blk-mq: Fix use after of free q->mq_map

blk-mq: Fix use after of free q->mq_map

CPU hotplug handling for blk-mq (blk_mq_queue_reinit) updates
q->mq_map by blk_mq_update_queue_map() for all request queues in
all_q_list.  On the other hand, q->mq_map is released before deleting
the queue from all_q_list.

So if CPU hotplug event occurs in the window, invalid memory access
can happen.  Fix it by releasing q->mq_map in blk_mq_release() to make
it happen latter than removal from all_q_list.

Signed-off-by: Akinobu Mita <[email protected]>
Suggested-by: Ming Lei <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Cc: Ming Lei <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>