linux-kernel - [PATCH net v3 1/4] mptcp: fix subflow rcvbuf adjust

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Message-Id: <20251028-net-tcp-recv-autotune-v3-1-74b43ba4c84c@kernel.org>
Date: Tue, 28 Oct 2025 12:57:59 +0100
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>, 
 Neal Cardwell <ncardwell@...gle.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
 "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 David Ahern <dsahern@...nel.org>, Matthieu Baerts <matttbe@...nel.org>, 
 Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 mptcp@...ts.linux.dev
Subject: [PATCH net v3 1/4] mptcp: fix subflow rcvbuf adjust

From: Paolo Abeni <pabeni@...hat.com>

The mptcp PM can add subflow to the conn_list before tcp_init_transfer().
Calling tcp_rcvbuf_grow() on such subflow is not correct as later
init will overwrite the update.

Fix the issue calling tcp_rcvbuf_grow() only after init buffer
initialization.

Fixes: e118cdc34dd1 ("mptcp: rcvbuf auto-tuning improvement")
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/mptcp/protocol.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 0292162a14ee..a8a3bdf95543 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2051,6 +2051,7 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)

 	msk->rcvq_space.space = msk->rcvq_space.copied;
 	if (mptcp_rcvbuf_grow(sk)) {
+		int copied = 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
@@ -2063,8 +2064,11 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)

 			ssk = mptcp_subflow_tcp_sock(subflow);
 			slow = lock_sock_fast(ssk);
-			tcp_sk(ssk)->rcvq_space.space = msk->rcvq_space.copied;
-			tcp_rcvbuf_grow(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);
+			}
 			unlock_sock_fast(ssk, slow);
 		}
 	}

-- 
2.51.0