summaryrefslogtreecommitdiff
path: root/lib/radix-tree.c
blob: 3c78e1e8b2ad60ead8b598eb03fc26b1da431155 (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
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2001 Momchil Velikov
 * Portions Copyright (C) 2001 Christoph Hellwig
 * Copyright (C) 2005 SGI, Christoph Lameter
 * Copyright (C) 2006 Nick Piggin
 * Copyright (C) 2012 Konstantin Khlebnikov
 * Copyright (C) 2016 Intel, Matthew Wilcox
 * Copyright (C) 2016 Intel, Ross Zwisler
 */

#include <linux/bitmap.h>
#include <linux/bitops.h>
#include <linux/bug.h>
#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/export.h>
#include <linux/idr.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kmemleak.h>
#include <linux/percpu.h>
#include <linux/preempt.h>		/* in_interrupt() */
#include <linux/radix-tree.h>
#include <linux/rcupdate.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/xarray.h>

/*
 * Radix tree node cache.
 */
struct kmem_cache *radix_tree_node_cachep;

/*
 * The radix tree is variable-height, so an insert operation not only has
 * to build the branch to its corresponding item, it also has to build the
 * branch to existing items if the size has to be increased (by
 * radix_tree_extend).
 *
 * The worst case is a zero height tree with just a single item at index 0,
 * and then inserting an item at index ULONG_MAX. This requires 2 new branches
 * of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
 * Hence:
 */
#define RADIX_TREE_PRELOAD_SIZE (RADIX_TREE_MAX_PATH * 2 - 1)

/*
 * The IDR does not have to be as high as the radix tree since it uses
 * signed integers, not unsigned longs.
 */
#define IDR_INDEX_BITS		(8 /* CHAR_BIT */ * sizeof(int) - 1)
#define IDR_MAX_PATH		(DIV_ROUND_UP(IDR_INDEX_BITS, \
						RADIX_TREE_MAP_SHIFT))
#define IDR_PRELOAD_SIZE	(IDR_MAX_PATH * 2 - 1)

/*
 * Per-cpu pool of preloaded nodes
 */
DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = {
	.lock = INIT_LOCAL_LOCK(lock),
};
EXPORT_PER_CPU_SYMBOL_GPL(radix_tree_preloads);

static inline struct radix_tree_node *entry_to_node(void *ptr)
{
	return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
}

static inline void *node_to_entry(void *ptr)
{
	return (void *)((unsigned long)ptr | RADIX_TREE_INTERNAL_NODE);
}

#define RADIX_TREE_RETRY	XA_RETRY_ENTRY

static inline unsigned long
get_slot_offset(const struct radix_tree_node *parent, void __rcu **slot)
{
	return parent ? slot - parent->slots : 0;
}

static unsigned int radix_tree_descend(const struct radix_tree_node *parent,
			struct radix_tree_node **nodep, unsigned long index)
{
	unsigned int offset = (index >> parent->shift) & RADIX_TREE_MAP_MASK;
	void __rcu **entry = rcu_dereference_raw(parent->slots[offset]);

	*nodep = (void *)entry;
	return offset;
}

static inline gfp_t root_gfp_mask(const struct radix_tree_root *root)
{
	return root->xa_flags & (__GFP_BITS_MASK & ~GFP_ZONEMASK);
}

static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
		int offset)
{
	__set_bit(offset, node->tags[tag]);
}

static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
		int offset)
{
	__clear_bit(offset, node->tags[tag]);
}

static inline int tag_get(const struct radix_tree_node *node, unsigned int tag,
		int offset)
{
	return test_bit(offset, node->tags[tag]);
}

static inline void root_tag_set(struct radix_tree_root *root, unsigned tag)
{
	root->xa_flags |= (__force gfp_t)(1 << (tag + ROOT_TAG_SHIFT));
}

static inline void root_tag_clear(struct radix_tree_root *root, unsigned tag)
{
	root->xa_flags &= (__force gfp_t)~(1 << (tag + ROOT_TAG_SHIFT));
}

static inline void root_tag_clear_all(struct radix_tree_root *root)
{
	root->xa_flags &= (__force gfp_t)((1 << ROOT_TAG_SHIFT) - 1);
}

static inline int root_tag_get(const struct radix_tree_root *root, unsigned tag)
{
	return (__force int)root->xa_flags & (1 << (tag + ROOT_TAG_SHIFT));
}

static inline unsigned root_tags_get(const struct radix_tree_root *root)
{
	return (__force unsigned)root->xa_flags >> ROOT_TAG_SHIFT;
}

static inline bool is_idr(const struct radix_tree_root *root)
{
	return !!(root->xa_flags & ROOT_IS_IDR);
}

/*
 * Returns 1 if any slot in the node has this tag set.
 * Otherwise returns 0.
 */
static inline int any_tag_set(const struct radix_tree_node *node,
							unsigned int tag)
{
	unsigned idx;
	for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
		if (node->tags[tag][idx])
			return 1;
	}
	return 0;
}

static inline void all_tag_set(struct radix_tree_node *node, unsigned int tag)
{
	bitmap_fill(node->tags[tag], RADIX_TREE_MAP_SIZE);
}

/**
 * radix_tree_find_next_bit - find the next set bit in a memory region
 *
 * @node: where to begin the search
 * @tag: the tag index
 * @offset: the bitnumber to start searching at
 *
 * Unrollable variant of find_next_bit() for constant size arrays.
 * Tail bits starting from size to roundup(size, BITS_PER_LONG) must be zero.
 * Returns next bit offset, or size if nothing found.
 */
static __always_inline unsigned long
radix_tree_find_next_bit(struct radix_tree_node *node, unsigned int tag,
			 unsigned long offset)
{
	const unsigned long *addr = node->tags[tag];

	if (offset < RADIX_TREE_MAP_SIZE) {
		unsigned long tmp;

		addr += offset / BITS_PER_LONG;
		tmp = *addr >> (offset % BITS_PER_LONG);
		if (tmp)
			return __ffs(tmp) + offset;
		offset = (offset + BITS_PER_LONG) & ~(BITS_PER_LONG - 1);
		while (offset < RADIX_TREE_MAP_SIZE) {
			tmp = *++addr;
			if (tmp)
				return __ffs(tmp) + offset;
			offset += BITS_PER_LONG;
		}
	}
	return RADIX_TREE_MAP_SIZE;
}

static unsigned int iter_offset(const struct radix_tree_iter *iter)
{
	return iter->index & RADIX_TREE_MAP_MASK;
}

