Re: SHUTDOWN_crash and vcpu deferrals

[Keir Fraser <keir.fraser@eu.citrix.com>]

On 20/02/2009 21:01, "John Levon" <levon@movementarian.org> wrote:

> If an HVM guest is waiting for an ioemu assist, when qemu isn't running, and
> domain_shutdown(SHUTDOWN_crash) is called, then the domain isn't crashed
> properly:
> 
> Nothing will ever end the deferral. I added code to bust through the
> deferral if SHUTDOWN_crash was the reason, and it seemed to help, but
> I'm not sure it's the right fix.

Hm. If qemu is down you're kind of screwed anyway. Even a non-crashed guest
will likely hang. If you care about that eventuality (i.e., you believe qemu
problems are possible/likely and need to detect them, defend against them,
or whatever), would it be better to have tools try to detect it through
keepalives or something, and basically tackle that class of problem head on?

If you want the hack, I think what you're doing is probably about right. I'd
have to go back over that code again to be exactly sure though, since it's a
bit subtle.

Personally I think a dead qemu is pretty bad, and bugs leading to such
should simply be found and fixed (oh for a perfect world :-). That bad
things happen to a guest, like SHUTDOWN_crash hanging, after qemu is dead...
I'd just live with that -- a worse thing has *already* happened to that
guest's virtualisation environment.

 -- Keir