Re: [PATCH 6.12.y] mptcp: update window_clamp on subflows when SO_RCVBUF is set

[Matthieu Baerts <matttbe@kernel.org>]

Hi Sasha,

On 01/06/2026 10:47, Sasha Levin wrote:
> From: Gang Yan <yangang@kylinos.cn>
> 
> [ 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.
See my message on the same patch for v7.0: b025461303d8 should be
backported first, but if not, better not to backport this patch.

Cheers,
Matt
-- 
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