/*
 * The maximum index which can be stored in a radix tree
 */
static inline unsigned long shift_maxindex(unsigned int shift)
{
	return (RADIX_TREE_MAP_SIZE << shift) - 1;
}

static inline unsigned long node_maxindex(const struct radix_tree_node *node)
{
	return shift_maxindex(node->shift);
}

static unsigned long next_index(unsigned long index,
				const struct radix_tree_node *node,
				unsigned long offset)
{
	return (index & ~node_maxindex(node)) + (offset << node->shift);
}

/*
 * This assumes that the caller has performed appropriate preallocation, and
 * that the caller has pinned this thread of control to the current CPU.
 */
static struct radix_tree_node *
radix_tree_node_alloc(gfp_t gfp_mask, struct radix_tree_node *parent,
			struct radix_tree_root *root,
			unsigned int shift, unsigned int offset,
			unsigned int count, unsigned int nr_values)
{
	struct radix_tree_node *ret = NULL;

	/*
	 * Preload code isn't irq safe and it doesn't make sense to use
	 * preloading during an interrupt anyway as all the allocations have
	 * to be atomic. So just do normal allocation when in interrupt.
	 */
	if (!gfpflags_allow_blocking(gfp_mask) && !in_interrupt()) {
		struct radix_tree_preload *rtp;

		/*
		 * Even if the caller has preloaded, try to allocate from the
		 * cache first for the new node to get accounted to the memory
		 * cgroup.
		 */
		ret = kmem_cache_alloc(radix_tree_node_cachep,
				       gfp_mask | __GFP_NOWARN);
		if (ret)
			goto out;

		/*
		 * Provided the caller has preloaded here, we will always
		 * succeed in getting a node here (and never reach
		 * kmem_cache_alloc)
		 */
		rtp = this_cpu_ptr(&radix_tree_preloads);
		if (rtp->nr) {
			ret = rtp->nodes;
			rtp->nodes = ret->parent;
			rtp->nr--;
		}
		/*
		 * Update the allocation stack trace as this is more useful
		 * for debugging.
		 */
		kmemleak_update_trace(ret);
		goto out;
	}
	ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
out:
	BUG_ON(radix_tree_is_internal_node(ret));
	if (ret) {
		ret->shift = shift;
		ret->offset = offset;
		ret->count = count;
		ret->nr_values = nr_values;
		ret->parent = parent;
		ret->array = root;
	}
	return ret;
}

void radix_tree_node_rcu_free(struct rcu_head *head)
{
	struct radix_tree_node *node =
			container_of(head, struct radix_tree_node, rcu_head);

	/*
	 * Must only free zeroed nodes into the slab.  We can be left with
	 * non-NULL entries by radix_tree_free_nodes, so clear the entries
	 * and tags here.
	 */
	memset(node->slots, 0, sizeof(node->slots));
	memset(node->tags, 0, sizeof(node->tags));
	INIT_LIST_HEAD(&node->private_list);

	kmem_cache_free(radix_tree_node_cachep, node);
}

static inline void
radix_tree_node_free(struct radix_tree_node *node)
{
	call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
}

/*
 * Load up this CPU's radix_tree_node buffer with sufficient objects to
 * ensure that the addition of a single element in the tree cannot fail.  On
 * success, return zero, with preemption disabled.  On error, return -ENOMEM
 * with preemption not disabled.
 *
 * To make use of this facility, the radix tree must be initialised without
 * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
 */
static __must_check int __radix_tree_preload(gfp_t gfp_mask, unsigned nr)
{
	struct radix_tree_preload *rtp;
	struct radix_tree_node *node;
	int ret = -ENOMEM;

	/*
	 * Nodes preloaded by one cgroup can be used by another cgroup, so
	 * they should never be accounted to any particular memory cgroup.
	 */
	gfp_mask &= ~__GFP_ACCOUNT;

	local_lock(&radix_tree_preloads.lock);
	rtp = this_cpu_ptr(&radix_tree_preloads);
	while (rtp->nr < nr) {
		local_unlock(&radix_tree_preloads.lock);
		node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
		if (node == NULL)
			goto out;
		local_lock(&radix_tree_preloads.lock);
		rtp = this_cpu_ptr(&radix_tree_preloads);
		if (rtp->nr < nr) {
			node->parent = rtp->nodes;
			rtp->nodes = node;
			rtp->nr++;
		} else {
			kmem_cache_free(radix_tree_node_cachep, node);
		}
	}
	ret = 0;
out:
	return ret;
}

/*
 * Load up this CPU's radix_tree_node buffer with sufficient objects to
 * ensure that the addition of a single element in the tree cannot fail.  On
 * success, return zero, with preemption disabled.  On error, return -ENOMEM
 * with preemption not disabled.
 *
 * To make use of this facility, the radix tree must be initialised without
 * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
 */
int radix_tree_preload(gfp_t gfp_mask)
{
	/* Warn on non-sensical use... */
	WARN_ON_ONCE(!gfpflags_allow_blocking(gfp_mask));
	return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
}
EXPORT_SYMBOL(radix_tree_preload);

/*
 * The same as above function, except we don't guarantee preloading happens.
 * We do it, if we decide it helps. On success, return zero with preemption
 * disabled. On error, return -ENOMEM with preemption not disabled.
 */
int radix_tree_maybe_preload(gfp_t gfp_mask)
{
	if (gfpflags_allow_blocking(gfp_mask))
		return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
	/* Preloading doesn't help anything with this gfp mask, skip it */
	local_lock(&radix_tree_preloads.lock);
	return 0;
}
EXPORT_SYMBOL(radix_tree_maybe_preload);

static unsigned radix_tree_load_root(const struct radix_tree_root *root,
		struct radix_tree_node **nodep, unsigned long *maxindex)
{
	struct radix_tree_node *node = rcu_dereference_raw(root->xa_head);

