[PATCH net 5/7] mptcp: refresh tcp rcv_wnd snapshot when syncing receive windows
From: Wesley Atwell <hidden>
Date: 2026-03-11 07:56:38
Also in:
linux-doc, linux-kselftest, linux-trace-kernel, lkml, mptcp, netdev
Subsystem:
networking [general], networking [mptcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Matthieu Baerts, Mat Martineau, Linus Torvalds
MPTCP rewrites the TCP shadow receive window on subflows when shared receive-window state changes. Once tp->rcv_wnd carries paired snapshot semantics, those subflow shadow updates have to refresh the snapshot too. Convert the MPTCP window-sync write sites to use the helper and keep the aggregate receive-space arithmetic using the explicit rwnd-availability helper. Signed-off-by: Wesley Atwell <redacted> --- net/mptcp/options.c | 12 ++++++++---- net/mptcp/protocol.h | 14 +++++++++++--- 2 files changed, 19 insertions(+), 7 deletions(-)
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 43df4293f58b..6e6aa084cbfa 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c@@ -1073,9 +1073,12 @@ static void rwin_update(struct mptcp_sock *msk, struct sock *ssk, return; /* Some other subflow grew the mptcp-level rwin since rcv_wup, - * resync. + * resync. Keep the TCP shadow window in its advertised u32 domain + * and refresh the advertise-time scaling snapshot while doing so. */ - tp->rcv_wnd += mptcp_rcv_wnd - subflow->rcv_wnd_sent; + tcp_set_rcv_wnd(tp, min_t(u64, (u64)tp->rcv_wnd + + (mptcp_rcv_wnd - subflow->rcv_wnd_sent), + U32_MAX)); subflow->rcv_wnd_sent = mptcp_rcv_wnd; }
@@ -1334,11 +1337,12 @@ static void mptcp_set_rwin(struct tcp_sock *tp, struct tcphdr *th) if (rcv_wnd_new != rcv_wnd_old) { raise_win: /* The msk-level rcv wnd is after the tcp level one, - * sync the latter. + * sync the latter and refresh its advertise-time scaling + * snapshot. */ rcv_wnd_new = rcv_wnd_old; win = rcv_wnd_old - ack_seq; - tp->rcv_wnd = min_t(u64, win, U32_MAX); + tcp_set_rcv_wnd(tp, min_t(u64, win, U32_MAX)); new_win = tp->rcv_wnd; /* Make sure we do not exceed the maximum possible
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 0bd1ee860316..4ea95c9c0c7a 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h@@ -408,11 +408,19 @@ static inline int mptcp_space_from_win(const struct sock *sk, int win) return __tcp_space_from_win(mptcp_sk(sk)->scaling_ratio, win); } +/* MPTCP exposes window space from the mptcp-level receive queue, so it tracks + * a separate backlog counter from the subflow backlog embedded in struct sock. + */ +static inline int mptcp_rwnd_avail(const struct sock *sk) +{ + return READ_ONCE(sk->sk_rcvbuf) - + READ_ONCE(mptcp_sk(sk)->backlog_len) - + tcp_rmem_used(sk); +} + static inline int __mptcp_space(const struct sock *sk) { - return mptcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf) - - READ_ONCE(mptcp_sk(sk)->backlog_len) - - sk_rmem_alloc_get(sk)); + return mptcp_win_from_space(sk, mptcp_rwnd_avail(sk)); } static inline struct mptcp_data_frag *mptcp_send_head(const struct sock *sk)
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2.34.1