Re: [PATCH net 0/7] tcp: preserve advertised rwnd accounting across receive-memory decisions

Eric Dumazet
2026-03-11T08:34:45Z

On Wed, Mar 11, 2026 at 8:56 AM Wesley Atwell <atwellwea@gmail.com> wrote:
>
> This series keeps sender-visible TCP receive-window accounting tied to the
> scaling basis that was in force when the window was advertised.
>
> Problem
> -------
>
> `tp->rcv_wnd` is an advertised promise to the sender, but later
> receive-memory admission and clamping could reconstruct that promise
> through the mutable live `scaling_ratio`. After ratio drift, the stack
> could retain or advertise a receive window that no longer matched the
> local hard rmem budget.
>
> Fix
> ---
>
> - store the advertise-time scaling basis alongside `tp->rcv_wnd`
> - refresh that pair at the TCP and MPTCP receive-window write sites
> - consume the snapshot in receive-memory admission, clamping, and the
> scaled-window quantization path
> - preserve the snapshot across `TCP_REPAIR_WINDOW` restore when userspace
> provides it, and fall back safely when legacy userspace cannot
> - expose the accounting in tracepoints and cover the ABI/runtime contract
> in selftests
>

Your series will heavily conflict with Simon's one

https://patchwork.kernel.org/project/netdevbpf/list/?series=1063486&state=%2A&archive=both

I suggest you rebase/retest/resend after we merge it.

> Series layout
> -------------
>
> 1. track the receive-window snapshot state and helpers
> 2. refresh the snapshot when TCP advertises or initializes windows
> 3. use the snapshot in receive-memory admission and clamping
> 4. extend `TCP_REPAIR_WINDOW` for exact restore plus legacy compatibility
> 5. refresh the TCP shadow window snapshot in MPTCP
> 6. expose rmem/backlog state in `rcvbuf_grow` tracepoints
> 7. cover legacy and extended repair-window layouts in selftests
>
> Testing
> -------
>
> - `git diff --check origin/main..HEAD`
> - `scripts/checkpatch.pl --strict --show-types` on patches 1-7
> - `make -j8 headers`
> - `make -j8 net/ipv4/tcp_input.o net/ipv4/tcp_output.o net/ipv4/tcp_minisocks.o net/ipv4/tcp.o`
> - `make -j8 C=1 CF='-D__CHECK_ENDIAN__' W=1 net/ipv4/tcp_input.o net/ipv4/tcp_output.o net/ipv4/tcp_minisocks.o net/ipv4/tcp.o`
> - `make SPHINXDIRS='networking/net_cachelines' htmldocs`
> - `make -j8 vmlinux bzImage modules`
> - `make -C tools/testing/selftests/net/tcp_ao -j8`
> - `make -C tools/testing/selftests/net/mptcp -j8`
> - `packetdrill --dry_run` for `tcp_rcv_toobig.pkt` and
> `tcp_rcv_toobig_default.pkt`
> - `virtme-run` guest pass for both packetdrill tests
> - feature-enabled guest pass for `restore_ipv4`, `self-connect_ipv4`, and
> `mptcp_sockopt.sh`
>
> Thanks,
> Wesley
>
> ---
> base-commit: 908c344d5cfa0ee6efb3226d22ea661e078ebfa0
> --
> 2.43.0
>