	*nodep = node;

	if (likely(radix_tree_is_internal_node(node))) {
		node = entry_to_node(node);
		*maxindex = node_maxindex(node);
		return node->shift + RADIX_TREE_MAP_SHIFT;
	}

	*maxindex = 0;
	return 0;
}

/*
 *	Extend a radix tree so it can store key @index.
 */
static int radix_tree_extend(struct radix_tree_root *root, gfp_t gfp,
				unsigned long index, unsigned int shift)
{
	void *entry;
	unsigned int maxshift;
	int tag;

	/* Figure out what the shift should be.  */
	maxshift = shift;
	while (index > shift_maxindex(maxshift))
		maxshift += RADIX_TREE_MAP_SHIFT;

	entry = rcu_dereference_raw(root->xa_head);
	if (!entry && (!is_idr(root) || root_tag_get(root, IDR_FREE)))
		goto out;

	do {
		struct radix_tree_node *node = radix_tree_node_alloc(gfp, NULL,
							root, shift, 0, 1, 0);
		if (!node)
			return -ENOMEM;

		if (is_idr(root)) {
			all_tag_set(node, IDR_FREE);
			if (!root_tag_get(root, IDR_FREE)) {
				tag_clear(node, IDR_FREE, 0);
				root_tag_set(root, IDR_FREE);
			}
		} else {
			/* Propagate the aggregated tag info to the new child */
			for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
				if (root_tag_get(root, tag))
					tag_set(node, tag, 0);
			}
		}

		BUG_ON(shift > BITS_PER_LONG);
		if (radix_tree_is_internal_node(entry)) {
			entry_to_node(entry)->parent = node;
		} else if (xa_is_value(entry)) {
			/* Moving a value entry root->xa_head to a node */
			node->nr_values = 1;
		}
		/*
		 * entry was already in the radix tree, so we do not need
		 * rcu_assign_pointer here
		 */
		node->slots[0] = (void __rcu *)entry;
		entry = node_to_entry(node);
		rcu_assign_pointer(root->xa_head, entry);
		shift += RADIX_TREE_MAP_SHIFT;
	} while (shift <= maxshift);
out:
	return maxshift + RADIX_TREE_MAP_SHIFT;
}

/**
 *	radix_tree_shrink    -    shrink radix tree to minimum height
 *	@root:		radix tree root
 */
static inline bool radix_tree_shrink(struct radix_tree_root *root)
{
	bool shrunk = false;

	for (;;) {
		struct radix_tree_node *node = rcu_dereference_raw(root->xa_head);
		struct radix_tree_node *child;

		if (!radix_tree_is_internal_node(node))
			break;
		node = entry_to_node(node);

		/*
		 * The candidate node has more than one child, or its child
		 * is not at the leftmost slot, we cannot shrink.
		 */
		if (node->count != 1)
			break;
		child = rcu_dereference_raw(node->slots[0]);
		if (!child)
			break;

		/*
		 * For an IDR, we must not shrink entry 0 into the root in
		 * case somebody calls idr_replace() with a pointer that
		 * appears to be an internal entry
		 */
		if (!node->shift && is_idr(root))
			break;

		if (radix_tree_is_internal_node(child))
			entry_to_node(child)->parent = NULL;

		/*
		 * We don't need rcu_assign_pointer(), since we are simply
		 * moving the node from one part of the tree to another: if it
		 * was safe to dereference the old pointer to it
		 * (node->slots[0]), it will be safe to dereference the new
		 * one (root->xa_head) as far as dependent read barriers go.
		 */
		root->xa_head = (void __rcu *)child;
		if (is_idr(root) && !tag_get(node, IDR_FREE, 0))
			root_tag_clear(root, IDR_FREE);

		/*
		 * We have a dilemma here. The node's slot[0] must not be
		 * NULLed in case there are concurrent lookups expecting to
		 * find the item. However if this was a bottom-level node,
		 * then it may be subject to the slot pointer being visible
		 * to callers dereferencing it. If item corresponding to
		 * slot[0] is subsequently deleted, these callers would expect
		 * their slot to become empty sooner or later.
		 *
		 * For example, lockless pagecache will look up a slot, deref
		 * the page pointer, and if the page has 0 refcount it means it
		 * was concurrently deleted from pagecache so try the deref
		 * again. Fortunately there is already a requirement for logic
		 * to retry the entire slot lookup -- the indirect pointer
		 * problem (replacing direct root node with an indirect pointer
		 * also results in a stale slot). So tag the slot as indirect
		 * to force callers to retry.
		 */
		node->count = 0;
		if (!radix_tree_is_internal_node(child)) {
			node->slots[0] = (void __rcu *)RADIX_TREE_RETRY;
		}

		WARN_ON_ONCE(!list_empty(&node->private_list));
		radix_tree_node_free(node);
		shrunk = true;
	}

	return shrunk;
}

static bool delete_node(struct radix_tree_root *root,
			struct radix_tree_node *node)
{
	bool deleted = false;

	do {
		struct radix_tree_node *parent;

		if (node->count) {
			if (node_to_entry(node) ==
					rcu_dereference_raw(root->xa_head))
				deleted |= radix_tree_shrink(root);
			return deleted;
		}

		parent = node->parent;
		if (parent) {
			parent->slots[node->offset] = NULL;
			parent->count--;
		} else {
			/*
			 * Shouldn't the tags already have all been cleared
			 * by the caller?
			 */
			if (!is_idr(root))
				root_tag_clear_all(root);
			root->xa_head = NULL;
		}

