct ubi_wl_entry *e1;

		parent = *p;
		e1 = rb_entry(parent, struct ubi_wl_entry, rb);

		if (e->ec < e1->ec)
			p = &(*p)->rb_left;
		else if (e->ec > e1->ec)
			p = &(*p)->rb_right;
		else {
			ubi_assert(e->pnum != e1->pnum);
			if (e->pnum < e1->pnum)
				p = &(*p)->rb_left;
			else
				p = &(*p)->rb_right;
		}
	}

	rb_link_node(&e->rb, parent, p);
	rb_insert_color(&e->rb, root);
}

/**
 * do_work - do one pending work.
 * @ubi: UBI device description object
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
static int do_work(struct ubi_device *ubi)
{
	int err;
	struct ubi_work *wrk;

	cond_resched();

	/*
	 * @ubi->work_sem is used to synchronize with the workers. Workers take
	 * it in read mode, so many of them may be doing works at a time. But
	 * the queue flush code has to be sure the whole queue of works is
	 * done, and it takes the mutex in write mode.
	 */
	down_read(&ubi->work_sem);
	spin_lock(&ubi->wl_lock);
	if (list_empty(&ubi->works)) {
		spin_unlock(&ubi->wl_lock);
		up_read(&ubi->work_sem);
		return 0;
	}

	wrk = list_entry(ubi->works.next, struct ubi_work, list);
	list_del(&wrk->list);
	ubi->works_count -= 1;
	ubi_assert(ubi->works_count >= 0);
	spin_unlock(&ubi->wl_lock);

	/*
	 * Call the worker function. Do not touch the work structure
	 * after this call as it will have been freed or reused by that
	 * time by the worker function.
	 */
	err = wrk->func(ubi, wrk, 0);
	if (err)
		ubi_err("work failed with error code %d", err);
	up_read(&ubi->work_sem);

	return err;
}

/**
 * produce_free_peb - produce a free physical eraseblock.
 * @ubi: UBI device description object
 *
 * This function tries to make a free PEB by means of synchronous execution of
 * pending works. This may be needed if, for example the background thread is
 * disabled. Returns zero in case of success and a negative error code in case
 * of failure.
 */
static int produce_free_peb(struct ubi_device *ubi)
{
	int err;

	spin_lock(&ubi->wl_lock);
	while (!ubi->free.rb_node) {
		spin_unlock(&ubi->wl_lock);

		dbg_wl("do one work synchronously");
		err = do_work(ubi);
		if (err)
			return err;

		spin_lock(&ubi->wl_lock);
	}
	spin_unlock(&ubi->wl_lock);

	return 0;
}

/**
 * in_wl_tree - check if wear-leveling entry is present in a WL RB-tree.
 * @e: the wear-leveling entry to check
 * @root: the root of the tree
 *
 * This function returns non-zero if @e is in the @root RB-tree and zero if it
 * is not.
 */
static int in_wl_tree(struct ubi_wl_entry *e, struct rb_root *root)
{
	struct rb_node *p;

	p = root->rb_node;
	while (p) {
		struct ubi_wl_entry *e1;

		e1 = rb_entry(p, struct ubi_wl_entry, rb);

		if (e->pnum == e1->pnum) {
			ubi_assert(e == e1);
			return 1;
		}

		if (e->ec < e1->ec)
			p = p->rb_left;
		else if (e->ec > e1->ec)
			p = p->rb_right;
		else {
			ubi_assert(e->pnum != e1->pnum);
			if (e->pnum < e1->pnum)
				p = p->rb_left;
			else
				p = p->rb_right;
		}
	}

	return 0;
}

/**
 * prot_tree_add - add physical eraseblock to protection trees.
 * @ubi: UBI device description object
 * @e: the physical eraseblock to add
 * @pe: protection entry object to use
 * @abs_ec: absolute erase counter value when this physical eraseblock has
 * to be removed from the protection trees.
 *
 * @wl->lock has to be locked.
 */
static void prot_tree_add(struct ubi_device *ubi, struct ubi_wl_entry *e,
			  struct ubi_wl_prot_entry *pe, int abs_ec)
{
	struct rb_node **p, *parent = NULL;
	struct ubi_wl_prot_entry *pe1;

	pe->e = e;
	pe->abs_ec = ubi->abs_ec + abs_ec;

	p = &ubi->prot.pnum.rb_node;
	while (*p) {
		parent = *p;
		pe1 = rb_entry(parent, struct ubi_wl_prot_entry, rb_pnum);

		if (e->pnum < pe1->e->pnum)
			p = &(*p)->rb_left;
		else
			p = &(*p)->rb_right;
	}
	rb_link_node(&pe->rb_pnum, parent, p);
	rb_insert_color(&pe->rb_pnum, &ubi->prot.pnum);

	p = &ubi->prot.aec.rb_node;
	parent = NULL;
	while (*p) {
		parent = *p;
		pe1 = rb_entry(parent, struct ubi_wl_prot_entry, rb_aec);

		if (pe->abs_ec < pe1->abs_ec)
			p = &(*p)->rb_left;
		else
			p = &(*p)->rb_right;
	}
	rb_link_node(&pe->rb_aec, parent, p);
	rb_insert_color(&pe->rb_aec, &ubi->prot.aec);
}

