summaryrefslogtreecommitdiffstats
path: root/fs/bcachefs/btree_locking.c
blob: b9b151e693ed60ecc3dc9147cc34902643cfc7aa (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
// SPDX-License-Identifier: GPL-2.0

#include "bcachefs.h"
#include "btree_locking.h"
#include "btree_types.h"

static struct lock_class_key bch2_btree_node_lock_key;

void bch2_btree_lock_init(struct btree_bkey_cached_common *b,
			  enum six_lock_init_flags flags)
{
	__six_lock_init(&b->lock, "b->c.lock", &bch2_btree_node_lock_key, flags);
	lockdep_set_novalidate_class(&b->lock);
}

#ifdef CONFIG_LOCKDEP
void bch2_assert_btree_nodes_not_locked(void)
{
#if 0
	//Re-enable when lock_class_is_held() is merged:
	BUG_ON(lock_class_is_held(&bch2_btree_node_lock_key));
#endif
}
#endif

/* Btree node locking: */

struct six_lock_count bch2_btree_node_lock_counts(struct btree_trans *trans,
						  struct btree_path *skip,
						  struct btree_bkey_cached_common *b,
						  unsigned level)
{
	struct btree_path *path;
	struct six_lock_count ret;
	unsigned i;

	memset(&ret, 0, sizeof(ret));

	if (IS_ERR_OR_NULL(b))
		return ret;

	trans_for_each_path(trans, path, i)
		if (path != skip && &path->l[level].b->c == b) {
			int t = btree_node_locked_type(path, level);

			if (t != BTREE_NODE_UNLOCKED)
				ret.n[t]++;
		}

	return ret;
}

/* unlock */

void bch2_btree_node_unlock_write(struct btree_trans *trans,
			struct btree_path *path, struct btree *b)
{
	bch2_btree_node_unlock_write_inlined(trans, path, b);
}

/* lock */

/*
 * @trans wants to lock @b with type @type
 */
struct trans_waiting_for_lock {
	struct btree_trans		*trans;
	struct btree_bkey_cached_common	*node_want;
	enum six_lock_type		lock_want;

	/* for iterating over held locks :*/
	u8				path_idx;
	u8				level;
	u64				lock_start_time;
};

struct lock_graph {
	struct trans_waiting_for_lock	g[8];
	unsigned			nr;
};

static noinline void print_cycle(struct printbuf *out, struct lock_graph *g)
{
	struct trans_waiting_for_lock *i;

	prt_printf(out, "Found lock cycle (%u entries):", g->nr);
	prt_newline(out);

	for (i = g->g; i < g->g + g->nr; i++) {
		struct task_struct *task = READ_ONCE(i->trans->locking_wait.task);
		if (!task)
			continue;

		bch2_btree_trans_to_text(out, i->trans);
		bch2_prt_task_backtrace(out, task, i == g->g ? 5 : 1, GFP_NOWAIT);
	}
}

static noinline void print_chain(struct printbuf *out, struct lock_graph *g)
{
	struct trans_waiting_for_lock *i;

	for (i = g->g; i != g->g + g->nr; i++) {
		struct task_struct *task = i->trans->locking_wait.task;
		if (i != g->g)
			prt_str(out, "<- ");
		prt_printf(out, "%u ", task ?task->pid : 0);
	}
	prt_newline(out);
}

static void lock_graph_up(struct lock_graph *g)
{
	closure_put(&g->g[--g->nr].trans->ref);
}

static noinline void lock_graph_pop_all(struct lock_graph *g)
{
	while (g->nr)
		lock_graph_up(g);
}

static void __lock_graph_down(struct lock_graph *g, struct btree_trans *trans)
{
	g->g[g->nr++] = (struct trans_waiting_for_lock) {
		.trans		= trans,
		.node_want	= trans->locking,
		.lock_want	= trans->locking_wait.lock_want,
	};
}

static void lock_graph_down(struct lock_graph *g, struct btree_trans *trans)
{
	closure_get(&trans->ref);
	__lock_graph_down(g, trans);
}

static bool lock_graph_remove_non_waiters(struct lock_graph *g)
{
	struct trans_waiting_for_lock *i;

	for (i = g->g + 1; i < g->g + g->nr; i++)
		if (i->trans->locking != i->node_want ||
		    i->trans->locking_wait.start_time != i[-1].lock_start_time) {
			while (g->g + g->nr > i)
				lock_graph_up(g);
			return true;
		}