		WARN_ON_ONCE(!list_empty(&node->private_list));
		radix_tree_node_free(node);
		deleted = true;

		node = parent;
	} while (node);

	return deleted;
}

/**
 *	__radix_tree_create	-	create a slot in a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *	@nodep:		returns node
 *	@slotp:		returns slot
 *
 *	Create, if necessary, and return the node and slot for an item
 *	at position @index in the radix tree @root.
 *
 *	Until there is more than one item in the tree, no nodes are
 *	allocated and @root->xa_head is used as a direct slot instead of
 *	pointing to a node, in which case *@nodep will be NULL.
 *
 *	Returns -ENOMEM, or 0 for success.
 */
static int __radix_tree_create(struct radix_tree_root *root,
		unsigned long index, struct radix_tree_node **nodep,
		void __rcu ***slotp)
{
	struct radix_tree_node *node = NULL, *child;
	void __rcu **slot = (void __rcu **)&root->xa_head;
	unsigned long maxindex;
	unsigned int shift, offset = 0;
	unsigned long max = index;
	gfp_t gfp = root_gfp_mask(root);

	shift = radix_tree_load_root(root, &child, &maxindex);

	/* Make sure the tree is high enough.  */
	if (max > maxindex) {
		int error = radix_tree_extend(root, gfp, max, shift);
		if (error < 0)
			return error;
		shift = error;
		child = rcu_dereference_raw(root->xa_head);
	}

	while (shift > 0) {
		shift -= RADIX_TREE_MAP_SHIFT;
		if (child == NULL) {
			/* Have to add a child node.  */
			child = radix_tree_node_alloc(gfp, node, root, shift,
							offset, 0, 0);
			if (!child)
				return -ENOMEM;
			rcu_assign_pointer(*slot, node_to_entry(child));
			if (node)
				node->count++;
		} else if (!radix_tree_is_internal_node(child))
			break;

		/* Go a level down */
		node = entry_to_node(child);
		offset = radix_tree_descend(node, &child, index);
		slot = &node->slots[offset];
	}

	if (nodep)
		*nodep = node;
	if (slotp)
		*slotp = slot;
	return 0;
}

/*
 * Free any nodes below this node.  The tree is presumed to not need
 * shrinking, and any user data in the tree is presumed to not need a
 * destructor called on it.  If we need to add a destructor, we can
 * add that functionality later.  Note that we may not clear tags or
 * slots from the tree as an RCU walker may still have a pointer into
 * this subtree.  We could replace the entries with RADIX_TREE_RETRY,
 * but we'll still have to clear those in rcu_free.
 */
static void radix_tree_free_nodes(struct radix_tree_node *node)
{
	unsigned offset = 0;
	struct radix_tree_node *child = entry_to_node(node);

	for (;;) {
		void *entry = rcu_dereference_raw(child->slots[offset]);
		if (xa_is_node(entry) && child->shift) {
			child = entry_to_node(entry);
			offset = 0;
			continue;
		}
		offset++;
		while (offset == RADIX_TREE_MAP_SIZE) {
			struct radix_tree_node *old = child;
			offset = child->offset + 1;
			child = child->parent;
			WARN_ON_ONCE(!list_empty(&old->private_list));
			radix_tree_node_free(old);
			if (old == entry_to_node(node))
				return;
		}
	}
}

static inline int insert_entries(struct radix_tree_node *node,
		void __rcu **slot, void *item)
{
	if (*slot)
		return -EEXIST;
	rcu_assign_pointer(*slot, item);
	if (node) {
		node->count++;
		if (xa_is_value(item))
			node->nr_values++;
	}
	return 1;
}

/**
 *	radix_tree_insert    -    insert into a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *	@item:		item to insert
 *
 *	Insert an item into the radix tree at position @index.
 */
int radix_tree_insert(struct radix_tree_root *root, unsigned long index,
			void *item)
{
	struct radix_tree_node *node;
	void __rcu **slot;
	int error;

	BUG_ON(radix_tree_is_internal_node(item));

	error = __radix_tree_create(root, index, &node, &slot);
	if (error)
		return error;

	error = insert_entries(node, slot, item);
	if (error < 0)
		return error;

	if (node) {
		unsigned offset = get_slot_offset(node, slot);
		BUG_ON(tag_get(node, 0, offset));
		BUG_ON(tag_get(node, 1, offset));
		BUG_ON(tag_get(node, 2, offset));
	} else {
		BUG_ON(root_tags_get(root));
	}

	return 0;
}
EXPORT_SYMBOL(radix_tree_insert);

/**
 *	__radix_tree_lookup	-	lookup an item in a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *	@nodep:		returns node
 *	@slotp:		returns slot
 *
 *	Lookup and return the item at position @index in the radix
 *	tree @root.
 *
 *	Until there is more than one item in the tree, no nodes are
 *	allocated and @root->xa_head is used as a direct slot instead of
 *	pointing to a node, in which case *@nodep will be NULL.
 */
void *__radix_tree_lookup(const struct radix_tree_root *root,
			  unsigned long index, struct radix_tree_node **nodep,
			  void __rcu ***slotp)
{
	struct radix_tree_node *node, *parent;
	unsigned long maxindex;
	void __rcu **slot;

 restart:
	parent = NULL;
	slot = (void __rcu **)&root->xa_head;
	radix_tree_load_root(root, &node, &maxindex);
	if (index > maxindex)
		return NULL;

	while (radix_tree_is_internal_node(node)) {
		unsigned offset;

		parent = entry_to_node(node);
		offset = radix_tree_descend(parent, &node, index);
		slot = parent->slots + offset;
		if (node == RADIX_TREE_RETRY)
			goto restart;
		if (parent->shift == 0)
			break;
	}

	if (nodep)
		*nodep = parent;
	if (slotp)
		*slotp = slot;
	return node;
}

/**
 *	radix_tree_lookup_slot    -    lookup a slot in a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *
 *	Returns:  the slot corresponding to the position @index in the
 *	radix tree @root. This is useful for update-if-exists operations.
 *
 *	This function can be called under rcu_read_lock iff the slot is not
 *	modified by radix_tree_replace_slot, otherwise it must be called
 *	exclusive from other writers. Any dereference of the slot must be done
 *	using radix_tree_deref_slot.
 */
void __rcu **radix_tree_lookup_slot(const struct radix_tree_root *root,
				unsigned long index)
{
	void __rcu **slot;

	if (!__radix_tree_lookup(root, index, NULL, &slot))
		return NULL;
	return slot;
}
EXPORT_SYMBOL(radix_tree_lookup_slot);

