block: clear iocb->private in blkdev_bio_end_io_async()

iocb_bio_iopoll() expects iocb->private to be cleared before
releasing the bio.

We already do this in blkdev_bio_end_io(), but we forgot in the
recently added blkdev_bio_end_io_async().

Fixes: 54a88eb ("block: add single bio async direct IO helper")
Cc: [email protected]
Signed-off-by: Stefano Garzarella <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

block/fops.c

@@ -289,6 +289,8 @@ static void blkdev_bio_end_io_async(struct bio *bio)
 	struct kiocb *iocb = dio->iocb;
 	ssize_t ret;
 
+	WRITE_ONCE(iocb->private, NULL);
+
 	if (likely(!bio->bi_status)) {
 		ret = dio->size;
 		iocb->ki_pos += ret;