Re: [dpdk-users] segmention fault while accessing mbuf

[Cliff Burdick <shaklee3@gmail.com>]

That shouldn't matter. The mbuf size is allocated when you create the
mempool, and data_len/pkt_len are just to specify the size of the total
packet and each segment. The underlying storage size is still the same.

Have you checked to see if it's potentially a hugepage issue?



On Sun, Jun 7, 2020, 02:59 Alex Kiselev <alex@therouter.net> wrote:

> 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@therouter.net>
> > wrote:
> >
> >>> 1 июня 2020 г., в 19:17, Stephen Hemminger
> >> <stephen@networkplumber.org> написал(а):
> >>>
> >>> On Mon, 01 Jun 2020 15:24:25 +0200
> >>> Alex Kiselev <alex@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?
>