Subject: [PATCH net-next v2 00/14] tcp: preserve receive-window accounting across ratio drift

From: [email-masked]
Date: Sat, 14 Mar 2026 14:13:34 -0600

From: Wesley Atwell <[email-masked]>

This series keeps sender-visible TCP receive-window accounting tied to the
scaling basis that was in force when the window was advertised, even if
later receive-side truesize inflation lowers scaling_ratio or the live
receive window retracts below the largest right edge already exposed to the
sender.

After the receive-window retraction changes, the receive path needs to keep
track of two related pieces of sender-visible state:

  1. the live advertised receive window
  2. the maximum advertised right edge and the basis it was exposed with

This repost snapshots both, uses them to repair receive-buffer backing when
ratio drift would otherwise strand sender-visible space, extends
TCP_REPAIR_WINDOW so repair/restore can round-trip the new state, and adds
truesize-drift coverage through TUN packetdrill tests and netdevsim-based
selftests.

v2:
- repost to net-next and use the [PATCH net-next v2] prefix
- rebase the receive-window accounting changes on top of the retraction
  model
- split the series more finely
- snapshot both the live rwnd basis and the max advertised-window basis
- extend TCP_REPAIR_WINDOW to preserve legacy, v1, and current layouts
- add TUN RX truesize injection and packetdrill coverage for ratio drift
- split the generic netdevsim PSP extension cleanup into its own final
  patch after the peer RX truesize support
- add the requested ABI/runtime comments at the non-obvious review points

Testing:

- full runtime selftest coverage for netdevsim, tcp_ao, mptcp, and
  packetdrill; all runtime suites completed successfully
- tcp_ao completed 24/24 top-level tests, covering 803 passing checks,
  6 expected failures, 36 skips, and 0 unexpected failures
- mptcp completed 588 passing checks in aggregate, with 28 skips and
  0 unexpected failures
- packetdrill completed 219/219 runtime cases with 0 failures,
  including the new tests
- netdevsim completed 18/18 top-level runtime tests with 0 failures,
  including the peer RX truesize and related netdevsim coverage used by
  this series

Wesley Atwell (14):
  tcp: factor receive-memory accounting helpers
  tcp: snapshot advertise-time scaling for rcv_wnd
  tcp: refresh rcv_wnd snapshots at TCP write sites
  tcp: snapshot the maximum advertised receive window
  tcp: grow rcvbuf to back scaled-window quantization slack
  tcp: regrow rcvbuf when scaling_ratio drops after advertisement
  tcp: honor the maximum advertised window after live retraction
  tcp: extend TCP_REPAIR_WINDOW for live and max-window snapshots
  mptcp: refresh TCP receive-window snapshots on subflows
  tcp: expose rmem and backlog in tcp and mptcp rcvbuf_grow tracepoints
  selftests: tcp_ao: cover legacy, v1, and retracted repair windows
  tun/selftests: add RX truesize injection for TCP window tests
  netdevsim: add peer RX truesize support for selftests
  netdevsim: release pinned PSP ext on drop paths

 .../networking/net_cachelines/tcp_sock.rst    |   2 +
 drivers/net/netdevsim/netdev.c                | 156 ++++++-
 drivers/net/netdevsim/netdevsim.h             |   4 +
 drivers/net/tun.c                             |  65 +++
 include/linux/tcp.h                           |   2 +
 include/net/tcp.h                             | 118 ++++-
 include/trace/events/mptcp.h                  |  11 +-
 include/trace/events/tcp.h                    |  12 +-
 include/uapi/linux/if_tun.h                   |   4 +
 include/uapi/linux/tcp.h                      |   8 +
 net/ipv4/tcp.c                                |  75 ++-
 net/ipv4/tcp_fastopen.c                       |   2 +-
 net/ipv4/tcp_input.c                          | 160 ++++++-
 net/ipv4/tcp_minisocks.c                      |   4 +-
 net/ipv4/tcp_output.c                         |  25 +-
 net/mptcp/options.c                           |  14 +-
 net/mptcp/protocol.h                          |  14 +-
 .../selftests/drivers/net/netdevsim/Makefile  |   1 +
 .../drivers/net/netdevsim/peer-rx-truesize.sh | 426 ++++++++++++++++++
 .../tcp_rcv_neg_window_truesize.pkt           | 143 ++++++
 .../net/packetdrill/tcp_rcv_toobig.pkt        |  35 ++
 .../packetdrill/tcp_rcv_toobig_default.pkt    |  97 ++++
 .../tcp_rcv_toobig_default_truesize.pkt       | 118 +++++
 .../tcp_rcv_wnd_shrink_allowed_truesize.pkt   |  49 ++
 .../testing/selftests/net/tcp_ao/lib/aolib.h  |  83 +++-
 .../testing/selftests/net/tcp_ao/lib/repair.c |  18 +-
 .../selftests/net/tcp_ao/self-connect.c       | 201 ++++++++-
 tools/testing/selftests/net/tun.c             | 140 +++++-
 28 files changed, 1911 insertions(+), 76 deletions(-)
 create mode 100755 tools/testing/selftests/drivers/net/netdevsim/peer-rx-truesize.sh
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_neg_window_truesize.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_toobig.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_toobig_default.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_toobig_default_truesize.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed_truesize.pkt

base-commit: f807b5b9b89eb9220d034115c272c312251cbcac
-- 
2.43.0