/**
 * find_wl_entry - find wear-leveling entry closest to certain erase counter.
 * @root: the RB-tree where to look for
 * @max: highest possible erase counter
 *
 * This function looks for a wear leveling entry with erase counter closest to
 * @max and less then @max.
 */
static struct ubi_wl_entry *find_wl_entry(struct rb_root *root, int max)
{
	struct rb_node *p;
	struct ubi_wl_entry *e;

	e = rb_entry(rb_first(root), struct ubi_wl_entry, rb);
	max += e->ec;

	p = root->rb_node;
	while (p) {
		struct ubi_wl_entry *e1;

		e1 = rb_entry(p, struct ubi_wl_entry, rb);
		if (e1->ec >= max)
			p = p->rb_left;
		else {
			p = p->rb_right;
			e = e1;
		}
	}

	return e;
}

/**
 * ubi_wl_get_peb - get a physical eraseblock.
 * @ubi: UBI device description object
 * @dtype: type of data which will be stored in this physical eraseblock
 *
 * This function returns a physical eraseblock in case of success and a
 * negative error code in case of failure. Might sleep.
 */
int ubi_wl_get_peb(struct ubi_device *ubi, int dtype)
{
	int err, protect, medium_ec;
	struct ubi_wl_entry *e, *first, *last;
	struct ubi_wl_prot_entry *pe;

	ubi_assert(dtype == UBI_LONGTERM || dtype == UBI_SHORTTERM ||
		   dtype == UBI_UNKNOWN);

	pe = kmalloc(sizeof(struct ubi_wl_prot_entry), GFP_NOFS);
	if (!pe)
		return -ENOMEM;

retry:
	spin_lock(&ubi->wl_lock);
	if (!ubi->free.rb_node) {
		if (ubi->works_count == 0) {
			ubi_assert(list_empty(&ubi->works));
			ubi_err("no free eraseblocks");
			spin_unlock(&ubi->wl_lock);
			kfree(pe);
			return -ENOSPC;
		}
		spin_unlock(&ubi->wl_lock);

		err = produce_free_peb(ubi);
		if (err < 0) {
			kfree(pe);
			return err;
		}
		goto retry;
	}

	switch (dtype) {
	case UBI_LONGTERM:
		/*
		 * For long term data we pick a physical eraseblock with high
		 * erase counter. But the highest erase counter we can pick is
		 * bounded by the the lowest erase counter plus
		 * %WL_FREE_MAX_DIFF.
		 */
		e = find_wl_entry(&ubi->free, WL_FREE_MAX_DIFF);
		protect = LT_PROTECTION;
		break;
	case UBI_UNKNOWN:
		/*
		 * For unknown data we pick a physical eraseblock with medium
		 * erase counter. But we by no means can pick a physical
		 * eraseblock with erase counter greater or equivalent than the
		 * lowest erase counter plus %WL_FREE_MAX_DIFF.
		 */
		first = rb_entry(rb_first(&ubi->free), struct ubi_wl_entry, rb);
		last = rb_entry(rb_last(&ubi->free), struct ubi_wl_entry, rb);

		if (last->ec - first->ec < WL_FREE_MAX_DIFF)
			e = rb_entry(ubi->free.rb_node,
					struct ubi_wl_entry, rb);
		else {
			medium_ec = (first->ec + WL_FREE_MAX_DIFF)/2;
			e = find_wl_entry(&ubi->free, medium_ec);
		}
		protect = U_PROTECTION;
		break;
	case UBI_SHORTTERM:
		/*
		 * For short term data we pick a physical eraseblock with the
		 * lowest erase counter as we expect it will be erased soon.
		 */
		e = rb_entry(rb_first(&ubi->free), struct ubi_wl_entry, rb);
		protect = ST_PROTECTION;
		break;
	default:
		protect = 0;
		e = NULL;
		BUG();
	}

	/*
	 * Move the physical eraseblock to the protection trees where it will
	 * be protected from being moved for some time.
	 */
	paranoid_check_in_wl_tree(e, &ubi->free);
	rb_erase(&e->rb, &ubi->free);
	prot_tree_add(ubi, e, pe, protect);

	dbg_wl("PEB %d EC %d, protection %d", e->pnum, e->ec, protect);
	spin_unlock(&ubi->wl_lock);

	return e->pnum;
}

/**
 * prot_tree_del - remove a physical eraseblock from the protection trees
 * @ubi: UBI device description object
 * @pnum: the physical eraseblock to remove
 *
 * This function returns PEB @pnum from the protection trees and returns zero
 * in case of success and %-ENODEV if the PEB was not found in the protection
 * trees.
 */
static int prot_tree_del(struct ubi_device *ubi, int pnum)
{
	struct rb_node *p;
	struct ubi_wl_prot_entry *pe = NULL;

	p = ubi->prot.pnum.rb_node;
	while (p) {

		pe = rb_entry(p, struct ubi_wl_prot_entry, rb_pnum);

		if (pnum == pe->e->pnum)
			goto found;

		if (pnum < pe->e->pnum)
			p = p->rb_left;
		else
			p = p->rb_right;
	}

	return -ENODEV;

found:
	ubi_assert(pe->e->pnum == pnum);
	rb_erase(&pe->rb_aec, &ubi->prot.aec);
	rb_erase(&pe->rb_pnum, &ubi->prot.pnum);
	kfree(pe);
	return 0;
}

