block: fix DIO handling regressions in blkdev_read_iter()

index 26bf15c770d2..4f59e0f5bf30 100644
@@ -566,34 +566,37 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 {
 	struct block_device *bdev = iocb->ki_filp->private_data;
 	loff_t size = bdev_nr_bytes(bdev);
-	size_t count = iov_iter_count(to);
 	loff_t pos = iocb->ki_pos;
 	size_t shorted = 0;
 	ssize_t ret = 0;
+	size_t count;
 
-	if (unlikely(pos + count > size)) {
+	if (unlikely(pos + iov_iter_count(to) > size)) {
 		if (pos >= size)
 			return 0;
 		size -= pos;
-		if (count > size) {
-			shorted = count - size;
-			iov_iter_truncate(to, size);
-		}
+		shorted = iov_iter_count(to) - size;
+		iov_iter_truncate(to, size);
 	}
 
+	count = iov_iter_count(to);
+	if (!count)
+		goto reexpand; /* skip atime */
+
 	if (iocb->ki_flags & IOCB_DIRECT) {
 		struct address_space *mapping = iocb->ki_filp->f_mapping;
 
 		if (iocb->ki_flags & IOCB_NOWAIT) {
-			if (filemap_range_needs_writeback(mapping, iocb->ki_pos,
-						iocb->ki_pos + count - 1))
-				return -EAGAIN;
+			if (filemap_range_needs_writeback(mapping, pos,
+							  pos + count - 1)) {
+				ret = -EAGAIN;
+				goto reexpand;
+			}
 		} else {
-			ret = filemap_write_and_wait_range(mapping,
-						iocb->ki_pos,
-					        iocb->ki_pos + count - 1);
+			ret = filemap_write_and_wait_range(mapping, pos,
+							   pos + count - 1);
 			if (ret < 0)
-				return ret;
+				goto reexpand;
 		}
 
 		file_accessed(iocb->ki_filp);

@@ -603,12 +606,14 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 			iocb->ki_pos += ret;
 			count -= ret;
 		}
+		iov_iter_revert(to, count - iov_iter_count(to));
 		if (ret < 0 || !count)
-			return ret;
+			goto reexpand;
 	}
 
 	ret = filemap_read(iocb, to, ret);
 
+reexpand:
 	if (unlikely(shorted))
 		iov_iter_reexpand(to, iov_iter_count(to) + shorted);
 	return ret;