Subject: Re: [PATCH v3 net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops

From: Jakub Kicinski <[email-masked]>
Date: Sun, 15 Mar 2026 14:51:20 -0700

On Sun, 15 Mar 2026 15:40:03 +0000 Eric Dumazet wrote:
> v3: fix tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c (Jakub)
> v2: fix tools/testing/selftests/bpf/progs/bpf_cc_cubic.c (Jakub)
> v1: https://lore.kernel.org/netdev/[email-masked]/

Builds but does not run:
https://github.com/kernel-patches/bpf/actions/runs/23116079851/job/67142296478

The BPF CI can be triggered by opening a pull request their
kernel-patches/bpf repo. We can also also Martin to help.

Error: #23 bpf_iter_setsockopt
  Error: #23 bpf_iter_setsockopt
  create_netns:PASS:create netns 0 nsec
  create_netns:PASS:bring up lo 0 nsec
  serial_test_bpf_iter_setsockopt:PASS:iter_skel 0 nsec
  serial_test_bpf_iter_setsockopt:PASS:attach iter 0 nsec
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': BPF program load failed: -ENOTSUPP
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': -- BEGIN PROG LOAD LOG --
  attach to unsupported member cwnd_event_tx_start of struct tcp_congestion_ops
  processed 0 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
  -- END PROG LOAD LOG --
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': failed to load: -ENOTSUPP
  libbpf: failed to load object 'bpf_cubic'
  libbpf: failed to load BPF skeleton 'bpf_cubic': -ENOTSUPP
  serial_test_bpf_iter_setsockopt:FAIL:cubic_skel unexpected error: -524
Error: #34 bpf_tcp_ca
Error: #34/2 bpf_tcp_ca/cubic
  Error: #34/2 bpf_tcp_ca/cubic
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': BPF program load failed: -ENOTSUPP
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': -- BEGIN PROG LOAD LOG --
  attach to unsupported member cwnd_event_tx_start of struct tcp_congestion_ops
  processed 0 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
  -- END PROG LOAD LOG --
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': failed to load: -ENOTSUPP
  libbpf: failed to load object 'bpf_cubic'
  libbpf: failed to load BPF skeleton 'bpf_cubic': -ENOTSUPP
  test_cubic:FAIL:bpf_cubic__open_and_load unexpected error: -524
Error: #34/14 bpf_tcp_ca/tcp_ca_kfunc
  Error: #34/14 bpf_tcp_ca/tcp_ca_kfunc
  libbpf: prog 'cwnd_event_tx_start': BPF program load failed: -ENOTSUPP
  libbpf: prog 'cwnd_event_tx_start': -- BEGIN PROG LOAD LOG --
  attach to unsupported member cwnd_event_tx_start of struct tcp_congestion_ops
  processed 0 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
  -- END PROG LOAD LOG --
  libbpf: prog 'cwnd_event_tx_start': failed to load: -ENOTSUPP
  libbpf: failed to load object 'tcp_ca_kfunc'
  libbpf: failed to load BPF skeleton 'tcp_ca_kfunc': -ENOTSUPP
  test_tcp_ca_kfunc:FAIL:tcp_ca_kfunc__open_and_load unexpected error: -524
Error: #34/15 bpf_tcp_ca/cc_cubic
  Error: #34/15 bpf_tcp_ca/cc_cubic
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': BPF program load failed: -ENOTSUPP
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': -- BEGIN PROG LOAD LOG --
  attach to unsupported member cwnd_event_tx_start of struct tcp_congestion_ops
  processed 0 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
  -- END PROG LOAD LOG --
  libbpf: prog 'bpf_cubic_cwnd_event_tx_start': failed to load: -ENOTSUPP
  libbpf: failed to load object 'bpf_cc_cubic'
  libbpf: failed to load BPF skeleton 'bpf_cc_cubic': -ENOTSUPP
  test_cc_cubic:FAIL:bpf_cc_cubic__open_and_load unexpected error: -524