/**
 * sync_erase - synchronously erase a physical eraseblock.
 * @ubi: UBI device description object
 * @e: the the physical eraseblock to erase
 * @torture: if the physical eraseblock has to be tortured
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
static int sync_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
		      int torture)
{
	int err;
	struct ubi_ec_hdr *ec_hdr;
	unsigned long long ec = e->ec;

	dbg_wl("erase PEB %d, old EC %llu", e->pnum, ec);

	err = paranoid_check_ec(ubi, e->pnum, e->ec);
	if (err > 0)
		return -EINVAL;

	ec_hdr = kzalloc(ubi->ec_hdr_alsize, GFP_NOFS);
	if (!ec_hdr)
		return -ENOMEM;

	err = ubi_io_sync_erase(ubi, e->pnum, torture);
	if (err < 0)
		goto out_free;

	ec += err;
	if (ec > UBI_MAX_ERASECOUNTER) {
		/*
		 * Erase counter overflow. Upgrade UBI and use 64-bit
		 * erase counters internally.
		 */
		ubi_err("erase counter overflow at PEB %d, EC %llu",
			e->pnum, ec);
		err = -EINVAL;
		goto out_free;
	}

	dbg_wl("erased PEB %d, new EC %llu", e->pnum, ec);

	ec_hdr->ec = cpu_to_be64(ec);

	err = ubi_io_write_ec_hdr(ubi, e->pnum, ec_hdr);
	if (err)
		goto out_free;

	e->ec = ec;
	spin_lock(&ubi->wl_lock);
	if (e->ec > ubi->max_ec)
		ubi->max_ec = e->ec;
	spin_unlock(&ubi->wl_lock);

out_free:
	kfree(ec_hdr);
	return err;
}

/**
 * check_protection_over - check if it is time to stop protecting some PEBs.
 * @ubi: UBI device description object
 *
 * This function is called after each erase operation, when the absolute erase
 * counter is incremented, to check if some physical eraseblock  have not to be
 * protected any longer. These physical eraseblocks are moved from the
 * protection trees to the used tree.
 */
static void check_protection_over(struct ubi_device *ubi)
{
	struct ubi_wl_prot_entry *pe;

	/*
	 * There may be several protected physical eraseblock to remove,
	 * process them all.
	 */
	while (1) {
		spin_lock(&ubi->wl_lock);
		if (!ubi->prot.aec.rb_node) {
			spin_unlock(&ubi->wl_lock);
			break;
		}

		pe = rb_entry(rb_first(&ubi->prot.aec),
			      struct ubi_wl_prot_entry, rb_aec);

		if (pe->abs_ec > ubi->abs_ec) {
			spin_unlock(&ubi->wl_lock);
			break;
		}

		dbg_wl("PEB %d protection over, abs_ec %llu, PEB abs_ec %llu",
		       pe->e->pnum, ubi->abs_ec, pe->abs_ec);
		rb_erase(&pe->rb_aec, &ubi->prot.aec);
		rb_erase(&pe->rb_pnum, &ubi->prot.pnum);
		wl_tree_add(pe->e, &ubi->used);
		spin_unlock(&ubi->wl_lock);

		kfree(pe);
		cond_resched();
	}
}

/**
 * schedule_ubi_work - schedule a work.
 * @ubi: UBI device description object
 * @wrk: the work to schedule
 *
 * This function enqueues a work defined by @wrk to the tail of the pending
 * works list.
 */
static void schedule_ubi_work(struct ubi_device *ubi, struct ubi_work *wrk)
{
	spin_lock(&ubi->wl_lock);
	list_add_tail(&wrk->list, &ubi->works);
	ubi_assert(ubi->works_count >= 0);
	ubi->works_count += 1;
	if (ubi->thread_enabled)
		wake_up_process(ubi->bgt_thread);
	spin_unlock(&ubi->wl_lock);
}

static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
			int cancel);

/**
 * schedule_erase - schedule an erase work.
 * @ubi: UBI device description object
 * @e: the WL entry of the physical eraseblock to erase
 * @torture: if the physical eraseblock has to be tortured
 *
 * This function returns zero in case of success and a %-ENOMEM in case of
 * failure.
 */
static int schedule_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
			  int torture)
{
	struct ubi_work *wl_wrk;

	dbg_wl("schedule erasure of PEB %d, EC %d, torture %d",
	       e->pnum, e->ec, torture);

	wl_wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
	if (!wl_wrk)
		return -ENOMEM;

	wl_wrk->func = &erase_worker;
	wl_wrk->e = e;
	wl_wrk->torture = torture;

	schedule_ubi_work(ubi, wl_wrk);
	return 0;
}

/**
 * wear_leveling_worker - wear-leveling worker function.
 * @ubi: UBI device description object
 * @wrk: the work object
 * @cancel: non-zero if the worker has to free memory and exit
 *
 * This function copies a more worn out physical eraseblock to a less worn out
 * one. Returns zero in case of success and a negative error code in case of
 * failure.
 */
static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
				int cancel)
{
	int err, put = 0, scrubbing = 0, protect = 0;
	struct ubi_wl_prot_entry *uninitialized_var(pe);
	struct ubi_wl_entry *e1, *e2;
	struct ubi_vid_hdr *vid_hdr;

	kfree(wrk);

	if (cancel)
		return 0;

	vid_hdr = ubi_zalloc_vid_hdr(ubi, GFP_NOFS);
	if (!vid_hdr)
		return -ENOMEM;

	mutex_lock(&ubi->move_mutex);
	spin_lock(&ubi->wl_lock);
	ubi_assert(!ubi->move_from && !ubi->move_to);
	ubi_assert(!ubi->move_to_put);

	if (!ubi->free.rb_node ||
	    (!ubi->used.rb_node && !ubi->scrub.rb_node)) {
		/*
		 * No free physical eraseblocks? Well, they must be waiting in
		 * the queue to be erased. Cancel movement - it will be
		 * triggered again when a free physical eraseblock appears.
		 *
		 * No used physical eraseblocks? They must be temporarily
		 * protected from being moved. They will be moved to the
		 * @ubi->used tree later and the wear-leveling will be
		 * triggered again.
		 */
		dbg_wl("cancel WL, a list is empty: free %d, used %d",
		       !ubi->free.rb_node, !ubi->used.rb_node);
		goto out_cancel;
	}

