Re: [PATCH mptcp-net v2 0/3] mptcp: fix TCP fallback on single-subflow MP_FAIL

[Matthieu Baerts <matttbe@kernel.org>]

Hi Chenguang,

On 15/07/2026 08:18, Chenguang Zhao wrote:
> From: Chenguang Zhao <zhaochenguang@kylinos.cn>
> 
> When a valid MP_FAIL is received and infinite fallback is still allowed
> (single contiguous subflow), RFC8684 section 3.7 requires leaving MPTCP
> mode. Today the stack only clears allow_subflows and defers the real
> fallback to the later infinite-map transmit path. If no data is sent in
> between, the peer can still complete the 4th ACK as MPTCP and keep using
> MPTCP options.
> 
> This series falls back immediately after the MP_FAIL response, rejects
> later joins via mptcp_is_fully_established(), annotates allow_subflows
> with READ/WRITE_ONCE, and adds an MPFailFallback MIB while switching to
> mptcp_try_fallback().
> 
> Patch 1 fixes the fallback behaviour.
> Patch 2 annotates allow_subflows accesses.
> Patch 3 adds the dedicated MIB and uses the common fallback helper.
Thank you for this series and your patience. It looks like the CI didn't
manage to validate this. Do you mind rebasing it on top of the 'export'
(or 'for-review') branch please?

I also have a couple of comments/questions on the different patches if
you don't mind.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.