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[108.212.132.20]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-4177e5e8185sm11914165fac.12.2026.03.14.13.14.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Mar 2026 13:14:54 -0700 (PDT) From: atwellwea@gmail.com To: netdev@vger.kernel.org, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, edumazet@google.com, ncardwell@google.com Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-trace-kernel@vger.kernel.org, mptcp@lists.linux.dev, dsahern@kernel.org, horms@kernel.org, kuniyu@google.com, andrew+netdev@lunn.ch, willemdebruijn.kernel@gmail.com, jasowang@redhat.com, skhan@linuxfoundation.org, corbet@lwn.net, matttbe@kernel.org, martineau@kernel.org, geliang@kernel.org, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, 0x7f454c46@gmail.com Subject: [PATCH net-next v2 09/14] mptcp: refresh TCP receive-window snapshots on subflows Date: Sat, 14 Mar 2026 14:13:43 -0600 Message-ID: <20260314201348.1786972-10-atwellwea@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260314201348.1786972-1-atwellwea@gmail.com> References: <20260314201348.1786972-1-atwellwea@gmail.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Wesley Atwell When MPTCP resynchronizes the per-subflow TCP shadow window from the mptcp-level receive state, refresh the live rwnd snapshot and the remembered maximum-window snapshot along with it. That keeps subflow TCP bookkeeping aligned with the sender-visible window state tracked in the core TCP patches. Signed-off-by: Wesley Atwell --- net/mptcp/options.c | 14 +++++++++----- net/mptcp/protocol.h | 14 +++++++++++--- 2 files changed, 20 insertions(+), 8 deletions(-) diff --git a/net/mptcp/options.c b/net/mptcp/options.c index 8a1c5698983c..64cd637484a4 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -1073,9 +1073,12 @@ static void rwin_update(struct mptcp_sock *msk, struct sock *ssk, return; /* 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 += 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)); tcp_update_max_rcv_wnd_seq(tp); subflow->rcv_wnd_sent = mptcp_rcv_wnd; } @@ -1335,12 +1338,13 @@ static void mptcp_set_rwin(struct tcp_sock *tp, struct tcphdr *th) if (rcv_wnd_new != 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 = rcv_wnd_old; win = rcv_wnd_old - ack_seq; - new_win = min_t(u64, win, U32_MAX); - tp->rcv_wnd = new_win; + tcp_set_rcv_wnd(tp, min_t(u64, win, U32_MAX)); + new_win = tp->rcv_wnd; tcp_update_max_rcv_wnd_seq(tp); /* 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 sock *sk, int win) return __tcp_space_from_win(mptcp_sk(sk)->scaling_ratio, win); } +/* MPTCP exposes window space from the mptcp-level receive queue, so it tracks + * 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)); } static inline struct mptcp_data_frag *mptcp_send_head(const struct sock *sk) -- 2.43.0