bcachefs: Fix extent_sort_fix_overlapping()

Recently the extent update path started emmiting 0 size whiteouts on
extent overwrite, as part of transitioning to moving extent handling
out of the core btree code.

Unfortunately, this broke the old code path that handles overlapping
extents when reading in btree nodes - it relies on sorting incomming
extents by start position, but the 0 size whiteouts broke that ordering.
Skipping over them before the main algorithm sees them fixes this.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bkey_sort.c

@@ -311,6 +311,25 @@ static inline int extent_sort_fix_overlapping_cmp(struct btree *b,
 		cmp_int((unsigned long) r, (unsigned long) l);
 }
 
+/*
+ * The algorithm in extent_sort_fix_overlapping() relies on keys in the same
+ * bset being ordered by start offset - but 0 size whiteouts (which are always
+ * KEY_TYPE_deleted) break this ordering, so we need to skip over them:
+ */
+static void extent_iter_advance(struct sort_iter *iter, unsigned idx)
+{
+	struct sort_iter_set *i = iter->data + idx;
+
+	do {
+		i->k = bkey_next_skip_noops(i->k, i->end);
+	} while (i->k != i->end && bkey_deleted(i->k));
+
+	if (i->k == i->end)
+		array_remove_item(iter->data, iter->used, idx);
+	else
+		__sort_iter_sift(iter, idx, extent_sort_fix_overlapping_cmp);
+}
+
 struct btree_nr_keys
 bch2_extent_sort_fix_overlapping(struct bch_fs *c, struct bset *dst,
 				 struct sort_iter *iter)
@@ -323,19 +342,26 @@ bch2_extent_sort_fix_overlapping(struct bch_fs *c, struct bset *dst,
 	struct bkey_s l, r;
 	struct btree_nr_keys nr;
 	struct bkey_on_stack split;
+	unsigned i;
 
 	memset(&nr, 0, sizeof(nr));
 	bkey_on_stack_init(&split);
 
 	sort_iter_sort(iter, extent_sort_fix_overlapping_cmp);
+	for (i = 0; i < iter->used;) {
+		if (bkey_deleted(iter->data[i].k))
+			__sort_iter_advance(iter, i,
+					    extent_sort_fix_overlapping_cmp);
+		else
+			i++;
+	}
 
 	while (!sort_iter_end(iter)) {
 		l = __bkey_disassemble(b, _l->k, &l_unpacked);
 
 		if (iter->used == 1) {
 			extent_sort_append(c, f, &nr, dst->start, &prev, l);
-			sort_iter_advance(iter,
-					  extent_sort_fix_overlapping_cmp);
+			extent_iter_advance(iter, 0);
 			continue;
 		}
 
@@ -344,15 +370,13 @@ bch2_extent_sort_fix_overlapping(struct bch_fs *c, struct bset *dst,
 		/* If current key and next key don't overlap, just append */
 		if (bkey_cmp(l.k->p, bkey_start_pos(r.k)) <= 0) {
 			extent_sort_append(c, f, &nr, dst->start, &prev, l);
-			sort_iter_advance(iter,
-					  extent_sort_fix_overlapping_cmp);
+			extent_iter_advance(iter, 0);
 			continue;
 		}
 
 		/* Skip 0 size keys */
 		if (!r.k->size) {
-			__sort_iter_advance(iter, 1,
-					    extent_sort_fix_overlapping_cmp);
+			extent_iter_advance(iter, 1);
 			continue;
 		}
 
@@ -369,8 +393,7 @@ bch2_extent_sort_fix_overlapping(struct bch_fs *c, struct bset *dst,
 		if (_l->k > _r->k) {
 			/* l wins, trim r */
 			if (bkey_cmp(l.k->p, r.k->p) >= 0) {
-				__sort_iter_advance(iter, 1,
-					 extent_sort_fix_overlapping_cmp);
+				extent_iter_advance(iter, 1);
 			} else {
 				bch2_cut_front_s(l.k->p, r);
 				extent_save(b, _r->k, r.k);