/**
 *	radix_tree_lookup    -    perform lookup operation on a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *
 *	Lookup the item at the position @index in the radix tree @root.
 *
 *	This function can be called under rcu_read_lock, however the caller
 *	must manage lifetimes of leaf nodes (eg. RCU may also be used to free
 *	them safely). No RCU barriers are required to access or modify the
 *	returned item, however.
 */
void *radix_tree_lookup(const struct radix_tree_root *root, unsigned long index)
{
	return __radix_tree_lookup(root, index, NULL, NULL);
}
EXPORT_SYMBOL(radix_tree_lookup);

static void replace_slot(void __rcu **slot, void *item,
		struct radix_tree_node *node, int count, int values)
{
	if (node && (count || values)) {
		node->count += count;
		node->nr_values += values;
	}

	rcu_assign_pointer(*slot, item);
}

static bool node_tag_get(const struct radix_tree_root *root,
				const struct radix_tree_node *node,
				unsigned int tag, unsigned int offset)
{
	if (node)
		return tag_get(node, tag, offset);
	return root_tag_get(root, tag);
}

/*
 * IDR users want to be able to store NULL in the tree, so if the slot isn't
 * free, don't adjust the count, even if it's transitioning between NULL and
 * non-NULL.  For the IDA, we mark slots as being IDR_FREE while they still
 * have empty bits, but it only stores NULL in slots when they're being
 * deleted.
 */
static int calculate_count(struct radix_tree_root *root,
				struct radix_tree_node *node, void __rcu **slot,
				void *item, void *old)
{
	if (is_idr(root)) {
		unsigned offset = get_slot_offset(node, slot);
		bool free = node_tag_get(root, node, IDR_FREE, offset);
		if (!free)
			return 0;
		if (!old)
			return 1;
	}
	return !!item - !!old;
}

/**
 * __radix_tree_replace		- replace item in a slot
 * @root:		radix tree root
 * @node:		pointer to tree node
 * @slot:		pointer to slot in @node
 * @item:		new item to store in the slot.
 *
 * For use with __radix_tree_lookup().  Caller must hold tree write locked
 * across slot lookup and replacement.
 */
void __radix_tree_replace(struct radix_tree_root *root,
			  struct radix_tree_node *node,
			  void __rcu **slot, void *item)
{
	void *old = rcu_dereference_raw(*slot);
	int values = !!xa_is_value(item) - !!xa_is_value(old);
	int count = calculate_count(root, node, slot, item, old);

	/*
	 * This function supports replacing value entries and
	 * deleting entries, but that needs accounting against the
	 * node unless the slot is root->xa_head.
	 */
	WARN_ON_ONCE(!node && (slot != (void __rcu **)&root->xa_head) &&
			(count || values));
	replace_slot(slot, item, node, count, values);

	if (!node)
		return;

	delete_node(root, node);
}

/**
 * radix_tree_replace_slot	- replace item in a slot
 * @root:	radix tree root
 * @slot:	pointer to slot
 * @item:	new item to store in the slot.
 *
 * For use with radix_tree_lookup_slot() and
 * radix_tree_gang_lookup_tag_slot().  Caller must hold tree write locked
 * across slot lookup and replacement.
 *
 * NOTE: This cannot be used to switch between non-entries (empty slots),
 * regular entries, and value entries, as that requires accounting
 * inside the radix tree node. When switching from one type of entry or
 * deleting, use __radix_tree_lookup() and __radix_tree_replace() or
 * radix_tree_iter_replace().
 */
void radix_tree_replace_slot(struct radix_tree_root *root,
			     void __rcu **slot, void *item)
{
	__radix_tree_replace(root, NULL, slot, item);
}
EXPORT_SYMBOL(radix_tree_replace_slot);

/**
 * radix_tree_iter_replace - replace item in a slot
 * @root:	radix tree root
 * @iter:	iterator state
 * @slot:	pointer to slot
 * @item:	new item to store in the slot.
 *
 * For use with radix_tree_for_each_slot().
 * Caller must hold tree write locked.
 */
void radix_tree_iter_replace(struct radix_tree_root *root,
				const struct radix_tree_iter *iter,
				void __rcu **slot, void *item)
{
	__radix_tree_replace(root, iter->node, slot, item);
}

static void node_tag_set(struct radix_tree_root *root,
				struct radix_tree_node *node,
				unsigned int tag, unsigned int offset)
{
	while (node) {
		if (tag_get(node, tag, offset))
			return;
		tag_set(node, tag, offset);
		offset = node->offset;
		node = node->parent;
	}

	if (!root_tag_get(root, tag))
		root_tag_set(root, tag);
}

/**
 *	radix_tree_tag_set - set a tag on a radix tree node
 *	@root:		radix tree root
 *	@index:		index key
 *	@tag:		tag index
 *
 *	Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
 *	corresponding to @index in the radix tree.  From
 *	the root all the way down to the leaf node.
 *
 *	Returns the address of the tagged item.  Setting a tag on a not-present
 *	item is a bug.
 */
void *radix_tree_tag_set(struct radix_tree_root *root,
			unsigned long index, unsigned int tag)
{
	struct radix_tree_node *node, *parent;
	unsigned long maxindex;

	radix_tree_load_root(root, &node, &maxindex);
	BUG_ON(index > maxindex);

	while (radix_tree_is_internal_node(node)) {
		unsigned offset;

		parent = entry_to_node(node);
		offset = radix_tree_descend(parent, &node, index);
		BUG_ON(!node);

		if (!tag_get(parent, tag, offset))
			tag_set(parent, tag, offset);
	}

	/* set the root's tag bit */
	if (!root_tag_get(root, tag))
		root_tag_set(root, tag);

	return node;
}
EXPORT_SYMBOL(radix_tree_tag_set);

static void node_tag_clear(struct radix_tree_root *root,
				struct radix_tree_node *node,
				unsigned int tag, unsigned int offset)
{
	while (node) {
		if (!tag_get(node, tag, offset))
			return;
		tag_clear(node, tag, offset);
		if (any_tag_set(node, tag))
			return;

		offset = node->offset;
		node = node->parent;
	}

	/* clear the root's tag bit */
	if (root_tag_get(root, tag))
		root_tag_clear(root, tag);
}

