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From: Thomas Monjalon <thomas@monjalon.net>
To: "Olivier Matz" <olivier.matz@6wind.com>,
	"Morten Brørup" <mb@smartsharesystems.com>
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
Subject: Re: [dpdk-dev] [PATCH] doc: add known issue with mbuf segment
Date: Fri, 06 Aug 2021 16:21:26 +0200	[thread overview]
Message-ID: <42851215.9SI46nDme2@thomas> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35C6195B@smartserver.smartshare.dk>

05/08/2021 08:08, Morten Brørup:
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> > Sent: Wednesday, 4 August 2021 15.30
> > 
> > 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>
> > ---
> >  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.
> > +
> > 
> 
> I have a couple of suggestions:
> 
> 1. Add that this bug was present in previous DPDK releases for many years. If possible, mention which release introduced the bug.
> 
> We don't want users to choose to stay on older release, thinking that it does not have this bug.
> 
> Also, if a user experiences unexplainable problems with segmented packets an older DPDK release, he might get lucky and find these release notes, which could reveal the root cause of the problems he is experiencing.
> 
> 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).
> 
> With those two additions,
> Acked-by: Morten Brørup <mb@smartsharesystems.com>

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/




  reply	other threads:[~2021-08-06 14:21 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-04 17:00 [dpdk-dev] [PATCH] mbuf: fix reset on mbuf free Olivier Matz
2020-11-05  0:15 ` Ananyev, Konstantin
2020-11-05  7:46   ` Olivier Matz
2020-11-05  8:26     ` Andrew Rybchenko
2020-11-05  9:10       ` Olivier Matz
2020-11-05 11:34         ` Ananyev, Konstantin
2020-11-05 12:31           ` Olivier Matz
2020-11-05 13:14             ` Ananyev, Konstantin
2020-11-05 13:24               ` Olivier Matz
2020-11-05 13:55                 ` Ananyev, Konstantin
2020-11-05 16:30                   ` Morten Brørup
2020-11-05 23:55                     ` Ananyev, Konstantin
2020-11-06  7:52                       ` Morten Brørup
2020-11-06  8:20                         ` Olivier Matz
2020-11-06  8:50                           ` Morten Brørup
2020-11-06 10:04                             ` Olivier Matz
2020-11-06 10:07                               ` Morten Brørup
2020-11-06 11:53                                 ` Ananyev, Konstantin
2020-11-06 12:23                                   ` Morten Brørup
2020-11-08 14:16                                     ` Andrew Rybchenko
2020-11-08 14:19                                       ` Ananyev, Konstantin
2020-11-10 16:26                                         ` Olivier Matz
2020-11-05  8:33     ` Morten Brørup
2020-11-05  9:03       ` Olivier Matz
2020-11-05  9:09     ` Andrew Rybchenko
2020-11-08  7:25 ` Ali Alnubani
2020-12-18 12:52 ` [dpdk-dev] [PATCH v2] " Olivier Matz
2020-12-18 13:18   ` Morten Brørup
2020-12-18 23:33     ` Ajit Khaparde
2021-01-06 13:33 ` [dpdk-dev] [PATCH v3] " Olivier Matz
2021-01-10  9:28   ` Ali Alnubani
2021-01-11 13:14   ` Ananyev, Konstantin
2021-01-13 13:27 ` [dpdk-dev] [PATCH v4] " Olivier Matz
2021-01-15 13:59   ` [dpdk-dev] [dpdk-stable] " David Marchand
2021-01-15 18:39     ` Ali Alnubani
2021-01-18 17:52       ` Ali Alnubani
2021-01-19  8:32         ` Olivier Matz
2021-01-19  8:53           ` Morten Brørup
2021-01-19 12:00             ` Ferruh Yigit
2021-01-19 12:27               ` Morten Brørup
2021-01-19 14:03                 ` Ferruh Yigit
2021-01-19 14:21                   ` Morten Brørup
2021-01-21  9:15                     ` Ferruh Yigit
2021-01-19 14:04           ` Slava Ovsiienko
2021-07-24  8:47             ` Thomas Monjalon
2021-07-30 12:36               ` Olivier Matz
2021-07-30 14:35                 ` Morten Brørup
2021-07-30 14:54                   ` Thomas Monjalon
2021-07-30 15:14                     ` Olivier Matz
2021-07-30 15:23                       ` Morten Brørup
2021-08-04 13:29                       ` [dpdk-dev] [PATCH] doc: add known issue with mbuf segment Thomas Monjalon
2021-08-04 14:25                         ` Ajit Khaparde
2021-08-05  6:08                         ` Morten Brørup
2021-08-06 14:21                           ` Thomas Monjalon [this message]
2021-08-06 14:24                             ` Morten Brørup
2021-09-28  8:28                     ` [dpdk-dev] [dpdk-stable] [PATCH v4] mbuf: fix reset on mbuf free Thomas Monjalon
2021-09-28  9:00                       ` Slava Ovsiienko
2021-09-28  9:25                         ` Ananyev, Konstantin
2021-09-28  9:39                         ` Morten Brørup
2021-09-29  8:03                           ` Ali Alnubani
2021-09-29 21:39                             ` Olivier Matz
2021-09-30 13:29                               ` Ali Alnubani
2021-10-21  8:26                                 ` Thomas Monjalon
2021-01-21  9:19       ` Ferruh Yigit
2021-01-21  9:29         ` Morten Brørup
2021-01-21 16:35           ` [dpdk-dev] [dpdklab] " Lincoln Lavoie
2021-01-23  8:57             ` Morten Brørup
2021-01-25 17:00               ` Brandon Lo
2021-01-25 18:42             ` Ferruh Yigit
2021-06-15 13:56   ` [dpdk-dev] " Morten Brørup
2021-09-29 21:37   ` [dpdk-dev] [PATCH v5] " Olivier Matz
2021-09-30 13:27     ` Ali Alnubani
2021-10-21  9:18     ` David Marchand
2022-07-28 14:06       ` CI performance test results might be misleading Morten Brørup

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