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Fri, 6 Aug 2021 10:21:28 -0400 (EDT) From: Thomas Monjalon To: Olivier Matz , Morten =?ISO-8859-1?Q?Br=F8rup?= Cc: dev@dpdk.org, alialnu@nvidia.com, david.marchand@redhat.com, akozyrev@nvidia.com, viacheslavo@nvidia.com, ferruh.yigit@intel.com, andrew.rybchenko@oktetlabs.ru, konstantin.ananyev@intel.com, ajit.khaparde@broadcom.com Date: Fri, 06 Aug 2021 16:21:26 +0200 Message-ID: <42851215.9SI46nDme2@thomas> In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35C6195B@smartserver.smartshare.dk> References: <20210804132952.2674942-1-thomas@monjalon.net> <98CBD80474FA8B44BF855DF32C47DC35C6195B@smartserver.smartshare.dk> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" Subject: Re: [dpdk-dev] [PATCH] doc: add known issue with mbuf segment X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 05/08/2021 08:08, Morten Br=F8rup: > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon > > Sent: Wednesday, 4 August 2021 15.30 > >=20 > > 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. > >=20 > > Suggested-by: Olivier Matz > > Signed-off-by: Thomas Monjalon > > --- > > doc/guides/rel_notes/release_21_08.rst | 12 ++++++++++++ > > 1 file changed, 12 insertions(+) > >=20 > > 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. > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D > >=20 > > +* **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. > > + > >=20 >=20 > I have a couple of suggestions: >=20 > 1. Add that this bug was present in previous DPDK releases for many years= =2E If possible, mention which release introduced the bug. >=20 > We don't want users to choose to stay on older release, thinking that it = does not have this bug. >=20 > Also, if a user experiences unexplainable problems with segmented packets= an older DPDK release, he might get lucky and find these release notes, wh= ich could reveal the root cause of the problems he is experiencing. >=20 > 2. Add a link to the patch that fixes the bug. It will let users affected= by the bug easily fix it (possibly at the expense of degraded performance). >=20 > With those two additions, > Acked-by: Morten Br=F8rup Applied with the suggested additions: + This issue has a root cause in DPDK 17.05, meaning it is 4 years old. + A fix is available and discussed but not merged in DPDK 21.08: + https://patches.dpdk.org/patch/86458/