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

[Julien Grall <julien.grall@linaro.org>]

On 18/07/14 17:39, 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.

I was thinking about the small fix below. If it's fine for everyone, I can
send a patch next week.

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index e9eb0bc..c44d047 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -311,7 +311,7 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
     }
 
     /* Do we have vcpus already? If not, no need to update node-affinity */
-    if ( d->vcpu )
+    if ( d->vcpu && d->vcpu[0] != NULL )
         domain_update_node_affinity(d);
 
     domain_unpause(d);


Regards,

-- 
Julien Grall