From 73db8a61af8b25dd0e99a8de52d545190829c690 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Tue, 3 Feb 2026 19:41:18 +0100 Subject: [PATCH] mptcp: fix receive space timestamp initialization [ Upstream commit 70274765fef555af92a1532d5bd5450c691fca9d ] MPTCP initialize the receive buffer stamp in mptcp_rcv_space_init(), using the provided subflow stamp. Such helper is invoked in several places; for passive sockets, space init happened at clone time. In such scenario, MPTCP ends-up accesses the subflow stamp before its initialization, leading to quite randomic timing for the first receive buffer auto-tune event, as the timestamp for newly created subflow is not refreshed there. Fix the issue moving the stamp initialization out of the mentioned helper, at the data transfer start, and always using a fresh timestamp. Fixes: 013e3179dbd2 ("mptcp: fix rcv space initialization") Reviewed-by: Mat Martineau Signed-off-by: Paolo Abeni Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-2-31ec8bfc56d1@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/mptcp/protocol.c | 8 ++++---- net/mptcp/protocol.h | 5 +++++ 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index f2bf78c019df..e682d52a06b7 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -2085,8 +2085,8 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied) msk->rcvq_space.copied += copied; - mstamp = div_u64(tcp_clock_ns(), NSEC_PER_USEC); - time = tcp_stamp_us_delta(mstamp, msk->rcvq_space.time); + mstamp = mptcp_stamp(); + time = tcp_stamp_us_delta(mstamp, READ_ONCE(msk->rcvq_space.time)); rtt_us = msk->rcvq_space.rtt_us; if (rtt_us && time < (rtt_us >> 3)) @@ -3493,6 +3493,7 @@ struct sock *mptcp_sk_clone_init(const struct sock *sk, __mptcp_propagate_sndbuf(nsk, ssk); mptcp_rcv_space_init(msk, ssk); + msk->rcvq_space.time = mptcp_stamp(); if (mp_opt->suboptions & OPTION_MPTCP_MPC_ACK) __mptcp_subflow_fully_established(msk, subflow, mp_opt); @@ -3510,8 +3511,6 @@ void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk) msk->rcvq_space.copied = 0; msk->rcvq_space.rtt_us = 0; - msk->rcvq_space.time = tp->tcp_mstamp; - /* initial rcv_space offering made to peer */ msk->rcvq_space.space = min_t(u32, tp->rcv_wnd, TCP_INIT_CWND * tp->advmss); @@ -3727,6 +3726,7 @@ void mptcp_finish_connect(struct sock *ssk) * accessing the field below */ WRITE_ONCE(msk->local_key, subflow->local_key); + WRITE_ONCE(msk->rcvq_space.time, mptcp_stamp()); mptcp_pm_new_connection(msk, ssk, 0); } diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index bdec5ad9defb..b266002660d7 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -861,6 +861,11 @@ static inline bool mptcp_is_fully_established(struct sock *sk) READ_ONCE(mptcp_sk(sk)->fully_established); } +static inline u64 mptcp_stamp(void) +{ + return div_u64(tcp_clock_ns(), NSEC_PER_USEC); +} + void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk); void mptcp_data_ready(struct sock *sk, struct sock *ssk); bool mptcp_finish_join(struct sock *sk);