On Wed, Jan 13, 2021 at 2:28 PM Olivier Matz <olivier.m...@6wind.com> wrote:
>
> m->nb_seg must be reset on mbuf free whatever the value of m->next,
> because it can happen that m->nb_seg is != 1. For instance in this
> case:
>
> m1 = rte_pktmbuf_alloc(mp);
> rte_pktmbuf_append(m1, 500);
> m2 = rte_pktmbuf_alloc(mp);
> rte_pktmbuf_append(m2, 500);
> rte_pktmbuf_chain(m1, m2);
> m0 = rte_pktmbuf_alloc(mp);
> rte_pktmbuf_append(m0, 500);
> rte_pktmbuf_chain(m0, m1);
>
> As rte_pktmbuf_chain() does not reset nb_seg in the initial m1
> segment (this is not required), after this code the mbuf chain
> have 3 segments:
> - m0: next=m1, nb_seg=3
> - m1: next=m2, nb_seg=2
> - m2: next=NULL, nb_seg=1
>
> Then split this chain between m1 and m2, it would result in 2 packets:
> - first packet
> - m0: next=m1, nb_seg=2
> - m1: next=NULL, nb_seg=2
> - second packet
> - m2: next=NULL, nb_seg=1
>
> Freeing the first packet will not restore nb_seg=1 in the second
> segment. This is an issue because it is expected that mbufs stored
> in pool have their nb_seg field set to 1.
>
> Fixes: 8f094a9ac5d7 ("mbuf: set mbuf fields while in pool")
> Cc: sta...@dpdk.org
>
> Signed-off-by: Olivier Matz <olivier.m...@6wind.com>
> Acked-by: Morten Brørup <m...@smartsharesystems.com>
> Acked-by: Ajit Khaparde <ajit.khapa...@broadcom.com>
> Acked-by: Konstantin Ananyev <konstantin.anan...@intel.com>
> ---
>
> v4
> * add a unit test (suggested by David)
Olivier,
Thanks, for adding it.
Ali,
You reported some performance regression, did you confirm it?
If I get no reply by monday, I'll proceed with this patch.
Thanks.
--
David Marchand
