summaryrefslogtreecommitdiff
path: root/fs/bcachefs/backpointers.c
blob: 4321f9fb73bd9f7e098b663e20f516b0c505f6d4 (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
// SPDX-License-Identifier: GPL-2.0
#include "bcachefs.h"
#include "bbpos.h"
#include "alloc_background.h"
#include "backpointers.h"
#include "bkey_buf.h"
#include "btree_cache.h"
#include "btree_update.h"
#include "btree_update_interior.h"
#include "btree_write_buffer.h"
#include "checksum.h"
#include "error.h"

#include <linux/mm.h>

static bool extent_matches_bp(struct bch_fs *c,
			      enum btree_id btree_id, unsigned level,
			      struct bkey_s_c k,
			      struct bpos bucket,
			      struct bch_backpointer bp)
{
	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
	const union bch_extent_entry *entry;
	struct extent_ptr_decoded p;

	rcu_read_lock();
	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
		struct bpos bucket2;
		struct bch_backpointer bp2;

		if (p.ptr.cached)
			continue;

		struct bch_dev *ca = bch2_dev_rcu(c, p.ptr.dev);
		if (!ca)
			continue;

		bch2_extent_ptr_to_bp(c, ca, btree_id, level, k, p, entry, &bucket2, &bp2);
		if (bpos_eq(bucket, bucket2) &&
		    !memcmp(&bp, &bp2, sizeof(bp))) {
			rcu_read_unlock();
			return true;
		}
	}
	rcu_read_unlock();

	return false;
}

int bch2_backpointer_invalid(struct bch_fs *c, struct bkey_s_c k,
			     enum bch_validate_flags flags,
			     struct printbuf *err)
{
	struct bkey_s_c_backpointer bp = bkey_s_c_to_backpointer(k);

	rcu_read_lock();
	struct bch_dev *ca = bch2_dev_rcu(c, bp.k->p.inode);
	if (!ca) {
		/* these will be caught by fsck */
		rcu_read_unlock();
		return 0;
	}

	struct bpos bucket = bp_pos_to_bucket(ca, bp.k->p);
	struct bpos bp_pos = bucket_pos_to_bp_noerror(ca, bucket, bp.v->bucket_offset);
	rcu_read_unlock();
	int ret = 0;

	bkey_fsck_err_on((bp.v->bucket_offset >> MAX_EXTENT_COMPRESS_RATIO_SHIFT) >= ca->mi.bucket_size ||
			 !bpos_eq(bp.k->p, bp_pos),
			 c, err,
			 backpointer_bucket_offset_wrong,
			 "backpointer bucket_offset wrong");
fsck_err:
	return ret;
}

void bch2_backpointer_to_text(struct printbuf *out, const struct bch_backpointer *bp)
{
	prt_printf(out, "btree=%s l=%u offset=%llu:%u len=%u pos=",
	       bch2_btree_id_str(bp->btree_id),
	       bp->level,
	       (u64) (bp->bucket_offset >> MAX_EXTENT_COMPRESS_RATIO_SHIFT),
	       (u32) bp->bucket_offset & ~(~0U << MAX_EXTENT_COMPRESS_RATIO_SHIFT),
	       bp->bucket_len);
	bch2_bpos_to_text(out, bp->pos);
}

void bch2_backpointer_k_to_text(struct printbuf *out, struct bch_fs *c, struct bkey_s_c k)
{
	rcu_read_lock();
	struct bch_dev *ca = bch2_dev_rcu(c, k.k->p.inode);
	if (ca) {
		struct bpos bucket = bp_pos_to_bucket(ca, k.k->p);
		rcu_read_unlock();
		prt_str(out, "bucket=");
		bch2_bpos_to_text(out, bucket);
		prt_str(out, " ");
	} else {
		rcu_read_unlock();
	}

	bch2_backpointer_to_text(out, bkey_s_c_to_backpointer(k).v);
}

void bch2_backpointer_swab(struct bkey_s k)
{
	struct bkey_s_backpointer bp = bkey_s_to_backpointer(k);

	bp.v->bucket_offset	= swab40(bp.v->bucket_offset);
	bp.v->bucket_len	= swab32(bp.v->bucket_len);
	bch2_bpos_swab(&bp.v->pos);
}

static noinline int backpointer_mod_err(struct btree_trans *trans,
					struct bch_backpointer bp,
					struct bkey_s_c bp_k,
					struct bkey_s_c orig_k,
					bool insert)
{
	struct bch_fs *c = trans->c;
	struct printbuf buf = PRINTBUF;

