Re: [PATCH v2 mptcp-net 2/2] mptcp: fix duplicate reset on fastclose

[Matthieu Baerts <matttbe@kernel.org>]

Hi Paolo,

On 07/11/2025 08:23, Paolo Abeni wrote:
> The CI reports sporadic failures of the fastclose self-tests. The root
> cause is a duplicate reset, not carrying the relevant MPTCP option.
> In the failing scenario the bad reset is received by the peer before
> the fastclose one, preventing the reception of the latter.
> 
> Indeed there is window of opportunity at fastclose time for the following
> race:
> 
> mptcp_do_fastclose
>   __mptcp_close_ssk
>     __tcp_close()
>       tcp_set_state() [1]
>       tcp_send_active_reset() [2]
> 
> After [1] the stack will send reset to in-flight data reaching the now
> closed port. Such reset may race with [2].
> 
> Address the issue explicitly sending a single reset on fastclose before
> explicitly moving the subflow to close status.

Thank you for the proper fix!

Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> Fixes: d21f83485518 ("mptcp: use fastclose on more edge scenarios");

When applying this patch, I will remove the extra ';' at the end of this
line, plus not removing a line below.

I will also revert "selftests: mptcp: join: fastclose: drop plain RST"
and only keep the removal of the two 'MPTCP_LIB_SUBTEST_FLAKY=1' lines.

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