	return false;
}

static void trace_would_deadlock(struct lock_graph *g, struct btree_trans *trans)
{
	struct bch_fs *c = trans->c;

	count_event(c, trans_restart_would_deadlock);

	if (trace_trans_restart_would_deadlock_enabled()) {
		struct printbuf buf = PRINTBUF;

		buf.atomic++;
		print_cycle(&buf, g);

		trace_trans_restart_would_deadlock(trans, buf.buf);
		printbuf_exit(&buf);
	}
}

static int abort_lock(struct lock_graph *g, struct trans_waiting_for_lock *i)
{
	if (i == g->g) {
		trace_would_deadlock(g, i->trans);
		return btree_trans_restart(i->trans, BCH_ERR_transaction_restart_would_deadlock);
	} else {
		i->trans->lock_must_abort = true;
		wake_up_process(i->trans->locking_wait.task);
		return 0;
	}
}

static int btree_trans_abort_preference(struct btree_trans *trans)
{
	if (trans->lock_may_not_fail)
		return 0;
	if (trans->locking_wait.lock_want == SIX_LOCK_write)
		return 1;
	if (!trans->in_traverse_all)
		return 2;
	return 3;
}

static noinline int break_cycle(struct lock_graph *g, struct printbuf *cycle)
{
	struct trans_waiting_for_lock *i, *abort = NULL;
	unsigned best = 0, pref;
	int ret;

	if (lock_graph_remove_non_waiters(g))
		return 0;

	/* Only checking, for debugfs: */
	if (cycle) {
		print_cycle(cycle, g);
		ret = -1;
		goto out;
	}

	for (i = g->g; i < g->g + g->nr; i++) {
		pref = btree_trans_abort_preference(i->trans);
		if (pref > best) {
			abort = i;
			best = pref;
		}
	}

	if (unlikely(!best)) {
		struct printbuf buf = PRINTBUF;

		prt_printf(&buf, bch2_fmt(g->g->trans->c, "cycle of nofail locks"));

		for (i = g->g; i < g->g + g->nr; i++) {
			struct btree_trans *trans = i->trans;

			bch2_btree_trans_to_text(&buf, trans);

			prt_printf(&buf, "backtrace:");
			prt_newline(&buf);
			printbuf_indent_add(&buf, 2);
			bch2_prt_task_backtrace(&buf, trans->locking_wait.task, 2, GFP_NOWAIT);
			printbuf_indent_sub(&buf, 2);
			prt_newline(&buf);
		}

		bch2_print_string_as_lines(KERN_ERR, buf.buf);
		printbuf_exit(&buf);
		BUG();
	}

	ret = abort_lock(g, abort);
out:
	if (ret)
		while (g->nr)
			lock_graph_up(g);
	return ret;
}

static int lock_graph_descend(struct lock_graph *g, struct btree_trans *trans,
			      struct printbuf *cycle)
{
	struct btree_trans *orig_trans = g->g->trans;
	struct trans_waiting_for_lock *i;

	for (i = g->g; i < g->g + g->nr; i++)
		if (i->trans == trans) {
			closure_put(&trans->ref);
			return break_cycle(g, cycle);
		}

	if (g->nr == ARRAY_SIZE(g->g)) {
		closure_put(&trans->ref);

		if (orig_trans->lock_may_not_fail)
			return 0;

		while (g->nr)
			lock_graph_up(g);

		if (cycle)
			return 0;

		trace_and_count(trans->c, trans_restart_would_deadlock_recursion_limit, trans, _RET_IP_);
		return btree_trans_restart(orig_trans, BCH_ERR_transaction_restart_deadlock_recursion_limit);
	}

	__lock_graph_down(g, trans);
	return 0;
}

static bool lock_type_conflicts(enum six_lock_type t1, enum six_lock_type t2)
{
	return t1 + t2 > 1;
}

int bch2_check_for_deadlock(struct btree_trans *trans, struct printbuf *cycle)
{
	struct lock_graph g;
	struct trans_waiting_for_lock *top;
	struct btree_bkey_cached_common *b;
	btree_path_idx_t path_idx;
	int ret = 0;

	g.nr = 0;

	if (trans->lock_must_abort) {
		if (cycle)
			return -1;

		trace_would_deadlock(&g, trans);
		return btree_trans_restart(trans, BCH_ERR_transaction_restart_would_deadlock);
	}

	lock_graph_down(&g, trans);