	if (insert) {
		prt_printf(&buf, "existing backpointer found when inserting ");
		bch2_backpointer_to_text(&buf, &bp);
		prt_newline(&buf);
		printbuf_indent_add(&buf, 2);

		prt_printf(&buf, "found ");
		bch2_bkey_val_to_text(&buf, c, bp_k);
		prt_newline(&buf);

		prt_printf(&buf, "for ");
		bch2_bkey_val_to_text(&buf, c, orig_k);

		bch_err(c, "%s", buf.buf);
	} else if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
		prt_printf(&buf, "backpointer not found when deleting\n");
		printbuf_indent_add(&buf, 2);

		prt_printf(&buf, "searching for ");
		bch2_backpointer_to_text(&buf, &bp);
		prt_newline(&buf);

		prt_printf(&buf, "got ");
		bch2_bkey_val_to_text(&buf, c, bp_k);
		prt_newline(&buf);

		prt_printf(&buf, "for ");
		bch2_bkey_val_to_text(&buf, c, orig_k);

		bch_err(c, "%s", buf.buf);
	}

	printbuf_exit(&buf);

	if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
		return bch2_inconsistent_error(c) ? BCH_ERR_erofs_unfixed_errors : 0;
	} else {
		return 0;
	}
}

int bch2_bucket_backpointer_mod_nowritebuffer(struct btree_trans *trans,
				struct bch_dev *ca,
				struct bpos bucket,
				struct bch_backpointer bp,
				struct bkey_s_c orig_k,
				bool insert)
{
	struct btree_iter bp_iter;
	struct bkey_s_c k;
	struct bkey_i_backpointer *bp_k;
	int ret;

	bp_k = bch2_trans_kmalloc_nomemzero(trans, sizeof(struct bkey_i_backpointer));
	ret = PTR_ERR_OR_ZERO(bp_k);
	if (ret)
		return ret;

	bkey_backpointer_init(&bp_k->k_i);
	bp_k->k.p = bucket_pos_to_bp(ca, bucket, bp.bucket_offset);
	bp_k->v = bp;

	if (!insert) {
		bp_k->k.type = KEY_TYPE_deleted;
		set_bkey_val_u64s(&bp_k->k, 0);
	}

	k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
			       bp_k->k.p,
			       BTREE_ITER_intent|
			       BTREE_ITER_slots|
			       BTREE_ITER_with_updates);
	ret = bkey_err(k);
	if (ret)
		goto err;

	if (insert
	    ? k.k->type
	    : (k.k->type != KEY_TYPE_backpointer ||
	       memcmp(bkey_s_c_to_backpointer(k).v, &bp, sizeof(bp)))) {
		ret = backpointer_mod_err(trans, bp, k, orig_k, insert);
		if (ret)
			goto err;
	}

	ret = bch2_trans_update(trans, &bp_iter, &bp_k->k_i, 0);
err:
	bch2_trans_iter_exit(trans, &bp_iter);
	return ret;
}

/*
 * Find the next backpointer >= *bp_offset:
 */
int bch2_get_next_backpointer(struct btree_trans *trans,
			      struct bch_dev *ca,
			      struct bpos bucket, int gen,
			      struct bpos *bp_pos,
			      struct bch_backpointer *bp,
			      unsigned iter_flags)
{
	struct bpos bp_end_pos = bucket_pos_to_bp(ca, bpos_nosnap_successor(bucket), 0);
	struct btree_iter alloc_iter = { NULL }, bp_iter = { NULL };
	struct bkey_s_c k;
	int ret = 0;

	if (bpos_ge(*bp_pos, bp_end_pos))
		goto done;

	if (gen >= 0) {
		k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
				       bucket, BTREE_ITER_cached|iter_flags);
		ret = bkey_err(k);
		if (ret)
			goto out;

		if (k.k->type != KEY_TYPE_alloc_v4 ||
		    bkey_s_c_to_alloc_v4(k).v->gen != gen)
			goto done;
	}

	*bp_pos = bpos_max(*bp_pos, bucket_pos_to_bp(ca, bucket, 0));

	for_each_btree_key_norestart(trans, bp_iter, BTREE_ID_backpointers,
				     *bp_pos, iter_flags, k, ret) {
		if (bpos_ge(k.k->p, bp_end_pos))
			break;

