block: check BLK_FEAT_POLL under q_usage_count

Otherwise feature reconfiguration can race with I/O submission.

Also drop the bio_clear_polled in the error path, as the flag does not
matter for instant error completions, it is a left over from when we
allowed polled I/O to proceed unpolled in this case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20250110054726.1499538-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

block/blk-core.c

@@ -629,8 +629,14 @@ static void __submit_bio(struct bio *bio)
 		blk_mq_submit_bio(bio);
 	} else if (likely(bio_queue_enter(bio) == 0)) {
 		struct gendisk *disk = bio->bi_bdev->bd_disk;
-
-		disk->fops->submit_bio(bio);
+	
+		if ((bio->bi_opf & REQ_POLLED) &&
+		    !(disk->queue->limits.features & BLK_FEAT_POLL)) {
+			bio->bi_status = BLK_STS_NOTSUPP;
+			bio_endio(bio);
+		} else {
+			disk->fops->submit_bio(bio);
+		}
 		blk_queue_exit(disk->queue);
 	}
 
@@ -805,12 +811,6 @@ void submit_bio_noacct(struct bio *bio)
 		}
 	}
 
-	if (!(q->limits.features & BLK_FEAT_POLL) &&
-			(bio->bi_opf & REQ_POLLED)) {
-		bio_clear_polled(bio);
-		goto not_supported;
-	}
-
 	switch (bio_op(bio)) {
 	case REQ_OP_READ:
 		break;
@@ -935,7 +935,7 @@ int bio_poll(struct bio *bio, struct io_comp_batch *iob, unsigned int flags)
 		return 0;
 
 	q = bdev_get_queue(bdev);
-	if (cookie == BLK_QC_T_NONE || !(q->limits.features & BLK_FEAT_POLL))
+	if (cookie == BLK_QC_T_NONE)
 		return 0;
 
 	blk_flush_plug(current->plug, false);
@@ -951,7 +951,9 @@ int bio_poll(struct bio *bio, struct io_comp_batch *iob, unsigned int flags)
 	 */
 	if (!percpu_ref_tryget(&q->q_usage_counter))
 		return 0;
-	if (queue_is_mq(q)) {
+	if (!(q->limits.features & BLK_FEAT_POLL)) {
+		ret = 0;
+	} else if (queue_is_mq(q)) {
 		ret = blk_mq_poll(q, cookie, iob, flags);
 	} else {
 		struct gendisk *disk = q->disk;

block/blk-mq.c

@@ -3096,14 +3096,22 @@ void blk_mq_submit_bio(struct bio *bio)
 	}
 
 	/*
-	 * Device reconfiguration may change logical block size, so alignment
-	 * check has to be done with queue usage counter held
+	 * Device reconfiguration may change logical block size or reduce the
+	 * number of poll queues, so the checks for alignment and poll support
+	 * have to be done with queue usage counter held.
 	 */
 	if (unlikely(bio_unaligned(bio, q))) {
 		bio_io_error(bio);
 		goto queue_exit;
 	}
 
+	if ((bio->bi_opf & REQ_POLLED) &&
+	    !(q->limits.features & BLK_FEAT_POLL)) {
+		bio->bi_status = BLK_STS_NOTSUPP;
+		bio_endio(bio);
+		goto queue_exit;
+	}
+
 	bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
 	if (!bio)
 		goto queue_exit;