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

[Alex Kiselev <alex@therouter.net>]

On 2020-06-01 18:17, Stephen Hemminger wrote:
> 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.

I usually use this options in some debug environments:

   CONFIG_RTE_LIBRTE_MEMPOOL_DEBUG=y
   CONFIG_RTE_MALLOC_DEBUG=y

as well as gcc sanitize options and
some custom memory sanitize techniques
to make sure there is no mempool leaks,
use after free or double free.

But what was your point? Could you please explain
what should I expect from enabling other debug options
or what should I pay attention to?
Should I take a look the PMD drivers debug options?

Unfortunately, there is no way to reproduce the bug.
So I need to understand what could cause it to make
my search more precise.