blk_mq_tag_to_rq() will always return a request if the command_id is
in the valid range. Check if the request has been started. If we
blindly process the request we might double complete a request which
can be fatal.
How did you get to this one? did the controller send a completion for
a completed/bogus request?
If that is the case, then that must mean it's possible the driver could
have started the command id just before the bogus completion check. Data
iorruption, right?