Re: [PATCH export v3 3/4] mptcp: reset subflow on MP_FAIL when OoO queue is non-empty

[Chenguang Zhao <chenguang.zhao@linux.dev>]

在 2026/8/12 18:02, Paolo Abeni 写道:
> On 8/12/26 7:46 AM, Chenguang Zhao wrote:
>> From: Chenguang Zhao <zhaochenguang@kylinos.cn>
>>
>> Infinite mapping needs contiguous data. If the MPTCP OoO queue is not
>> empty, reset the subflow instead of falling back.
> Why? the RFC says:
>
> """if all unacknowledged data in flight is contiguous"""
>
> That statement can be true even when the RTX queue is not empty.
>
> It will become false if/when some mptcp-level retransmission will happen.
>
> __mptcp_push_retrans() atomically sets `allow_infinite_fallback` to
> false when such retransmission happen. The code just before the newly
> added one checks such condition under the relevant lock.
>
> I don't think this change is needed.
>
> /P
>
Hi Paolo

I misread the RFC here. "If all unacknowledged data in flight is
contiguous" is about send-side in-flight data, not about the MPTCP
receive OoO queue being empty. Contiguous in-flight data can still
hold when the RTX queue is not empty; it only becomes false after an
MPTCP-level retransmission.

That is already tracked by allow_infinite_fallback, which
__mptcp_push_retrans() clears under fallback_lock. The existing
check of that flag at the start of mptcp_pm_mp_fail_received()
covers the RFC condition.

I will drop this patch in the next revision.

Thanks,
Chenguang