[dm-devel] [PATCHv2 0/4] blk-mq support for dm multipath

[Mike Snitzer]

On Fri, Dec 05 2014 at  6:33pm -0500,
Keith Busch <keith.busch at intel.com> wrote:

> On Fri, 5 Dec 2014, Mike Snitzer wrote:
> >Hi Keith,
> >
> >I've found a few issues with your v2.  I've been working through the
> >code and fixing things as I see them.  Please see this branch:
> >https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-for-3.19-blk-mq
> >
> >My changes build on your v2 baseline.
> >
> >How much testing have you done?  It could be that my changes screwed
> >something up but... I just tried simply creating a normal request-based
> >DM multipath device (using non blk-mq devices) and hit this crash:
> 
> Thanks, Mike. I'll take a look at your fixes next week.
> 
> I only tested on nvme blk-mq. I don't have any SCSI devices to try,
> but I _really_ need to get one if I'm serious about making this work,
> so I'll find something next week as well.

I'll continue review to see if I can sort out why we're getting this crash.

FYI, you don't _need_ real SCSI devices to test dm-multipath.  Easy
enough to just use scsi_debug so long as you have free memory:

 modprobe scsi_debug dev_size_mb=100 num_tgts=1 vpd_use_hostno=0 add_host=4

add_host makes multiple paths
vpd_use_hostno=0 makes sure that all paths will have the same wwid