Re: [Qemu-devel] Intermittent e1000 failure on qemu-kvm 1.0

[Stefan Hajnoczi]

On Tue, Apr 3, 2012 at 9:13 AM, Chris Webb <address@hidden> wrote:
> Stefan Hajnoczi <address@hidden> writes:
>> On Mon, Apr 02, 2012 at 04:37:23PM +0100, Chris Webb wrote:
>> It sounds like this is not the issue, but are you sure the bridge has
>> forwarding delay set to 0 or Spanning Tree Protocol disabled?  With STP
>> enabled no traffic will be forwarded by the bridge for a configured
>> timeout, and depending on the timing of your VM bootup you could see
>> weird things.  You can check with brctl showstp br0.
>
> No STP enabled, but the networking is permanently broken on these guests in
> any case, not just slow to get started. Usually they've been sat there for
> half an hour or more by the time I get back to the stopped reboot loop, and
> I left one broken over a weekend without it fixing itself. The network is
> statically configured, so if it were down temporarily and came back, pings
> would then start working fine.

In a case like this it might be most effective to catch a VM in the
bad state and then go in with gdb to see what is broken.  The basic
approach would be putting breakpoints on the e1000 device model's
transmit/receive paths to see if the guest is giving us packets and
whether the tap device is transmitting/receiving.  If guest and host
appear to be working then QEMU's e1000 model must be in a bad state
and it's a question of looking at the tx/rx rings and other hardware
emulation state to figure out what went wrong.

Have you tried unloading the e1000 kernel module inside the guest and
then modprobing it again?  Does this "fix" the issue?

Stefan