Re: Xen crashing when killing a domain with no VCPUs allocated

[George Dunlap <george.dunlap@eu.citrix.com>]

On 07/18/2014 05:39 PM, Ian Campbell wrote:
> On Fri, 2014-07-18 at 14:27 +0100, Julien Grall wrote:
>> Hi all,
>>
>> I've been played with the function alloc_vcpu on ARM. And I hit one case
>> where this function can failed.
>>
>> During domain creation, the toolstack will call DOMCTL_max_vcpus which may
>> fail, for instance because alloc_vcpu didn't succeed. In this case, the
>> toolstack will call DOMCTL_domaindestroy. And I got the below stack trace.
>>
>> It can be reproduced on Xen 4.5 (and I also suspect Xen 4.4) by returning
>> in an error in vcpu_initialize.
>>
>> I'm not sure how to correctly fix it.
> I think a simple check at the head of the function would be ok.
>
> Alternatively perhaps in sched_mode_domain, which could either detect
> this or could detect a domain in pool0 being moved to pool0 and short
> circuit.
>
> [...]
>> (XEN)    [<00226870>] sched_move_domain+0x3cc/0x42c
>> (XEN)    [<0020925c>] domain_kill+0xc8/0x178
> This call path surprised me but it is from:
>
> commit bac6334b51d9bcfe57ecf4a4cb5288348fcf044a
> Author: Juergen Gross <juergen.gross@ts.fujitsu.com>
> Date:   Tue May 20 15:55:42 2014 +0200
>
>      move domain to cpupool0 before destroying it

And this is the second unforseen hypervisor crash that happened as a 
side effect of this patch.  Obviously I need to be more of a bastard as 
a mainainer.

  -George