/**
 *	radix_tree_tag_clear - clear a tag on a radix tree node
 *	@root:		radix tree root
 *	@index:		index key
 *	@tag:		tag index
 *
 *	Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
 *	corresponding to @index in the radix tree.  If this causes
 *	the leaf node to have no tags set then clear the tag in the
 *	next-to-leaf node, etc.
 *
 *	Returns the address of the tagged item on success, else NULL.  ie:
 *	has the same return value and semantics as radix_tree_lookup().
 */
void *radix_tree_tag_clear(struct radix_tree_root *root,
			unsigned long index, unsigned int tag)
{
	struct radix_tree_node *node, *parent;
	unsigned long maxindex;
	int offset;

	radix_tree_load_root(root, &node, &maxindex);
	if (index > maxindex)
		return NULL;

	parent = NULL;

	while (radix_tree_is_internal_node(node)) {
		parent = entry_to_node(node);
		offset = radix_tree_descend(parent, &node, index);
	}

	if (node)
		node_tag_clear(root, parent, tag, offset);

	return node;
}
EXPORT_SYMBOL(radix_tree_tag_clear);

/**
  * radix_tree_iter_tag_clear - clear a tag on the current iterator entry
  * @root: radix tree root
  * @iter: iterator state
  * @tag: tag to clear
  */
void radix_tree_iter_tag_clear(struct radix_tree_root *root,
			const struct radix_tree_iter *iter, unsigned int tag)
{
	node_tag_clear(root, iter->node, tag, iter_offset(iter));
}

/**
 * radix_tree_tag_get - get a tag on a radix tree node
 * @root:		radix tree root
 * @index:		index key
 * @tag:		tag index (< RADIX_TREE_MAX_TAGS)
 *
 * Return values:
 *
 *  0: tag not present or not set
 *  1: tag set
 *
 * Note that the return value of this function may not be relied on, even if
 * the RCU lock is held, unless tag modification and node deletion are excluded
 * from concurrency.
 */
int radix_tree_tag_get(const struct radix_tree_root *root,
			unsigned long index, unsigned int tag)
{
	struct radix_tree_node *node, *parent;
	unsigned long maxindex;

	if (!root_tag_get(root, tag))
		return 0;

	radix_tree_load_root(root, &node, &maxindex);
	if (index > maxindex)
		return 0;

	while (radix_tree_is_internal_node(node)) {
		unsigned offset;

		parent = entry_to_node(node);
		offset = radix_tree_descend(parent, &node, index);

		if (!tag_get(parent, tag, offset))
			return 0;
		if (node == RADIX_TREE_RETRY)
			break;
	}

	return 1;
}
EXPORT_SYMBOL(radix_tree_tag_get);

/* Construct iter->tags bit-mask from node->tags[tag] array */
static void set_iter_tags(struct radix_tree_iter *iter,
				struct radix_tree_node *node, unsigned offset,
				unsigned tag)
{
	unsigned tag_long = offset / BITS_PER_LONG;
	unsigned tag_bit  = offset % BITS_PER_LONG;

	if (!node) {
		iter->tags = 1;
		return;
	}

	iter->tags = node->tags[tag][tag_long] >> tag_bit;

	/* This never happens if RADIX_TREE_TAG_LONGS == 1 */
	if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
		/* Pick tags from next element */
		if (tag_bit)
			iter->tags |= node->tags[tag][tag_long + 1] <<
						(BITS_PER_LONG - tag_bit);
		/* Clip chunk size, here only BITS_PER_LONG tags */
		iter->next_index = __radix_tree_iter_add(iter, BITS_PER_LONG);
	}
}

void __rcu **radix_tree_iter_resume(void __rcu **slot,
					struct radix_tree_iter *iter)
{
	slot++;
	iter->index = __radix_tree_iter_add(iter, 1);
	iter->next_index = iter->index;
	iter->tags = 0;
	return NULL;
}
EXPORT_SYMBOL(radix_tree_iter_resume);

/**
 * radix_tree_next_chunk - find next chunk of slots for iteration
 *
 * @root:	radix tree root
 * @iter:	iterator state
 * @flags:	RADIX_TREE_ITER_* flags and tag index
 * Returns:	pointer to chunk first slot, or NULL if iteration is over
 */
void __rcu **radix_tree_next_chunk(const struct radix_tree_root *root,
			     struct radix_tree_iter *iter, unsigned flags)
{
	unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;
	struct radix_tree_node *node, *child;
	unsigned long index, offset, maxindex;

	if ((flags & RADIX_TREE_ITER_TAGGED) && !root_tag_get(root, tag))
		return NULL;

	/*
	 * Catch next_index overflow after ~0UL. iter->index never overflows
	 * during iterating; it can be zero only at the beginning.
	 * And we cannot overflow iter->next_index in a single step,
	 * because RADIX_TREE_MAP_SHIFT < BITS_PER_LONG.
	 *
	 * This condition also used by radix_tree_next_slot() to stop
	 * contiguous iterating, and forbid switching to the next chunk.
	 */
	index = iter->next_index;
	if (!index && iter->index)
		return NULL;

 restart:
	radix_tree_load_root(root, &child, &maxindex);
	if (index > maxindex)
		return NULL;
	if (!child)
		return NULL;

	if (!radix_tree_is_internal_node(child)) {
		/* Single-slot tree */
		iter->index = index;
		iter->next_index = maxindex + 1;
		iter->tags = 1;
		iter->node = NULL;
		return (void __rcu **)&root->xa_head;
	}

	do {
		node = entry_to_node(child);
		offset = radix_tree_descend(node, &child, index);

		if ((flags & RADIX_TREE_ITER_TAGGED) ?
				!tag_get(node, tag, offset) : !child) {
			/* Hole detected */
			if (flags & RADIX_TREE_ITER_CONTIG)
				return NULL;

			if (flags & RADIX_TREE_ITER_TAGGED)
				offset = radix_tree_find_next_bit(node, tag,
						offset + 1);
			else
				while (++offset	< RADIX_TREE_MAP_SIZE) {
					void *slot = rcu_dereference_raw(
							node->slots[offset]);
					if (slot)
						break;
				}
			index &= ~node_maxindex(node);
			index += offset << node->shift;
			/* Overflow after ~0UL */
			if (!index)
				return NULL;
			if (offset == RADIX_TREE_MAP_SIZE)
				goto restart;
			child = rcu_dereference_raw(node->slots[offset]);
		}

		if (!child)
			goto restart;
		if (child == RADIX_TREE_RETRY)
			break;
	} while (node->shift && radix_tree_is_internal_node(child));

