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[108.212.132.20]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-4177e6ae0e3sm1568938fac.16.2026.03.11.00.56.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Mar 2026 00:56:36 -0700 (PDT) From: Wesley Atwell To: davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, edumazet@google.com, ncardwell@google.com, dsahern@kernel.org, matttbe@kernel.org, martineau@kernel.org, netdev@vger.kernel.org, mptcp@lists.linux.dev Cc: kuniyu@google.com, horms@kernel.org, geliang@kernel.org, corbet@lwn.net, skhan@linuxfoundation.org, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, 0x7f454c46@gmail.com, linux-doc@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, atwellwea@gmail.com Subject: [PATCH net 5/7] mptcp: refresh tcp rcv_wnd snapshot when syncing receive windows Date: Wed, 11 Mar 2026 01:55:58 -0600 Message-Id: <20260311075600.948413-6-atwellwea@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260311075600.948413-1-atwellwea@gmail.com> References: <20260311075600.948413-1-atwellwea@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" MPTCP rewrites the TCP shadow receive window on subflows when shared receive-window state changes. Once tp->rcv_wnd carries paired snapshot semantics, those subflow shadow updates have to refresh the snapshot too. Convert the MPTCP window-sync write sites to use the helper and keep the aggregate receive-space arithmetic using the explicit rwnd-availability helper. Signed-off-by: Wesley Atwell --- net/mptcp/options.c | 12 ++++++++---- net/mptcp/protocol.h | 14 +++++++++++--- 2 files changed, 19 insertions(+), 7 deletions(-) diff --git a/net/mptcp/options.c b/net/mptcp/options.c index 43df4293f58b..6e6aa084cbfa 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -1073,9 +1073,12 @@ static void rwin_update(struct mptcp_sock *msk, stru= ct sock *ssk, return; =20 /* Some other subflow grew the mptcp-level rwin since rcv_wup, - * resync. + * resync. Keep the TCP shadow window in its advertised u32 domain + * and refresh the advertise-time scaling snapshot while doing so. */ - tp->rcv_wnd +=3D mptcp_rcv_wnd - subflow->rcv_wnd_sent; + tcp_set_rcv_wnd(tp, min_t(u64, (u64)tp->rcv_wnd + + (mptcp_rcv_wnd - subflow->rcv_wnd_sent), + U32_MAX)); subflow->rcv_wnd_sent =3D mptcp_rcv_wnd; } =20 @@ -1334,11 +1337,12 @@ static void mptcp_set_rwin(struct tcp_sock *tp, str= uct tcphdr *th) if (rcv_wnd_new !=3D rcv_wnd_old) { raise_win: /* The msk-level rcv wnd is after the tcp level one, - * sync the latter. + * sync the latter and refresh its advertise-time scaling + * snapshot. */ rcv_wnd_new =3D rcv_wnd_old; win =3D rcv_wnd_old - ack_seq; - tp->rcv_wnd =3D min_t(u64, win, U32_MAX); + tcp_set_rcv_wnd(tp, min_t(u64, win, U32_MAX)); new_win =3D tp->rcv_wnd; =20 /* Make sure we do not exceed the maximum possible diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 0bd1ee860316..4ea95c9c0c7a 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -408,11 +408,19 @@ static inline int mptcp_space_from_win(const struct s= ock *sk, int win) return __tcp_space_from_win(mptcp_sk(sk)->scaling_ratio, win); } =20 +/* MPTCP exposes window space from the mptcp-level receive queue, so it tr= acks + * a separate backlog counter from the subflow backlog embedded in struct = sock. + */ +static inline int mptcp_rwnd_avail(const struct sock *sk) +{ + return READ_ONCE(sk->sk_rcvbuf) - + READ_ONCE(mptcp_sk(sk)->backlog_len) - + tcp_rmem_used(sk); +} + static inline int __mptcp_space(const struct sock *sk) { - return mptcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf) - - READ_ONCE(mptcp_sk(sk)->backlog_len) - - sk_rmem_alloc_get(sk)); + return mptcp_win_from_space(sk, mptcp_rwnd_avail(sk)); } =20 static inline struct mptcp_data_frag *mptcp_send_head(const struct sock *s= k) --=20 2.34.1