ext4: fix error handling in migrate

Set i_nlink to zero for temporary inode from very beginning.
otherwise we may fail to start new journal handle and this
inode will be unreferenced but with i_nlink == 1
Since we hold inode reference it can not be pruned.

Also add missed journal_start retval check.
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/migrate.c

@@ -503,14 +503,10 @@ int ext4_ext_migrate(struct inode *inode)
 	}
 	i_size_write(tmp_inode, i_size_read(inode));
 	/*
-	 * We don't want the inode to be reclaimed
-	 * if we got interrupted in between. We have
-	 * this tmp inode carrying reference to the
-	 * data blocks of the original file. We set
-	 * the i_nlink to zero at the last stage after
-	 * switching the original file to extent format
+	 * Set the i_nlink to zero so it will be deleted later
+	 * when we drop inode reference.
 	 */
-	tmp_inode->i_nlink = 1;
+	tmp_inode->i_nlink = 0;
 
 	ext4_ext_tree_init(handle, tmp_inode);
 	ext4_orphan_add(handle, tmp_inode);
@@ -537,6 +533,16 @@ int ext4_ext_migrate(struct inode *inode)
 	up_read((&EXT4_I(inode)->i_data_sem));
 
 	handle = ext4_journal_start(inode, 1);
+	if (IS_ERR(handle)) {
+		/*
+		 * It is impossible to update on-disk structures without
+		 * a handle, so just rollback in-core changes and live other
+		 * work to orphan_list_cleanup()
+		 */
+		ext4_orphan_del(NULL, tmp_inode);
+		retval = PTR_ERR(handle);
+		goto out;
+	}
 
 	ei = EXT4_I(inode);
 	i_data = ei->i_data;
@@ -618,15 +624,8 @@ int ext4_ext_migrate(struct inode *inode)
 
 	/* Reset the extent details */
 	ext4_ext_tree_init(handle, tmp_inode);
-
-	/*
-	 * Set the i_nlink to zero so that
-	 * generic_drop_inode really deletes the
-	 * inode
-	 */
-	tmp_inode->i_nlink = 0;
-
 	ext4_journal_stop(handle);
+out:
 	unlock_new_inode(tmp_inode);
 	iput(tmp_inode);