f2fs: delete DIO read lock

This lock can be a contention with multi 4k random read IO with single inode.

example) fio --output=test --name=test --numjobs=60 --filename=/media/samsung960pro/file_test --rw=randread --bs=4k
 --direct=1 --time_based --runtime=7 --ioengine=libaio --iodepth=256 --group_reporting --size=10G

With this commit, it remove that possible lock contention.
Signed-off-by: NDongjoo Seo <commisori28@gmail.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -3453,7 +3453,8 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	err = __blockdev_direct_IO(iocb, inode, inode->i_sb->s_bdev,
 			iter, rw == WRITE ? get_data_block_dio_write :
 			get_data_block_dio, NULL, f2fs_dio_submit_bio,
-			DIO_LOCKING | DIO_SKIP_HOLES);
+			rw == WRITE ? DIO_LOCKING | DIO_SKIP_HOLES :
+			DIO_SKIP_HOLES);
 
 	if (do_opu)
 		up_read(&fi->i_gc_rwsem[READ]);