So we need to make sure in the block layer or I/O submitter that
REQ_HIPRI is only set if QUEUE_FLAG_POLL is supported. I think it would
also help if we rename it to REQ_POLL to make this more obvious.
It used to check for it, but was changed to look at nr_maps instead...
So I think this is a regression...
blk_mq_map_queue looks at both QUEUE_FLAG_POLL and nr_maps for the
queue selection, but that doesn't help with the problem that we should
never pass poll requests through stacking devices.
Yea I agree.. Would probably make better sense to forbid it in the core,
but I'm not entirely sure how this is possible make_request drivers...
