Re: [Xen-devel] null domains after xl destroy

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/04/2017 23:13, Glenn Enright wrote:
> On 11/04/17 21:49, Dietmar Hahn wrote:
>> Am Dienstag, 11. April 2017, 20:03:14 schrieb Glenn Enright:
>>> On 11/04/17 17:59, Juergen Gross wrote:
>>>> On 11/04/17 07:25, Glenn Enright wrote:
>>>>> Hi all
>>>>>
>>>>> We are seeing an odd issue with domu domains from xl destroy, under
>>>>> recent 4.9 kernels a (null) domain is left behind.
>>>>
>>>> I guess this is the dom0 kernel version?
>>>>
>>>>> This has occurred on a variety of hardware, with no obvious
>>>>> commonality.
>>>>>
>>>>> 4.4.55 does not show this behavior.
>>>>>
>>>>> On my test machine I have the following packages installed under
>>>>> centos6, from https://xen.crc.id.au/
>>>>>
>>>>> ~]# rpm -qa | grep xen
>>>>> xen47-licenses-4.7.2-4.el6.x86_64
>>>>> xen47-4.7.2-4.el6.x86_64
>>>>> kernel-xen-4.9.21-1.el6xen.x86_64
>>>>> xen47-ocaml-4.7.2-4.el6.x86_64
>>>>> xen47-libs-4.7.2-4.el6.x86_64
>>>>> xen47-libcacard-4.7.2-4.el6.x86_64
>>>>> xen47-hypervisor-4.7.2-4.el6.x86_64
>>>>> xen47-runtime-4.7.2-4.el6.x86_64
>>>>> kernel-xen-firmware-4.9.21-1.el6xen.x86_64
>>>>>
>>>>> I've also replicated the issue with 4.9.17 and 4.9.20
>>>>>
>>>>> To replicate, on a cleanly booted dom0 with one pv VM, I run the
>>>>> following on the VM
>>>>>
>>>>> {
>>>>> while true; do
>>>>>  dd bs=1M count=512 if=/dev/zero of=test conv=fdatasync
>>>>> done
>>>>> }
>>>>>
>>>>> Then on the dom0 I do this sequence to reliably get a null domain.
>>>>> This
>>>>> occurs with oxenstored and xenstored both.
>>>>>
>>>>> {
>>>>> xl sync 1
>>>>> xl destroy 1
>>>>> }
>>>>>
>>>>> xl list then renders something like ...
>>>>>
>>>>> (null)                                       1     4     4     --p--d
>>>>> 9.8     0
>>>>
>>>> Something is referencing the domain, e.g. some of its memory pages are
>>>> still mapped by dom0.
>>
>> You can try
>> # xl debug-keys q
>> and further
>> # xl dmesg
>> to see the output of the previous command. The 'q' dumps domain
>> (and guest debug) info.
>> # xl debug-keys h
>> prints all possible parameters for more informations.
>>
>> Dietmar.
>>
>
> I've done this as requested, below is the output.
>
> <snip>
> (XEN) Memory pages belonging to domain 1:
> (XEN)     DomPage 0000000000071c00: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c01: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c02: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c03: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c04: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c05: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c06: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c07: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c08: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c09: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c0a: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c0b: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c0c: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c0d: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c0e: caf=00000001, taf=7400000000000001
> (XEN)     DomPage 0000000000071c0f: caf=00000001, taf=7400000000000001

There are 16 pages still referenced from somewhere.

Can you grab all of `xenstore-ls -f` in dom0?  There is probably a
backend still attached.

~Andrew

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