[Devel] 2.6.26 panic (skb->dev==NULL), NFS support

[Denis V. Lunev]

On Fri, 2008-08-01 at 02:26 +0200, Karel Tuma wrote:
> Hello list,
> 
> I hope this is the right place to post.
> 
> I've recently moved to 2.6.26 git (i hope that's the bleeding edge) OpenVZ
> to find out how usable it is. I'm running it on a box under fair IO load
> (100-300 BIO/s). The thing panics in net/ipv4/tcp_ipv4.c:tcp_v4_send_ack()
> once every couple of hours, during io spikes. Apparently skb->dev is NULL,
> inside an irq context on top of that. It's very hard to pinpoint the actual
> trigger. Vanilla 2.6.26 runs just fine.
> 
> Treating the symptoms, rather than the reason behind it, by testing
> the pointer seems to work ok, without disrupting any service. However,
> it would be nice to figure out the real cause to avoid such a hideous hack.
> 
> NFS seems to work (mounting from CT0 so far) after minor changes for
> /proc interfacing (it was throwing ENOMEM). It's mounted in udp so it's
> unlikely to be the cause for tcp panic.
> 
> oops, ugly fix and nfs patches are attached.

good place for this stuff is bugzilla.openvz.org :) Could you describe a
bit your setup: what modules are loaded, how network is configured,
which .config is used?

Unfortunately, NFS right now is not VE aware in 2.6.26 entirely :( I am
working on this problem and hope something mainstreamable will be ready
quite soon.

Regards,
	Den