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

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Message-ID: <CANn89iK92fYoHOerB_wArODthu30dcY753fmN6GQf1UP8ciwqg@mail.gmail.com>
Date: Tue, 16 Apr 2024 11:37:01 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Davide Caratti <dcaratti@...hat.com>
Cc: Jamal Hadi Salim <jhs@...atatu.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 11:28 AM Davide Caratti <dcaratti@...hat.com> wrote:
>
> hi Eric, thanks for looking at this!
>
> On Tue, Apr 16, 2024 at 11:14 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Tue, Apr 16, 2024 at 10:05 AM Davide Caratti <dcaratti@...hat.com> wrote:
>
> [...]
>
> (FTR, the discussion started off-list :) more context at
> https://github.com/multipath-tcp/mptcp_net-next/issues/451 )
>
> > > 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/
> > >
> >
> > Hmmm, I think I missed that lockdep_unregister_key() was a NOP unless
> > CONFIG_LOCKDEP=y
>
> yes, the slowdown is there only on debug kernels.
>
> > Sorry for this, can you repost your patch ?
>
> Sure, but please leave me some time to understand what to do with HTB
> (you were right at [1] and I didn't notice
> htb_set_lockdep_class_child()  [2] at that time).
>
> thanks!
>
> [1] https://lore.kernel.org/netdev/CANn89iLXjstLx-=hFR0Rhav462+9pH3JTyE45t+nyiszKKCPTQ@mail.gmail.com/
> [2] https://elixir.bootlin.com/linux/latest/source/net/sched/sch_htb.c#L1042

Great, thanks for your help !