Btrfs: remove unnecessary dget_parent/dput when creating the pending snapshot

Since we have grabbed the parent inode at the beginning of the
snapshot creation, and both sync and async snapshot creation
release it after the pending snapshots are actually created,
it is safe to access the parent inode directly during the snapshot
creation, we needn't use dget_parent/dput to fix the parent dentry
and get the dir inode.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/ioctl.c

@@ -530,9 +530,10 @@ static noinline int create_subvol(struct btrfs_root *root,
 	return ret;
 }
 
-static int create_snapshot(struct btrfs_root *root, struct dentry *dentry,
-			   char *name, int namelen, u64 *async_transid,
-			   bool readonly, struct btrfs_qgroup_inherit *inherit)
+static int create_snapshot(struct btrfs_root *root, struct inode *dir,
+			   struct dentry *dentry, char *name, int namelen,
+			   u64 *async_transid, bool readonly,
+			   struct btrfs_qgroup_inherit *inherit)
 {
 	struct inode *inode;
 	struct btrfs_pending_snapshot *pending_snapshot;
@@ -551,6 +552,7 @@ static int create_snapshot(struct btrfs_root *root, struct dentry *dentry,
 	pending_snapshot->dentry = dentry;
 	pending_snapshot->root = root;
 	pending_snapshot->readonly = readonly;
+	pending_snapshot->dir = dir;
 	pending_snapshot->inherit = inherit;
 
 	trans = btrfs_start_transaction(root->fs_info->extent_root, 6);
@@ -728,7 +730,7 @@ static noinline int btrfs_mksubvol(struct path *parent,
 		goto out_up_read;
 
 	if (snap_src) {
-		error = create_snapshot(snap_src, dentry, name, namelen,
+		error = create_snapshot(snap_src, dir, dentry, name, namelen,
 					async_transid, readonly, inherit);
 	} else {
 		error = create_subvol(BTRFS_I(dir)->root, dentry,

fs/btrfs/transaction.c

@@ -1068,7 +1068,6 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
 	struct inode *parent_inode;
 	struct btrfs_path *path;
 	struct btrfs_dir_item *dir_item;
-	struct dentry *parent;
 	struct dentry *dentry;
 	struct extent_buffer *tmp;
 	struct extent_buffer *old;
@@ -1126,8 +1125,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
 	trans->bytes_reserved = trans->block_rsv->reserved;
 
 	dentry = pending->dentry;
-	parent = dget_parent(dentry);
-	parent_inode = parent->d_inode;
+	parent_inode = pending->dir;
 	parent_root = BTRFS_I(parent_inode)->root;
 	record_root_in_trans(trans, parent_root);
 
@@ -1275,7 +1273,6 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
 	if (ret)
 		btrfs_abort_transaction(trans, root, ret);
 fail:
-	dput(parent);
 	trans->block_rsv = rsv;
 	trans->bytes_reserved = 0;
 no_free_objectid:

fs/btrfs/transaction.h

@@ -84,6 +84,7 @@ struct btrfs_trans_handle {
 
 struct btrfs_pending_snapshot {
 	struct dentry *dentry;
+	struct inode *dir;
 	struct btrfs_root *root;
 	struct btrfs_root *snap;
 	struct btrfs_qgroup_inherit *inherit;