On Tue, Feb 24, 2015 at 02:42:46PM +0000, Marc Zyngier wrote:
> On 24/02/15 14:36, Richard W.M. Jones wrote:
> > On Tue, Feb 24, 2015 at 02:10:28PM +0000, Marc Zyngier wrote:
> >> On 24/02/15 13:45, Richard W.M. Jones wrote:
> >>> On Tue, Feb 24, 2015 at 01:12:49PM +0000, Marc Zyngier wrote:
> >>>> Here's my theory: userspace is accessing something it should never
> >>>> access (outside of RAM, basically), and doing so via a kernel interface.
> >>>>
> >>>> Is this process accessing /dev/mem by any chance? dmidecode anyone?
> >>>
> >>> Not as far as I know.  The userspace process is inserting modules.
> >>>
> >>> Here is the userspace function which is most likely to be running:
> >>>
> >>> https://github.com/libguestfs/supermin/blob/master/src/init.c#L292
> >>
> >> Hmmm. That seems quite inoffensive indeed...
> >>
> >>> Unfortunately because of lack of a full stack trace, I can't be sure
> >>> exactly what system call is failing, but I'll probably add more debug
> >>> to the userspace program later.
> >>>
> >>> BTW this worked fine in 3.19.  It's started failing in 3.20/4.0.  It
> >>> also works fine on x86.
> >>
> >> Any chance you could find out whether that's a host or guest regression?
> > 
> > Here is a summary of the test combinations that I have run:
> > 
> >   guest kernel         host kernel         result
> > --------------------------------------------------------
> >   3.19.0-0.rc7         3.19.0-0.rc7        no bug seen
> > 
> >   3.20.0-0.rc0         3.19.0-0.rc7        bug seen
> > 
> >   3.19.0-0.rc7         4.0.0-0.rc1         no bug seen
> > 
> >   4.0.0-0.rc1          4.0.0-0.rc1         bug seen
> > 
> > So a guest regression, I think?
> 
> Looks like it. Is your .config stashed somewhere? I'd like to give it a
> go on my own setup...

Attached.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top