ext4: start handle at least possible moment when renaming files

In ext4_rename(), don't start the journal handle until the the
directory entries have been successfully looked up.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/namei.c

@@ -3009,7 +3009,7 @@ static struct buffer_head *ext4_get_first_dir_block(handle_t *handle,
 static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 		       struct inode *new_dir, struct dentry *new_dentry)
 {
-	handle_t *handle;
+	handle_t *handle = NULL;
 	struct inode *old_inode, *new_inode;
 	struct buffer_head *old_bh, *new_bh, *dir_bh;
 	struct ext4_dir_entry_2 *old_de, *new_de;
@@ -3026,14 +3026,6 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 	 * in separate transaction */
 	if (new_dentry->d_inode)
 		dquot_initialize(new_dentry->d_inode);
-	handle = ext4_journal_start(old_dir, EXT4_HT_DIR,
-		(2 * EXT4_DATA_TRANS_BLOCKS(old_dir->i_sb) +
-		 EXT4_INDEX_EXTRA_TRANS_BLOCKS + 2));
-	if (IS_ERR(handle))
-		return PTR_ERR(handle);
-
-	if (IS_DIRSYNC(old_dir) || IS_DIRSYNC(new_dir))
-		ext4_handle_sync(handle);
 
 	old_bh = ext4_find_entry(old_dir, &old_dentry->d_name, &old_de, NULL);
 	/*
@@ -3056,6 +3048,16 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 			new_bh = NULL;
 		}
 	}
+
+	handle = ext4_journal_start(old_dir, EXT4_HT_DIR,
+		(2 * EXT4_DATA_TRANS_BLOCKS(old_dir->i_sb) +
+		 EXT4_INDEX_EXTRA_TRANS_BLOCKS + 2));
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
+
+	if (IS_DIRSYNC(old_dir) || IS_DIRSYNC(new_dir))
+		ext4_handle_sync(handle);
+
 	if (S_ISDIR(old_inode->i_mode)) {
 		if (new_inode) {
 			retval = -ENOTEMPTY;
@@ -3195,7 +3197,8 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 	brelse(dir_bh);
 	brelse(old_bh);
 	brelse(new_bh);
-	ext4_journal_stop(handle);
+	if (handle)
+		ext4_journal_stop(handle);
 	if (retval == 0 && force_da_alloc)
 		ext4_alloc_da_blocks(old_inode);
 	return retval;