Zombie domains

[David Lie <lie@eecg.toronto.edu>]

I'm using the grant table to map a shared frame between two domains.  
Domain 1 shares the frame, and Domain 2 maps it into it's address space. 
I then make sure Domain 2 unmaps the frame, and releases all event 
channels, etc... before shutting down.  Domain 2 always remains as a 
zombie though when I do xm list.  If I dump the domain info in the Xen 
console, I get this information for the zombie domain:

(XEN) General information for domain 12:
(XEN)     flags=6 refcnt=1 nr_pages=0 xenheap_pages=0 dirty_cpus={}
(XEN)     handle=f4a55907-26db-d7c3-f6a7-392637013289
(XEN) Rangesets belonging to domain 12:
(XEN)     Interrupts { }
(XEN)     I/O Memory { }
(XEN)     I/O Ports  { }
(XEN) Memory pages belonging to domain 12:
(XEN) VCPU information and callbacks for domain 12:
(XEN)     VCPU0: CPU0 [has=F] flags=10 upcall_pend = 01, upcall_mask = 
00 dirty}(XEN)     Notifying guest (virq 1, port 0, stat 0/0/-1)

Unfortunately, these fields do not mean very much to me.  What does 
upcall_pend mean?  Sometimes this field is 01, sometimes it's 00.  What 
about refcnt?  Note that Domain 2 is not running XenoLinux, but 
something similar to Mini-OS.  Can anyone on this list see what might be 
stopping this domain from shutting down cleanly?  If not, is there any 
documentation as to what these fields mean?

Thanks in advance.

-DL