		*bp_pos = k.k->p;
		*bp = *bkey_s_c_to_backpointer(k).v;
		goto out;
	}
done:
	*bp_pos = SPOS_MAX;
out:
	bch2_trans_iter_exit(trans, &bp_iter);
	bch2_trans_iter_exit(trans, &alloc_iter);
	return ret;
}

static void backpointer_not_found(struct btree_trans *trans,
				  struct bpos bp_pos,
				  struct bch_backpointer bp,
				  struct bkey_s_c k)
{
	struct bch_fs *c = trans->c;
	struct printbuf buf = PRINTBUF;

	/*
	 * If we're using the btree write buffer, the backpointer we were
	 * looking at may have already been deleted - failure to find what it
	 * pointed to is not an error:
	 */
	if (likely(!bch2_backpointers_no_use_write_buffer))
		return;

	struct bpos bucket;
	if (!bp_pos_to_bucket_nodev(c, bp_pos, &bucket))
		return;

	prt_printf(&buf, "backpointer doesn't match %s it points to:\n  ",
		   bp.level ? "btree node" : "extent");
	prt_printf(&buf, "bucket: ");
	bch2_bpos_to_text(&buf, bucket);
	prt_printf(&buf, "\n  ");

	prt_printf(&buf, "backpointer pos: ");
	bch2_bpos_to_text(&buf, bp_pos);
	prt_printf(&buf, "\n  ");

	bch2_backpointer_to_text(&buf, &bp);
	prt_printf(&buf, "\n  ");
	bch2_bkey_val_to_text(&buf, c, k);
	if (c->curr_recovery_pass >= BCH_RECOVERY_PASS_check_extents_to_backpointers)
		bch_err_ratelimited(c, "%s", buf.buf);
	else
		bch2_trans_inconsistent(trans, "%s", buf.buf);

	printbuf_exit(&buf);
}

struct bkey_s_c bch2_backpointer_get_key(struct btree_trans *trans,
					 struct btree_iter *iter,
					 struct bpos bp_pos,
					 struct bch_backpointer bp,
					 unsigned iter_flags)
{
	if (likely(!bp.level)) {
		struct bch_fs *c = trans->c;

		struct bpos bucket;
		if (!bp_pos_to_bucket_nodev(c, bp_pos, &bucket))
			return bkey_s_c_err(-EIO);

		bch2_trans_node_iter_init(trans, iter,
					  bp.btree_id,
					  bp.pos,
					  0, 0,
					  iter_flags);
		struct bkey_s_c k = bch2_btree_iter_peek_slot(iter);
		if (bkey_err(k)) {
			bch2_trans_iter_exit(trans, iter);
			return k;
		}

		if (k.k && extent_matches_bp(c, bp.btree_id, bp.level, k, bucket, bp))
			return k;

		bch2_trans_iter_exit(trans, iter);
		backpointer_not_found(trans, bp_pos, bp, k);
		return bkey_s_c_null;
	} else {
		struct btree *b = bch2_backpointer_get_node(trans, iter, bp_pos, bp);

		if (IS_ERR_OR_NULL(b)) {
			bch2_trans_iter_exit(trans, iter);
			return IS_ERR(b) ? bkey_s_c_err(PTR_ERR(b)) : bkey_s_c_null;
		}
		return bkey_i_to_s_c(&b->key);
	}
}

struct btree *bch2_backpointer_get_node(struct btree_trans *trans,
					struct btree_iter *iter,
					struct bpos bp_pos,
					struct bch_backpointer bp)
{
	struct bch_fs *c = trans->c;

	BUG_ON(!bp.level);

	struct bpos bucket;
	if (!bp_pos_to_bucket_nodev(c, bp_pos, &bucket))
		return ERR_PTR(-EIO);

	bch2_trans_node_iter_init(trans, iter,
				  bp.btree_id,
				  bp.pos,
				  0,
				  bp.level - 1,
				  0);
	struct btree *b = bch2_btree_iter_peek_node(iter);
	if (IS_ERR_OR_NULL(b))
		goto err;

