netdev - Re: [PATCHv2 net-next] sctp: sctp should change socket state when shutdown is received

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Date:	Wed, 8 Jun 2016 18:17:55 +0800
From:	Xin Long <lucien.xin@...il.com>
To:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:	network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
	Vlad Yasevich <vyasevich@...il.com>, daniel@...earbox.net,
	davem <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCHv2 net-next] sctp: sctp should change socket state when
 shutdown is received

On Tue, Jun 7, 2016 at 8:08 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> On Tue, Jun 07, 2016 at 07:03:55PM +0800, Xin Long wrote:
>> On Sat, Jun 4, 2016 at 8:22 PM, Marcelo Ricardo Leitner
>> <marcelo.leitner@...il.com> wrote:
>> >
>> > Return error? Please don't. Adam Endrodi asked in May (linux-sctp@) a way to
>> > return the addresses used on such attempts and currently this address
>> > returned by accept() is the only one we can get.
>> [1] I've checked Adam's email, what he asked  was different case,  in
>> his case, the assoc
>> closed *after* sctp_accept, that's why he can catch the SCTP_COMM_UP event on
>> accept_sk but asoc is freed already.
>
> It doesn't have to be after sctp_accept because we will queue
> SCTP_COMM_UP as reactions to COOKIE_ECHO and COOKIE_ACK, and then such
> event will be moved to the new socket upon sctp_accept() call (which
> calls sctp_sock_migrate()).
I meant in his case, assoc close must be *after* sctp_accept.
and he said he couldn't get it as asoc was gone.

cause if assoc close is *before* sctp_accept return, assoc won't
be freed [2], he can still  get the addrs from asoc in SCTP_COMM_UP event


>
>>
>> [2] if assoc close *before* sctp_accept return, I mean asoc close
>> during sctp_accept schedule out.
>> listen sk will be the assoc's parent sk, in sctp_cmd_delete_tcb
>> (SCTP_CMD_DELETE_TCB):
>>
>>         if (sctp_style(sk, TCP) && sctp_sstate(sk, LISTENING) &&
>>             (!asoc->temp) && (sk->sk_shutdown != SHUTDOWN_MASK))
>>                 return;
>>
>> assoc can't be freed. and the event skb will be appended to
>> listen_sk->sk_receive_queue
>> when sctp_accept schedule back, it will transfer to
>> accept_sk->sk_receive_queue. we can
>> still get the closed assoc information. until we call sctp_close:
>>                         if (sctp_state(asoc, CLOSED)) {
>>                                 sctp_association_free(asoc);
>>                                 continue;
>>                         }
>>
>> and your suggestion to improve for his case [1] is to not schedule
>> SCTP_CMD_DELETE_TCB
>> (only for tcp style). right ?
>
> Yes
>
>>
>> if so, in the case [2] that assoc close *before* sctp_accept return,
>> we should also update
>> the newsk->sk_state, like:
>>
>> --- a/net/sctp/socket.c
>> +++ b/net/sctp/socket.c
>> @@ -7565,10 +7565,12 @@ static void sctp_sock_migrate(struct sock
>> *oldsk, struct sock *newsk,
>>         /* If the association on the newsk is already closed before accept()
>>          * is called, set RCV_SHUTDOWN flag.
>>          */
>> -       if (sctp_state(assoc, CLOSED) && sctp_style(newsk, TCP))
>> +       if (sctp_state(assoc, CLOSED) && sctp_style(newsk, TCP)) {
>> +               newsk->sk_state = SCTP_SS_CLOSING;
>>                 newsk->sk_shutdown |= RCV_SHUTDOWN;
>> +       } else
>> +               newsk->sk_state = SCTP_SS_ESTABLISHED;
>>
>> -       newsk->sk_state = SCTP_SS_ESTABLISHED;
>>
>> so that this two cases have the similar process, and wait for
>> sctp_close to clean assoc.
>> what do you think ?
>
> I don't agree with before/after thing, but I agree with the solution. :)
ok, I will post v3. :D

>
>   Marcelo
>