btrfs: hold a ref on the root in btrfs_recover_relocation

We look up the fs root in various places in here when recovering from a
crashed relcoation.  Make sure we hold a ref on the root whenever we
look them up.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -4647,6 +4647,12 @@ int btrfs_recover_relocation(struct btrfs_root *root)
 					err = ret;
 					goto out;
 				}
+			} else {
+				if (!btrfs_grab_fs_root(fs_root)) {
+					err = -ENOENT;
+					goto out;
+				}
+				btrfs_put_fs_root(fs_root);
 			}
 		}
 
@@ -4696,10 +4702,15 @@ int btrfs_recover_relocation(struct btrfs_root *root)
 			list_add_tail(&reloc_root->root_list, &reloc_roots);
 			goto out_free;
 		}
+		if (!btrfs_grab_fs_root(fs_root)) {
+			err = -ENOENT;
+			goto out_free;
+		}
 
 		err = __add_reloc_root(reloc_root);
 		BUG_ON(err < 0); /* -ENOMEM or logic error */
 		fs_root->reloc_root = reloc_root;
+		btrfs_put_fs_root(fs_root);
 	}
 
 	err = btrfs_commit_transaction(trans);
@@ -4731,10 +4742,14 @@ int btrfs_recover_relocation(struct btrfs_root *root)
 	if (err == 0) {
 		/* cleanup orphan inode in data relocation tree */
 		fs_root = read_fs_root(fs_info, BTRFS_DATA_RELOC_TREE_OBJECTID);
-		if (IS_ERR(fs_root))
+		if (IS_ERR(fs_root)) {
 			err = PTR_ERR(fs_root);
-		else
-			err = btrfs_orphan_cleanup(fs_root);
+		} else {
+			if (btrfs_grab_fs_root(fs_root)) {
+				err = btrfs_orphan_cleanup(fs_root);
+				btrfs_put_fs_root(fs_root);
+			}
+		}
 	}
 	return err;
 }