[dm-devel] data corruption with 'splt' workload to XFS on DM cache with its 3 underlying devices being on same NVMe device

[Christoph Hellwig]

On Tue, Jul 24, 2018 at 09:07:03AM -0400, Mike Snitzer wrote:
> True.  We only ever support mapping the partitions ontop of
> request-based multipath (via dm-linear volumes created by kpartx).
> 
> > So, have you tested that request-based multipathing works on a
> > partition _at all_? I'm not sure if partition mapping is done
> > correctly here; we never remap the start of the request (nor bio,
> > come to speak of it), so it looks as if we would be doing the wrong
> > things here.
> > 
> > Have you checked that partition remapping is done correctly?
> 
> It clearly doesn't work.  Not quite following why but...

blk_insert_cloned_request seems to be missing a call to
blk_partition_remap.  Given that no one but dm-multipath uses this
request clone insert helper, and people generally run multipath on
the whole device this is a code path that is almost never exercised.