Re: x86 VM Boot hang with latest linux-next

[Alexander Duyck]

On Sat, Mar 2, 2019 at 7:48 PM Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
>
> On Sat, Mar 02 2019 at  6:34pm -0500,
> Alexander Duyck <alexander.duyck@xxxxxxxxx> wrote:
>
> > So I have been seeing an issue with an intermittent boot hang on my
> > x86 KVM VM with the latest linux-next and have bisected it down to the
> > following commit:
> > 1efa3bb79d3de8ca1b7f6770313a1fc0bebe25c7 is the first bad commit
> > commit 1efa3bb79d3de8ca1b7f6770313a1fc0bebe25c7
> > Author: Mike Snitzer <snitzer@xxxxxxxxxx>
> > Date:   Fri Feb 22 11:23:01 2019 -0500
> >
> >     dm: must allocate dm_noclone for stacked noclone devices
> >
> >     Otherwise various lvm2 testsuite tests fail because the lower layers of
> >     the stacked noclone device aren't updated to allocate a new 'struct
> >     dm_clone' that reflects the upper layer bio that was issued to it.
> >
> >     Fixes: 97a89458020b38 ("dm: improve noclone bio support")
> >     Reported-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> >     Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> >
> > What I am seeing is in about 3 out of 4 boots the startup just hangs
> > at the filesystem check stage with the following message:
> > [  OK  ] Reached target Local File Systems (Pre).
> >          Starting File System Check on /dev/â127-ad57-426f-bb45-363950544c0c...
> > [    **] (1 of 2) A start job is running forân on device 252:2 (19s / no limit)
> >
> > I did some googling and it looks like a similar issue has been
> > reported for s390. Based on the request for data there I have the
> > following info:
> > [root@localhost ~]# dmsetup ls --tree
> > fedora-swap (253:1)
> >  ââ (252:2)
> > fedora-root (253:0)
> >  ââ (252:2)
> >
> > [root@localhost ~]# dmsetup table
> > fedora-swap: 0 4194304 linear 252:2 2048
> > fedora-root: 0 31457280 linear 252:2 4196352
>
> Thanks, which version of Fedora are you running?

The VM is running Fedora 27 with a kernel built off of latest
linux-next as of March 1st.

> Your case is more straightforward in that you're clearly using bio-based
> DM linear (which was updated to leverage "noclone" support); whereas the
> s390 case is using request-based DM which isn't impacted by the commit
> in question at all.
>
> I'll attempt to reproduce first thing Monday.
>
> Mike

Thanks. The behavior of it has me wondering if we are looking at
something like an uninitialized data issue or something like that
since as I mentioned I don't see this occur on every boot, just on
most of them. So every now and then I can boot up the VM without any
issues, but most of the time it will boot and then get stuck waiting
on jobs that take forever.

- Alex