linux-kernel - [PATCH net-next 01/15] mptcp: do not account for OoO in mptcp_rcvbuf

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Message-Id: <20260203-net-next-mptcp-misc-feat-6-20-v1-1-31ec8bfc56d1@kernel.org>
Date: Tue, 03 Feb 2026 19:41:17 +0100
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>, Shuah Khan <shuah@...nel.org>
Cc: netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Subject: [PATCH net-next 01/15] mptcp: do not account for OoO in
 mptcp_rcvbuf_grow()

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

MPTCP-level OoOs are physiological when multiple subflows are active
concurrently and will not cause retransmissions nor are caused by
drops.

Accounting for them in mptcp_rcvbuf_grow() causes the rcvbuf slowly
drifting towards tcp_rmem[2].

Remove such accounting. Note that subflows will still account for TCP-level
OoO when the MPTCP-level rcvbuf is propagated.

This also closes a subtle and very unlikely race condition with rcvspace
init; active sockets with user-space holding the msk-level socket lock,
could complete such initialization in the receive callback, after that the
first OoO data reaches the rcvbuf and potentially triggering a divide by
zero Oops.

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

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 9b8c51937eb2..758a6dcb1d7b 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -224,9 +224,6 @@ static bool mptcp_rcvbuf_grow(struct sock *sk, u32 newval)
 	do_div(grow, oldval);
 	rcvwin += grow << 1;

-	if (!RB_EMPTY_ROOT(&msk->out_of_order_queue))
-		rcvwin += MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq - msk->ack_seq;
-
 	cap = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);

 	rcvbuf = min_t(u32, mptcp_space_from_win(sk, rcvwin), cap);
@@ -350,9 +347,6 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 end:
 	skb_condense(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, msk->rcvq_space.space);
 }

 static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,

-- 
2.51.0