This should fix the recent instabilities seen by MPTCP and NIPA CIs
where the 'mptcp_connect.sh' tests fail regularly when running the
'disconnect' subtests with "plain" TCP sockets, e.g.

  # INFO: disconnect
  # 63 ns1 MPTCP -> ns1 (10.0.1.1:20001      ) MPTCP     (duration   996ms) [ OK ]
  # 64 ns1 MPTCP -> ns1 (10.0.1.1:20002      ) TCP       (duration   851ms) [ OK ]
  # 65 ns1 TCP   -> ns1 (10.0.1.1:20003      ) MPTCP     Unexpected revents: POLLERR/POLLNVAL(19)
  # (duration   896ms) [FAIL] file received by server does not match (in, out):
  # -rw-r--r-- 1 root root 11112852 Aug 19 09:16 /tmp/tmp.hlJe5DoMoq.disconnect
  # Trailing bytes are:
  # /{ga 6@=#.8:-rw------- 1 root root 10085368 Aug 19 09:16 /tmp/tmp.blClunilxx
  # Trailing bytes are:
  # /{ga 6@=#.8:66 ns1 MPTCP -> ns1 (dead:beef:1::1:20004) MPTCP     (duration   987ms) [ OK ]
  # 67 ns1 MPTCP -> ns1 (dead:beef:1::1:20005) TCP       (duration   911ms) [ OK ]
  # 68 ns1 TCP   -> ns1 (dead:beef:1::1:20006) MPTCP     (duration   980ms) [ OK ]
  # [FAIL] Tests of the full disconnection have failed

Patch 3 fixes this issue, but a fix in MPTCP in patch 1 is also needed
to fix MPTCP behaviour, and simplify patch 3. Patches 2 and 4 improve
some errors reported by the selftests, and patch 5 helps with the
debugging. I guess all these patches can be sent to 'net'

Note: Patch 1 will cause errors in Packetdrill, that's normal, see [1].

Link: https://github.com/multipath-tcp/packetdrill/pull/171 [1]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Changes in v2:
- Patch 1: new
- Patch 3: no more state filtering needed thanks to patch 1
- Patch 4: switch from hexdump to od (Mat)
- Patch 5: new
- Link to v1: https://lore.kernel.org/r/20250819-sft-mptcp-disc-err-v1-0-9d0cf296bc13@kernel.org

---
Matthieu Baerts (NGI0) (5):
      mptcp: propagate shutdown to subflows when possible
      selftests: mptcp: connect: catch IO errors on listen side
      selftests: mptcp: avoid spurious errors on TCP disconnect
      selftests: mptcp: print trailing bytes with od
      selftests: mptcp: connect: print pcap suffix

 net/mptcp/protocol.c                               | 16 ++++++++++++++++
 tools/testing/selftests/net/mptcp/mptcp_connect.c  | 10 +++++++---
 tools/testing/selftests/net/mptcp/mptcp_connect.sh |  6 +++++-
 tools/testing/selftests/net/mptcp/mptcp_lib.sh     |  2 +-
 4 files changed, 29 insertions(+), 5 deletions(-)
---
base-commit: 9335a0684b0967cc704105e953f2a9d893fbcf57
change-id: 20250806-sft-mptcp-disc-err-3357b769bcdb

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>

Hi Matthieu,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal: Unstable: 3 failed test(s): packetdrill_dss packetdrill_fastopen packetdrill_syscalls 🔴
- KVM Validation: debug: Unstable: 3 failed test(s): packetdrill_dss packetdrill_fastopen packetdrill_syscalls 🔴
- KVM Validation: btf-normal (only bpftest_all): Success! ✅
- KVM Validation: btf-debug (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/17501634949

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/8e609acad818
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=999479


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)

Hello,

On 05/09/2025 22:46, MPTCP CI wrote:
> Hi Matthieu,
> 
> Thank you for your modifications, that's great!
> 
> Our CI did some validations and here is its report:
> 
> - KVM Validation: normal: Unstable: 3 failed test(s): packetdrill_dss packetdrill_fastopen packetdrill_syscalls 🔴
> - KVM Validation: debug: Unstable: 3 failed test(s): packetdrill_dss packetdrill_fastopen packetdrill_syscalls 🔴

As mentioned in the cover letter, these failures were expected:

Note: Patch 1 will cause errors in Packetdrill, that's normal, see:

  https://github.com/multipath-tcp/packetdrill/pull/171

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.