scsi: sd: Consider max_xfer_blocks if opt_xfer_blocks is unusable

If device reports a small max_xfer_blocks and a zero opt_xfer_blocks, we
end up using BLK_DEF_MAX_SECTORS, which is wrong and r/w of that size
may get error.

[mkp: tweaked to avoid setting rw_max twice and added typecast]

Cc: <stable@vger.kernel.org> # v4.4+
Fixes: ca369d51 ("block/sd: Fix device-imposed transfer length limits")
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sd.c

@@ -2956,7 +2956,8 @@ static int sd_revalidate_disk(struct gendisk *disk)
 		q->limits.io_opt = logical_to_bytes(sdp, sdkp->opt_xfer_blocks);
 		rw_max = logical_to_sectors(sdp, sdkp->opt_xfer_blocks);
 	} else
-		rw_max = BLK_DEF_MAX_SECTORS;
+		rw_max = min_not_zero(logical_to_sectors(sdp, dev_max),
+				      (sector_t)BLK_DEF_MAX_SECTORS);
 
 	/* Combine with controller limits */
 	q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q));