	if (!ubi->scrub.rb_node) {
		/*
		 * Now pick the least worn-out used physical eraseblock and a
		 * highly worn-out free physical eraseblock. If the erase
		 * counters differ much enough, start wear-leveling.
		 */
		e1 = rb_entry(rb_first(&ubi->used), struct ubi_wl_entry, rb);
		e2 = find_wl_entry(&ubi->free, WL_FREE_MAX_DIFF);

		if (!(e2->ec - e1->ec >= UBI_WL_THRESHOLD)) {
			dbg_wl("no WL needed: min used EC %d, max free EC %d",
			       e1->ec, e2->ec);
			goto out_cancel;
		}
		paranoid_check_in_wl_tree(e1, &ubi->used);
		rb_erase(&e1->rb, &ubi->used);
		dbg_wl("move PEB %d EC %d to PEB %d EC %d",
		       e1->pnum, e1->ec, e2->pnum, e2->ec);
	} else {
		/* Perform scrubbing */
		scrubbing = 1;
		e1 = rb_entry(rb_first(&ubi->scrub), struct ubi_wl_entry, rb);
		e2 = find_wl_entry(&ubi->free, WL_FREE_MAX_DIFF);
		paranoid_check_in_wl_tree(e1, &ubi->scrub);
		rb_erase(&e1->rb, &ubi->scrub);
		dbg_wl("scrub PEB %d to PEB %d", e1->pnum, e2->pnum);
	}

	paranoid_check_in_wl_tree(e2, &ubi->free);
	rb_erase(&e2->rb, &ubi->free);
	ubi->move_from = e1;
	ubi->move_to = e2;
	spin_unlock(&ubi->wl_lock);

	/*
	 * Now we are going to copy physical eraseblock @e1->pnum to @e2->pnum.
	 * We so far do not know which logical eraseblock our physical
	 * eraseblock (@e1) belongs to. We have to read the volume identifier
	 * header first.
	 *
	 * Note, we are protected from this PEB being unmapped and erased. The
	 * 'ubi_wl_put_peb()' would wait for moving to be finished if the PEB
	 * which is being moved was unmapped.
	 */

	err = ubi_io_read_vid_hdr(ubi, e1->pnum, vid_hdr, 0);
	if (err && err != UBI_IO_BITFLIPS) {
		if (err == UBI_IO_PEB_FREE) {
			/*
			 * We are trying to move PEB without a VID header. UBI
			 * always write VID headers shortly after the PEB was
			 * given, so we have a situation when it did not have
			 * chance to write it down because it was preempted.
			 * Just re-schedule the work, so that next time it will
			 * likely have the VID header in place.
			 */
			dbg_wl("PEB %d has no VID header", e1->pnum);
			goto out_not_moved;
		}

		ubi_err("error %d while reading VID header from PEB %d",
			err, e1->pnum);
		if (err > 0)
			err = -EIO;
		goto out_error;
	}

	err = ubi_eba_copy_leb(ubi, e1->pnum, e2->pnum, vid_hdr);
	if (err) {

		if (err < 0)
			goto out_error;
		if (err == 1)
			goto out_not_moved;

		/*
		 * For some reason the LEB was not moved - it might be because
		 * the volume is being deleted. We should prevent this PEB from
		 * being selected for wear-levelling movement for some "time",
		 * so put it to the protection tree.
		 */

		dbg_wl("cancelled moving PEB %d", e1->pnum);
		pe = kmalloc(sizeof(struct ubi_wl_prot_entry), GFP_NOFS);
		if (!pe) {
			err = -ENOMEM;
			goto out_error;
		}

		protect = 1;
	}

	ubi_free_vid_hdr(ubi, vid_hdr);
	if (scrubbing && !protect)
		ubi_msg("scrubbed PEB %d, data moved to PEB %d",
			e1->pnum, e2->pnum);

	spin_lock(&ubi->wl_lock);
	if (protect)
		prot_tree_add(ubi, e1, pe, protect);
	if (!ubi->move_to_put)
		wl_tree_add(e2, &ubi->used);
	else
		put = 1;
	ubi->move_from = ubi->move_to = NULL;
	ubi->move_to_put = ubi->wl_scheduled = 0;
	spin_unlock(&ubi->wl_lock);

	if (put) {
		/*
		 * Well, the target PEB was put meanwhile, schedule it for
		 * erasure.
		 */
		dbg_wl("PEB %d was put meanwhile, erase", e2->pnum);
		err = schedule_erase(ubi, e2, 0);
		if (err)
			goto out_error;
	}

	if (!protect) {
		err = schedule_erase(ubi, e1, 0);
		if (err)
			goto out_error;
	}


	dbg_wl("done");
	mutex_unlock(&ubi->move_mutex);
	return 0;

	/*
	 * For some reasons the LEB was not moved, might be an error, might be
	 * something else. @e1 was not changed, so return it back. @e2 might
	 * be changed, schedule it for erasure.
	 */
out_not_moved:
	ubi_free_vid_hdr(ubi, vid_hdr);
	spin_lock(&ubi->wl_lock);
	if (scrubbing)
		wl_tree_add(e1, &ubi->scrub);
	else
		wl_tree_add(e1, &ubi->used);
	ubi->move_from = ubi->move_to = NULL;
	ubi->move_to_put = ubi->wl_scheduled = 0;
	spin_unlock(&ubi->wl_lock);

	err = schedule_erase(ubi, e2, 0);
	if (err)
		goto out_error;

	mutex_unlock(&ubi->move_mutex);
	return 0;

out_error:
	ubi_err("error %d while moving PEB %d to PEB %d",
		err, e1->pnum, e2->pnum);

	ubi_free_vid_hdr(ubi, vid_hdr);
	spin_lock(&ubi->wl_lock);
	ubi->move_from = ubi->move_to = NULL;
	ubi->move_to_put = ubi->wl_scheduled = 0;
	spin_unlock(&ubi->wl_lock);

	kmem_cache_free(ubi_wl_entry_slab, e1);
	kmem_cache_free(ubi_wl_entry_slab, e2);
	ubi_ro_mode(ubi);

	mutex_unlock(&ubi->move_mutex);
	return err;

out_cancel:
	ubi->wl_scheduled = 0;
	spin_unlock(&ubi->wl_lock);
	mutex_unlock(&ubi->move_mutex);
	ubi_free_vid_hdr(ubi, vid_hdr);
	return 0;
}

