From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: PV DomU running linux 3.17.3 causing xen-netback
 fatal error in Dom0
Date: Mon, 1 Dec 2014 18:17:19 +0000
Message-ID: <547CB0AF.6010901@citrix.com>
References: <5478926A.80503@overnetdata.com> <547C79C0.4010608@citrix.com>
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To: David Vrabel <david.vrabel@citrix.com>, Anthony Wright <anthony@overnetdata.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
Cc: Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>
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On 01/12/14 14:22, David Vrabel wrote:
> On 28/11/14 15:19, Anthony Wright wrote:
>> We have a 64 bit PV DomU that we recently upgraded from linux 3.3.2 to
>> 3.17.3 running on a 64 bit 3.17.3 Dom0 with Xen 4.4.0.
>>
>> Shortly after the upgrade we started to lose network connectivity to the
>> DomU a few times a day that required a reboot to fix. We see nothing in
>> the xen logs or xl dmesg, but when we looked at the dmesg output we saw
>> the following output for the two incidents we investigated in detail:
>>
>> [69332.026586] vif vif-4-0 vif4.0: txreq.offset: 85e, size: 4002, end: 6144
>> [69332.026607] vif vif-4-0 vif4.0: fatal error; disabling device
>> [69332.031069] br-default: port 2(vif4.0) entered disabled state
> 
> The guest's frontend driver isn't putting valid requests onto the ring
> (it crosses a page boundary) so this is a frontend bug.

This VIF protocol is weird.  The first slot contains a txreq with a size
for the total length of the packet, subsequent slots have sizes for that
fragment only.

netback then has to calculate how long the first slot is, by subtracting
all the size from the following slots.

So something has gone wrong but it's not obvious what it is.  Any chance
you can dump the ring state when it happens?

> What guest are you running?

Sorry, I missed that you said 3.17.3 for the domU as well.

David