Re: [Xen-devel] Unplugging a dom0 vcpu and domain destruction

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Fri, Feb 20, 2009 at 9:17 PM, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:
> On 20/02/2009 18:59, "George Dunlap" <dunlapg@xxxxxxxxx> wrote:
>
>>> In the pvops kernels we also keep a reference to the vcpu info structure,
>>> since we place it the kernel's memory rather than keeping it in the shared
>>> info structure.  For a while that had bugs that left zombie domains lying
>>> around, but I don't think anyone backported that stuff to 2.6.18.
>>
>> Hmm, I'll take a look tomorrow and see if I can work out what those
>> two pages that were being kept are.
>
> Jeremy's hunch might be worth following up -- that the offline vcpu holds
> onto an mm, which doesn't get dropped until the vcpu comes back (at which
> point unmap_vmas() would happen). It seems likely it'll be something silly
> like that.

The problem with that theory is how the offline vcpu got "hold" of the
mm in the first place.  The sequence of events to reproduce is:

* offline cpu1
* create domain
* destroy domain
 + zombie domain
* online cpu1
 + domain finally destroyed

Is there a good way to trigger a Linux stack dump from within Xen?
Even crashing dom0 would be OK if it will get a good stack dump. :-)
If I could see how we got to the final unmap_vma(), I might be able to
track things down easier...

Thanks,
 -George

>
>  -- Keir
>
>
>
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