	/* trans->paths is rcu protected vs. freeing */
	rcu_read_lock();
	if (cycle)
		cycle->atomic++;
next:
	if (!g.nr)
		goto out;

	top = &g.g[g.nr - 1];

	struct btree_path *paths = rcu_dereference(top->trans->paths);
	if (!paths)
		goto up;

	unsigned long *paths_allocated = trans_paths_allocated(paths);

	trans_for_each_path_idx_from(paths_allocated, *trans_paths_nr(paths),
				     path_idx, top->path_idx) {
		struct btree_path *path = paths + path_idx;
		if (!path->nodes_locked)
			continue;

		if (path_idx != top->path_idx) {
			top->path_idx		= path_idx;
			top->level		= 0;
			top->lock_start_time	= 0;
		}

		for (;
		     top->level < BTREE_MAX_DEPTH;
		     top->level++, top->lock_start_time = 0) {
			int lock_held = btree_node_locked_type(path, top->level);

			if (lock_held == BTREE_NODE_UNLOCKED)
				continue;

			b = &READ_ONCE(path->l[top->level].b)->c;

			if (IS_ERR_OR_NULL(b)) {
				/*
				 * If we get here, it means we raced with the
				 * other thread updating its btree_path
				 * structures - which means it can't be blocked
				 * waiting on a lock:
				 */
				if (!lock_graph_remove_non_waiters(&g)) {
					/*
					 * If lock_graph_remove_non_waiters()
					 * didn't do anything, it must be
					 * because we're being called by debugfs
					 * checking for lock cycles, which
					 * invokes us on btree_transactions that
					 * aren't actually waiting on anything.
					 * Just bail out:
					 */
					lock_graph_pop_all(&g);
				}

				goto next;
			}

			if (list_empty_careful(&b->lock.wait_list))
				continue;

			raw_spin_lock(&b->lock.wait_lock);
			list_for_each_entry(trans, &b->lock.wait_list, locking_wait.list) {
				BUG_ON(b != trans->locking);

				if (top->lock_start_time &&
				    time_after_eq64(top->lock_start_time, trans->locking_wait.start_time))
					continue;

				top->lock_start_time = trans->locking_wait.start_time;

				/* Don't check for self deadlock: */
				if (trans == top->trans ||
				    !lock_type_conflicts(lock_held, trans->locking_wait.lock_want))
					continue;

				closure_get(&trans->ref);
				raw_spin_unlock(&b->lock.wait_lock);

				ret = lock_graph_descend(&g, trans, cycle);
				if (ret)
					goto out;
				goto next;

			}
			raw_spin_unlock(&b->lock.wait_lock);
		}
	}
up:
	if (g.nr > 1 && cycle)
		print_chain(cycle, &g);
	lock_graph_up(&g);
	goto next;
out:
	if (cycle)
		--cycle->atomic;
	rcu_read_unlock();
	return ret;
}

int bch2_six_check_for_deadlock(struct six_lock *lock, void *p)
{
	struct btree_trans *trans = p;

	return bch2_check_for_deadlock(trans, NULL);
}

int __bch2_btree_node_lock_write(struct btree_trans *trans, struct btree_path *path,
				 struct btree_bkey_cached_common *b,
				 bool lock_may_not_fail)
{
	int readers = bch2_btree_node_lock_counts(trans, NULL, b, b->level).n[SIX_LOCK_read];
	int ret;

	/*
	 * Must drop our read locks before calling six_lock_write() -
	 * six_unlock() won't do wakeups until the reader count
	 * goes to 0, and it's safe because we have the node intent
	 * locked:
	 */
	six_lock_readers_add(&b->lock, -readers);
	ret = __btree_node_lock_nopath(trans, b, SIX_LOCK_write,
				       lock_may_not_fail, _RET_IP_);
	six_lock_readers_add(&b->lock, readers);

	if (ret)
		mark_btree_node_locked_noreset(path, b->level, BTREE_NODE_INTENT_LOCKED);

	return ret;
}

void bch2_btree_node_lock_write_nofail(struct btree_trans *trans,
				       struct btree_path *path,
				       struct btree_bkey_cached_common *b)
{
	struct btree_path *linked;
	unsigned i, iter;
	int ret;

