Currently, it is possible to add a "signal" MPTCP endpoint with a v6
address and a port, or to directly request to send an ADD_ADDR with a v6
address and a port, but such signalling option cannot be sent when TCP
timestamps is used due to a lack of option space. Instead of simply
dropping such ADD_ADDR, the TCP timestamps can be dropped only for this
packet.

- Patch 1: fix for PREEMPT_RT kernels, for -net.

- Patches 2-4: small cleanups to avoid computing ADD/RM_ADDR twice.

- Patches 5-8: the new feature, controlled by a new sysctl knob.

- Patch 9: extra checks in the selftests.

- Patches 10-16: refactoring/cleanups: some of them were part of a
  previous patch: "mptcp: pm: clearer ADD_ADDR related helpers names"
  [1].

Note that the mptcp/add_addr/add_addr6_port_ts_server.pkt packetdrill
test is supposed to fail with this series, until this PR is applied:

  https://github.com/multipath-tcp/packetdrill/pull/198

Link: https://lore.kernel.org/20260415-mptcp-inc-limits-v5-20-e54c3bf80e4e@kernel.org [1]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Changes in v3:
- Patch 1: sk_stop_timer() should still be called under rcu.
- Patches 6-7: split + s/has_ts/add_addr_drop_ts/.
- Link to v2: https://patch.msgid.link/20260519-mptcp-add-addr6-port-ts-v2-0-3b36a51e6a86@kernel.org

Changes in v2:
- Patch 1: new.
- Patch 3: reset size in mptcp_pm_add_addr_signal for dropped options.
- Patches 4-5: split from previous patch 3. (Paolo)
- Patch 4: fix typo.
- Patch 5: fix reverse Xmas tree order + change label. (Paolo)
- Patch 6: back to v6 connection.
- Patch 10: fix comment.
- Patch 14: fix typo.
- Link to v1: https://patch.msgid.link/20260518-mptcp-add-addr6-port-ts-v1-0-f1ca26977fcd@kernel.org

---
Matthieu Baerts (NGI0) (16):
      [mptcp-net] mptcp: pm: avoid sleeping while holding rcu_read_lock
      mptcp: options: ADD_ADDR size can be negative
      mptcp: pm: avoid computing rm_addr size twice
      mptcp: pm: avoid computing add_addr size twice
      mptcp: introduce add_addr_v6_port_drop_ts sysctl knob
      tcp: allow mptcp to drop TS for some packets
      mptcp: pm: drop TCP TS with ADD_ADDRv6 + port
      selftests: mptcp: validate ADD_ADDRv6 + TS + port
      selftests: mptcp: always check sent/dropped ADD_ADDRs
      mptcp: pm: use for_each_subflow helper
      mptcp: pm: rename add_entry structure to add_addr
      mptcp: pm: uniform announced addresses helpers
      mptcp: pm: remove add_ prefix from timer
      mptcp: pm: make mptcp_pm_add_addr_send_ack static
      mptcp: pm: avoid using del_timer directly
      mptcp: pm: avoid confusing check_id in del_timer

 Documentation/networking/mptcp-sysctl.rst       |  13 ++
 include/net/mptcp.h                             |   3 +-
 net/ipv4/tcp_output.c                           |   6 +-
 net/mptcp/ctrl.c                                |  18 ++-
 net/mptcp/options.c                             |  43 ++----
 net/mptcp/pm.c                                  | 189 ++++++++++++++----------
 net/mptcp/pm_kernel.c                           |  22 +--
 net/mptcp/pm_userspace.c                        |   6 +-
 net/mptcp/protocol.h                            |  46 ++----
 net/mptcp/subflow.c                             |   4 +-
 tools/testing/selftests/net/mptcp/mptcp_join.sh |  83 +++++------
 11 files changed, 232 insertions(+), 201 deletions(-)
---
base-commit: 08d7466136ffa606d823f1fc4879f97d366d9e92
change-id: 20260508-mptcp-add-addr6-port-ts-371653e0f843

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 (except selftest_mptcp_join): Unstable: 1 failed test(s): packetdrill_add_addr ⚠️ 
- KVM Validation: normal (only selftest_mptcp_join): Success! ✅
- KVM Validation: debug (except selftest_mptcp_join): Unstable: 3 failed test(s): packetdrill_add_addr packetdrill_dss packetdrill_mp_capable ⚠️ 
- KVM Validation: debug (only selftest_mptcp_join): Success! ✅
- 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/26127754617

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/5468c1adc049
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1097625


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)