On 2013/07/29 13:21, Eric Dumazet wrote:

On Mon, 2013-07-29 at 11:21 -0700, Ben Greear wrote:

quoted

We have a test case on 3.9.9+ (local patches applied) where sending from
VETH interface, through peer VETH bridged (with our own emulator bridge module)
to physical interface, which is then looped to another physical interface (B).
The VETH and the wired B interface are sending UDP traffic to each other.
Routing rules should be configured such that this all works appropriately.

Replacing our bridging module with a user-space bridge has same behaviour.

This setup works on the 3.7.y kernel, but we only get one-way traffic
(B to VETH) on 3.9.9+.

I sniffed the B port, and traffic appears to be sent and received
properly (ie, no checksum errors, etc).  But, our user-space app
shows no received UDP frames on B, and netstat -s gives the
output below.

Is there any way to get more details about what these 'packet receive errors'
are caused by using normal-ish tools?

You could try dropwatch for this kind of obscure drops

https://fedorahosted.org/dropwatch/

If the drop happens in __udp_queue_rcv_skb() you can also get some info from
the udp_fail_queue_rcv_skb tracepoint. See "296f7ea udp: add tracepoints for
queueing skb to rcvbuf (v3.1-rc1)".