netdev - Re: VETH & AF_PACKET problem

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Message-ID: <CACeb84ubWOXj54mGjqnhX6Rbw3Vk3Kx1d0e1MVqOFSOFr2Ro_A@mail.gmail.com>
Date:   Wed, 14 Nov 2018 10:25:35 +0530
From:   "Anand H. Krishnan" <anandhkrishnan@...il.com>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org
Subject: Re: VETH & AF_PACKET problem

Ok. I have 4.18.11 ubuntu. I will try out the latest kernel and will
let you know.
Thank you for your opinion and help.

Thanks,
Anand
On Wed, Nov 14, 2018 at 10:11 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> On Tue, Nov 13, 2018 at 8:29 PM Anand H. Krishnan
> <anandhkrishnan@...il.com> wrote:
> >
> > skb_scrub_packet calls skb_orphan and from there the destructor is called.
>
> Not since
>
>   commit 9c4c325252c54b34d53b3d0ffd535182b744e03d
>   skbuff: preserve sock reference when scrubbing the skb.
>   v4.19-rc1~140^2~523^2
>
> But the general issue is valid that the tx_ring slot should not be
> released until all users of the pages are freed, not just when the
> skb is orphaned (e.g., on skb_set_owner_r).
>
> I think that this can happen even on a transmit to a physical
> nic, if a clone is queued for reception on a packet socket. That
> clone does not clone the destructor, so if the reader is slow,
> the slot may be released from consume_skb on the original
> path.
>
> I have not verified this yet. But if correct, then the long term
> solution is to use refcounted uarg, similar to msg_zerocopy.