	/* Update the iterator state */
	iter->index = (index &~ node_maxindex(node)) | offset;
	iter->next_index = (index | node_maxindex(node)) + 1;
	iter->node = node;

	if (flags & RADIX_TREE_ITER_TAGGED)
		set_iter_tags(iter, node, offset, tag);

	return node->slots + offset;
}
EXPORT_SYMBOL(radix_tree_next_chunk);

/**
 *	radix_tree_gang_lookup - perform multiple lookup on a radix tree
 *	@root:		radix tree root
 *	@results:	where the results of the lookup are placed
 *	@first_index:	start the lookup from this key
 *	@max_items:	place up to this many items at *results
 *
 *	Performs an index-ascending scan of the tree for present items.  Places
 *	them at *@results and returns the number of items which were placed at
 *	*@results.
 *
 *	The implementation is naive.
 *
 *	Like radix_tree_lookup, radix_tree_gang_lookup may be called under
 *	rcu_read_lock. In this case, rather than the returned results being
 *	an atomic snapshot of the tree at a single point in time, the
 *	semantics of an RCU protected gang lookup are as though multiple
 *	radix_tree_lookups have been issued in individual locks, and results
 *	stored in 'results'.
 */
unsigned int
radix_tree_gang_lookup(const struct radix_tree_root *root, void **results,
			unsigned long first_index, unsigned int max_items)
{
	struct radix_tree_iter iter;
	void __rcu **slot;
	unsigned int ret = 0;

	if (unlikely(!max_items))
		return 0;

	radix_tree_for_each_slot(slot, root, &iter, first_index) {
		results[ret] = rcu_dereference_raw(*slot);
		if (!results[ret])
			continue;
		if (radix_tree_is_internal_node(results[ret])) {
			slot = radix_tree_iter_retry(&iter);
			continue;
		}
		if (++ret == max_items)
			break;
	}

	return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup);

/**
 *	radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
 *	                             based on a tag
 *	@root:		radix tree root
 *	@results:	where the results of the lookup are placed
 *	@first_index:	start the lookup from this key
 *	@max_items:	place up to this many items at *results
 *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
 *
 *	Performs an index-ascending scan of the tree for present items which
 *	have the tag indexed by @tag set.  Places the items at *@results and
 *	returns the number of items which were placed at *@results.
 */
unsigned int
radix_tree_gang_lookup_tag(const struct radix_tree_root *root, void **results,
		unsigned long first_index, unsigned int max_items,
		unsigned int tag)
{
	struct radix_tree_iter iter;
	void __rcu **slot;
	unsigned int ret = 0;

	if (unlikely(!max_items))
		return 0;

	radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
		results[ret] = rcu_dereference_raw(*slot);
		if (!results[ret])
			continue;
		if (radix_tree_is_internal_node(results[ret])) {
			slot = radix_tree_iter_retry(&iter);
			continue;
		}
		if (++ret == max_items)
			break;
	}

	return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup_tag);

/**
 *	radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
 *					  radix tree based on a tag
 *	@root:		radix tree root
 *	@results:	where the results of the lookup are placed
 *	@first_index:	start the lookup from this key
 *	@max_items:	place up to this many items at *results
 *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
 *
 *	Performs an index-ascending scan of the tree for present items which
 *	have the tag indexed by @tag set.  Places the slots at *@results and
 *	returns the number of slots which were placed at *@results.
 */
unsigned int
radix_tree_gang_lookup_tag_slot(const struct radix_tree_root *root,
		void __rcu ***results, unsigned long first_index,
		unsigned int max_items, unsigned int tag)
{
	struct radix_tree_iter iter;
	void __rcu **slot;
	unsigned int ret = 0;

	if (unlikely(!max_items))
		return 0;

	radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
		results[ret] = slot;
		if (++ret == max_items)
			break;
	}

	return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);

static bool __radix_tree_delete(struct radix_tree_root *root,
				struct radix_tree_node *node, void __rcu **slot)
{
	void *old = rcu_dereference_raw(*slot);
	int values = xa_is_value(old) ? -1 : 0;
	unsigned offset = get_slot_offset(node, slot);
	int tag;

	if (is_idr(root))
		node_tag_set(root, node, IDR_FREE, offset);
	else
		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
			node_tag_clear(root, node, tag, offset);

	replace_slot(slot, NULL, node, -1, values);
	return node && delete_node(root, node);
}

/**
 * radix_tree_iter_delete - delete the entry at this iterator position
 * @root: radix tree root
 * @iter: iterator state
 * @slot: pointer to slot
 *
 * Delete the entry at the position currently pointed to by the iterator.
 * This may result in the current node being freed; if it is, the iterator
 * is advanced so that it will not reference the freed memory.  This
 * function may be called without any locking if there are no other threads
 * which can access this tree.
 */
void radix_tree_iter_delete(struct radix_tree_root *root,
				struct radix_tree_iter *iter, void __rcu **slot)
{
	if (__radix_tree_delete(root, iter->node, slot))
		iter->index = iter->next_index;
}
EXPORT_SYMBOL(radix_tree_iter_delete);

/**
 * radix_tree_delete_item - delete an item from a radix tree
 * @root: radix tree root
 * @index: index key
 * @item: expected item
 *
 * Remove @item at @index from the radix tree rooted at @root.
 *
 * Return: the deleted entry, or %NULL if it was not present
 * or the entry at the given @index was not @item.
 */
void *radix_tree_delete_item(struct radix_tree_root *root,
			     unsigned long index, void *item)
{
	struct radix_tree_node *node = NULL;
	void __rcu **slot = NULL;
	void *entry;

	entry = __radix_tree_lookup(root, index, &node, &slot);
	if (!slot)
		return NULL;
	if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE,
						get_slot_offset(node, slot))))
		return NULL;

	if (item && entry != item)
		return NULL;

