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[108.212.132.20]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-4177e5e8185sm11914165fac.12.2026.03.14.13.14.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Mar 2026 13:14:50 -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 06/14] tcp: regrow rcvbuf when scaling_ratio drops after advertisement Date: Sat, 14 Mar 2026 14:13:40 -0600 Message-ID: <20260314201348.1786972-7-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: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Wesley Atwell When tcp_measure_rcv_mss() lowers scaling_ratio after a window was already advertised, grow sk_rcvbuf so the remaining live sender-visible window still has matching hard receive-memory backing. This repairs the live advertised window only. Retracted-window rescue is handled separately in a later patch. Signed-off-by: Wesley Atwell --- net/ipv4/tcp_input.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 32256519a085..d76e4e4c0e57 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -221,6 +221,31 @@ static __cold void tcp_gro_dev_warn(const struct sock *sk, const struct sk_buff rcu_read_unlock(); } +/* If scaling_ratio drops after we already advertised tp->rcv_wnd, grow + * sk_rcvbuf so the remaining live window still maps back to hard memory + * units under the old advertise-time basis. + */ +static void tcp_try_grow_advertised_window(struct sock *sk, + const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + int needed; + + /* Keep this repair aligned with tcp_rcvbuf_grow(): do not adjust + * receive-buffer backing for not-yet-accepted or orphaned sockets. + */ + if (!tcp_rcvbuf_grow_allowed(sk)) + return; + + if (!tcp_receive_window(tp)) + return; + + if (!tcp_space_from_rcv_wnd(tp, tcp_receive_window(tp), &needed)) + return; + + tcp_try_grow_rcvbuf(sk, needed); +} + /* Adapt the MSS value used to make delayed ack decision to the * real world. */ @@ -251,6 +276,7 @@ static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb) if (old_ratio != tcp_sk(sk)->scaling_ratio) { struct tcp_sock *tp = tcp_sk(sk); + tcp_try_grow_advertised_window(sk, skb); val = tcp_win_from_space(sk, sk->sk_rcvbuf); tcp_set_window_clamp(sk, val); -- 2.43.0