Re: HVMs terminating as (null)

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 23/11/13 20:09, Steven Haigh wrote:
> On 24/11/13 07:03, Andrew Cooper wrote:
>> On 23/11/13 19:56, Steven Haigh wrote:
>>> On 24/11/13 06:38, Steven Haigh wrote:
>>>> On 24/11/13 06:27, Olaf Hering wrote:
>>>>> On Sun, Nov 24, Steven Haigh wrote:
>>>>>
>>>>>> Running Xen 4.2.3 with all the current XSA fixes.
>>>>>
>>>>> How exactly did you start the guests?
>>>>
>>>> The DomUs were started with: xl create /etc/xen/<configfile>
>>>>
>>>>> Does 'ps faxu' show qemu processes for the listed domain_ids?
>>>>> What is the 'xenstore-ls -f | sort' output?
>>>>
>>>> I'll have to check this when I manage to reproduce it. So far, I have
>>>> been unable to get a reliable way to reproduce it. I managed to get a
>>>> system to do it every time a HVM DomU was shutdown OR restarted - but
>>>> after a reboot of the Dom0 I can't get it into that state again.
>>>>
>>>> As soon as I can get a system in this state again, I'll leave it to see
>>>> what information I can extract.
>>>
>>> Ha! As always, as soon as I send this, I notice its happened on a Dom0.
>>>
>>> # xl list
>>> Name                                        ID   Mem VCPUs      State
>>> Time(s)
>>> Domain-0                                     0  1579     2     r-----
>>>  2731.3
>>> planner.vm                                   1  1013     1     -b----
>>>   189.3
>>> (null)                                       2     0     1     --psrd
>>>   301.1
>>> tracker.vm                                   3  1013     2     -b----
>>>   834.4
>>>
>>> Attached is the output of:
>>> # xl debug-keys q
>>> # xl dmesg  > xen-dmesg.log
>>> # gzip xen-dmesg.log
>>
>> Ok - from dmesg.
>>
>> (XEN) General information for domain 2:
>> (XEN)     refcnt=1 dying=2 pause_count=2
>> (XEN)     nr_pages=2 xenheap_pages=0 shared_pages=0 paged_pages=0
>> dirty_cpus={} max_pages=262400
>> (XEN)     handle=ef58ef1a-784d-4e59-8079-42bdee87f219 vm_assist=00000000
>> (XEN)     paging assistance: hap refcounts translate external
>> ...
>> (XEN) Memory pages belonging to domain 2:
>> (XEN)     DomPage 00000000000866e0: caf=00000001, taf=0000000000000000
>> (XEN)     DomPage 00000000000866e1: caf=00000001, taf=0000000000000000
>> (XEN)     PoD entries=0 cachesize=0
>>
>>
>> So there are indeed two outstanding pages causing this domain to become
>> a zombie.  They are normal pages, with 1 outstanding ref.
>>
>> Can you collect "xl debug-keys g" as well?
>
> Sure - attached.

(XEN)       -------- active --------       -------- shared --------
(XEN) [ref] localdom mfn      pin          localdom gmfn     flags
(XEN) grant-table for remote domain:    2 (v1)
(XEN) [16302]        0 0x0866e1 0x00000001          0 0x0064e1 0x19
(XEN) [16320]        0 0x0866e0 0x00000001          0 0x0064e0 0x19

Ok - so domain 2 has two outstanding grants.  This explains why it is a
zombie.

Both these grants are GFT_writing | GFT_reading | GFT_permit_access, but
seemingly unmapped.

I will have to defer to someone who knows the grant code better.  Is it
possible for a domain to be a zombie just because it has two grants it
hasn't manually invalidated?

~Andrew


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