[ovs-discuss] tnl arp causes infinite reentrant stack death.

Jesse Gross jesse at nicira.com
Wed Sep 16 17:05:21 UTC 2015


That's great, thanks a lot for testing.

On Wed, Sep 16, 2015 at 9:32 AM, David Evans <davidjoshuaevans at gmail.com> wrote:
> Thank you Jesse,
> The patch stopped the program call stack from killing ovs.
> Awesome.
> Will do some more tests today.
>
>
> On 9/15/15, 10:54 PM, "Jesse Gross" <jesse at nicira.com> wrote:
>
>>On Tue, Sep 15, 2015 at 7:38 PM, David Evans <davidjoshuaevans at gmail.com>
>>wrote:
>>> Thanks Jesse!
>>> I think you may be close, but it is the ovs code that is re-entering
>>>it's
>>> self, this isn't an arp storm from a circle of traffic path, as far as
>>>i can
>>> tell. it is an attempt to transmit a single packet.. but never gets
>>>even the
>>> arp out to the stack at all.
>>> you can see build_tunnel_send 3 times as the stack trace goes in the
>>> original post. but no packets make it out. the program call stack is
>>>13000
>>> frames deep - which is why it crashed.
>>
>>When tunneling is done in userspace (such as with DPDK), the Linux
>>stack is not involved at all since the point of DPDK is to avoid the
>>kernel for performance reasons. That's why you see OVS reentering
>>itself repeatedly as it tries to forward and then generate more ARP
>>frames.
>>
>>I just sent out a patch CC'd to you that should fix this issue. Can
>>you test it? Note that in this case 'fix' means that it will prevent
>>OVS from crashing. However, traffic won't flow until the loop in the
>>configuration is resolved. Based on the stack trace, my guess is that
>>you have one or more patch ports connecting the bridges.
>
>



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