	/*
	 * XXX BIG FAT NOTICE
	 *
	 * Drop all read locks before taking a write lock:
	 *
	 * This is a hack, because bch2_btree_node_lock_write_nofail() is a
	 * hack - but by dropping read locks first, this should never fail, and
	 * we only use this in code paths where whatever read locks we've
	 * already taken are no longer needed:
	 */

	trans_for_each_path(trans, linked, iter) {
		if (!linked->nodes_locked)
			continue;

		for (i = 0; i < BTREE_MAX_DEPTH; i++)
			if (btree_node_read_locked(linked, i)) {
				btree_node_unlock(trans, linked, i);
				btree_path_set_dirty(linked, BTREE_ITER_NEED_RELOCK);
			}
	}

	ret = __btree_node_lock_write(trans, path, b, true);
	BUG_ON(ret);
}

/* relock */

static inline bool btree_path_get_locks(struct btree_trans *trans,
					struct btree_path *path,
					bool upgrade,
					struct get_locks_fail *f)
{
	unsigned l = path->level;
	int fail_idx = -1;

	do {
		if (!btree_path_node(path, l))
			break;

		if (!(upgrade
		      ? bch2_btree_node_upgrade(trans, path, l)
		      : bch2_btree_node_relock(trans, path, l))) {
			fail_idx	= l;

			if (f) {
				f->l	= l;
				f->b	= path->l[l].b;
			}
		}

		l++;
	} while (l < path->locks_want);

	/*
	 * When we fail to get a lock, we have to ensure that any child nodes
	 * can't be relocked so bch2_btree_path_traverse has to walk back up to
	 * the node that we failed to relock:
	 */
	if (fail_idx >= 0) {
		__bch2_btree_path_unlock(trans, path);
		btree_path_set_dirty(path, BTREE_ITER_NEED_TRAVERSE);

		do {
			path->l[fail_idx].b = upgrade
				? ERR_PTR(-BCH_ERR_no_btree_node_upgrade)
				: ERR_PTR(-BCH_ERR_no_btree_node_relock);
			--fail_idx;
		} while (fail_idx >= 0);
	}

	if (path->uptodate == BTREE_ITER_NEED_RELOCK)
		path->uptodate = BTREE_ITER_UPTODATE;

	bch2_trans_verify_locks(trans);

	return path->uptodate < BTREE_ITER_NEED_RELOCK;
}

bool __bch2_btree_node_relock(struct btree_trans *trans,
			      struct btree_path *path, unsigned level,
			      bool trace)
{
	struct btree *b = btree_path_node(path, level);
	int want = __btree_lock_want(path, level);

	if (race_fault())
		goto fail;

	if (six_relock_type(&b->c.lock, want, path->l[level].lock_seq) ||
	    (btree_node_lock_seq_matches(path, b, level) &&
	     btree_node_lock_increment(trans, &b->c, level, want))) {
		mark_btree_node_locked(trans, path, level, want);
		return true;
	}
fail:
	if (trace && !trans->notrace_relock_fail)
		trace_and_count(trans->c, btree_path_relock_fail, trans, _RET_IP_, path, level);
	return false;
}

/* upgrade */

bool bch2_btree_node_upgrade(struct btree_trans *trans,
			     struct btree_path *path, unsigned level)
{
	struct btree *b = path->l[level].b;
	struct six_lock_count count = bch2_btree_node_lock_counts(trans, path, &b->c, level);

	if (!is_btree_node(path, level))
		return false;

	switch (btree_lock_want(path, level)) {
	case BTREE_NODE_UNLOCKED:
		BUG_ON(btree_node_locked(path, level));
		return true;
	case BTREE_NODE_READ_LOCKED:
		BUG_ON(btree_node_intent_locked(path, level));
		return bch2_btree_node_relock(trans, path, level);
	case BTREE_NODE_INTENT_LOCKED:
		break;
	case BTREE_NODE_WRITE_LOCKED:
		BUG();
	}

	if (btree_node_intent_locked(path, level))
		return true;

	if (race_fault())
		return false;

	if (btree_node_locked(path, level)) {
		bool ret;

		six_lock_readers_add(&b->c.lock, -count.n[SIX_LOCK_read]);
		ret = six_lock_tryupgrade(&b->c.lock);
		six_lock_readers_add(&b->c.lock, count.n[SIX_LOCK_read]);

		if (ret)
			goto success;
	} else {
		if (six_relock_type(&b->c.lock, SIX_LOCK_intent, path->l[level].lock_seq))
			goto success;
	}

	/*
	 * Do we already have an intent lock via another path? If so, just bump
	 * lock count:
	 */
	if (btree_node_lock_seq_matches(path, b, level) &&
	    btree_node_lock_increment(trans, &b->c, level, BTREE_NODE_INTENT_LOCKED)) {
		btree_node_unlock(trans, path, level);
		goto success;
	}

	trace_and_count(trans->c, btree_path_upgrade_fail, trans, _RET_IP_, path, level);
	return false;
success:
	mark_btree_node_locked_noreset(path, level, BTREE_NODE_INTENT_LOCKED);
	return true;
}

