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

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Date:	Tue, 7 Jun 2016 09:08:45 -0300
From:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:	Xin Long <lucien.xin@...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 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()).

> 
> [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. :)

  Marcelo