	BUG_ON(b->c.level != bp.level - 1);

	if (extent_matches_bp(c, bp.btree_id, bp.level,
			      bkey_i_to_s_c(&b->key),
			      bucket, bp))
		return b;

	if (btree_node_will_make_reachable(b)) {
		b = ERR_PTR(-BCH_ERR_backpointer_to_overwritten_btree_node);
	} else {
		backpointer_not_found(trans, bp_pos, bp, bkey_i_to_s_c(&b->key));
		b = NULL;
	}
err:
	bch2_trans_iter_exit(trans, iter);
	return b;
}

static int bch2_check_btree_backpointer(struct btree_trans *trans, struct btree_iter *bp_iter,
					struct bkey_s_c k)
{
	struct bch_fs *c = trans->c;
	struct btree_iter alloc_iter = { NULL };
	struct bkey_s_c alloc_k;
	struct printbuf buf = PRINTBUF;
	int ret = 0;

	struct bpos bucket;
	if (!bp_pos_to_bucket_nodev_noerror(c, k.k->p, &bucket)) {
		if (fsck_err(c, backpointer_to_missing_device,
			     "backpointer for missing device:\n%s",
			     (bch2_bkey_val_to_text(&buf, c, k), buf.buf)))
			ret = bch2_btree_delete_at(trans, bp_iter, 0);
		goto out;
	}

	alloc_k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc, bucket, 0);
	ret = bkey_err(alloc_k);
	if (ret)
		goto out;

	if (fsck_err_on(alloc_k.k->type != KEY_TYPE_alloc_v4, c,
			backpointer_to_missing_alloc,
			"backpointer for nonexistent alloc key: %llu:%llu:0\n%s",
			alloc_iter.pos.inode, alloc_iter.pos.offset,
			(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
		ret = bch2_btree_delete_at(trans, bp_iter, 0);
		goto out;
	}
out:
fsck_err:
	bch2_trans_iter_exit(trans, &alloc_iter);
	printbuf_exit(&buf);
	return ret;
}

/* verify that every backpointer has a corresponding alloc key */
int bch2_check_btree_backpointers(struct bch_fs *c)
{
	int ret = bch2_trans_run(c,
		for_each_btree_key_commit(trans, iter,
			BTREE_ID_backpointers, POS_MIN, 0, k,
			NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
		  bch2_check_btree_backpointer(trans, &iter, k)));
	bch_err_fn(c, ret);
	return ret;
}

static inline bool bkey_and_val_eq(struct bkey_s_c l, struct bkey_s_c r)
{
	return bpos_eq(l.k->p, r.k->p) &&
		bkey_bytes(l.k) == bkey_bytes(r.k) &&
		!memcmp(l.v, r.v, bkey_val_bytes(l.k));
}

struct extents_to_bp_state {
	struct bpos	bucket_start;
	struct bpos	bucket_end;
	struct bkey_buf last_flushed;
};

static int drop_dev_and_update(struct btree_trans *trans, enum btree_id btree,
			       struct bkey_s_c extent, unsigned dev)
{
	struct bkey_i *n = bch2_bkey_make_mut_noupdate(trans, extent);
	int ret = PTR_ERR_OR_ZERO(n);
	if (ret)
		return ret;

	bch2_bkey_drop_device(bkey_i_to_s(n), dev);
	return bch2_btree_insert_trans(trans, btree, n, 0);
}

static int check_extent_checksum(struct btree_trans *trans,
				 enum btree_id btree, struct bkey_s_c extent,
				 enum btree_id o_btree, struct bkey_s_c extent2, unsigned dev)
{
	struct bch_fs *c = trans->c;
	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(extent);
	const union bch_extent_entry *entry;
	struct extent_ptr_decoded p;
	struct printbuf buf = PRINTBUF;
	void *data_buf = NULL;
	struct bio *bio = NULL;
	size_t bytes;
	int ret = 0;

	if (bkey_is_btree_ptr(extent.k))
		return false;

	bkey_for_each_ptr_decode(extent.k, ptrs, p, entry)
		if (p.ptr.dev == dev)
			goto found;
	BUG();
found:
	if (!p.crc.csum_type)
		return false;

	bytes = p.crc.compressed_size << 9;

	struct bch_dev *ca = bch2_dev_get_ioref(c, dev, READ);
	if (!ca)
		return false;

	data_buf = kvmalloc(bytes, GFP_KERNEL);
	if (!data_buf) {
		ret = -ENOMEM;
		goto err;
	}

	bio = bio_alloc(ca->disk_sb.bdev, buf_pages(data_buf, bytes), REQ_OP_READ, GFP_KERNEL);
	bio->bi_iter.bi_sector = p.ptr.offset;
	bch2_bio_map(bio, data_buf, bytes);
	ret = submit_bio_wait(bio);
	if (ret)
		goto err;

