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Sun, 7 Jun 2026 03:20:33 -0400 (EDT) Date: Sun, 7 Jun 2026 09:19:37 +0200 From: Greg KH To: Matthieu Baerts Cc: Sasha Levin , Gang Yan , Paolo Abeni , stable@vger.kernel.org Subject: Re: [PATCH 7.0.y] mptcp: update window_clamp on subflows when SO_RCVBUF is set Message-ID: <2026060758-democrat-wipe-0671@gregkh> References: <2026052819-liberty-cramp-97fe@gregkh> <20260601003905.84041-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jun 01, 2026 at 10:50:33AM +1000, Matthieu Baerts wrote: > Hi Sasha, > > On 01/06/2026 10:39, Sasha Levin wrote: > > From: Gang Yan > > > > [ Upstream commit 3a543ae0e2092d5c2085d5f21f7a7dbafdffea3c ] > > > > Add __mptcp_subflow_set_rcvbuf() helper to write the subflow sk_rcvbuf, > > but also to call the recently added tcp_set_rcvbuf() helper to update > > window_clamp. This is needed because the window clap is updated when > > scaling_ratio changes, in tcp_measure_rcv_mss(). Until scaling_ratio > > changes, the subflow is stuck with the old window clamp which may be > > based on a small initial buffer. > > > > Use this new helper in both mptcp_sol_socket_sync_intval() (setsockopt > > path) and sync_socket_options() (new subflow creation path). > > > > Note that this patch depends on commit b025461303d8 ("tcp: update > > window_clamp when SO_RCVBUF is set"): it fixes the issue on TCP side, > > but the same fix is needed on MPTCP side as well. > Thank you for the backport. I guess there is a conflict, because commit > b025461303d8 ("tcp: update window_clamp when SO_RCVBUF is set") has not > been backported to 7.0 (nor 6.18, 6.12 and 6.6). See the note above for > more details. > > In other words, MPTCP is imitating TCP's behaviour. So no need to > backport this patch if the fix on TCP side is not backported either. > > I think it would be better to take both the TCP fix (b025461303d8), and > this one (3a543ae0e209). But maybe the TCP fix has not been backported > on purpose? It was not tagged for stable inclusion, so it was not applied to any stable trees. As the tcp change isn't included, I'll just drop this one too, thanks. greg k-h