Re: [patch]blk-mq: blk_mq_tag_to_rq should handle flush request

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jun 04, 2014 at 08:54:23AM -0600, Jens Axboe wrote:
> >It's not as simple as the added code wants to get a queue from the
> >hwctx, which we can't get at.  I was planning to look into this, but
> >there are various other regressions in the recent block updates that I
> >need to fix before I can even test a tree with this one reverted.
> 
> Which regressions? Performance or crashes?

Both.  I've tracked down the SCSI boot crash and you'll have a patch for
that soon, still working on bisecting the performance crawl, but I'm
getting close.

> >If you can get to sorting this out soon I'd love you to handle it,
> >otherwise I'll look into it as soon as I can.
> 
> Just took a look at it, but I don't see the problematic path. I'm
> looking at wip-9.

scsi_mq_find_tag only gets the scsi host, which may have multiple
queues.  When called from scsi_find_tag we actually have a scsi device,
so that's not an issue, but when called from scsi_host_find_tag the
driver only provides the host.