From: Stephen Hemminger <stephen@networkplumber.org>
To: David Marchand <david.marchand@redhat.com>
Cc: "Zhang, Yuying" <yuying.zhang@intel.com>, dev <dev@dpdk.org>,
Maxime Coquelin <maxime.coquelin@redhat.com>,
"Xia, Chenbo" <chenbo.xia@intel.com>,
dpdk stable <stable@dpdk.org>
Subject: Re: [PATCH v1] net/vhost: clear data of packet mbuf after sending pkts
Date: Tue, 1 Mar 2022 09:05:06 -0800 [thread overview]
Message-ID: <20220301090506.6fed12a5@hermes.local> (raw)
In-Reply-To: <CAJFAV8y5so5ML0_E7e1npc8jD=_P+83t4inXk53aVxhAkim9_g@mail.gmail.com>
On Tue, 1 Mar 2022 10:47:32 +0100
David Marchand <david.marchand@redhat.com> wrote:
> On Tue, Mar 1, 2022 at 10:02 AM Zhang, Yuying <yuying.zhang@intel.com> wrote:
> > > -----Original Message-----
> > > From: David Marchand <david.marchand@redhat.com>
> > > Sent: Tuesday, March 1, 2022 4:44 PM
> > > To: Zhang, Yuying <yuying.zhang@intel.com>
> > > Cc: dev <dev@dpdk.org>; Maxime Coquelin <maxime.coquelin@redhat.com>;
> > > Xia, Chenbo <chenbo.xia@intel.com>; dpdk stable <stable@dpdk.org>
> > > Subject: Re: [PATCH v1] net/vhost: clear data of packet mbuf after sending pkts
> > >
> > > On Tue, Mar 1, 2022 at 8:29 AM Yuying Zhang <yuying.zhang@intel.com> wrote:
> > > >
> > > > The PMD frees a packet mbuf back into its original mempool after
> > > > sending a packet. However, old data is not cleaned up which causes
> > > > error in payload of new packets. This patch clear data of packet mbuf
> > > > before freeing mbuf.
> > >
> > > This patch looks wrong to me.
> > > What is the actual issue you want to fix?
> >
> > eth_vhost_tx() frees the packet mbuf back into its original mempool every time after a packet sent without clearing the data field.
> > Then packet transmit function will get bulk directly without reset. New generated packet contains old data of previous packet. This is wrong.
>
> With the proposed patch, if the mbuf refcnt is != 0, you are shooting
> the data while some other part of the application might be needing it.
>
> Plus, there should be no expectation about a mbuf data content when
> retrieving one from a mempool.
> The only bytes that are guaranteed to be initialised by the mbuf API
> are its metadata.
>
>
> If there is an issue somewhere in dpdk where the mbuf data content is
> expected to be 0 on allocation, please point at it.
> Or share the full test that failed.
>
>
Agree. There is no guarantee that mbuf you get was not just used by
some other driver or library. Only the fields in rte_pktmbuf_reset are
guaranteed to be set.
next prev parent reply other threads:[~2022-03-01 17:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-01 7:28 Yuying Zhang
2022-03-01 8:38 ` Ling, WeiX
2022-03-01 8:43 ` David Marchand
2022-03-01 9:02 ` Zhang, Yuying
2022-03-01 9:47 ` David Marchand
2022-03-01 17:05 ` Stephen Hemminger [this message]
2022-03-02 8:58 ` Zhang, Yuying
2022-03-03 6:49 ` Xia, Chenbo
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