From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0744B34F49C; Wed, 3 Dec 2025 16:13:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764778392; cv=none; b=iKtd/2wvPP7fjkxVC8YTVlDErFqislwmqUfeezj7iIs0vpv4KGsX5j/yR/qoVuMEODJyV2109Xifswhnrm2AFsQmQxbRu606mahy6CAkN7sJGfdK01OvDj/fWh3bKGuU2oIJt+RvPePpVNO+SHLUT3B3asNJlwymyg79suYqSdE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764778392; c=relaxed/simple; bh=cEoLVAAPLkhcNvt1BzJCCTaMS+c1GhD/vOOXHwcfxTY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YEgd6N3+kqmy+NqlwTYAP2lX0EbAArmwXQbECPj7bq8FZUuVdk7ZOmEV6V8VsmWi9eaBasKw9MlKn15yo8wI+cWTxu9UiVrBRuC6hbbZE9RU4jtsG8DLt1fHXhnUpcRkBuHnA8JR540Jo6QrYG/q5sognr92dd79YyFNeMAhhYM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=b3mntrv+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="b3mntrv+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2C6BC4CEF5; Wed, 3 Dec 2025 16:13:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1764778391; bh=cEoLVAAPLkhcNvt1BzJCCTaMS+c1GhD/vOOXHwcfxTY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=b3mntrv+2UTqea0yswvSSJxbAVjpf0/Ur3MogM1+zvCRQ4YjLghOBCHnTY7bE1GpI Na2Yx7u7v7hTcl3i6swHly7gx2hP4wsw293Gru6ztCND0IbQmcW72e8XtRF8Xj4oHk K+5PlEBFrSX9+ljiLyMj5OL0XCUlJiiKzr+xSPZ0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Paolo Abeni , Geliang Tang , "Matthieu Baerts (NGI0)" , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.15 331/392] mptcp: fix ack generation for fallback msk Date: Wed, 3 Dec 2025 16:28:01 +0100 Message-ID: <20251203152426.348293192@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251203152414.082328008@linuxfoundation.org> References: <20251203152414.082328008@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paolo Abeni [ Upstream commit 5e15395f6d9ec07395866c5511f4b4ac566c0c9b ] mptcp_cleanup_rbuf() needs to know the last most recent, mptcp-level rcv_wnd sent, and such information is tracked into the msk->old_wspace field, updated at ack transmission time by mptcp_write_options(). Fallback socket do not add any mptcp options, such helper is never invoked, and msk->old_wspace value remain stale. That in turn makes ack generation at recvmsg() time quite random. Address the issue ensuring mptcp_write_options() is invoked even for fallback sockets, and just update the needed info in such a case. The issue went unnoticed for a long time, as mptcp currently overshots the fallback socket receive buffer autotune significantly. It is going to change in the near future. Fixes: e3859603ba13 ("mptcp: better msk receive window updates") Cc: stable@vger.kernel.org Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/594 Signed-off-by: Paolo Abeni Reviewed-by: Geliang Tang Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251118-net-mptcp-misc-fixes-6-18-rc6-v1-1-806d3781c95f@kernel.org Signed-off-by: Jakub Kicinski [ Adjust context ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- net/mptcp/options.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -810,8 +810,11 @@ bool mptcp_established_options(struct so opts->suboptions = 0; + /* Force later mptcp_write_options(), but do not use any actual + * option space. + */ if (unlikely(__mptcp_check_fallback(msk))) - return false; + return true; if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST)) { if (mptcp_established_options_mp_fail(sk, &opt_size, remaining, opts)) { @@ -1222,6 +1225,20 @@ static void mptcp_set_rwin(const struct WRITE_ONCE(msk->rcv_wnd_sent, ack_seq); } +static void mptcp_track_rwin(const struct tcp_sock *tp) +{ + const struct sock *ssk = (const struct sock *)tp; + struct mptcp_subflow_context *subflow; + struct mptcp_sock *msk; + + if (!ssk) + return; + + subflow = mptcp_subflow_ctx(ssk); + msk = mptcp_sk(subflow->conn); + WRITE_ONCE(msk->old_wspace, tp->rcv_wnd); +} + __sum16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum) { struct csum_pseudo_header header; @@ -1283,6 +1300,12 @@ void mptcp_write_options(__be32 *ptr, co return; } + /* Fallback to TCP */ + if (unlikely(!opts->suboptions)) { + mptcp_track_rwin(tp); + return; + } + /* DSS, MPC, MPJ and ADD_ADDR are mutually exclusive, see * mptcp_established_options*() */