	prt_str(&buf, "extents pointing to same space, but first extent checksum bad:");
	prt_printf(&buf, "\n  %s ", bch2_btree_id_str(btree));
	bch2_bkey_val_to_text(&buf, c, extent);
	prt_printf(&buf, "\n  %s ", bch2_btree_id_str(o_btree));
	bch2_bkey_val_to_text(&buf, c, extent2);

	struct nonce nonce = extent_nonce(extent.k->version, p.crc);
	struct bch_csum csum = bch2_checksum(c, p.crc.csum_type, nonce, data_buf, bytes);
	if (fsck_err_on(bch2_crc_cmp(csum, p.crc.csum),
			c, dup_backpointer_to_bad_csum_extent,
			"%s", buf.buf))
		ret = drop_dev_and_update(trans, btree, extent, dev) ?: 1;
fsck_err:
err:
	if (bio)
		bio_put(bio);
	kvfree(data_buf);
	percpu_ref_put(&ca->io_ref);
	printbuf_exit(&buf);
	return ret;
}

static int check_bp_exists(struct btree_trans *trans,
			   struct extents_to_bp_state *s,
			   struct bpos bucket,
			   struct bch_backpointer bp,
			   struct bkey_s_c orig_k)
{
	struct bch_fs *c = trans->c;
	struct btree_iter bp_iter = {};
	struct btree_iter other_extent_iter = {};
	struct printbuf buf = PRINTBUF;
	struct bkey_s_c bp_k;
	struct bkey_buf tmp;
	int ret = 0;

	bch2_bkey_buf_init(&tmp);

	struct bch_dev *ca = bch2_dev_bucket_tryget(c, bucket);
	if (!ca) {
		prt_str(&buf, "extent for nonexistent device:bucket ");
		bch2_bpos_to_text(&buf, bucket);
		prt_str(&buf, "\n  ");
		bch2_bkey_val_to_text(&buf, c, orig_k);
		bch_err(c, "%s", buf.buf);
		ret = -BCH_ERR_fsck_repair_unimplemented;
		goto err;
	}

	if (bpos_lt(bucket, s->bucket_start) ||
	    bpos_gt(bucket, s->bucket_end))
		goto out;

	bp_k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
				  bucket_pos_to_bp(ca, bucket, bp.bucket_offset),
				  0);
	ret = bkey_err(bp_k);
	if (ret)
		goto err;

	if (bp_k.k->type != KEY_TYPE_backpointer ||
	    memcmp(bkey_s_c_to_backpointer(bp_k).v, &bp, sizeof(bp))) {
		bch2_bkey_buf_reassemble(&tmp, c, orig_k);

		if (!bkey_and_val_eq(orig_k, bkey_i_to_s_c(s->last_flushed.k))) {
			if (bp.level) {
				bch2_trans_unlock(trans);
				bch2_btree_interior_updates_flush(c);
			}

			ret = bch2_btree_write_buffer_flush_sync(trans);
			if (ret)
				goto err;

			bch2_bkey_buf_copy(&s->last_flushed, c, tmp.k);
			ret = -BCH_ERR_transaction_restart_write_buffer_flush;
			goto out;
		}

		goto check_existing_bp;
	}
out:
err:
fsck_err:
	bch2_trans_iter_exit(trans, &other_extent_iter);
	bch2_trans_iter_exit(trans, &bp_iter);
	bch2_bkey_buf_exit(&tmp, c);
	bch2_dev_put(ca);
	printbuf_exit(&buf);
	return ret;
check_existing_bp:
	/* Do we have a backpointer for a different extent? */
	if (bp_k.k->type != KEY_TYPE_backpointer)
		goto missing;

	struct bch_backpointer other_bp = *bkey_s_c_to_backpointer(bp_k).v;

	struct bkey_s_c other_extent =
		bch2_backpointer_get_key(trans, &other_extent_iter, bp_k.k->p, other_bp, 0);
	ret = bkey_err(other_extent);
	if (ret == -BCH_ERR_backpointer_to_overwritten_btree_node)
		ret = 0;
	if (ret)
		goto err;

	if (!other_extent.k)
		goto missing;

	if (bch2_extents_match(orig_k, other_extent)) {
		printbuf_reset(&buf);
		prt_printf(&buf, "duplicate versions of same extent, deleting smaller\n  ");
		bch2_bkey_val_to_text(&buf, c, orig_k);
		prt_str(&buf, "\n  ");
		bch2_bkey_val_to_text(&buf, c, other_extent);
		bch_err(c, "%s", buf.buf);

