block: clear REQ_HIPRI if polling is not supported

This prevents a HIPRI bio from being submitted through a stacking
driver that does not support polling and thus won't poll for I/O
completion.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -921,6 +921,9 @@ generic_make_request_checks(struct bio *bio)
 		}
 	}
 
+	if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
+		bio->bi_opf &= ~REQ_HIPRI;
+
 	switch (bio_op(bio)) {
 	case REQ_OP_DISCARD:
 		if (!blk_queue_discard(q))