Andrew Morton wrote:

> Where queue_requests_store() does wake_up(&rl->wait[READ]);
> 
> It looks like nobody has called blk_init_queue() for this queue and the
> waitqueue head is uninitialised.
> 

DM, MD, rd and loop use blk_alloc_queue and blk_queue_make_request to 
initialize their queue, because they only use the make_request_fn. The 
attached patch prevents the queue from being registered if only 
blk_alloc_queue was called.

Mike Christie