ext4: Create helper function for EXT4_IO_END_UNWRITTEN and i_aiodio_unwritten

EXT4_IO_END_UNWRITTEN flag set and the increase of i_aiodio_unwritten
should be done simultaneously since ext4_end_io_nolock always clear
the flag and decrease the counter in the same time.

We have found some bugs that the flag is set while leaving
i_aiodio_unwritten unchanged(commit 32c80b32c053d). So this patch just tries
to create a helper function to wrap them to avoid any future bug.
The idea is inspired by Eric.

Cc: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 36a0f17..a5c8caa 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3472,12 +3472,9 @@
 		 * that this IO needs to conversion to written when IO is
 		 * completed
 		 */
-		if (io) {
-			if (!(io->flag & EXT4_IO_END_UNWRITTEN)) {
-				io->flag = EXT4_IO_END_UNWRITTEN;
-				atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
-			}
-		} else
+		if (io)
+			ext4_set_io_unwritten_flag(inode, io);
+		else
 			ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
 		if (ext4_should_dioread_nolock(inode))
 			map->m_flags |= EXT4_MAP_UNINIT;
@@ -4030,12 +4027,9 @@
 		 * that we need to perform conversion when IO is done.
 		 */
 		if ((flags & EXT4_GET_BLOCKS_PRE_IO)) {
-			if (io) {
-				if (!(io->flag & EXT4_IO_END_UNWRITTEN)) {
-					io->flag = EXT4_IO_END_UNWRITTEN;
-					atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
-				}
-			} else
+			if (io)
+				ext4_set_io_unwritten_flag(inode, io);
+			else
 				ext4_set_inode_state(inode,
 						     EXT4_STATE_DIO_UNWRITTEN);
 		}