/* Btree path locking: */

/*
 * Only for btree_cache.c - only relocks intent locks
 */
int bch2_btree_path_relock_intent(struct btree_trans *trans,
				  struct btree_path *path)
{
	unsigned l;

	for (l = path->level;
	     l < path->locks_want && btree_path_node(path, l);
	     l++) {
		if (!bch2_btree_node_relock(trans, path, l)) {
			__bch2_btree_path_unlock(trans, path);
			btree_path_set_dirty(path, BTREE_ITER_NEED_TRAVERSE);
			trace_and_count(trans->c, trans_restart_relock_path_intent, trans, _RET_IP_, path);
			return btree_trans_restart(trans, BCH_ERR_transaction_restart_relock_path_intent);
		}
	}

	return 0;
}

__flatten
bool bch2_btree_path_relock_norestart(struct btree_trans *trans, struct btree_path *path)
{
	struct get_locks_fail f;

	return btree_path_get_locks(trans, path, false, &f);
}

int __bch2_btree_path_relock(struct btree_trans *trans,
			struct btree_path *path, unsigned long trace_ip)
{
	if (!bch2_btree_path_relock_norestart(trans, path)) {
		trace_and_count(trans->c, trans_restart_relock_path, trans, trace_ip, path);
		return btree_trans_restart(trans, BCH_ERR_transaction_restart_relock_path);
	}

	return 0;
}

bool bch2_btree_path_upgrade_noupgrade_sibs(struct btree_trans *trans,
			       struct btree_path *path,
			       unsigned new_locks_want,
			       struct get_locks_fail *f)
{
	EBUG_ON(path->locks_want >= new_locks_want);

	path->locks_want = new_locks_want;

	return btree_path_get_locks(trans, path, true, f);
}

bool __bch2_btree_path_upgrade(struct btree_trans *trans,
			       struct btree_path *path,
			       unsigned new_locks_want,
			       struct get_locks_fail *f)
{
	if (bch2_btree_path_upgrade_noupgrade_sibs(trans, path, new_locks_want, f))
		return true;

	/*
	 * XXX: this is ugly - we'd prefer to not be mucking with other
	 * iterators in the btree_trans here.
	 *
	 * On failure to upgrade the iterator, setting iter->locks_want and
	 * calling get_locks() is sufficient to make bch2_btree_path_traverse()
	 * get the locks we want on transaction restart.
	 *
	 * But if this iterator was a clone, on transaction restart what we did
	 * to this iterator isn't going to be preserved.
	 *
	 * Possibly we could add an iterator field for the parent iterator when
	 * an iterator is a copy - for now, we'll just upgrade any other
	 * iterators with the same btree id.
	 *
	 * The code below used to be needed to ensure ancestor nodes get locked
	 * before interior nodes - now that's handled by
	 * bch2_btree_path_traverse_all().
	 */
	if (!path->cached && !trans->in_traverse_all) {
		struct btree_path *linked;
		unsigned i;

		trans_for_each_path(trans, linked, i)
			if (linked != path &&
			    linked->cached == path->cached &&
			    linked->btree_id == path->btree_id &&
			    linked->locks_want < new_locks_want) {
				linked->locks_want = new_locks_want;
				btree_path_get_locks(trans, linked, true, NULL);
			}
	}

	return false;
}

void __bch2_btree_path_downgrade(struct btree_trans *trans,
				 struct btree_path *path,
				 unsigned new_locks_want)
{
	unsigned l, old_locks_want = path->locks_want;

	if (trans->restarted)
		return;

	EBUG_ON(path->locks_want < new_locks_want);

	path->locks_want = new_locks_want;

	while (path->nodes_locked &&
	       (l = btree_path_highest_level_locked(path)) >= path->locks_want) {
		if (l > path->level) {
			btree_node_unlock(trans, path, l);
		} else {
			if (btree_node_intent_locked(path, l)) {
				six_lock_downgrade(&path->l[l].b->c.lock);
				mark_btree_node_locked_noreset(path, l, BTREE_NODE_READ_LOCKED);
			}
			break;
		}
	}

	bch2_btree_path_verify_locks(path);

