netloop

Am I going about this wrong? It's quite trivial to deadlock
the Fedora 
kernel.

# modprobe netloop ; rmmod netloop
unregister_netdevice: waiting for veth3 to become free.
Usage count = 1
unregister_netdevice: waiting for veth3 to become free.
Usage count = 1
unregister_netdevice: waiting for veth3 to become free.
Usage count = 1
...

This is without doing anything else with xend or the other
modules. So 
why/who/what grabbed a hold of that veth?

I just did this today on 2.6.20-1.2933 and have done it
before with one or 
more of the 2.6.18 builds.

../C

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On Fri, Apr 13, 2007 at 01:52:46PM -0700, Curtis Doty
wrote:
> Am I going about this wrong? It's quite trivial to
deadlock the Fedora 
> kernel.
> 
> # modprobe netloop ; rmmod netloop
> unregister_netdevice: waiting for veth3 to become free.
Usage count = 1
> unregister_netdevice: waiting for veth3 to become free.
Usage count = 1
> unregister_netdevice: waiting for veth3 to become free.
Usage count = 1
> ...
> 
> This is without doing anything else with xend or the
other modules. So 
> why/who/what grabbed a hold of that veth?

This is basically a limitation of the netloop module - its
not written to
allow its removal once loaded. Fortunately we don't need to
worry about
fixing this, because in the very near future we will be
blasting netloop
into oblivion   This will
make networking in Dom0 much simpler because
you won't have this crazy set of extra devices for Dom0 -
just the real
eth*, the bridge device & any VIFs for guest VMs.

Regards,
Dan.
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978 392 2496 -=|
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On Sat, Apr 14, 2007 at 12:18:26AM +0100, Daniel P. Berrange
wrote:
> On Fri, Apr 13, 2007 at 01:52:46PM -0700, Curtis Doty
wrote:
> > Am I going about this wrong? It's quite trivial to
deadlock the Fedora 
> > kernel.
> > 
> > # modprobe netloop ; rmmod netloop
> > unregister_netdevice: waiting for veth3 to become
free. Usage count = 1
> > unregister_netdevice: waiting for veth3 to become
free. Usage count = 1
> > unregister_netdevice: waiting for veth3 to become
free. Usage count = 1
> > ...
> > 
> > This is without doing anything else with xend or
the other modules. So 
> > why/who/what grabbed a hold of that veth?
> 
> This is basically a limitation of the netloop module -
its not written to
> allow its removal once loaded. Fortunately we don't
need to worry about
> fixing this, because in the very near future we will be
blasting netloop
> into oblivion   This will
make networking in Dom0 much simpler because
> you won't have this crazy set of extra devices for Dom0
- just the real
> eth*, the bridge device & any VIFs for guest VMs.
> 

Can you tell more about this? Redhat is planning not to use
the xen
network-bridge script anymore and allow more flexible
configuration with
the tools provided by the distro? 

What does "in the very near future" mean.. ? for
fc7? fc8?

I'm interested in this because I've made my own scripts for
use in dom0
instead of xen network-bridge.. kind of "add-on"
scripts for standard fedora
network scripts.

Thanks!

-- Pasi

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On Sat, Apr 14, 2007 at 08:26:16PM +0300, Pasi K?rkk?inen
wrote:
> On Sat, Apr 14, 2007 at 12:18:26AM +0100, Daniel P.
Berrange wrote:
> > On Fri, Apr 13, 2007 at 01:52:46PM -0700, Curtis
Doty wrote:
> > > Am I going about this wrong? It's quite
trivial to deadlock the Fedora 
> > > kernel.
> > > 
> > > # modprobe netloop ; rmmod netloop
> > > unregister_netdevice: waiting for veth3 to
become free. Usage count = 1
> > > unregister_netdevice: waiting for veth3 to
become free. Usage count = 1
> > > unregister_netdevice: waiting for veth3 to
become free. Usage count = 1
> > > ...
> > > 
> > > This is without doing anything else with xend
or the other modules. So 
> > > why/who/what grabbed a hold of that veth?
> > 
> > This is basically a limitation of the netloop
module - its not written to
> > allow its removal once loaded. Fortunately we
don't need to worry about
> > fixing this, because in the very near future we
will be blasting netloop
> > into oblivion   This will
make networking in Dom0 much simpler because
> > you won't have this crazy set of extra devices for
Dom0 - just the real
> > eth*, the bridge device & any VIFs for guest
VMs.
> > 
> 
> Can you tell more about this? Redhat is planning not to
use the xen
> network-bridge script anymore and allow more flexible
configuration with
> the tools provided by the distro? 

For compatability with FC5/6 we need to keep using
network-bridge in the
default RPM setup. What we're trying to do is alter the
network-bridge
script so that it doesn't need to use the netloop module.
Part of this
work involves kernel changes to the way the Xen network
module transfer
data to avoid some potential denial-of-service conditions
that arise if
you're not using netloop.

So we'll have a simplified network-bridge, but will also
have the option 
of just setting the config file option '(network-script
/bin/true)' and 
then using normal distro networking scripts for
bridging/bonding/whatever.

> What does "in the very near future" mean.. ?
for fc7? fc8?

Fedora 7 is the goal.

> I'm interested in this because I've made my own scripts
for use in dom0
> instead of xen network-bridge.. kind of
"add-on" scripts for standard fedora
> network scripts.

