block: don't try to poll multi-bio I/Os in __blkdev_direct_IO

If an iocb is split into multiple bios we can't poll for both.  So don't
even bother to try to poll in that case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211012111226.760968-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/fops.c

@@ -197,7 +197,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	struct blk_plug plug;
 	struct blkdev_dio *dio;
 	struct bio *bio;
-	bool is_poll = (iocb->ki_flags & IOCB_HIPRI) != 0;
+	bool do_poll = (iocb->ki_flags & IOCB_HIPRI);
 	bool is_read = (iov_iter_rw(iter) == READ), is_sync;
 	loff_t pos = iocb->ki_pos;
 	blk_qc_t qc = BLK_QC_T_NONE;
@@ -226,7 +226,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	 * Don't plug for HIPRI/polled IO, as those should go straight
 	 * to issue
 	 */
-	if (!is_poll)
+	if (!(iocb->ki_flags & IOCB_HIPRI))
 		blk_start_plug(&plug);
 
 	for (;;) {
@@ -260,20 +260,13 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 
 		nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS);
 		if (!nr_pages) {
-			bool polled = false;
-
-			if (iocb->ki_flags & IOCB_HIPRI) {
+			if (do_poll)
 				bio_set_polled(bio, iocb);
-				polled = true;
-			}
-
 			qc = submit_bio(bio);
-
-			if (polled)
+			if (do_poll)
 				WRITE_ONCE(iocb->ki_cookie, qc);
 			break;
 		}
-
 		if (!dio->multi_bio) {
 			/*
 			 * AIO needs an extra reference to ensure the dio
@@ -284,6 +277,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 				bio_get(bio);
 			dio->multi_bio = true;
 			atomic_set(&dio->ref, 2);
+			do_poll = false;
 		} else {
 			atomic_inc(&dio->ref);
 		}
@@ -292,7 +286,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 		bio = bio_alloc(GFP_KERNEL, nr_pages);
 	}
 
-	if (!is_poll)
+	if (!(iocb->ki_flags & IOCB_HIPRI))
 		blk_finish_plug(&plug);
 
 	if (!is_sync)
@@ -303,8 +297,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 		if (!READ_ONCE(dio->waiter))
 			break;
 
-		if (!(iocb->ki_flags & IOCB_HIPRI) ||
-		    !blk_poll(bdev_get_queue(bdev), qc, true))
+		if (!do_poll || !blk_poll(bdev_get_queue(bdev), qc, true))
 			blk_io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);