	__radix_tree_delete(root, node, slot);

	return entry;
}
EXPORT_SYMBOL(radix_tree_delete_item);

/**
 * radix_tree_delete - delete an entry from a radix tree
 * @root: radix tree root
 * @index: index key
 *
 * Remove the entry at @index from the radix tree rooted at @root.
 *
 * Return: The deleted entry, or %NULL if it was not present.
 */
void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
{
	return radix_tree_delete_item(root, index, NULL);
}
EXPORT_SYMBOL(radix_tree_delete);

/**
 *	radix_tree_tagged - test whether any items in the tree are tagged
 *	@root:		radix tree root
 *	@tag:		tag to test
 */
int radix_tree_tagged(const struct radix_tree_root *root, unsigned int tag)
{
	return root_tag_get(root, tag);
}
EXPORT_SYMBOL(radix_tree_tagged);

/**
 * idr_preload - preload for idr_alloc()
 * @gfp_mask: allocation mask to use for preloading
 *
 * Preallocate memory to use for the next call to idr_alloc().  This function
 * returns with preemption disabled.  It will be enabled by idr_preload_end().
 */
void idr_preload(gfp_t gfp_mask)
{
	if (__radix_tree_preload(gfp_mask, IDR_PRELOAD_SIZE))
		local_lock(&radix_tree_preloads.lock);
}
EXPORT_SYMBOL(idr_preload);

void __rcu **idr_get_free(struct radix_tree_root *root,
			      struct radix_tree_iter *iter, gfp_t gfp,
			      unsigned long max)
{
	struct radix_tree_node *node = NULL, *child;
	void __rcu **slot = (void __rcu **)&root->xa_head;
	unsigned long maxindex, start = iter->next_index;
	unsigned int shift, offset = 0;

 grow:
	shift = radix_tree_load_root(root, &child, &maxindex);
	if (!radix_tree_tagged(root, IDR_FREE))
		start = max(start, maxindex + 1);
	if (start > max)
		return ERR_PTR(-ENOSPC);

	if (start > maxindex) {
		int error = radix_tree_extend(root, gfp, start, shift);
		if (error < 0)
			return ERR_PTR(error);
		shift = error;
		child = rcu_dereference_raw(root->xa_head);
	}
	if (start == 0 && shift == 0)
		shift = RADIX_TREE_MAP_SHIFT;

	while (shift) {
		shift -= RADIX_TREE_MAP_SHIFT;
		if (child == NULL) {
			/* Have to add a child node.  */
			child = radix_tree_node_alloc(gfp, node, root, shift,
							offset, 0, 0);
			if (!child)
				return ERR_PTR(-ENOMEM);
			all_tag_set(child, IDR_FREE);
			rcu_assign_pointer(*slot, node_to_entry(child));
			if (node)
				node->count++;
		} else if (!radix_tree_is_internal_node(child))
			break;

		node = entry_to_node(child);
		offset = radix_tree_descend(node, &child, start);
		if (!tag_get(node, IDR_FREE, offset)) {
			offset = radix_tree_find_next_bit(node, IDR_FREE,
							offset + 1);
			start = next_index(start, node, offset);
			if (start > max || start == 0)
				return ERR_PTR(-ENOSPC);
			while (offset == RADIX_TREE_MAP_SIZE) {
				offset = node->offset + 1;
				node = node->parent;
				if (!node)
					goto grow;
				shift = node->shift;
			}
			child = rcu_dereference_raw(node->slots[offset]);
		}
		slot = &node->slots[offset];
	}

	iter->index = start;
	if (node)
		iter->next_index = 1 + min(max, (start | node_maxindex(node)));
	else
		iter->next_index = 1;
	iter->node = node;
	set_iter_tags(iter, node, offset, IDR_FREE);

	return slot;
}

/**
 * idr_destroy - release all internal memory from an IDR
 * @idr: idr handle
 *
 * After this function is called, the IDR is empty, and may be reused or
 * the data structure containing it may be freed.
 *
 * A typical clean-up sequence for objects stored in an idr tree will use
 * idr_for_each() to free all objects, if necessary, then idr_destroy() to
 * free the memory used to keep track of those objects.
 */
void idr_destroy(struct idr *idr)
{
	struct radix_tree_node *node = rcu_dereference_raw(idr->idr_rt.xa_head);
	if (radix_tree_is_internal_node(node))
		radix_tree_free_nodes(node);
	idr->idr_rt.xa_head = NULL;
	root_tag_set(&idr->idr_rt, IDR_FREE);
}
EXPORT_SYMBOL(idr_destroy);

static void
radix_tree_node_ctor(void *arg)
{
	struct radix_tree_node *node = arg;

	memset(node, 0, sizeof(*node));
	INIT_LIST_HEAD(&node->private_list);
}

static int radix_tree_cpu_dead(unsigned int cpu)
{
	struct radix_tree_preload *rtp;
	struct radix_tree_node *node;

	/* Free per-cpu pool of preloaded nodes */
	rtp = &per_cpu(radix_tree_preloads, cpu);
	while (rtp->nr) {
		node = rtp->nodes;
		rtp->nodes = node->parent;
		kmem_cache_free(radix_tree_node_cachep, node);
		rtp->nr--;
	}
	return 0;
}

void __init radix_tree_init(void)
{
	int ret;

	BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32);
	BUILD_BUG_ON(ROOT_IS_IDR & ~GFP_ZONEMASK);
	BUILD_BUG_ON(XA_CHUNK_SIZE > 255);
	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
			sizeof(struct radix_tree_node), 0,
			SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
			radix_tree_node_ctor);
	ret = cpuhp_setup_state_nocalls(CPUHP_RADIX_DEAD, "lib/radix:dead",
					NULL, radix_tree_cpu_dead);
	WARN_ON(ret < 0);
}