[dm-devel] [PATCH v3 0/8] dm: add request-based blk-mq support

[Mike Snitzer]

On Wed, Dec 24 2014 at  1:21pm -0500,
Mike Snitzer <snitzer at redhat.com> wrote:

> This is odd considering blk-mq defaults to setting QUEUE_FLAG_IO_STAT,
> so each request will have REQ_IO_STAT set.
> 
> I'm not sure what would account for this NULL pointer (my code appears
> to be slightly different than yours but AFAICT req->part is NULL in your
> crash, which shouldn't ever happen if IO stats are enabled).
> 
> Are you manually enabling/disabling IO stats via sysfs at all?

Answering my own question: unlikely.  Considering I was able to
reproduce merely by creating an mpath device ontop of a blk-mq device
(now that dm-mpath.c:__multipath_map sets rq->rq_disk).

I'll try to get to the bottom of it (it still seems pretty weird to me).