netdev - Re: [PATCH net-next 2/2] act_mirred: use the backlog for nested calls to mirred ingress

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Message-ID: <CAM0EoMm-noMkXrbrP+ioDxd6HRMZNgLTqs7EV=CH104=d1WLpg@mail.gmail.com>
Date:   Mon, 23 Jan 2023 14:41:04 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Davide Caratti <dcaratti@...hat.com>, jiri@...nulli.us,
        lucien.xin@...il.com, netdev@...r.kernel.org, pabeni@...hat.com,
        wizhao@...hat.com, xiyou.wangcong@...il.com
Subject: Re: [PATCH net-next 2/2] act_mirred: use the backlog for nested calls
 to mirred ingress

On Mon, Jan 23, 2023 at 12:22 PM Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
>
> On Fri, Jan 20, 2023 at 06:01:40PM +0100, Davide Caratti wrote:
> > William reports kernel soft-lockups on some OVS topologies when TC mirred
> > egress->ingress action is hit by local TCP traffic [1].
> > The same can also be reproduced with SCTP (thanks Xin for verifying), when
> > client and server reach themselves through mirred egress to ingress, and
> > one of the two peers sends a "heartbeat" packet (from within a timer).
> >
> > Enqueueing to backlog proved to fix this soft lockup; however, as Cong
> > noticed [2], we should preserve - when possible - the current mirred
> > behavior that counts as "overlimits" any eventual packet drop subsequent to
> > the mirred forwarding action [3]. A compromise solution might use the
> > backlog only when tcf_mirred_act() has a nest level greater than one:
> > change tcf_mirred_forward() accordingly.
> >
> > Also, add a kselftest that can reproduce the lockup and verifies TC mirred
> > ability to account for further packet drops after TC mirred egress->ingress
> > (when the nest level is 1).
> >
> >  [1] https://lore.kernel.org/netdev/33dc43f587ec1388ba456b4915c75f02a8aae226.1663945716.git.dcaratti@redhat.com/
> >  [2] https://lore.kernel.org/netdev/Y0w%2FWWY60gqrtGLp@pop-os.localdomain/
> >  [3] such behavior is not guaranteed: for example, if RPS or skb RX
> >      timestamping is enabled on the mirred target device, the kernel
> >      can defer receiving the skb and return NET_RX_SUCCESS inside
> >      tcf_mirred_forward().
> >
> > Reported-by: William Zhao <wizhao@...hat.com>
> > CC: Xin Long <lucien.xin@...il.com>
> > Signed-off-by: Davide Caratti <dcaratti@...hat.com>
>
> Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal