[dpdk-dev] phantom old packets received in new mbuf

[Helmut Sim <simhelmut@gmail.com>]

Hi All,

I face a very strange behavior.
I do:
rte_eth_rx_burst(port[i].portid, 0, pkts_burst, MAX_PKT_BURST)

then I reassemble the received UDP segments into one packet (i used the
ip_reassembly example), manipulate its content and send it back to the
network after fragmenting the packet.
This works great, ...well only most of the time it works great...

sometimes it happens that a packet is reassembled and retransmitted to the
network, and after a while I receive one of its segment instead of a a
segment of a totally different packet...

i.e.
rx seg 1 of pkt.id x
rx seg 2 of pkt.id x
rx seg 3 of pkt.id x
rx seg 4 of pkt.id x

packet is reassembled and sent to the network.

then i get:
rx seg 1 of pkt.id y
rx seg 2 of pkt.id y
rx seg 3 of pkt.id y
rx seg 2 of pkt.id x

....

it looks like the pmd gives me a mbuf that points to an old  freed buffer
instead of a new allocated buffer with the new segment data.
or alternatively, the pmd allocates the buffer but doesn't copy the rx data
into it...

the input packets were checked with a wireshark and it fits my description
above.

I checked it with different level of delay between the packets, but it
still happens.

I am using dpdk 1.6.0 r2.
specifically running over an ubuntu 14.04 server on a xen hypervisor using
the NIC 82576 as pci passthrough mode.
using one single port and one single queue.

obviously I suspect that the problem is at my side, but couldn't find it,
...yet.

Any idea or known issue?

Thanks
Sim