Re: [PATCH v8 net-next 0/2] Explicit TSO segment count

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Mon Aug 24, 2026 at 10:05 PM CEST, Jakub Kicinski wrote:
> On Mon, 24 Aug 2026 18:31:37 +0200 chia-yu.chang@nokia-bell-labs.com
> wrote:
>> From: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
>>
>> Hello,
>>
>> This series replaces the existing min_tso_segs() congestion control
>> callback with a new tso_segs() callback that allows congestion control
>> algorithms to provide an explicit TSO segment count for each data burst.
>>  
>> To support BPF congestion controls, the series also exposes
>> tcp_tso_autosize() as a BPF kfunc, allowing BPF implementations to
>> reuse the kernel TSO autosizing logic while implementing custom
>> tso_segs() callbacks.
>
> AI CI says:
>
> The bpf-ci build jobs are failing for this patch on all tested
> architectures/toolchains (x86-64 gcc-15, x86-64 llvm-21, aarch64 gcc-15,
> s390x gcc-15), all with the same link-time error:
>
>   net/ipv4/tcp_bbr.o: in function `__BTF_ID__set8__tcp_bbr_check_kfunc_ids':
>   tcp_bbr.c:(.BTF_ids+0x...): undefined reference to `KF_DEPRECATED'
>
> This comes from the change to net/ipv4/tcp_bbr.c that marks the retained
> bbr_min_tso_segs() kfunc entry with the KF_DEPRECATED flag:
>
>   BTF_ID_FLAGS(func, bbr_min_tso_segs, KF_DEPRECATED)
>   BTF_ID_FLAGS(func, bbr_tso_segs)
>
> KF_DEPRECATED does not resolve to a usable symbol/flag in this tree, so
> the BTF id set for tcp_bbr fails to link into vmlinux on every
> architecture and toolchain -- it's a straight undefined-reference error,
> not a per-arch/per-config issue.
>
> Could you drop the KF_DEPRECATED flag (or use a flag that this kfunc
> infrastructure actually defines) on bbr_min_tso_segs, and re-verify that
> the kernel links cleanly? A local `make net/ipv4/tcp_bbr.o vmlinux`
> build (or the bpf-ci selftest build job) should reproduce this quickly.
>
> Full build log for reference:
>
>   ld.lld-21: error: undefined symbol: KF_DEPRECATED
>   >>> referenced by usercopy_64.c
>   >>>               vmlinux.o:(__BTF_ID__set8__tcp_bbr_check_kfunc_ids)

I think Chia-Yu's AI is hallucinating, it was a proposed flag but not added yet...