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

[Cliff Burdick <shaklee3@gmail.com>]

I don't think so since they're completely independent mempools. I also
didn't think the mtu function actually has anything to do with prepping the
card for the mbuf size you want, and that it's typically done in
rte_eth_dev_configure inside of eth_conf in rx_mode and tx_mode.
I would have to look at the code to confirm, but also check what you're
setting this structures to.


On Sun, Jun 7, 2020, 10:11 Alex Kiselev <alex@therouter.net> wrote:

> On 2020-06-07 17:21, Cliff Burdick wrote:
> > 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.
>
> I am using rte_eth_dev_set_mtu() call with mtu value that is consistent
> with the mbuf size. Therefore I believe I don't have any overflow bugs
> in the
> RX code.
>
> And I've found a couple of bugs in the TX code. Both of them are
> have to do with the incorrect use of pkt_len/data_len mbufs field.
>
> But, the crash happened while receiving packets, that's why
> I am wondering could the bugs I found in the TX code cause the crush
> in RX?
>
>
> >
> > 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?
>