Re: [Xen-devel] Frag is bigger than frame.

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Jun 03, 2013 at 05:49:11PM -0700, Alex A wrote:
> On Fri, Apr 26, 2013 at 05:21:06AM +0100, Steven Haigh wrote:
> >* On 26/04/2013 1:36 AM, Wei Liu wrote:*
> >* > On Thu, Apr 25, 2013 at 4:11 PM, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:*
> >* >> On Thu, Apr 25, 2013 at 12:24:22PM +0100, Steven Haigh wrote:*
> >* >>> Hi all,*
> >* >>>*
> >* >>> I've noticed a couple of DomUs have networking freeze with the 
> >following*
> >* >>> getting printed to the Dom0's /var/log/messages:*
> >* >>>*
> >* >>> Apr 25 12:09:25 hosting kernel: vif vif-4-0 vif.crc: Frag is bigger 
> >than*
> >* >>> frame.*
> >* >>> Apr 25 12:09:25 hosting kernel: vif vif-4-0 vif.crc: fatal error;*
> >* >>> disabling device*
> >* >>> Apr 25 12:09:25 hosting kernel: br0: port 5(vif.crc) entered disabled *
> >* >>> state*
> >* >>>*
> >* >>> I thought this was something to do with MAX_SKB_FRAGS - however the*
> >* >>> kernel I use has this increased to 19 - so in theory I shouldn't hit*
> >* >>> this (as far as I know).*
> >* >>>*
> >* >>> Are there any other things that could trigger this?*
> >* >>>*
> >* >>*
> >* >> You're seeing a netfront bug which is fixed in that series. And it is*
> >* >> not related to MAX_SKB_FRAGS but related to GSO.*
> >* >>*
> >* >> Could you try applying my patch set "Bundle fixes for Xen netfront /*
> >* >> netback" version 7. That series has been applied to DaveM's net-next.*
> >* >>*
> >* >*
> >* > BTW with that series you should be able to get rid of the*
> >* > MAX_SKB_FRAGS -> 19 hack.*
> >* *
> >* This could be quite difficult. The DomU kernel is RHEL based - and not *
> >* easily changed without sending the patch upstream to RH - which may or *
> >* may not apply it.*
> >* *
> >* My google-fu has failed a little here - do you have a link to the *
> >* patches? Is it against Xen or the kernel? Further, is it something that *
> >* just altering the Dom0 part would resolve?*
> >* *
> 
> They are for Linux kernel only. Xen is not involved.
> 
> To get rid of your MAX_SKB_FRAGS hack, you need to patch Dom0 only.
> 
> To fix "Frag is bigger than frame", you need to patch DomU. If that's
> not possible at the moment, I remember seeing a thread about disabling
> guest GSO can workaround ths problem. You can give it a shot.
> 
> 
> Wei.
> 
> >* -- *
> >* Steven Haigh*
> >* *
> >* Email: netwiz@xxxxxxxxx*
> >* Web: https://www.crc.id.au*
> >* Phone: (03) 9001 6090 - 0412 935 897*
> >* Fax: (03) 8338 0299*
> 
> 
> Wei,
> 
> we just hit this bug as well on CentOS 5.9 with kernels
> 2.6.18-348.4.1.el5 and 2.6.18-348.6.1.el5, however I checked it on all
> domUs and dom0s GSO is off, only TSO is on. Would TSO still cause this
> issue?
> 

I really think the proper thing to do is to fix your backend instead of
working around that problem -- the patch is available now and you're
running your customized kernel, right?


Wei.

> Alex

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