From: Eric Dumazet <edumazet@google.com>

This patch has no functional change, and prepares the following one.

tcp_rcvbuf_grow() will need to have access to tp->rcvq_space.space
old and new values.

Change mptcp_rcvbuf_grow() in a similar way.

Signed-off-by: Eric Dumazet <edumazet@google.com>
[ Moved 'oldval' declaration to the next patch to avoid warnings at
 build time. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 include/net/tcp.h    |  2 +-
 net/ipv4/tcp_input.c | 14 +++++++-------
 net/mptcp/protocol.c | 20 ++++++++------------
 3 files changed, 16 insertions(+), 20 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 5ca230ed526a..ab20f549b8f9 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -370,7 +370,7 @@ void tcp_delack_timer_handler(struct sock *sk);
 int tcp_ioctl(struct sock *sk, int cmd, int *karg);
 enum skb_drop_reason tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);
 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb);
-void tcp_rcvbuf_grow(struct sock *sk);
+void tcp_rcvbuf_grow(struct sock *sk, u32 newval);
 void tcp_rcv_space_adjust(struct sock *sk);
 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
 void tcp_twsk_destructor(struct sock *sk);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 31ea5af49f2d..cb4e07f84ae2 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -891,18 +891,20 @@ static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 	}
 }
 
-void tcp_rcvbuf_grow(struct sock *sk)
+void tcp_rcvbuf_grow(struct sock *sk, u32 newval)
 {
 	const struct net *net = sock_net(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
-	int rcvwin, rcvbuf, cap;
+	u32 rcvwin, rcvbuf, cap;
+
+	tp->rcvq_space.space = newval;
 
 	if (!READ_ONCE(net->ipv4.sysctl_tcp_moderate_rcvbuf) ||
 	    (sk->sk_userlocks & SOCK_RCVBUF_LOCK))
 		return;
 
 	/* slow start: allow the sender to double its rate. */
-	rcvwin = tp->rcvq_space.space << 1;
+	rcvwin = newval << 1;
 
 	if (!RB_EMPTY_ROOT(&tp->out_of_order_queue))
 		rcvwin += TCP_SKB_CB(tp->ooo_last_skb)->end_seq - tp->rcv_nxt;
@@ -943,9 +945,7 @@ void tcp_rcv_space_adjust(struct sock *sk)
 
 	trace_tcp_rcvbuf_grow(sk, time);
 
-	tp->rcvq_space.space = copied;
-
-	tcp_rcvbuf_grow(sk);
+	tcp_rcvbuf_grow(sk, copied);
 
 new_measure:
 	tp->rcvq_space.seq = tp->copied_seq;
@@ -5270,7 +5270,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
 	}
 	/* do not grow rcvbuf for not-yet-accepted or orphaned sockets. */
 	if (sk->sk_socket)
-		tcp_rcvbuf_grow(sk);
+		tcp_rcvbuf_grow(sk, tp->rcvq_space.space);
 }
 
 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index a8a3bdf95543..052a0c62023f 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -194,17 +194,18 @@ static bool mptcp_ooo_try_coalesce(struct mptcp_sock *msk, struct sk_buff *to,
  * - mptcp does not maintain a msk-level window clamp
  * - returns true when  the receive buffer is actually updated
  */
-static bool mptcp_rcvbuf_grow(struct sock *sk)
+static bool mptcp_rcvbuf_grow(struct sock *sk, u32 newval)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	const struct net *net = sock_net(sk);
-	int rcvwin, rcvbuf, cap;
+	u32 rcvwin, rcvbuf, cap;
 
+	msk->rcvq_space.space = newval;
 	if (!READ_ONCE(net->ipv4.sysctl_tcp_moderate_rcvbuf) ||
 	    (sk->sk_userlocks & SOCK_RCVBUF_LOCK))
 		return false;
 
-	rcvwin = msk->rcvq_space.space << 1;
+	rcvwin = newval << 1;
 
 	if (!RB_EMPTY_ROOT(&msk->out_of_order_queue))
 		rcvwin += MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq - msk->ack_seq;
@@ -334,7 +335,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 	skb_set_owner_r(skb, sk);
 	/* do not grow rcvbuf for not-yet-accepted or orphaned sockets. */
 	if (sk->sk_socket)
-		mptcp_rcvbuf_grow(sk);
+		mptcp_rcvbuf_grow(sk, msk->rcvq_space.space);
 }
 
 static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,
@@ -2049,10 +2050,7 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
 	if (msk->rcvq_space.copied <= msk->rcvq_space.space)
 		goto new_measure;
 
-	msk->rcvq_space.space = msk->rcvq_space.copied;
-	if (mptcp_rcvbuf_grow(sk)) {
-		int copied = msk->rcvq_space.copied;
-
+	if (mptcp_rcvbuf_grow(sk, msk->rcvq_space.copied)) {
 		/* Make subflows follow along.  If we do not do this, we
 		 * get drops at subflow level if skbs can't be moved to
 		 * the mptcp rx queue fast enough (announced rcv_win can
@@ -2065,10 +2063,8 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
 			ssk = mptcp_subflow_tcp_sock(subflow);
 			slow = lock_sock_fast(ssk);
 			/* subflows can be added before tcp_init_transfer() */
-			if (tcp_sk(ssk)->rcvq_space.space) {
-				tcp_sk(ssk)->rcvq_space.space = copied;
-				tcp_rcvbuf_grow(ssk);
-			}
+			if (tcp_sk(ssk)->rcvq_space.space)
+				tcp_rcvbuf_grow(ssk, msk->rcvq_space.copied);
 			unlock_sock_fast(ssk, slow);
 		}
 	}

-- 
2.51.0

On Tue, Oct 28, 2025 at 7:58 AM Matthieu Baerts (NGI0)
<matttbe@kernel.org> wrote:
>
> From: Eric Dumazet <edumazet@google.com>
>
> This patch has no functional change, and prepares the following one.
>
> tcp_rcvbuf_grow() will need to have access to tp->rcvq_space.space
> old and new values.
>
> Change mptcp_rcvbuf_grow() in a similar way.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> [ Moved 'oldval' declaration to the next patch to avoid warnings at
>  build time. ]
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> ---

Reviewed-by: Neal Cardwell <ncardwell@google.com>

Thanks, Eric and Matthieu!

neal