ublk: don't dereference ublk_queue in ublk_check_and_get_req()

For ublk servers with many ublk queues, accessing the ublk_queue in
ublk_ch_{read,write}_iter() is a frequent cache miss. Get the flags and
queue depth from the ublk_device instead, which is accessed just before.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: calebsander

drivers/block/ublk_drv.c

@@ -2527,10 +2527,10 @@ static struct request *ublk_check_and_get_req(struct kiocb *iocb,
 		return ERR_PTR(-EINVAL);
 
 	ubq = ublk_get_queue(ub, q_id);
-	if (!ublk_support_user_copy(ubq))
+	if (!ublk_dev_support_user_copy(ub))
 		return ERR_PTR(-EACCES);
 
-	if (tag >= ubq->q_depth)
+	if (tag >= ub->dev_info.queue_depth)
 		return ERR_PTR(-EINVAL);
 
 	*io = &ubq->ios[tag];