Date: Fri, 6 Oct 2023 11:16:39 +0200
From: "Linux regression tracking (Thorsten Leemhuis)"
 <regressions@...mhuis.info>
To: Christian Theune <ct@...ingcircus.io>,
 Linux regressions mailing list <regressions@...ts.linux.dev>
Cc: stable@...r.kernel.org, netdev@...r.kernel.org, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Subject: Re: [REGRESSION] Userland interface breaks due to hard HFSC_FSC
 requirement

On 06.10.23 11:07, Christian Theune wrote:
> 
> it seems that 6.6rc4 is affected as well:
> 
> ----
> commit b3d26c5702c7d6c45456326e56d2ccf3f103e60f
> 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
> ——

Did you actually try if the problem occurs with 6.6-rc4? That the commit
is in there is expected (everything that lands in stable trees has to go
to mainline first).

Ciao, Thorsten

> I have not found newer commits that would suggest they change any behaviour around this in any way, but I might be wrong.
> 
> Christian
> 
>> On 6. Oct 2023, at 11:01, Linux regression tracking (Thorsten Leemhuis) <regressions@...mhuis.info> wrote:
>>
>> On 06.10.23 10:37, Christian Theune wrote:
>>>
>>> (prefix, I was not aware of the regression reporting process and incorrectly reported this informally with the developers mentioned in the change)
>>
>> Don't worry too much about that, but thx for taking care of all the
>> details. FWIW, there is one more thing that would be good to know:
>>
>> Does the problem happen with mainline (e.g. 6.6-rc4) as well? That's
>> relevant, as different people might care[1].
>>
>> Ciao, Thorsten
>>
>> [1] this among others is explained here:
>> https://linux-regtracking.leemhuis.info/post/frequent-reasons-why-linux-kernel-bug-reports-are-ignored/
>>
>>> 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
>>>
>>>
> 
> Liebe Grüße,
> Christian Theune
> 

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