/**
 * ensure_wear_leveling - schedule wear-leveling if it is needed.
 * @ubi: UBI device description object
 *
 * This function checks if it is time to start wear-leveling and schedules it
 * if yes. This function returns zero in case of success and a negative error
 * code in case of failure.
 */
static int ensure_wear_leveling(struct ubi_device *ubi)
{
	int err = 0;
	struct ubi_wl_entry *e1;
	struct ubi_wl_entry *e2;
	struct ubi_work *wrk;

	spin_lock(&ubi->wl_lock);
	if (ubi->wl_scheduled)
		/* Wear-leveling is already in the work queue */
		goto out_unlock;

	/*
	 * If the ubi->scrub tree is not empty, scrubbing is needed, and the
	 * the WL worker has to be scheduled anyway.
	 */
	if (!ubi->scrub.rb_node) {
		if (!ubi->used.rb_node || !ubi->free.rb_node)
			/* No physical eraseblocks - no deal */
			goto out_unlock;

		/*
		 * We schedule wear-leveling only if the difference between the
		 * lowest erase counter of used physical eraseblocks and a high
		 * erase counter of free physical eraseblocks is greater then
		 * %UBI_WL_THRESHOLD.
		 */
		e1 = rb_entry(rb_first(&ubi->used), struct ubi_wl_entry, rb);
		e2 = find_wl_entry(&ubi->free, WL_FREE_MAX_DIFF);

		if (!(e2->ec - e1->ec >= UBI_WL_THRESHOLD))
			goto out_unlock;
		dbg_wl("schedule wear-leveling");
	} else
		dbg_wl("schedule scrubbing");

	ubi->wl_scheduled = 1;
	spin_unlock(&ubi->wl_lock);

	wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
	if (!wrk) {
		err = -ENOMEM;
		goto out_cancel;
	}

	wrk->func = &wear_leveling_worker;
	schedule_ubi_work(ubi, wrk);
	return err;

out_cancel:
	spin_lock(&ubi->wl_lock);
	ubi->wl_scheduled = 0;
out_unlock:
	spin_unlock(&ubi->wl_lock);
	return err;
}

/**
 * erase_worker - physical eraseblock erase worker function.
 * @ubi: UBI device description object
 * @wl_wrk: the work object
 * @cancel: non-zero if the worker has to free memory and exit
 *
 * This function erases a physical eraseblock and perform torture testing if
 * needed. It also takes care about marking the physical eraseblock bad if
 * needed. Returns zero in case of success and a negative error code in case of
 * failure.
 */
static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
			int cancel)
{
	struct ubi_wl_entry *e = wl_wrk->e;
	int pnum = e->pnum, err, need;

	if (cancel) {
		dbg_wl("cancel erasure of PEB %d EC %d", pnum, e->ec);
		kfree(wl_wrk);
		kmem_cache_free(ubi_wl_entry_slab, e);
		return 0;
	}

	dbg_wl("erase PEB %d EC %d", pnum, e->ec);

	err = sync_erase(ubi, e, wl_wrk->torture);
	if (!err) {
		/* Fine, we've erased it successfully */
		kfree(wl_wrk);

		spin_lock(&ubi->wl_lock);
		ubi->abs_ec += 1;
		wl_tree_add(e, &ubi->free);
		spin_unlock(&ubi->wl_lock);

		/*
		 * One more erase operation has happened, take care about
		 * protected physical eraseblocks.
		 */
		check_protection_over(ubi);

		/* And take care about wear-leveling */
		err = ensure_wear_leveling(ubi);
		return err;
	}

	ubi_err("failed to erase PEB %d, error %d", pnum, err);
	kfree(wl_wrk);
	kmem_cache_free(ubi_wl_entry_slab, e);

	if (err == -EINTR || err == -ENOMEM || err == -EAGAIN ||
	    err == -EBUSY) {
		int err1;

		/* Re-schedule the LEB for erasure */
		err1 = schedule_erase(ubi, e, 0);
		if (err1) {
			err = err1;
			goto out_ro;
		}
		return err;
	} else if (err != -EIO) {
		/*
		 * If this is not %-EIO, we have no idea what to do. Scheduling
		 * this physical eraseblock for erasure again would cause
		 * errors again and again. Well, lets switch to RO mode.
		 */
		goto out_ro;
	}