		if (other_extent.k->size <= orig_k.k->size) {
			ret = drop_dev_and_update(trans, other_bp.btree_id, other_extent, bucket.inode);
			if (ret)
				goto err;
			goto out;
		} else {
			ret = drop_dev_and_update(trans, bp.btree_id, orig_k, bucket.inode);
			if (ret)
				goto err;
			goto missing;
		}
	}

	ret = check_extent_checksum(trans, other_bp.btree_id, other_extent, bp.btree_id, orig_k, bucket.inode);
	if (ret < 0)
		goto err;
	if (ret) {
		ret = 0;
		goto missing;
	}

	ret = check_extent_checksum(trans, bp.btree_id, orig_k, other_bp.btree_id, other_extent, bucket.inode);
	if (ret < 0)
		goto err;
	if (ret) {
		ret = 0;
		goto out;
	}

	printbuf_reset(&buf);
	prt_printf(&buf, "duplicate extents pointing to same space on dev %llu\n  ", bucket.inode);
	bch2_bkey_val_to_text(&buf, c, orig_k);
	prt_str(&buf, "\n  ");
	bch2_bkey_val_to_text(&buf, c, other_extent);
	bch_err(c, "%s", buf.buf);
	ret = -BCH_ERR_fsck_repair_unimplemented;
	goto err;
missing:
	printbuf_reset(&buf);
	prt_printf(&buf, "missing backpointer for btree=%s l=%u ",
	       bch2_btree_id_str(bp.btree_id), bp.level);
	bch2_bkey_val_to_text(&buf, c, orig_k);
	prt_printf(&buf, "\n  got:   ");
	bch2_bkey_val_to_text(&buf, c, bp_k);

	struct bkey_i_backpointer n_bp_k;
	bkey_backpointer_init(&n_bp_k.k_i);
	n_bp_k.k.p = bucket_pos_to_bp(ca, bucket, bp.bucket_offset);
	n_bp_k.v = bp;
	prt_printf(&buf, "\n  want:  ");
	bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&n_bp_k.k_i));

	if (fsck_err(c, ptr_to_missing_backpointer, "%s", buf.buf))
		ret = bch2_bucket_backpointer_mod(trans, ca, bucket, bp, orig_k, true);

	goto out;
}

static int check_extent_to_backpointers(struct btree_trans *trans,
					struct extents_to_bp_state *s,
					enum btree_id btree, unsigned level,
					struct bkey_s_c k)
{
	struct bch_fs *c = trans->c;
	struct bkey_ptrs_c ptrs;
	const union bch_extent_entry *entry;
	struct extent_ptr_decoded p;
	int ret;

	ptrs = bch2_bkey_ptrs_c(k);
	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
		struct bpos bucket_pos = POS_MIN;
		struct bch_backpointer bp;

		if (p.ptr.cached)
			continue;

		rcu_read_lock();
		struct bch_dev *ca = bch2_dev_rcu(c, p.ptr.dev);
		if (ca)
			bch2_extent_ptr_to_bp(c, ca, btree, level, k, p, entry, &bucket_pos, &bp);
		rcu_read_unlock();

		if (!ca)
			continue;

		ret = check_bp_exists(trans, s, bucket_pos, bp, k);
		if (ret)
			return ret;
	}

	return 0;
}

static int check_btree_root_to_backpointers(struct btree_trans *trans,
					    struct extents_to_bp_state *s,
					    enum btree_id btree_id,
					    int *level)
{
	struct bch_fs *c = trans->c;
	struct btree_iter iter;
	struct btree *b;
	struct bkey_s_c k;
	int ret;
retry:
	bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN,
				  0, bch2_btree_id_root(c, btree_id)->b->c.level, 0);
	b = bch2_btree_iter_peek_node(&iter);
	ret = PTR_ERR_OR_ZERO(b);
	if (ret)
		goto err;

	if (b != btree_node_root(c, b)) {
		bch2_trans_iter_exit(trans, &iter);
		goto retry;
	}

