netdev - Re: [PATCH RFC net 1/1] net/sched: Fix mirred to self recursion

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Message-ID: <CAM0EoMmjxPF8TXfqEO2iUeHcEfnpD50CPGJ7dHiSMWmTU40PaA@mail.gmail.com>
Date: Tue, 16 Apr 2024 06:30:24 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Davide Caratti <dcaratti@...hat.com>
Cc: Eric Dumazet <edumazet@...gle.com>, davem@...emloft.net, kuba@...nel.org, 
	pabeni@...hat.com, jiri@...nulli.us, xiyou.wangcong@...il.com, 
	netdev@...r.kernel.org, renmingshuai@...wei.com, 
	Victor Nogueira <victor@...atatu.com>
Subject: Re: [PATCH RFC net 1/1] net/sched: Fix mirred to self recursion

On Tue, Apr 16, 2024 at 4:05 AM Davide Caratti <dcaratti@...hat.com> wrote:
>
> hello,
>
> On Mon, Apr 15, 2024 at 11:15 PM Jamal Hadi Salim <jhs@...atatu.com> wrote:
> >
> [...]
>
> > Victor sent the patch. As i mentioned earlier, we found a lockdep
> > false positive for the case of redirect from eth0->eth1->eth0
> > (potential fix attached)
>
> I tried a similar approach some months ago [1],  but  _ like Eric
> noticed  _ it might slowdown qdisc_destroy() too much because of the
> call to synchronize_rcu(). Maybe the key unregistering can be done
> later (e.g. when the qdisc is freed) ?
>
> [1] https://lore.kernel.org/netdev/73065927a49619fcd60e5b765c929f899a66cd1a.1701853200.git.dcaratti@redhat.com/

I wish i'd remembered this ;->  It is exactly the same scenario.
Triggered  example(eth0-->eth1-->eth0) as such:

tc qdisc add dev eth0 root handle 1: htb default 30
tc filter add dev eth0 handle 1: protocol ip prio 2 matchall \
     action mirred egress redirect dev eth1

tc qdisc add dev eth1 root handle 1: htb default 30
tc filter add dev eth1 handle 1: protocol ip prio 2 matchall \
     action mirred egress redirect dev eth0

So leaving it to you Davide..

cheers,
jamal

> --
> davide
>