	/* It is %-EIO, the PEB went bad */

	if (!ubi->bad_allowed) {
		ubi_err("bad physical eraseblock %d detected", pnum);
		goto out_ro;
	}

	spin_lock(&ubi->volumes_lock);
	need = ubi->beb_rsvd_level - ubi->beb_rsvd_pebs + 1;
	if (need > 0) {
		need = ubi->avail_pebs >= need ? need : ubi->avail_pebs;
		ubi->avail_pebs -= need;
		ubi->rsvd_pebs += need;
		ubi->beb_rsvd_pebs += need;
		if (need > 0)
			ubi_msg("reserve more %d PEBs", need);
	}

	if (ubi->beb_rsvd_pebs == 0) {
		spin_unlock(&ubi->volumes_lock);
		ubi_err("no reserved physical eraseblocks");
		goto out_ro;
	}

	spin_unlock(&ubi->volumes_lock);
	ubi_msg("mark PEB %d as bad", pnum);

	err = ubi_io_mark_bad(ubi, pnum);
	if (err)
		goto out_ro;

	spin_lock(&ubi->volumes_lock);
	ubi->beb_rsvd_pebs -= 1;
	ubi->bad_peb_count += 1;
	ubi->good_peb_count -= 1;
	ubi_calculate_reserved(ubi);
	if (ubi->beb_rsvd_pebs == 0)
		ubi_warn("last PEB from the reserved pool was used");
	spin_unlock(&ubi->volumes_lock);

	return err;

out_ro:
	ubi_ro_mode(ubi);
	return err;
}

/**
 * ubi_wl_put_peb - return a PEB to the wear-leveling sub-system.
 * @ubi: UBI device description object
 * @pnum: physical eraseblock to return
 * @torture: if this physical eraseblock has to be tortured
 *
 * This function is called to return physical eraseblock @pnum to the pool of
 * free physical eraseblocks. The @torture flag has to be set if an I/O error
 * occurred to this @pnum and it has to be tested. This function returns zero
 * in case of success, and a negative error code in case of failure.
 */
int ubi_wl_put_peb(struct ubi_device *ubi, int pnum, int torture)
{
	int err;
	struct ubi_wl_entry *e;

	dbg_wl("PEB %d", pnum);
	ubi_assert(pnum >= 0);
	ubi_assert(pnum < ubi->peb_count);

retry:
	spin_lock(&ubi->wl_lock);
	e = ubi->lookuptbl[pnum];
	if (e == ubi->move_from) {
		/*
		 * User is putting the physical eraseblock which was selected to
		 * be moved. It will be scheduled for erasure in the
		 * wear-leveling worker.
		 */
		dbg_wl("PEB %d is being moved, wait", pnum);
		spin_unlock(&ubi->wl_lock);

		/* Wait for the WL worker by taking the @ubi->move_mutex */
		mutex_lock(&ubi->move_mutex);
		mutex_unlock(&ubi->move_mutex);
		goto retry;
	} else if (e == ubi->move_to) {
		/*
		 * User is putting the physical eraseblock which was selected
		 * as the target the data is moved to. It may happen if the EBA
		 * sub-system already re-mapped the LEB in 'ubi_eba_copy_leb()'
		 * but the WL sub-system has not put the PEB to the "used" tree
		 * yet, but it is about to do this. So we just set a flag which
		 * will tell the WL worker that the PEB is not needed anymore
		 * and should be scheduled for erasure.
		 */
		dbg_wl("PEB %d is the target of data moving", pnum);
		ubi_assert(!ubi->move_to_put);
		ubi->move_to_put = 1;
		spin_unlock(&ubi->wl_lock);
		return 0;
	} else {
		if (in_wl_tree(e, &ubi->used)) {
			paranoid_check_in_wl_tree(e, &ubi->used);
			rb_erase(&e->rb, &ubi->used);
		} else if (in_wl_tree(e, &ubi->scrub)) {
			paranoid_check_in_wl_tree(e, &ubi->scrub);
			rb_erase(&e->rb, &ubi->scrub);
		} else {
			err = prot_tree_del(ubi, e->pnum);
			if (err) {
				ubi_err("PEB %d not found", pnum);
				ubi_ro_mode(ubi);
				spin_unlock(&ubi->wl_lock);
				return err;
			}
		}
	}
	spin_unlock(&ubi->wl_lock);

	err = schedule_erase(ubi, e, torture);
	if (err) {
		spin_lock(&ubi->wl_lock);
		wl_tree_add(e, &ubi->used);
		spin_unlock(&ubi->wl_lock);
	}

	return err;
}

/**
 * ubi_wl_scrub_peb - schedule a physical eraseblock for scrubbing.
 * @ubi: UBI device description object
 * @pnum: the physical eraseblock to schedule
 *
 * If a bit-flip in a physical eraseblock is detected, this physical eraseblock
 * needs scrubbing. This function schedules a physical eraseblock for
 * scrubbing which is done in background. This function returns zero in case of
 * success and a negative error code in case of failure.
 */
int ubi_wl_scrub_peb(struct ubi_device *ubi, int pnum)
{
	struct ubi_wl_entry *e;

	dbg_msg("schedule PEB %d for scrubbing", pnum);

retry:
	spin_lock(&ubi->wl_lock);
	e = ubi->lookuptbl[pnum];
	if (e == ubi->move_from || in_wl_tree(e, &ubi->scrub)) {
		spin_unlock(&ubi->wl_lock);
		return 0;
	}

	if (e == ubi->move_to) {
		/*
		 * This physical eraseblock was used to move data to. The data
		 * was moved but the PEB was not yet inserted to the proper
		 * tree. We should just wait a little and let the WL worker
		 * proceed.
		 */
		spin_unlock(&ubi->wl_lock);
		dbg_wl("the PEB %d is not in proper tree, retry", pnum);
		yield();
		goto retry;
	}

	if (in_wl_tree(e, &ubi->used)) {
		paranoid_check_in_wl_tree(e, &ubi->used);
		rb_erase(&e->rb, &ubi->used);
	} else {
		int err;

		err = prot_tree_del(ubi, e->pnum);
		if (err) {
			ubi_err("PEB %d not found", pnum);
			ubi_ro_mode(ubi);
			spin_unlock(&ubi->wl_lock);
			return err;
		}
	}

	wl_tree_add(e, &ubi->scrub);
	spin_unlock(&ubi->wl_lock);

	/*
	 * Technically scrubbing is the same as wear-leveling, so it is done
	 * by the WL worker.
	 */
	return ensure_wear_leveling(ubi);
}

/**
 * ubi_wl_flush - flush all pending works.
 * @ubi: UBI device description object
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
int ubi_wl_flush(struct ubi_device *ubi)
{
	int err;

	/*
	 * Erase while the pending works queue is not empty, but not more then
	 * the number of currently pending works.
	 */
	dbg_wl("flush (%d pending works)", ubi->works_count);
	while (ubi->works_count) {
		err = do_work(ubi);
		if (err)
			return err;
	}

	/*
	 * Make sure all the works which have been done in parallel are
	 * finished.
	 */
	down_write(&ubi->work_sem);
	up_write(&ubi->work_sem);

	/*
	 * And in case last was the WL worker and it cancelled the LEB
	 * movement, flush again.
	 */
	while (ubi->works_count) {
		dbg_wl("flush more (%d pending works)", ubi->works_count);
		err = do_work(ubi);
		if (err)
			return err;
	}

	return 0;
}

/**
 * tree_destroy - destroy an RB-tree.
 * @root: the root of the tree to destroy
 */
static void tree_destroy(struct rb_root *root)
{
	struct rb_node *rb;
	struct ubi_wl_entry *e;

	rb = root->rb_node;
	while (rb) {
		if (rb->rb_left)
			rb = rb->rb_left;
		else if (rb->rb_right)
			rb = rb->rb_right;
		else {
			e = rb_entry(rb, struct ubi_wl_entry, rb);

			rb = rb_parent(rb);
			if (rb) {
				if (rb->rb_left == &e->rb)
					rb->rb_left = NULL;
				else
					rb->rb_right = NULL;
			}

			kmem_cache_free(ubi_wl_entry_slab, e);
		}
	}
}

/**
 * ubi_thread - UBI background thread.
 * @u: the UBI device description object pointer
 */
int ubi_thread(void *u)
{
	int failures = 0;
	struct ubi_device *ubi = u;

	ubi_msg("background thread \"%s\" started, PID %d",
		ubi->bgt_name, task_pid_nr(current));

	set_freezable();
	for (;;) {
		int err;

		if (kthread_should_stop())
			break;

		if (try_to_freeze())
			continue;

		spin_lock(&ubi->wl_lock);
		if (list_empty(&ubi->works) || ubi->ro_mode ||
			       !ubi->thread_enabled) {
			set_current_state(TASK_INTERRUPTIBLE);
			spin_unlock(&ubi->wl_lock);
			schedule();
			continue;
		}
		spin_unlock(&ubi->wl_lock);

		err = do_work(ubi);
		if (err) {
			ubi_err("%s: work failed with error code %d",
				ubi->bgt_name, err);
			if (failures++ > WL_MAX_FAILURES) {
				/*
				 * Too many failures, disable the thread and
				 * switch to read-only mode.
				 */
				ubi_msg("%s: %d consecutive failures",
					ubi->bgt_name, WL_MAX_FAILURES);
				ubi_ro_mode(ubi);
				break;
			}
		} else
			failures = 0;

		cond_resched();
	}

	dbg_wl("background thread \"%s\" is killed", ubi->bgt_name);
	return 0;
}

/**
 * cancel_pending - cancel all pending works.
 * @ubi: UBI device description object
 */
static void cancel_pending(struct ubi_device *ubi)
{
	while (!list_empty(&ubi->works)) {
		struct ubi_work *wrk;

		wrk = list_entry(ubi->works.next, struct ubi_work, list);
		list_del(&wrk->list);
		wrk->func(ubi, wrk, 1);
		ubi->works_count -= 1;
		ubi_assert(ubi->works_count >= 0);
	}
}

/**
 * ubi_wl_init_scan - initialize the WL sub-system using scanning information.
 * @ubi: UBI device description object
 * @si: scanning information
 *
 * This function returns zero in case of success, and a negative error code in
 * case of failure.
 */
int ubi_wl_init_scan(struct ubi_device *ubi, struct ubi_scan_info *si)
{
	int err;
	struct rb_node *rb1, *rb2;
	struct ubi_scan_volume *sv;
	struct ubi_scan_leb *seb, *tmp;
	struct ubi_wl_entry *e;


	ubi->used = ubi->free = ubi->scrub = RB_ROOT;
	ubi->prot.pnum = ubi->prot.aec = RB_ROOT;
	spin_lock_init(&ubi->wl_lock);
	mutex_init(&ubi->move_mutex);
	init_rwsem(&ubi->work_sem);
	ubi->max_ec = si->max_ec;
	INIT_LIST_HEAD(&ubi->works);

	sprintf(ubi->bgt_name, UBI_BGT_NAME_PATTERN, ubi->ubi_num);

	err = -ENOMEM;
	ubi->lookuptbl = kzalloc(ubi->peb_count * sizeof(void *), GFP_KERNEL);
	if (!ubi->lookuptbl)
		return err;

	list_for_each_entry_safe(seb, tmp, &si->erase, u.list) {
		cond_resched();

		e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
		if (!e)
			goto out_free;

		e->pnum = seb->pnum;
		e->ec = seb->ec;
		ubi->lookuptbl[e->pnum] = e;
		if (schedule_erase(ubi, e, 0)) {
			kmem_cache_free(ubi_wl_entry_slab, e);
			goto out_free;
		}
	}

