bcachefs: Check subvol <-> inode pointers in check_subvol()

Subvolumes and subvolume root inodes point to each other: this verifies
the subvolume -> inode -> subvolme path.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/inode.c

@@ -324,7 +324,7 @@ int bch2_inode_unpack(struct bkey_s_c k,
 	return bch2_inode_unpack_slowpath(k, unpacked);
 }
 
-static int bch2_inode_peek_nowarn(struct btree_trans *trans,
+int bch2_inode_peek_nowarn(struct btree_trans *trans,
 		    struct btree_iter *iter,
 		    struct bch_inode_unpacked *inode,
 		    subvol_inum inum, unsigned flags)

fs/bcachefs/inode.h

@@ -95,6 +95,8 @@ struct bkey_i *bch2_inode_to_v3(struct btree_trans *, struct bkey_i *);
 
 void bch2_inode_unpacked_to_text(struct printbuf *, struct bch_inode_unpacked *);
 
+int bch2_inode_peek_nowarn(struct btree_trans *, struct btree_iter *,
+		    struct bch_inode_unpacked *, subvol_inum, unsigned);
 int bch2_inode_peek(struct btree_trans *, struct btree_iter *,
 		    struct bch_inode_unpacked *, subvol_inum, unsigned);
 

fs/bcachefs/subvolume.c

@@ -42,6 +42,36 @@ static int check_subvol(struct btree_trans *trans,
 		return ret ?: -BCH_ERR_transaction_restart_nested;
 	}
 
+	struct bch_inode_unpacked inode;
+	struct btree_iter inode_iter = {};
+	ret = bch2_inode_peek_nowarn(trans, &inode_iter, &inode,
+				    (subvol_inum) { k.k->p.offset, le64_to_cpu(subvol.v->inode) },
+				    0);
+	bch2_trans_iter_exit(trans, &inode_iter);
+
+	if (ret && !bch2_err_matches(ret, ENOENT))
+		return ret;
+
+	if (fsck_err_on(ret, c, subvol_to_missing_root,
+			"subvolume %llu points to missing subvolume root %llu:%u",
+			k.k->p.offset, le64_to_cpu(subvol.v->inode),
+			le32_to_cpu(subvol.v->snapshot))) {
+		ret = bch2_subvolume_delete(trans, iter->pos.offset);
+		bch_err_msg(c, ret, "deleting subvolume %llu", iter->pos.offset);
+		return ret ?: -BCH_ERR_transaction_restart_nested;
+	}
+
+	if (fsck_err_on(inode.bi_subvol != subvol.k->p.offset,
+			c, subvol_root_wrong_bi_subvol,
+			"subvol root %llu:%u has wrong bi_subvol field: got %u, should be %llu",
+			inode.bi_inum, inode_iter.k.p.snapshot,
+			inode.bi_subvol, subvol.k->p.offset)) {
+		inode.bi_subvol = subvol.k->p.offset;
+		ret = __bch2_fsck_write_inode(trans, &inode, le32_to_cpu(subvol.v->snapshot));
+		if (ret)
+			goto err;
+	}
+
 	if (!BCH_SUBVOLUME_SNAP(subvol.v)) {
 		u32 snapshot_root = bch2_snapshot_root(c, le32_to_cpu(subvol.v->snapshot));
 		u32 snapshot_tree;
@@ -73,6 +103,7 @@ static int check_subvol(struct btree_trans *trans,
 		}
 	}
 
+err:
 fsck_err:
 	return ret;
 }