[dpdk-users] segmention fault while accessing mbuf

[Alex Kiselev]

On 2020-06-07 04:41, Cliff Burdick wrote:
> I can't tell from your code, but you assigned nb_rx to the number of
> packets received, but then used vec_size, which might be larger. Does
> this happen if you use nb_rx in your loops?

No, this doesn't happen.
I just skip the part of the code that translates nb_rx to vec_size,
since that code is double checked.

My actual question now is about possible impact of using
incorrect values of mbuf's pkt_len and data_len fields.

> 
> On Sat, Jun 6, 2020 at 5:59 AM Alex Kiselev <alex at therouter.net>
> wrote:
> 
>>> 1 июня 2020 г., в 19:17, Stephen Hemminger
>> <stephen at networkplumber.org> написал(а):
>>> 
>>> On Mon, 01 Jun 2020 15:24:25 +0200
>>> Alex Kiselev <alex at therouter.net> wrote:
>>> 
>>>> Hello,
>>>> 
>>>> I've got a segmentation fault error in my data plane path.
>>>> I am pretty sure the code where the segfault happened is ok,
>>>> so my guess is that I somehow received a corrupted mbuf.
>>>> How could I troubleshoot this? Is there any way?
>>>> Is it possible that other threads of the application
>>>> corrupted that mbuf?
>>>> 
>>>> I would really appriciate any advice.
>>>> Thanks.
>>>> 
>>>> DPDK 18.11.3
>>>> NIC: 82599ES
>>>> 
>>>> Code:
>>>> 
>>>> nb_rx = rte_eth_rx_burst(port_id, queue_id, pkts_burst,
>>>> MAX_PKT_BURST);
>>>> 
>>>> ...
>>>> 
>>>> for (i=0; i < vec_size; i++) {
>>>> rte_prefetch0(rte_pktmbuf_mtod(m_v[i], void *));
>>>> 
>>>> for (i=0; i < vec_size; i++) {
>>>> m = m_v[i];
>>>> eth_hdr = rte_pktmbuf_mtod(m, struct ether_hdr *);
>>>> eth_type = rte_be_to_cpu_16(eth_hdr->ether_type);
>> <---
>>>> Segmentation fault
>>>> ...
>>>> 
>>>> #0  rte_arch_bswap16 (_x=<error reading variable: Cannot access
>> memory
>>>> at address 0x4d80000000053010>)
>>> 
>>> Build with as many of the debug options turned on in the DPDK
>> config,
>>> and build with EXTRA_CFLAGS of -g.
>> 
>> Could using an incorrect (a very big one) value of mbuf pkt_len and
>> data_len while transmitting cause mbuf corruption and following
>> segmentation fault on rx?