xfs: match lock mode in xfs_buffered_write_iomap_begin()

Commit 1aa91d9c ("xfs: Add async buffered write support") replace
xfs_ilock(XFS_ILOCK_EXCL) with xfs_ilock_for_iomap() when locking the
writing inode, and a new variable lockmode is used to indicate the lock
mode. Although the lockmode should always be XFS_ILOCK_EXCL, it's still
better to use this variable instead of useing XFS_ILOCK_EXCL directly
when unlocking the inode.

Fixes: 1aa91d9c ("xfs: Add async buffered write support")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

fs/xfs/xfs_iomap.c

@@ -1175,13 +1175,13 @@ xfs_buffered_write_iomap_begin(
 	 * them out if the write happens to fail.
 	 */
 	seq = xfs_iomap_inode_sequence(ip, IOMAP_F_NEW);
-	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	xfs_iunlock(ip, lockmode);
 	trace_xfs_iomap_alloc(ip, offset, count, allocfork, &imap);
 	return xfs_bmbt_to_iomap(ip, iomap, &imap, flags, IOMAP_F_NEW, seq);
 
 found_imap:
 	seq = xfs_iomap_inode_sequence(ip, 0);
-	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	xfs_iunlock(ip, lockmode);
 	return xfs_bmbt_to_iomap(ip, iomap, &imap, flags, 0, seq);
 
 found_cow:
@@ -1191,17 +1191,17 @@ xfs_buffered_write_iomap_begin(
 		if (error)
 			goto out_unlock;
 		seq = xfs_iomap_inode_sequence(ip, IOMAP_F_SHARED);
-		xfs_iunlock(ip, XFS_ILOCK_EXCL);
+		xfs_iunlock(ip, lockmode);
 		return xfs_bmbt_to_iomap(ip, iomap, &cmap, flags,
 					 IOMAP_F_SHARED, seq);
 	}
 
 	xfs_trim_extent(&cmap, offset_fsb, imap.br_startoff - offset_fsb);
-	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	xfs_iunlock(ip, lockmode);
 	return xfs_bmbt_to_iomap(ip, iomap, &cmap, flags, 0, seq);
 
 out_unlock:
-	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	xfs_iunlock(ip, lockmode);
 	return error;
 }