[Xen-devel] Re: [PATCH] [XEN][ACM] fix missing spin_unlock

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 26/2/07 19:57, "Stefan Berger" <stefanb@xxxxxxxxxx> wrote:

>  I have a question regarding the event channel data structure. It looks
> like a stale entry is in the event channel array indicating that a event
> channel at a given port has a certain remote domain as target. However,
> that domain does not exist anymore and therefore the code section where
> I add the spin_unlock() call gets triggered now. Could this be a bug in
> the domain-cleanup code?
> 
>   I can trigger this problem when running the xm-test suite with ACM
> compiled into Xen. After 159 domains have been created, which happens to
> be during the list tests, the stale port entry shows up and remains. The
> list tests when run after a reboot do not trigger this, though.

When one end of a fully-bound interdomain event channel is closed, the
remote port enters state ECS_UNBOUND. At this point it still refers to the
remote domain by domid, even if the remote domain subsequently dies. In fact
this is exactly the state that all currently-interdomain-bound remote ports
will immediately enter when a domain is destroyed. It's safe and expected.
Since an ACM check will happen when moving from state ECS_UNBOUND to
ECS_INTERDOMAIN you get the chance to check credentials are okay and hence
deal with the case that the domid gets reused by a domain who should not be
allowed to communicate to the ECS_UNBOUND port.

 -- Keir



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