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Re: [Xen-users] [Xen-devel] Dom0 freeze on HVM DomU Windows reboot with VGA passthrough

On Mar 17,  7:30pm, Pasi =?iso-8859-1?Q?K=E4rkk=E4inen?= wrote:
} Subject: Re: [Xen-devel] [Xen-users] Dom0 freeze on HVM DomU Windows reboo

Hi Pasi, hope your day is goin gwell.

> On Sun, Mar 17, 2013 at 10:01:58AM -0500, Dr. Greg Wettstein wrote:
> > We just found a bug in blktap2 teardown which we have
> > been hunting since 4.2.x came out so hopefully we will find some
> > cycles for it.

> Is this possibly the libxl blktap bug that has already been fixed in
> xen-unstable?
> http://xenbits.xen.org/hg/xen-unstable.hg/rev/948f232e0228
> 4.2 backport of the patch can be found from xen-devel archives.

No its a completely different problem which has probably been around
as long as blktap2 has existed.  Something in 4.2.1 seems to really be
provoking it, at least in our test platforms.

It is about a one function call wide race which causes the select call
in the blktap2 IPC control plane to get interrupted and since we don't
retry the system call the teardown of the tapdisk instance collapses,
leaving the framework in various states of composition.  Adding a
function call anywhere in the call chain makes it go away so it was a
classic Heisenbug.

I suspect this bug may have been implicated in a lot of the rather
strange behavior with blktap2 cleanup.

I'm putting a patch together right now so people can evaluate it.

> -- Pasi

Have a good day.

}-- End of excerpt from Pasi =?iso-8859-1?Q?K=E4rkk=E4inen?=

As always,
Dr. G.W. Wettstein, Ph.D.   Enjellic Systems Development, LLC.
4206 N. 19th Ave.           Specializing in information infra-structure
Fargo, ND  58102            development.
PH: 701-281-1686
FAX: 701-281-3949           EMAIL: greg@xxxxxxxxxxxx
"I had far rather walk, as I do, in daily terror of eternity, than feel
 that this was only a children's game in which all of the contestants
 would get equally worthless prizes in the end."
                                -- T. S. Elliot

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