Re: [Xen-devel] Problems using xl migrate

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Mon, Nov 24, 2014 at 12:07 AM, M A Young <m.a.young@xxxxxxxxxxxx> wrote:
> On Sat, 22 Nov 2014, M A Young wrote:
>
>> While investigating a bug reported on Red Hat Bugzilla
>> https://bugzilla.redhat.com/show_bug.cgi?id=1166461
>> I discovered the following
>>
>> xl migrate --debug domid localhost does indeed fail for Xen 4.4 pv (the
>> bug report is for Xen 4.3 hvm ) when xl migrate domid localhost works. There
>> are actually two issues here
>>
>> * the segfault in libxl-save-helper --restore-domain (as reported in the
>> bug above) occurs if the guest memory is 1024M (on my 4G box) and is
>> presumably because the allocated memory eventually runs out
>
>
> I have found a bit more out about this. The segfault at at line 1378 of
> tools/libxc/xc_domain_restore.c which is
>                 DPRINTF("************** pfn=%lx type=%lx gotcs=%08lx "
>                         "actualcs=%08lx\n", pfn, pagebuf->pfn_types[pfn],
>                         csum_page(region_base + (i + curbatch)*PAGE_SIZE),
>                         csum_page(buf));
> and is because pfn in pagebuf->pfn_types[pfn] is beyond the end of the
> array. This occurs in the verification phase.
>
>> * the segfault doesn't occur if the guest memory is 128M, but the
>> migration still fails. The first attached file contains the log from a run
>> with xl -v migrate --debug domid localhost (with mfn and duplicated lines
>> stripped out to make the size manageable).
>
>
> The difference actually seems to be down to how active the VM is rather than
> the memory size (my small memory test system was doing very little, my
> larger system was a full OS install). In the non-segfault case the problem
> was the printf and printf_info commands in the create_domain() routine in
> tools/libxl/xl_cmdimpl.c . As xl migrate uses stdout to pass status messages
> back from the restoring dom0, these commands cause an unexpected message. If
> you move them onto stderr then the migration completes in the non-segfault
> case.

Good job tracking those down -- are there patches in the works?

 -George

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