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

[Cliff Burdick <shaklee3@gmail.com>]

The mbuf pool said be configured to be the size of the largest packet you
expect to receive. If you're getting packets longer than that, I would
expect you to see problems. Same goes for transmitting; I believe it will
just read past the end of the mbuf data.



On Sun, Jun 7, 2020, 06:36 Alex Kiselev <alex@therouter.net> wrote:

> On 2020-06-07 15:16, Cliff Burdick wrote:
> > 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.
>
> It does matter. I've done some tests and after
> sending a few mbufs with data_len/pkt_len bigger than the size
> of mbuf's underlying buffer the app stops sending/receiving packets.
> The PMD apparently goes beyong the mbuf's buffer, that's why
> I sill think that my question about the impact of using incorrect
> data_len/pkt is valid.
>
> >
> > Have you checked to see if it's potentially a hugepage issue?
>
> Please, explain.
>
> The app had been working two monghts before the crush
> and the load was 3-4 gbit/s, so no, I don't think that
> something is wrong with hugepages on that machine.
>
>
> >
> > 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?
>