	list_for_each_entry(seb, &si->free, u.list) {
		cond_resched();

		e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
		if (!e)
			goto out_free;

		e->pnum = seb->pnum;
		e->ec = seb->ec;
		ubi_assert(e->ec >= 0);
		wl_tree_add(e, &ubi->free);
		ubi->lookuptbl[e->pnum] = e;
	}

	list_for_each_entry(seb, &si->corr, u.list) {
		cond_resched();

		e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
		if (!e)
			goto out_free;

		e->pnum = seb->pnum;
		e->ec = seb->ec;
		ubi->lookuptbl[e->pnum] = e;
		if (schedule_erase(ubi, e, 0)) {
			kmem_cache_free(ubi_wl_entry_slab, e);
			goto out_free;
		}
	}

	ubi_rb_for_each_entry(rb1, sv, &si->volumes, rb) {
		ubi_rb_for_each_entry(rb2, seb, &sv->root, u.rb) {
			cond_resched();

			e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
			if (!e)
				goto out_free;

			e->pnum = seb->pnum;
			e->ec = seb->ec;
			ubi->lookuptbl[e->pnum] = e;
			if (!seb->scrub) {
				dbg_wl("add PEB %d EC %d to the used tree",
				       e->pnum, e->ec);
				wl_tree_add(e, &ubi->used);
			} else {
				dbg_wl("add PEB %d EC %d to the scrub tree",
				       e->pnum, e->ec);
				wl_tree_add(e, &ubi->scrub);
			}
		}
	}

	if (ubi->avail_pebs < WL_RESERVED_PEBS) {
		ubi_err("no enough physical eraseblocks (%d, need %d)",
			ubi->avail_pebs, WL_RESERVED_PEBS);
		goto out_free;
	}
	ubi->avail_pebs -= WL_RESERVED_PEBS;
	ubi->rsvd_pebs += WL_RESERVED_PEBS;

	/* Schedule wear-leveling if needed */
	err = ensure_wear_leveling(ubi);
	if (err)
		goto out_free;

	return 0;

out_free:
	cancel_pending(ubi);
	tree_destroy(&ubi->used);
	tree_destroy(&ubi->free);
	tree_destroy(&ubi->scrub);
	kfree(ubi->lookuptbl);
	return err;
}

/**
 * protection_trees_destroy - destroy the protection RB-trees.
 * @ubi: UBI device description object
 */
static void protection_trees_destroy(struct ubi_device *ubi)
{
	struct rb_node *rb;
	struct ubi_wl_prot_entry *pe;

	rb = ubi->prot.aec.rb_node;
	while (rb) {
		if (rb->rb_left)
			rb = rb->rb_left;
		else if (rb->rb_right)
			rb = rb->rb_right;
		else {
			pe = rb_entry(rb, struct ubi_wl_prot_entry, rb_aec);

			rb = rb_parent(rb);
			if (rb) {
				if (rb->rb_left == &pe->rb_aec)
					rb->rb_left = NULL;
				else
					rb->rb_right = NULL;
			}

			kmem_cache_free(ubi_wl_entry_slab, pe->e);
			kfree(pe);
		}
	}
}

/**
 * ubi_wl_close - close the wear-leveling sub-system.
 * @ubi: UBI device description object
 */
void ubi_wl_close(struct ubi_device *ubi)
{
	dbg_wl("close the WL sub-system");
	cancel_pending(ubi);
	protection_trees_destroy(ubi);
	tree_destroy(&ubi->used);
	tree_destroy(&ubi->free);
	tree_destroy(&ubi->scrub);
	kfree(ubi->lookuptbl);
}

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID

/**
 * paranoid_check_ec - make sure that the erase counter of a PEB is correct.
 * @ubi: UBI device description object
 * @pnum: the physical eraseblock number to check
 * @ec: the erase counter to check
 *
 * This function returns zero if the erase counter of physical eraseblock @pnum
 * is equivalent to @ec, %1 if not, and a negative error code if an error
 * occurred.
 */
static int paranoid_check_ec(struct ubi_device *ubi, int pnum, int ec)
{
	int err;
	long long read_ec;
	struct ubi_ec_hdr *ec_hdr;

	ec_hdr = kzalloc(ubi->ec_hdr_alsize, GFP_NOFS);
	if (!ec_hdr)
		return -ENOMEM;

	err = ubi_io_read_ec_hdr(ubi, pnum, ec_hdr, 0);
	if (err && err != UBI_IO_BITFLIPS) {
		/* The header does not have to exist */
		err = 0;
		goto out_free;
	}

	read_ec = be64_to_cpu(ec_hdr->ec);
	if (ec != read_ec) {
		ubi_err("paranoid check failed for PEB %d", pnum);
		ubi_err("read EC is %lld, should be %d", read_ec, ec);
		ubi_dbg_dump_stack();
		err = 1;
	} else
		err = 0;

out_free:
	kfree(ec_hdr);
	return err;
}

/**
 * paranoid_check_in_wl_tree - check that wear-leveling entry is in WL RB-tree.
 * @e: the wear-leveling entry to check
 * @root: the root of the tree
 *
 * This function returns zero if @e is in the @root RB-tree and %1 if it is
 * not.
 */
static int paranoid_check_in_wl_tree(struct ubi_wl_entry *e,
				     struct rb_root *root)
{
	if (in_wl_tree(e, root))
		return 0;

	ubi_err("paranoid check failed for PEB %d, EC %d, RB-tree %p ",
		e->pnum, e->ec, root);
	ubi_dbg_dump_stack();
	return 1;
}

#endif /* CONFIG_MTD_UBI_DEBUG_PARANOID */