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

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Message-Id: <BBEA77E4-D376-45CE-9A93-415F2E0703D7@flyingcircus.io>
Date: Fri, 6 Oct 2023 12:51:32 +0200
From: Christian Theune <ct@...ingcircus.io>
To: 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

Hi,

sorry, no I didn’t. I don’t have a testbed available right now to try this out quickly.

Christian

> On 6. Oct 2023, at 11:16, Linux regression tracking (Thorsten Leemhuis) <regressions@...mhuis.info> wrote:
> 
> 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
>> 

Liebe Grüße,
Christian Theune

-- 
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