netdev - Re: [REGRESSION] Userland interface breaks due to hard HFSC

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Date: Fri, 6 Oct 2023 15:51:14 -0300
From: Pedro Tammela <pctammela@...atatu.com>
To: Christian Theune <ct@...ingcircus.io>, stable@...r.kernel.org,
 netdev@...r.kernel.org
Cc: regressions@...ts.linux.dev, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [REGRESSION] Userland interface breaks due to hard HFSC_FSC
 requirement

On 06/10/2023 05:37, Christian Theune wrote:
> Hi,
> 
> (prefix, I was not aware of the regression reporting process and incorrectly reported this informally with the developers mentioned in the change)
> 
> I upgraded from 6.1.38 to 6.1.55 this morning and it broke my traffic shaping script, leaving me with a non-functional uplink on a remote router.
> 
> The script errors out like this:
> 
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + ext=ispA
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + ext_ingress=ifb0
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + modprobe ifb
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + modprobe act_mirred
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc del dev ispA root
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2061]: Error: Cannot delete qdisc with handle of zero.
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + true
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc del dev ispA ingress
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2064]: Error: Cannot find specified qdisc on specified device.
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + true
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc del dev ifb0 root
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2066]: Error: Cannot delete qdisc with handle of zero.
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + true
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc del dev ifb0 ingress
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2067]: Error: Cannot find specified qdisc on specified device.
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + true
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc add dev ispA handle ffff: ingress
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + ifconfig ifb0 up
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc filter add dev ispA parent ffff: protocol all u32 match u32 0 0 action mirred egress redirect dev ifb0
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc qdisc add dev ifb0 root handle 1: hfsc default 1
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc class add dev ifb0 parent 1: classid 1:999 hfsc rt m2 2.5gbit
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2053]: + tc class add dev ifb0 parent 1:999 classid 1:1 hfsc sc rate 50mbit
> Oct 06 05:49:22 wendy00 isp-setup-shaping-start[2077]: Error: Invalid parent - parent class must have FSC.
> 
> The error message is also a bit weird (but that’s likely due to iproute2 being weird) as the CLI interface for `tc` and the error message do not map well. (I think I would have to choose `hfsc sc` on the parent to enable the FSC option which isn’t mentioned anywhere in the hfsc manpage).
> 
> The breaking change was introduced in 6.1.53[1] and a multitude of other currently supported kernels:
> 
> ----
> commit a1e820fc7808e42b990d224f40e9b4895503ac40
> Author: Budimir Markovic <markovicbudimir@...il.com>
> Date: Thu Aug 24 01:49:05 2023 -0700
> 
> net/sched: sch_hfsc: Ensure inner classes have fsc curve
> 
> [ Upstream commit b3d26c5702c7d6c45456326e56d2ccf3f103e60f ]
> 
> HFSC assumes that inner classes have an fsc curve, but it is currently
> possible for classes without an fsc curve to become parents. This leads
> to bugs including a use-after-free.
> 
> Don't allow non-root classes without HFSC_FSC to become parents.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: Budimir Markovic <markovicbudimir@...il.com>
> Signed-off-by: Budimir Markovic <markovicbudimir@...il.com>
> Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
> Link: https://lore.kernel.org/r/20230824084905.422-1-markovicbudimir@gmail.com
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ----
> 
> Regards,
> Christian
> 
> [1] https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.1.53
> 
> #regzbot introduced: a1e820fc7808e42b990d224f40e9b4895503ac40
> 
> 

I will take a look,
Thanks!