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Subject: Re: [PATCH] Periodically flow expire from flow offload tables
From:   Michael Lilja <michael.lilja@gmail.com>
In-Reply-To: <25246B91-B5BE-43CA-9D98-67950F17F0A1@gmail.com>
Date:   Wed, 26 Oct 2022 21:40:11 +0200
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>, netdev@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        netfilter-devel@vger.kernel.org, coreteam@netfilter.org
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References: <20221023171658.69761-1-michael.lilja@gmail.com>
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To:     Pablo Neira Ayuso <pablo@netfilter.org>
Precedence: bulk

Hi,

I just quickly tried following the flow_offload_teardown() path instead =
of clearing IPS_OFFLOAD in flow_offload_del() and it does have some side =
effects. The flow is added again before the HW has actually reported it =
to be NF_FLOW_HW_DEAD.=20

The sequence with my patch is:
  : Retire -> Remove from hw tables -> Remove from sw tables -> =
kfree(flow) -> flow_offload_add()

But if flow_offload_teardown() is called on expire I see:
  : Retire -> Remove from hw tables -> flow_offload_add() -> Remove from =
sw tables -> kfree(flow)
=20
I need to investigate why this happens, maybe the IPS_OFFLOAD flag is =
cleared too early and should not be cleared until the flow is actually =
removed, like I do? Maybe the issue is not seen before because on =
timeout or flow_is_dying() no packet arrive to create the flow again =
prematurely?

Thanks,
Michael