netdev - Re: [PATCH net] netfilter: flowtable: Fix expired flow not being deleted from software

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Message-ID: <20200511084243.GA18188@salvia>
Date:   Mon, 11 May 2020 10:42:43 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Paul Blakey <paulb@...lanox.com>
Cc:     Oz Shlomo <ozsh@...lanox.com>, Roi Dayan <roid@...lanox.com>,
        netdev@...r.kernel.org, Saeed Mahameed <saeedm@...lanox.com>,
        netfilter-devel@...r.kernel.org
Subject: Re: [PATCH net] netfilter: flowtable: Fix expired flow not being
 deleted from software

On Mon, May 11, 2020 at 10:24:44AM +0300, Paul Blakey wrote:
> 
> 
> On 5/11/2020 1:26 AM, Pablo Neira Ayuso wrote:
> > On Wed, May 06, 2020 at 02:27:29PM +0300, Paul Blakey wrote:
> >> Once a flow is considered expired, it is marked as DYING, and
> >> scheduled a delete from hardware. The flow will be deleted from
> >> software, in the next gc_step after hardware deletes the flow
> >> (and flow is marked DEAD). Till that happens, the flow's timeout
> >> might be updated from a previous scheduled stats, or software packets
> >> (refresh). This will cause the gc_step to no longer consider the flow
> >> expired, and it will not be deleted from software.
> >>
> >> Fix that by looking at the DYING flag as in deciding
> >> a flow should be deleted from software.
> > Would this work for you?
> >
> > The idea is to skip the refresh if this has already expired.
> >
> > Thanks.
> 
> The idea is ok, but timeout check + update isn't atomic (need atomic_inc_unlesss
> or something like that), and there is also
> the hardware stats which if comes too late (after gc finds it expired) might
> bring a flow back to life.

Right. Once the entry has expired, there should not be a way turning
back.

I'm attaching a new sketch, it's basically using the teardown state to
specify that the gc already made the decision to remove this entry.

Thanks.

View attachment "x.patch" of type "text/x-diff" (1047 bytes)