	*level = b->c.level;

	k = bkey_i_to_s_c(&b->key);
	ret = check_extent_to_backpointers(trans, s, btree_id, b->c.level + 1, k);
err:
	bch2_trans_iter_exit(trans, &iter);
	return ret;
}

static inline struct bbpos bp_to_bbpos(struct bch_backpointer bp)
{
	return (struct bbpos) {
		.btree	= bp.btree_id,
		.pos	= bp.pos,
	};
}

static u64 mem_may_pin_bytes(struct bch_fs *c)
{
	struct sysinfo i;
	si_meminfo(&i);

	u64 mem_bytes = i.totalram * i.mem_unit;
	return div_u64(mem_bytes * c->opts.fsck_memory_usage_percent, 100);
}

static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
{
	return div_u64(mem_may_pin_bytes(c), c->opts.btree_node_size);
}

static int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
					u64 btree_leaf_mask,
					u64 btree_interior_mask,
					struct bbpos start, struct bbpos *end)
{
	struct bch_fs *c = trans->c;
	s64 mem_may_pin = mem_may_pin_bytes(c);
	int ret = 0;

	btree_interior_mask |= btree_leaf_mask;

	c->btree_cache.pinned_nodes_leaf_mask		= btree_leaf_mask;
	c->btree_cache.pinned_nodes_interior_mask	= btree_interior_mask;
	c->btree_cache.pinned_nodes_start		= start;
	c->btree_cache.pinned_nodes_end			= *end = BBPOS_MAX;

	for (enum btree_id btree = start.btree;
	     btree < BTREE_ID_NR && !ret;
	     btree++) {
		unsigned depth = ((1U << btree) & btree_leaf_mask) ? 0 : 1;
		struct btree_iter iter;
		struct btree *b;

		if (!((1U << btree) & btree_leaf_mask) &&
		    !((1U << btree) & btree_interior_mask))
			continue;

		__for_each_btree_node(trans, iter, btree,
				      btree == start.btree ? start.pos : POS_MIN,
				      0, depth, BTREE_ITER_prefetch, b, ret) {
			mem_may_pin -= btree_buf_bytes(b);
			if (mem_may_pin <= 0) {
				c->btree_cache.pinned_nodes_end = *end =
					BBPOS(btree, b->key.k.p);
				bch2_trans_iter_exit(trans, &iter);
				return 0;
			}
		}
		bch2_trans_iter_exit(trans, &iter);
	}

	return ret;
}

static int bch2_check_extents_to_backpointers_pass(struct btree_trans *trans,
						   struct extents_to_bp_state *s)
{
	struct bch_fs *c = trans->c;
	int ret = 0;

	for (enum btree_id btree_id = 0;
	     btree_id < btree_id_nr_alive(c);
	     btree_id++) {
		int level, depth = btree_type_has_ptrs(btree_id) ? 0 : 1;

		ret = commit_do(trans, NULL, NULL,
				BCH_TRANS_COMMIT_no_enospc,
				check_btree_root_to_backpointers(trans, s, btree_id, &level));
		if (ret)
			return ret;

		while (level >= depth) {
			struct btree_iter iter;
			bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0, level,
						  BTREE_ITER_prefetch);

			ret = for_each_btree_key_continue(trans, iter, 0, k, ({
				check_extent_to_backpointers(trans, s, btree_id, level, k) ?:
				bch2_trans_commit(trans, NULL, NULL, BCH_TRANS_COMMIT_no_enospc);
			}));
			if (ret)
				return ret;

			--level;
		}
	}

	return 0;
}

int bch2_check_extents_to_backpointers(struct bch_fs *c)
{
	struct btree_trans *trans = bch2_trans_get(c);
	struct extents_to_bp_state s = { .bucket_start = POS_MIN };
	int ret;

	bch2_bkey_buf_init(&s.last_flushed);
	bkey_init(&s.last_flushed.k->k);

	while (1) {
		struct bbpos end;
		ret = bch2_get_btree_in_memory_pos(trans,
				BIT_ULL(BTREE_ID_backpointers),
				BIT_ULL(BTREE_ID_backpointers),
				BBPOS(BTREE_ID_backpointers, s.bucket_start), &end);
		if (ret)
			break;

		s.bucket_end = end.pos;

		if ( bpos_eq(s.bucket_start, POS_MIN) &&
		    !bpos_eq(s.bucket_end, SPOS_MAX))
			bch_verbose(c, "%s(): alloc info does not fit in ram, running in multiple passes with %zu nodes per pass",
				    __func__, btree_nodes_fit_in_ram(c));

		if (!bpos_eq(s.bucket_start, POS_MIN) ||
		    !bpos_eq(s.bucket_end, SPOS_MAX)) {
			struct printbuf buf = PRINTBUF;

			prt_str(&buf, "check_extents_to_backpointers(): ");
			bch2_bpos_to_text(&buf, s.bucket_start);
			prt_str(&buf, "-");
			bch2_bpos_to_text(&buf, s.bucket_end);

