Re: [Qemu-devel] [PATCH] vl.c/exit: pause cpus before closing block devices

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Stefan Hajnoczi (stefanha@gmail.com) wrote:
> On Thu, Jul 13, 2017 at 08:01:16PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > There's a rare exit seg if the guest is accessing
> > IO during exit.
> > It's always hitting the atomic_inc(&bs->in_flight) with a NULL
> > bs. This was added recently in 99723548  but I don't see it
> > as the cause.
> > 
> > Flip vl.c around so we pause the cpus before closing the block devices,
> > that way we shouldn't have anything trying to access them when
> > they're gone.
> > 
> > This was originally Red Hat bz https://bugzilla.redhat.com/show_bug.cgi?id=1451015
> > 
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > Reported-by: Cong Li <coli@redhat.com>
> > 
> > --
> > This is a very rare race, I'll leave it running in a loop to see if
> > we hit anything else and to check this really fixes it.
> > 
> > I do worry if there are other cases that can trigger this - e.g.
> > hot-unplug or ejecting a CD.
> > 
> > ---
> >  vl.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

Thanks;  and the test I left running seems solid - ~12k runs
over the weekend with no seg.

Dave

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK