Re: [PATCH net 1/1] mptcp: hold subflow request owners when cloning reqsk

[Matthieu Baerts <matttbe@kernel.org>]

Hi Yuan Tan,

On 19/04/2026 11:51, Yuan Tan wrote:
> 
> On 4/16/2026 11:48 AM, Kuniyuki Iwashima wrote:
>> On Thu, Apr 16, 2026 at 10:45 AM Matthieu Baerts <matttbe@kernel.org> wrote:
>>> Hi Ren,
>>>
>>> On 15/04/2026 11:31, Ren Wei wrote:
>>>> From: Ruide Cao <caoruide123@gmail.com>
>>>>
>>>> TCP request migration clones pending request sockets with
>>>> inet_reqsk_clone(). For MPTCP MP_JOIN requests this raw-copies
>>>> subflow_req->msk, but the cloned request does not take a new reference.
>>>>
>>>> Both the original and the cloned request can later drop the same msk in
>>>> subflow_req_destructor(), and a migrated request may keep a dangling msk
>>>> pointer after the original owner has already been released.
>>>>
>>>> Add a request_sock clone callback and let MPTCP grab a reference for cloned
>>>> subflow requests that carry an msk. This keeps ownership balanced across
>>>> both successful migrations and failed clone/insert paths without changing
>>>> other protocols.

(...)

>>>> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
>>>> index e961936b6be7..140a9e96ad58 100644
>>>> --- a/net/ipv4/inet_connection_sock.c
>>>> +++ b/net/ipv4/inet_connection_sock.c
>>>> @@ -954,6 +954,9 @@ static struct request_sock *inet_reqsk_clone(struct request_sock *req,
>>>>       if (sk->sk_protocol == IPPROTO_TCP && tcp_rsk(nreq)->tfo_listener)
>>>>               rcu_assign_pointer(tcp_sk(nreq->sk)->fastopen_rsk, nreq);
>>> (Maybe TCP with fastopen could be this other user to call
>>> rcu_assign_pointer()? (net-next material))
>>>
>>>> +     if (req->rsk_ops->init_clone)
>>>> +             req->rsk_ops->init_clone(req, nreq);
>> I think a simple direct call is better.
>>
>> #ifdef CONFIG_MPTCP
>>     if (tcp_rsk(req)->is_mptcp)
>>         mptcp_reqsk_clone(nreq);
>> #endif
>>
>  Thank you very much for your suggestion. We will use this approach in
> the next version of the patch. Would you like us to add your
> Suggested-by tag?
No need to add a Suggested-by tag: this tag is used when the whole patch
idea has been suggested by someone. That's not the case here: we only
proposed a small modification in the code, without changing the idea.

https://docs.kernel.org/process/submitting-patches.html#using-reported-by-tested-by-reviewed-by-suggested-by-and-fixes

Cheers,
Matt
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