btrfs: hold a ref on the root in get_subvol_name_from_objectid

We lookup the name of a subvol which means we'll cross into different
roots.  Hold a ref while we're doing the look ups in the fs_root we're
searching.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index a2c2e71..2c459d2 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1028,7 +1028,7 @@ static char *get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
                                           u64 subvol_objectid)
 {
        struct btrfs_root *root = fs_info->tree_root;
-       struct btrfs_root *fs_root;
+       struct btrfs_root *fs_root = NULL;
        struct btrfs_root_ref *root_ref;
        struct btrfs_inode_ref *inode_ref;
        struct btrfs_key key;
@@ -1099,6 +1099,12 @@ static char *get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
                fs_root = btrfs_get_fs_root(fs_info, &key, true);
                if (IS_ERR(fs_root)) {
                        ret = PTR_ERR(fs_root);
+                       fs_root = NULL;
+                       goto err;
+               }
+               if (!btrfs_grab_fs_root(fs_root)) {
+                       ret = -ENOENT;
+                       fs_root = NULL;
                        goto err;
                }
 
@@ -1143,6 +1149,8 @@ static char *get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
                        ptr[0] = '/';
                        btrfs_release_path(path);
                }
+               btrfs_put_fs_root(fs_root);
+               fs_root = NULL;
        }
 
        btrfs_free_path(path);
@@ -1155,6 +1163,7 @@ static char *get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
        return name;
 
 err:
+       btrfs_put_fs_root(fs_root);
        btrfs_free_path(path);
        kfree(name);
        return ERR_PTR(ret);