[PATCH v1] net/vhost: clear data of packet mbuf after sending pkts

[David Marchand]

On Tue, Mar 1, 2022 at 10:02 AM Zhang, Yuying <yuying.zhang at intel.com> wrote:
> > -----Original Message-----
> > From: David Marchand <david.marchand at redhat.com>
> > Sent: Tuesday, March 1, 2022 4:44 PM
> > To: Zhang, Yuying <yuying.zhang at intel.com>
> > Cc: dev <dev at dpdk.org>; Maxime Coquelin <maxime.coquelin at redhat.com>;
> > Xia, Chenbo <chenbo.xia at intel.com>; dpdk stable <stable at 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 at 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.


-- 
David Marchand