	trace_path_downgrade(trans, _RET_IP_, path, old_locks_want);
}

/* Btree transaction locking: */

void bch2_trans_downgrade(struct btree_trans *trans)
{
	struct btree_path *path;
	unsigned i;

	if (trans->restarted)
		return;

	trans_for_each_path(trans, path, i)
		if (path->ref)
			bch2_btree_path_downgrade(trans, path);
}

int bch2_trans_relock(struct btree_trans *trans)
{
	struct btree_path *path;
	unsigned i;

	if (unlikely(trans->restarted))
		return -((int) trans->restarted);

	trans_for_each_path(trans, path, i) {
		struct get_locks_fail f;

		if (path->should_be_locked &&
		    !btree_path_get_locks(trans, path, false, &f)) {
			if (trace_trans_restart_relock_enabled()) {
				struct printbuf buf = PRINTBUF;

				bch2_bpos_to_text(&buf, path->pos);
				prt_printf(&buf, " l=%u seq=%u node seq=",
					   f.l, path->l[f.l].lock_seq);
				if (IS_ERR_OR_NULL(f.b)) {
					prt_str(&buf, bch2_err_str(PTR_ERR(f.b)));
				} else {
					prt_printf(&buf, "%u", f.b->c.lock.seq);

					struct six_lock_count c =
						bch2_btree_node_lock_counts(trans, NULL, &f.b->c, f.l);
					prt_printf(&buf, " self locked %u.%u.%u", c.n[0], c.n[1], c.n[2]);

					c = six_lock_counts(&f.b->c.lock);
					prt_printf(&buf, " total locked %u.%u.%u", c.n[0], c.n[1], c.n[2]);
				}

				trace_trans_restart_relock(trans, _RET_IP_, buf.buf);
				printbuf_exit(&buf);
			}

			count_event(trans->c, trans_restart_relock);
			return btree_trans_restart(trans, BCH_ERR_transaction_restart_relock);
		}
	}

	return 0;
}

int bch2_trans_relock_notrace(struct btree_trans *trans)
{
	struct btree_path *path;
	unsigned i;

	if (unlikely(trans->restarted))
		return -((int) trans->restarted);

	trans_for_each_path(trans, path, i)
		if (path->should_be_locked &&
		    !bch2_btree_path_relock_norestart(trans, path)) {
			return btree_trans_restart(trans, BCH_ERR_transaction_restart_relock);
		}
	return 0;
}

void bch2_trans_unlock_noassert(struct btree_trans *trans)
{
	struct btree_path *path;
	unsigned i;

	trans_for_each_path(trans, path, i)
		__bch2_btree_path_unlock(trans, path);
}

void bch2_trans_unlock(struct btree_trans *trans)
{
	struct btree_path *path;
	unsigned i;

	trans_for_each_path(trans, path, i)
		__bch2_btree_path_unlock(trans, path);
}

void bch2_trans_unlock_long(struct btree_trans *trans)
{
	bch2_trans_unlock(trans);
	bch2_trans_srcu_unlock(trans);
}

bool bch2_trans_locked(struct btree_trans *trans)
{
	struct btree_path *path;
	unsigned i;

	trans_for_each_path(trans, path, i)
		if (path->nodes_locked)
			return true;
	return false;
}

int __bch2_trans_mutex_lock(struct btree_trans *trans,
			    struct mutex *lock)
{
	int ret = drop_locks_do(trans, (mutex_lock(lock), 0));

	if (ret)
		mutex_unlock(lock);
	return ret;
}

/* Debug */

#ifdef CONFIG_BCACHEFS_DEBUG

void bch2_btree_path_verify_locks(struct btree_path *path)
{
	unsigned l;

	if (!path->nodes_locked) {
		BUG_ON(path->uptodate == BTREE_ITER_UPTODATE &&
		       btree_path_node(path, path->level));
		return;
	}

	for (l = 0; l < BTREE_MAX_DEPTH; l++) {
		int want = btree_lock_want(path, l);
		int have = btree_node_locked_type(path, l);

		BUG_ON(!is_btree_node(path, l) && have != BTREE_NODE_UNLOCKED);

		BUG_ON(is_btree_node(path, l) &&
		       (want == BTREE_NODE_UNLOCKED ||
			have != BTREE_NODE_WRITE_LOCKED) &&
		       want != have);
	}
}

void bch2_trans_verify_locks(struct btree_trans *trans)
{
	struct btree_path *path;
	unsigned i;

	trans_for_each_path(trans, path, i)
		bch2_btree_path_verify_locks(path);
}

#endif