bcachefs: Ensure btree node scan runs before checking for scanned nodes

Previously, calling bch2_btree_has_scanned_nodes() when btree node
scan hadn't actually run would erroniously return false - causing us to
think a btree was entirely gone.

This fixes a 6.16 regression from moving the scheduling of btree node
scan out of bch2_btree_lost_data() (fixing the bug where we'd schedule
it persistently in the superblock) and only scheduling it when
check_toploogy() is asking for scanned btree nodes.

Signed-off-by: Kent Overstreet <[email protected]>

Author: Kent Overstreet

fs/bcachefs/btree_gc.c

@@ -534,32 +534,39 @@ static int bch2_btree_repair_topology_recurse(struct btree_trans *trans, struct
 	return ret;
 }
 
-static int bch2_check_root(struct btree_trans *trans, enum btree_id i,
+static int bch2_check_root(struct btree_trans *trans, enum btree_id btree,
 			   bool *reconstructed_root)
 {
 	struct bch_fs *c = trans->c;
-	struct btree_root *r = bch2_btree_id_root(c, i);
+	struct btree_root *r = bch2_btree_id_root(c, btree);
 	struct printbuf buf = PRINTBUF;
 	int ret = 0;
 
-	bch2_btree_id_to_text(&buf, i);
+	bch2_btree_id_to_text(&buf, btree);
 
 	if (r->error) {
 		bch_info(c, "btree root %s unreadable, must recover from scan", buf.buf);
 
-		r->alive = false;
-		r->error = 0;
+		ret = bch2_btree_has_scanned_nodes(c, btree);
+		if (ret < 0)
+			goto err;
 
-		if (!bch2_btree_has_scanned_nodes(c, i)) {
+		if (!ret) {
 			__fsck_err(trans,
-				   FSCK_CAN_FIX|(!btree_id_important(i) ? FSCK_AUTOFIX : 0),
+				   FSCK_CAN_FIX|(!btree_id_important(btree) ? FSCK_AUTOFIX : 0),
 				   btree_root_unreadable_and_scan_found_nothing,
 				   "no nodes found for btree %s, continue?", buf.buf);
-			bch2_btree_root_alloc_fake_trans(trans, i, 0);
+
+			r->alive = false;
+			r->error = 0;
+			bch2_btree_root_alloc_fake_trans(trans, btree, 0);
 		} else {
-			bch2_btree_root_alloc_fake_trans(trans, i, 1);
-			bch2_shoot_down_journal_keys(c, i, 1, BTREE_MAX_DEPTH, POS_MIN, SPOS_MAX);
-			ret = bch2_get_scanned_nodes(c, i, 0, POS_MIN, SPOS_MAX);
+			r->alive = false;
+			r->error = 0;
+			bch2_btree_root_alloc_fake_trans(trans, btree, 1);
+
+			bch2_shoot_down_journal_keys(c, btree, 1, BTREE_MAX_DEPTH, POS_MIN, SPOS_MAX);
+			ret = bch2_get_scanned_nodes(c, btree, 0, POS_MIN, SPOS_MAX);
 			if (ret)
 				goto err;
 		}

fs/bcachefs/btree_node_scan.c

@@ -521,8 +521,12 @@ bool bch2_btree_node_is_stale(struct bch_fs *c, struct btree *b)
 	return false;
 }
 
-bool bch2_btree_has_scanned_nodes(struct bch_fs *c, enum btree_id btree)
+int bch2_btree_has_scanned_nodes(struct bch_fs *c, enum btree_id btree)
 {
+	int ret = bch2_run_print_explicit_recovery_pass(c, BCH_RECOVERY_PASS_scan_for_btree_nodes);
+	if (ret)
+		return ret;
+
 	struct found_btree_node search = {
 		.btree_id	= btree,
 		.level		= 0,

fs/bcachefs/btree_node_scan.h

@@ -4,7 +4,7 @@
 
 int bch2_scan_for_btree_nodes(struct bch_fs *);
 bool bch2_btree_node_is_stale(struct bch_fs *, struct btree *);
-bool bch2_btree_has_scanned_nodes(struct bch_fs *, enum btree_id);
+int bch2_btree_has_scanned_nodes(struct bch_fs *, enum btree_id);
 int bch2_get_scanned_nodes(struct bch_fs *, enum btree_id, unsigned, struct bpos, struct bpos);
 void bch2_find_btree_nodes_exit(struct find_btree_nodes *);