netdev - Re: [PATCH net] net/sched: act_mirred: use the backlog for mirred ingress

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Message-ID: <20240212070213.504d6930@kernel.org>
Date: Mon, 12 Feb 2024 07:02:13 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
 Davide Caratti <dcaratti@...hat.com>, xiyou.wangcong@...il.com,
 jiri@...nulli.us, shmulik.ladkani@...il.com
Subject: Re: [PATCH net] net/sched: act_mirred: use the backlog for mirred
 ingress

On Mon, 12 Feb 2024 09:51:20 -0500 Jamal Hadi Salim wrote:
> > The test Davide added in commit ca22da2fbd69 ("act_mirred: use the backlog
> > for nested calls to mirred ingress") hangs our testing VMs every 10 or so
> > runs, with the familiar tcp_v4_rcv -> tcp_v4_rcv deadlock reported by
> > lockdep.
> >
> > In the past there was a concern that the backlog indirection will
> > lead to loss of error reporting / less accurate stats. But the current
> > workaround does not seem to address the issue.
> 
> Let us run some basic tests on this first - it's a hairy spot. 

Thanks!

> Also, IIRC Cong had some reservations about this in the past. Can't
> remember what they were.

He was worried that the overlimits stats are no longer counted when we
decouple (and Davide's selftest actually checks for that so I had to
modify it).

I'm not married to the solution in any way but bugs much less serious
get three letter acronyms, we can't pretend this one doesn't exist.