System not booting since dm changes? (was Linux 4.20-rc1)

[Satheesh Rajendran]

On Mon, Nov 05, 2018 at 08:51:57AM -0500, Mike Snitzer wrote:
> On Mon, Nov 05 2018 at  5:25am -0500,
> Michael Ellerman <mpe at ellerman.id.au> wrote:
> 
> > Linus Torvalds <torvalds at linux-foundation.org> writes:
> > ...
> > > Mike Snitzer (1):
> > >     device mapper updates
> > 
> > Hi Mike,
> > 
> > Replying here because I can't find the device-mapper pull or the patch
> > in question on LKML. I guess I should be subscribed to dm-devel.
> > 
> > We have a box that doesn't boot any more, bisect points at one of:
> > 
> >   cef6f55a9fb4 Mike Snitzer       dm table: require that request-based DM be layered on blk-mq devices 
> >   953923c09fe8 Mike Snitzer       dm: rename DM_TYPE_MQ_REQUEST_BASED to DM_TYPE_REQUEST_BASED 
> >   6a23e05c2fe3 Jens Axboe         dm: remove legacy request-based IO path 
> > 
> > 
> > It's a Power8 system running Rawhide, it does have multipath, but I'm
> > told it was setup by the Fedora installer, ie. nothing fancy.
> > 
> > The symptom is the system can't find its root filesystem and drops into
> > the initramfs shell. The dmesg includes a bunch of errors like below:
> > 
> >   [   43.263460] localhost multipathd[1344]: sdb: fail to get serial
> >   [   43.268762] localhost multipathd[1344]: mpatha: failed in domap for addition of new path sdb
> >   [   43.268762] localhost multipathd[1344]: uevent trigger error
> >   [   43.282065] localhost kernel: device-mapper: table: table load rejected: not all devices are blk-mq request-stackable
> ...
> >
> > Any ideas what's going wrong here?
> 
> "table load rejected: not all devices are blk-mq request-stackable"
> speaks to the fact that you aren't using blk-mq for scsi (aka scsi-mq).
> 
> You need to use scsi_mod.use_blk_mq=Y on the kernel commandline (or set
> CONFIG_SCSI_MQ_DEFAULT in your kernel config)

Thanks Mike!, above solution worked and the system booted fine now:-)

# uname -r
4.20.0-rc1+
# cat /proc/cmdline 
root=/dev/mapper/fedora_ltc--test--ci2-root ro rd.lvm.lv=fedora_ltc-test-ci2/root rd.lvm.lv=fedora_ltc-test-ci2/swap scsi_mod.use_blk_mq=Y

CONFIG_SCSI_MQ_DEFAULT kernel was not set in my kernel config, will set in future runs.

Thanks Michael!

Regards,
-Satheesh.

> 
> Mike
>