Re: [dpdk-dev] [PATCH] doc: add known issue with mbuf segment

[Ajit Khaparde <ajit.khaparde@broadcom.com>]

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On Wed, Aug 4, 2021 at 6:30 AM Thomas Monjalon <thomas@monjalon.net> wrote:
>
> A bug with segmented packets has been discovered but the agreement
> to apply the fix is not concluded at the time of DPDK 21.08 release.
> This bug seems to be in DPDK for many years and should be fixed in 21.11.
>
> Suggested-by: Olivier Matz <olivier.matz@6wind.com>
> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>

> ---
>  doc/guides/rel_notes/release_21_08.rst | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/doc/guides/rel_notes/release_21_08.rst b/doc/guides/rel_notes/release_21_08.rst
> index d7559ec6bf..14e32585b8 100644
> --- a/doc/guides/rel_notes/release_21_08.rst
> +++ b/doc/guides/rel_notes/release_21_08.rst
> @@ -251,6 +251,18 @@ Known Issues
>     Also, make sure to start the actual text at the margin.
>     =======================================================
>
> +* **Last mbuf segment not implicitly reset.**
> +
> +  It is expected that free mbufs have their field ``nb_seg`` set to 1,
> +  so that when it is allocated, the user does not need to set its value.
> +  The mbuf free functions are responsible of resetting this field to 1
> +  before returning the mbuf to the pool.
> +
> +  When a multi-segment mbuf is freed, the field ``nb_seg`` is not reset
> +  to 1 for the last segment of the chain. On next allocation of this segment,
> +  if the field is not explicitly reset by the user,
> +  an invalid mbuf can be created, and can cause an undefined behavior.
> +
>
>  Tested Platforms
>  ----------------
> --
> 2.31.1
>