netdev - Re: [PATCH net] net/sched: ets: use old 'nbands' while purging unused classes

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Message-ID: <aJmge28EVB0jKOLF@dcaratti.users.ipa.redhat.com>
Date: Mon, 11 Aug 2025 09:49:15 +0200
From: Davide Caratti <dcaratti@...hat.com>
To: Victor Nogueira <victor@...atatu.com>
Cc: Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, Lion Ackermann <nnamrec@...il.com>,
	Petr Machata <petrm@...lanox.com>, netdev@...r.kernel.org,
	Ivan Vecera <ivecera@...hat.com>, Li Shuang <shuali@...hat.com>
Subject: Re: [PATCH net] net/sched: ets: use old 'nbands' while purging
 unused classes

On Fri, Aug 08, 2025 at 03:15:13PM -0300, Victor Nogueira wrote:
> On 8/7/25 12:48, Davide Caratti wrote:

[...]
 
> > Fixes: 103406b38c60 ("net/sched: Always pass notifications when child class becomes empty")
> > Fixes: c062f2a0b04d ("net/sched: sch_ets: don't remove idle classes from the round-robin list")
> > Fixes: dcc68b4d8084 ("net: sch_ets: Add a new Qdisc")
> > Reported-by: Li Shuang <shuali@...hat.com>
> > Closes: https://issues.redhat.com/browse/RHEL-108026
> > Co-developed-by: Ivan Vecera <ivecera@...hat.com>
> > Signed-off-by: Ivan Vecera <ivecera@...hat.com>
> > Signed-off-by: Davide Caratti <dcaratti@...hat.com>
> 
> Can you submit a tdc test case for this bug?

hello Victor,

Thanks for looking at this!

At a first look: TDC is not the correct tool here, because it doesn't
allow changing the qdisc tree while the scapy plugin emits traffic.
Maybe it's better to extend sch_ets.sh from net/forwarding instead?

If so, I can follow-up on net-next with a patch that adds a new
test-case that includes the 3-lines in [1] - while this patch can go
as-is in 'net' (and eventually in stable). In alternative, I can
investigate on TDC adding "sch_plug" to the qdisc tree in a way
that DWRR never deplete, and the crash would then happen with "verifyCmd".


WDYT?

-- 
davide

[1] https://lore.kernel.org/netdev/e08c7f4a6882f260011909a868311c6e9b54f3e4.1639153474.git.dcaratti@redhat.com/