This an attempt to fix the data transfer stall reported by Geliang and
Gang more carefully enforcing memory constraints at the MPTCP level.

Patch 1/10 moves the bound check before entering the TCP socket.
Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely re-using
TCP helpers on MPTCP skbs.
Patch 6 makes TCP pruning related helpers available to MPTCP and patch 7
makes use of them. Patch 8 addresses an edge scenario that could still
lead to transfer stall under memory pressure.
Finally patch 9 and 10 improve the MPTCP-level retransmission schema to
make recovery from memory pressure significanly faster.

Note that the diffstat is biases by the quite large patch 4/9, which
contains mechanical transformation of existing code; "real" changes are
noticiable smaller.

Tested successfully vs the test cases proposed by Geliang and Gang and
vs the selftests.
---
Some notes on each patch WRT ignored or false positive issues noticed
by sashiko so far.

Paolo Abeni (10):
  mptcp: move checks vs rcvbuf size earlier in the RX path
  mptcp: drop the mptcp_ooo_try_coalesce() helper
  mptcp: drop the cant_coalesce CB field
  mptcp: remove CB offset field
  mptcp: sync mptcp skb cb layout with tcp one
  tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too
  mptcp: implemented OoO queue pruning
  mptcp: track prune recovery status
  mptcp: move the retrans loop to a separate helper
  mptcp: let the retrans scheduler do its job.

 include/net/tcp.h    |   8 +
 net/ipv4/tcp_input.c |  55 +++---
 net/mptcp/fastopen.c |  17 +-
 net/mptcp/mib.c      |   3 +
 net/mptcp/mib.h      |   3 +
 net/mptcp/options.c  |  64 ++++++-
 net/mptcp/protocol.c | 399 ++++++++++++++++++++++++++++---------------
 net/mptcp/protocol.h |  24 ++-
 net/mptcp/subflow.c  |  11 ++
 9 files changed, 414 insertions(+), 170 deletions(-)

-- 
2.54.0

Hi Paolo,

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): Success! ✅
- KVM Validation: normal (only selftest_mptcp_join): Success! ✅
- KVM Validation: debug (except selftest_mptcp_join): Unstable: 1 failed test(s): packetdrill_sockopts ⚠️ 
- 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/25329194631

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/4ee2213ed212
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1089374


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)