			bch_verbose(c, "%s", buf.buf);
			printbuf_exit(&buf);
		}

		ret = bch2_check_extents_to_backpointers_pass(trans, &s);
		if (ret || bpos_eq(s.bucket_end, SPOS_MAX))
			break;

		s.bucket_start = bpos_successor(s.bucket_end);
	}
	bch2_trans_put(trans);
	bch2_bkey_buf_exit(&s.last_flushed, c);

	c->btree_cache.pinned_nodes_leaf_mask = 0;
	c->btree_cache.pinned_nodes_interior_mask = 0;

	bch_err_fn(c, ret);
	return ret;
}

static int check_one_backpointer(struct btree_trans *trans,
				 struct bbpos start,
				 struct bbpos end,
				 struct bkey_s_c_backpointer bp,
				 struct bpos *last_flushed_pos)
{
	struct bch_fs *c = trans->c;
	struct btree_iter iter;
	struct bbpos pos = bp_to_bbpos(*bp.v);
	struct bkey_s_c k;
	struct printbuf buf = PRINTBUF;
	int ret;

	if (bbpos_cmp(pos, start) < 0 ||
	    bbpos_cmp(pos, end) > 0)
		return 0;

	k = bch2_backpointer_get_key(trans, &iter, bp.k->p, *bp.v, 0);
	ret = bkey_err(k);
	if (ret == -BCH_ERR_backpointer_to_overwritten_btree_node)
		return 0;
	if (ret)
		return ret;

	if (!k.k && !bpos_eq(*last_flushed_pos, bp.k->p)) {
		*last_flushed_pos = bp.k->p;
		ret = bch2_btree_write_buffer_flush_sync(trans) ?:
			-BCH_ERR_transaction_restart_write_buffer_flush;
		goto out;
	}

	if (fsck_err_on(!k.k, c,
			backpointer_to_missing_ptr,
			"backpointer for missing %s\n  %s",
			bp.v->level ? "btree node" : "extent",
			(bch2_bkey_val_to_text(&buf, c, bp.s_c), buf.buf))) {
		ret = bch2_btree_delete_at_buffered(trans, BTREE_ID_backpointers, bp.k->p);
		goto out;
	}
out:
fsck_err:
	bch2_trans_iter_exit(trans, &iter);
	printbuf_exit(&buf);
	return ret;
}

static int bch2_check_backpointers_to_extents_pass(struct btree_trans *trans,
						   struct bbpos start,
						   struct bbpos end)
{
	struct bpos last_flushed_pos = SPOS_MAX;

	return for_each_btree_key_commit(trans, iter, BTREE_ID_backpointers,
				  POS_MIN, BTREE_ITER_prefetch, k,
				  NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
		check_one_backpointer(trans, start, end,
				      bkey_s_c_to_backpointer(k),
				      &last_flushed_pos));
}

int bch2_check_backpointers_to_extents(struct bch_fs *c)
{
	struct btree_trans *trans = bch2_trans_get(c);
	struct bbpos start = (struct bbpos) { .btree = 0, .pos = POS_MIN, }, end;
	int ret;

	while (1) {
		ret = bch2_get_btree_in_memory_pos(trans,
						   (1U << BTREE_ID_extents)|
						   (1U << BTREE_ID_reflink),
						   ~0,
						   start, &end);
		if (ret)
			break;

		if (!bbpos_cmp(start, BBPOS_MIN) &&
		    bbpos_cmp(end, BBPOS_MAX))
			bch_verbose(c, "%s(): extents do not fit in ram, running in multiple passes with %zu nodes per pass",
				    __func__, btree_nodes_fit_in_ram(c));

		if (bbpos_cmp(start, BBPOS_MIN) ||
		    bbpos_cmp(end, BBPOS_MAX)) {
			struct printbuf buf = PRINTBUF;

			prt_str(&buf, "check_backpointers_to_extents(): ");
			bch2_bbpos_to_text(&buf, start);
			prt_str(&buf, "-");
			bch2_bbpos_to_text(&buf, end);

			bch_verbose(c, "%s", buf.buf);
			printbuf_exit(&buf);
		}

		ret = bch2_check_backpointers_to_extents_pass(trans, start, end);
		if (ret || !bbpos_cmp(end, BBPOS_MAX))
			break;

		start = bbpos_successor(end);
	}
	bch2_trans_put(trans);

	c->btree_cache.pinned_nodes_leaf_mask = 0;
	c->btree_cache.pinned_nodes_interior_mask = 0;

	bch_err_fn(c, ret);
	return ret;
}