get rid of useless dget_parent() in fs/btrfs/ioctl.c

both callers there have dentry->d_parent stabilized by the fact that
their caller had obtained dentry from lookup_one_len() and had not
dropped ->i_mutex on parent since then.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/btrfs/ioctl.c

@@ -323,7 +323,7 @@ static noinline int create_subvol(struct btrfs_root *root,
 	struct btrfs_inode_item *inode_item;
 	struct extent_buffer *leaf;
 	struct btrfs_root *new_root;
-	struct dentry *parent = dget_parent(dentry);
+	struct dentry *parent = dentry->d_parent;
 	struct inode *dir;
 	int ret;
 	int err;
@@ -332,10 +332,8 @@ static noinline int create_subvol(struct btrfs_root *root,
 	u64 index = 0;
 
 	ret = btrfs_find_free_objectid(root->fs_info->tree_root, &objectid);
-	if (ret) {
-		dput(parent);
+	if (ret)
 		return ret;
-	}
 
 	dir = parent->d_inode;
 
@@ -346,10 +344,8 @@ static noinline int create_subvol(struct btrfs_root *root,
 	 * 2 - dir items
 	 */
 	trans = btrfs_start_transaction(root, 6);
-	if (IS_ERR(trans)) {
-		dput(parent);
+	if (IS_ERR(trans))
 		return PTR_ERR(trans);
-	}
 
 	leaf = btrfs_alloc_free_block(trans, root, root->leafsize,
 				      0, objectid, NULL, 0, 0, 0);
@@ -439,7 +435,6 @@ static noinline int create_subvol(struct btrfs_root *root,
 
 	d_instantiate(dentry, btrfs_lookup_dentry(dir, dentry));
 fail:
-	dput(parent);
 	if (async_transid) {
 		*async_transid = trans->transid;
 		err = btrfs_commit_transaction_async(trans, root, 1);
@@ -456,7 +451,6 @@ static int create_snapshot(struct btrfs_root *root, struct dentry *dentry,
 			   bool readonly)
 {
 	struct inode *inode;
-	struct dentry *parent;
 	struct btrfs_pending_snapshot *pending_snapshot;
 	struct btrfs_trans_handle *trans;
 	int ret;
@@ -504,9 +498,7 @@ static int create_snapshot(struct btrfs_root *root, struct dentry *dentry,
 	if (ret)
 		goto fail;
 
-	parent = dget_parent(dentry);
-	inode = btrfs_lookup_dentry(parent->d_inode, dentry);
-	dput(parent);
+	inode = btrfs_lookup_dentry(dentry->d_parent->d_inode, dentry);
 	if (IS_ERR(inode)) {
 		ret = PTR_ERR(inode);
 		goto fail;