You'll be able to keep using these - netloop will still
exist for compatability
with any user custom scripts, we simply won't use it in the
default scripts


Dan.
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On Sat, Apr 14, 2007 at 07:12:16PM +0100, Daniel P. Berrange
wrote:
> On Sat, Apr 14, 2007 at 08:26:16PM +0300, Pasi
K?rkk?inen wrote:
> > On Sat, Apr 14, 2007 at 12:18:26AM +0100, Daniel
P. Berrange wrote:
> > > On Fri, Apr 13, 2007 at 01:52:46PM -0700,
Curtis Doty wrote:
> > > > Am I going about this wrong? It's quite
trivial to deadlock the Fedora 
> > > > kernel.
> > > > 
> > > > # modprobe netloop ; rmmod netloop
> > > > unregister_netdevice: waiting for veth3
to become free. Usage count = 1
> > > > unregister_netdevice: waiting for veth3
to become free. Usage count = 1
> > > > unregister_netdevice: waiting for veth3
to become free. Usage count = 1
> > > > ...
> > > > 
> > > > This is without doing anything else with
xend or the other modules. So 
> > > > why/who/what grabbed a hold of that
veth?
> > > 
> > > This is basically a limitation of the netloop
module - its not written to
> > > allow its removal once loaded. Fortunately we
don't need to worry about
> > > fixing this, because in the very near future
we will be blasting netloop
> > > into oblivion   This will
make networking in Dom0 much simpler because
> > > you won't have this crazy set of extra
devices for Dom0 - just the real
> > > eth*, the bridge device & any VIFs for
guest VMs.
> > > 
> > 
> > Can you tell more about this? Redhat is planning
not to use the xen
> > network-bridge script anymore and allow more
flexible configuration with
> > the tools provided by the distro? 
> 
> For compatability with FC5/6 we need to keep using
network-bridge in the
> default RPM setup. What we're trying to do is alter the
network-bridge
> script so that it doesn't need to use the netloop
module. Part of this
> work involves kernel changes to the way the Xen network
module transfer
> data to avoid some potential denial-of-service
conditions that arise if
> you're not using netloop.
> 
> So we'll have a simplified network-bridge, but will
also have the option 
> of just setting the config file option '(network-script
/bin/true)' and 
> then using normal distro networking scripts for
bridging/bonding/whatever.
> 

OK. That's a good thing. 

The biggest problem with default xen network-bridge for me
is the lack of VLAN
support..

> > What does "in the very near future"
mean.. ? for fc7? fc8?
> 
> Fedora 7 is the goal.
> 
> > I'm interested in this because I've made my own
scripts for use in dom0
> > instead of xen network-bridge.. kind of
"add-on" scripts for standard fedora
> > network scripts.
> 
> You'll be able to keep using these - netloop will still
exist for compatability
> with any user custom scripts, we simply won't use it in
the default scripts
> 
> 

OK. My scripts are meant for using VLAN interfaces with xen
bridges, and
also with bonding. 

Example:

With the normal distro (fc6) network scripts I do:

- Reset MAC addresses of ethX devices
- Set up bond0 (from ethX+ethY)
- Create VLAN interfaces (bond0.xyz)
- Configure vethX for dom0 mgmt (including MAC address from
physical dev)
- Create bridges for VLAN interfaces

Then with my custom scripts:

- Set NOARP for interfaces
- Do the bridge "addif" to connect the VLAN
interfaces to corresponding
  bridges

All of that basicly should be doable with the normal fc6
network scripts,
but it seems bridging with MAC changes doesn't seem to work,
and there were
some problems with NOARP too.. 

-- Pasi

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On Sat, 2007-04-14 at 19:12 +0100, Daniel P. Berrange
wrote:

> For compatability with FC5/6 we need to keep using
network-bridge in the
> default RPM setup. What we're trying to do is alter the
network-bridge
> script so that it doesn't need to use the netloop
module. Part of this
> work involves kernel changes to the way the Xen network
module transfer
> data to avoid some potential denial-of-service
conditions that arise if
> you're not using netloop.

	Just to elaborate ...

	The only reason netloop exists is to prevent the netback
driver from
"seizing up" if packets from DomU, destined for
Dom0, are queued up
indefinitely in Dom0 socket buffers causing hypervisor
resources (grant
table entries?) to be exhausted. The netloop solution is to
copy packets
from DomU just before they are delivered to Dom0's
networking stack.

	The new solution is for netback to keep track of packets
and to
periodically copy any packets which have been queued up for
too long.
That way you don't need the netloop device at all.

Cheers,
Mark.

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Will this decrease or increase the chance of a domU loosing
its network 
and the dom0 complaining about memory squeezes in the
netback driver?

On Mon, 16 Apr 2007, Mark McLoughlin wrote:

> On Sat, 2007-04-14 at 19:12 +0100, Daniel P. Berrange
wrote:
>
>> For compatability with FC5/6 we need to keep using
network-bridge in the
>> default RPM setup. What we're trying to do is alter
the network-bridge
>> script so that it doesn't need to use the netloop
module. Part of this
>> work involves kernel changes to the way the Xen
network module transfer
>> data to avoid some potential denial-of-service
conditions that arise if
>> you're not using netloop.
>
> 	Just to elaborate ...
>
> 	The only reason netloop exists is to prevent the
netback driver from
> "seizing up" if packets from DomU, destined
for Dom0, are queued up
> indefinitely in Dom0 socket buffers causing hypervisor
resources (grant
> table entries?) to be exhausted. The netloop solution
is to copy packets
> from DomU just before they are delivered to Dom0's
networking stack.
>
> 	The new solution is for netback to keep track of
packets and to
> periodically copy any packets which have been queued up
for too long.
> That way you don't need the netloop device at all.
>
> Cheers,
> Mark.
>
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