Xen users - Aug 2007 - kexec into dom0? my machine can''t reboot reliably

I have a couple of Xen servers which can''t reboot reliably - only
rarely
it reboots fine; mostly, it will end up with a blank screen, and someone 
has to physically reboot the machine. Not that great if you''re working 
remotely.


I thought a good workaround would be to use kexec when the machine needs 
to be rebooted.

So I tried:

# kexec -l xen-3.1
# kexec -e

And xen kernel started, complaining that the dom0 kernel was not 
specified. So it works, kind of. So, let''s add the dom0 kernel:


# kexec --initrd vmlinuz-2.6.18-xen-uncomp -l xen-3.1
Invalid memory segment 0xc0100000 - 0xc034cfff


Not that great. Is there something I''m missing?

I tried to execute it from two machines: running a 2.6.18 dom0 kernel, 
and running a regular 2.6.22 kernel - both failed in the same way.

kexec version I''m running is:

kexec 1.101 released 15 February 2005

Any hints?


-- 
Tomasz Chmielewski
http://wpkg.org

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Tomasz Chmielewski wrote:
> # kexec --initrd vmlinuz-2.6.18-xen-uncomp -l xen-3.1
> Invalid memory segment 0xc0100000 - 0xc034cfff
> 
> 
> Not that great. Is there something I''m missing?
> 
You''d have to kexec the hypervisor and give it a module of the vmlinuz 
file, in the same way that grub does it.  I''ve no idea if kexec has
that
functionality though.

Tony

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Tony Hoyle schrieb:
> Tomasz Chmielewski wrote:
>> # kexec --initrd vmlinuz-2.6.18-xen-uncomp -l xen-3.1
>> Invalid memory segment 0xc0100000 - 0xc034cfff
>>
>>
>> Not that great. Is there something I''m missing?
>>
> 
> You''d have to kexec the hypervisor and give it a module of the
vmlinuz
> file, in the same way that grub does it.  I''ve no idea if kexec
has that
> functionality though.
All right, something like that gets me farther:

kexec -l xen-3.1 --module="vmlinuz-2.6.18-xen-uncomp
initrd-2.6.18-xenU.img"

But ends with a xen kernel panic:

(XEN) Panic on CPU 0:
(XEN) IO-APIC + timer doesn''t work!


Adding "noapic" seems to help; so far I''m stuck with
inability to find
root. Which is rather strange, as I append exactly the same options as 
to original kernel.


-- 
Tomasz Chmielewski
http://wpkg.org

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Tomasz Chmielewski schrieb:
> Tony Hoyle schrieb:
>> Tomasz Chmielewski wrote:
>>> # kexec --initrd vmlinuz-2.6.18-xen-uncomp -l xen-3.1
>>> Invalid memory segment 0xc0100000 - 0xc034cfff
>>>
>>>
>>> Not that great. Is there something I''m missing?
>>>
>>
>> You''d have to kexec the hypervisor and give it a module of the
vmlinuz
>> file, in the same way that grub does it.  I''ve no idea if
kexec has
>> that functionality though.
> 
> All right, something like that gets me farther:
> 
> kexec -l xen-3.1 --module="vmlinuz-2.6.18-xen-uncomp 
> initrd-2.6.18-xenU.img"
Obviously, the module entry is wrong.

# kexec -l xen-3.1 --module="vmlinuz-2.6.18-xen netloop.nloopbacks=16 
other_params..." --module="initrd-2.6.18-xenU.img"
--append="noapic
dom0_mem=128M"
# kexec -e

Ends with:

(XEN) not enough memory to stash the DOM0 kernel image.

Hmm.


-- 
Tomasz Chmielewski
http://wpkg.org


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> >> You''d have to kexec the hypervisor and give it a module
of the vmlinuz
> >> file, in the same way that grub does it.  I''ve no idea if
kexec has
> >> that functionality though.
> >
> > All right, something like that gets me farther:
> >
> > kexec -l xen-3.1 --module="vmlinuz-2.6.18-xen-uncomp
> > initrd-2.6.18-xenU.img"
>
> Obviously, the module entry is wrong.
>
> # kexec -l xen-3.1 --module="vmlinuz-2.6.18-xen netloop.nloopbacks=16
> other_params..." --module="initrd-2.6.18-xenU.img"
--append="noapic
> dom0_mem=128M"
> # kexec -e
>
> Ends with:
>
> (XEN) not enough memory to stash the DOM0 kernel image.
That''s strange, given it obviously is capable of rebooting into dom0,
given
your previous errors not finding root.

I think your initrd line may be wrong, by the way - you''re specifying a
xenU
initrd, not a xen0 initrd.  Did you mean to do this?

I''m afraid I''m not so familiar with the start of day code, so
I''m not sure
what''s going on...  but it does look like it really ought to be
possible to
get things working better!

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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Mark Williamson schrieb:
>>>> You''d have to kexec the hypervisor and give it a
module of the vmlinuz
>>>> file, in the same way that grub does it.  I''ve no idea
if kexec has
>>>> that functionality though.
>>> All right, something like that gets me farther:
>>>
>>> kexec -l xen-3.1 --module="vmlinuz-2.6.18-xen-uncomp
>>> initrd-2.6.18-xenU.img"
>> Obviously, the module entry is wrong.
>>
>> # kexec -l xen-3.1 --module="vmlinuz-2.6.18-xen
netloop.nloopbacks=16
>> other_params..." --module="initrd-2.6.18-xenU.img"
--append="noapic
>> dom0_mem=128M"
>> # kexec -e
>>
>> Ends with:
>>
>> (XEN) not enough memory to stash the DOM0 kernel image.
> 
> That''s strange, given it obviously is capable of rebooting into
dom0, given
> your previous errors not finding root.
> 
> I think your initrd line may be wrong, by the way - you''re
specifying a xenU
> initrd, not a xen0 initrd.  Did you mean to do this?
> 
> I''m afraid I''m not so familiar with the start of day
code, so I''m not sure
> what''s going on...  but it does look like it really ought to be
possible to
> get things working better!
It indeed works.

The strange "not enough memory" only happens when I give
vmlinuz-...-xen
and initrd as two separate modules (so, like with grub).

If I integrate initrd in the kernel (building it as initramfs), it boots 
correctly.

I''ll write a more detailed update on this tomorrow.


-- 
Tomasz Chmielewski
http://wpkg.org

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