Re: [PATCH mptcp-net v3 0/2] mptcp: pm: fix ADD_ADDR timer infinite retry on option space shortage

[Matthieu Baerts <matttbe@kernel.org>]

Hi Li,

On 07/05/2026 14:52, Li Xiasong wrote:
> This series fixes a bug where the ADD_ADDR timer can keep rescheduling
> indefinitely when TCP option space is insufficient, blocking subsequent
> addresses in the endpoint list from being announced.
> 
> The issue is reproducible when sending an IPv6 ADD_ADDR with port while
> tcp_timestamps is enabled. In that case, option space may be exhausted on
> pure ACKs, and ADD_ADDR retransmission can stall PM forward progress.
> 
> Patch 1 clears the signal in this path, skips the matching ADD_ADDR
> retransmission entry, and preserves PM state-machine progression.
> 
> Note on concurrency: timer cancellation in this path is best-effort.
> A concurrent add_timer callback that acquires pm.lock first may still
> perform one final ADD_ADDR send attempt before cancel state is applied.
> After cancel sets entry->retrans_times to ADD_ADDR_RETRANS_MAX, the
> callback-side check prevents further ADD_ADDR retransmissions.
> 
> Patch 2 adds a selftest to cover this behavior and prevent regressions.
> 
> Patch summary:
>   - patch 1: mptcp: pm: fix ADD_ADDR timer infinite retry on option space
>     insufficient
>   - patch 2: selftests: mptcp: join: cover ADD_ADDR tx drop and list
>     progress
> 
> Changes since v2:
>   - document the possible timer-cancel race window in the commit message
>     and code comments
>   - keep best-effort cancellation semantics (possible one extra send
>     attempt under lock-order race), while preventing further retries via
>     retrans_times gating
>   - selftests: remove the redundant ADD_ADDR tx-drop subtest that
>     duplicated existing coverage for list progression behavior
>   - link to v2:
>     https://lore.kernel.org/mptcp/20260430112026.343691-1-lixiasong1@huawei.com/
Thank you for the v3, it looks good to me!

Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

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