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

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

[Xin Long]

Now sctp doesn't change socket state upon shutdown reception. It changes
just the assoc state, even though it's a TCP-style socket.

For some cases, if we really need to check sk->sk_state, it's necessary to
fix this issue, at least when we use ss or netstat to dump, we can get a
more exact information.

As an improvement, we will change sk->sk_state when we change asoc->state
to SHUTDOWN_RECEIVED, and also do it in sctp_shutdown to keep consistent with
sctp_close.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/sm_sideeffect.c | 4 +++-
 net/sctp/socket.c        | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index aa37122..12d4519 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -806,8 +806,10 @@ static void sctp_cmd_new_state(sctp_cmd_seq_t *cmds,
 
 		/* Set the RCV_SHUTDOWN flag when a SHUTDOWN is received. */
 		if (sctp_state(asoc, SHUTDOWN_RECEIVED) &&
-		    sctp_sstate(sk, ESTABLISHED))
+		    sctp_sstate(sk, ESTABLISHED)) {
+			sk->sk_state = SCTP_SS_CLOSING;
 			sk->sk_shutdown |= RCV_SHUTDOWN;
+		}
 	}
 
 	if (sctp_state(asoc, COOKIE_WAIT)) {
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 67154b8..91a460d 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4193,6 +4193,7 @@ static void sctp_shutdown(struct sock *sk, int how)
 		return;
 
 	if (how & SEND_SHUTDOWN) {
+		sk->sk_state = SCTP_SS_CLOSING;
 		ep = sctp_sk(sk)->ep;
 		if (!list_empty(&ep->asocs)) {
 			asoc = list_entry(ep->asocs.next,
-- 
2.1.0

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

[Marcelo Ricardo Leitner]

On Fri, Jun 03, 2016 at 10:42:45PM +0800, Xin Long wrote:
> Now sctp doesn't change socket state upon shutdown reception. It changes
> just the assoc state, even though it's a TCP-style socket.
> 
> For some cases, if we really need to check sk->sk_state, it's necessary to
> fix this issue, at least when we use ss or netstat to dump, we can get a
> more exact information.
> 
> As an improvement, we will change sk->sk_state when we change asoc->state
> to SHUTDOWN_RECEIVED, and also do it in sctp_shutdown to keep consistent with
> sctp_close.
> 
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  net/sctp/sm_sideeffect.c | 4 +++-
>  net/sctp/socket.c        | 1 +
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index aa37122..12d4519 100644
> --- a/net/sctp/sm_sideeffect.c
> +++ b/net/sctp/sm_sideeffect.c
> @@ -806,8 +806,10 @@ static void sctp_cmd_new_state(sctp_cmd_seq_t *cmds,
>  
>  		/* Set the RCV_SHUTDOWN flag when a SHUTDOWN is received. */
>  		if (sctp_state(asoc, SHUTDOWN_RECEIVED) &&
> -		    sctp_sstate(sk, ESTABLISHED))
> +		    sctp_sstate(sk, ESTABLISHED)) {
> +			sk->sk_state = SCTP_SS_CLOSING;
>  			sk->sk_shutdown |= RCV_SHUTDOWN;
> +		}
>  	}
>  
>  	if (sctp_state(asoc, COOKIE_WAIT)) {
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 67154b8..91a460d 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -4193,6 +4193,7 @@ static void sctp_shutdown(struct sock *sk, int how)
>  		return;
>  
>  	if (how & SEND_SHUTDOWN) {
> +		sk->sk_state = SCTP_SS_CLOSING;
>  		ep = sctp_sk(sk)->ep;
>  		if (!list_empty(&ep->asocs)) {
>  			asoc = list_entry(ep->asocs.next,

Oh but I think the removed chunk was important, it just needed fixing.

A comment in there said:
	/* If the association on the newsk is already closed before
	 * accept() is called, set RCV_SHUTDOWN flag.
	 */
Meaning that there is a way that it will create a socket in the state
you're trying to avoid here, which now is not handled.

  Marcelo

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

[Xin Long]

On Sat, Jun 4, 2016 at 1:49 AM, Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
> On Fri, Jun 03, 2016 at 10:42:45PM +0800, Xin Long wrote:
>> Now sctp doesn't change socket state upon shutdown reception. It changes
>> just the assoc state, even though it's a TCP-style socket.
>>
>> For some cases, if we really need to check sk->sk_state, it's necessary to
>> fix this issue, at least when we use ss or netstat to dump, we can get a
>> more exact information.
>>
>> As an improvement, we will change sk->sk_state when we change asoc->state
>> to SHUTDOWN_RECEIVED, and also do it in sctp_shutdown to keep consistent with
>> sctp_close.
>>
>> Signed-off-by: Xin Long <lucien.xin@gmail.com>
>> ---
>>  net/sctp/sm_sideeffect.c | 4 +++-
>>  net/sctp/socket.c        | 1 +
>>  2 files changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
>> index aa37122..12d4519 100644
>> --- a/net/sctp/sm_sideeffect.c
>> +++ b/net/sctp/sm_sideeffect.c
>> @@ -806,8 +806,10 @@ static void sctp_cmd_new_state(sctp_cmd_seq_t *cmds,
>>
>>               /* Set the RCV_SHUTDOWN flag when a SHUTDOWN is received. */
>>               if (sctp_state(asoc, SHUTDOWN_RECEIVED) &&
>> -                 sctp_sstate(sk, ESTABLISHED))
>> +                 sctp_sstate(sk, ESTABLISHED)) {
>> +                     sk->sk_state = SCTP_SS_CLOSING;
>>                       sk->sk_shutdown |= RCV_SHUTDOWN;
>> +             }
>>       }
>>
>>       if (sctp_state(asoc, COOKIE_WAIT)) {
>> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
>> index 67154b8..91a460d 100644
>> --- a/net/sctp/socket.c
>> +++ b/net/sctp/socket.c
>> @@ -4193,6 +4193,7 @@ static void sctp_shutdown(struct sock *sk, int how)
>>               return;
>>
>>       if (how & SEND_SHUTDOWN) {
>> +             sk->sk_state = SCTP_SS_CLOSING;
>>               ep = sctp_sk(sk)->ep;
>>               if (!list_empty(&ep->asocs)) {
>>                       asoc = list_entry(ep->asocs.next,
>
> Oh but I think the removed chunk was important, it just needed fixing.
>
> A comment in there said:
>         /* If the association on the newsk is already closed before
>          * accept() is called, set RCV_SHUTDOWN flag.
>          */
> Meaning that there is a way that it will create a socket in the state
> you're trying to avoid here, which now is not handled.
agreed, but it's another problem
there, we'd better free newsk and assoc after sctp_sock_migrate,
and let sctp_accept return err. I will think more about it and see if
I cook another patch for it.


>
>   Marcelo

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

[Marcelo Ricardo Leitner]

Em 04-06-2016 06:45, Xin Long escreveu:
> On Sat, Jun 4, 2016 at 1:49 AM, Marcelo Ricardo Leitner
> <marcelo.leitner@gmail.com> wrote:
>> On Fri, Jun 03, 2016 at 10:42:45PM +0800, Xin Long wrote:
>>> Now sctp doesn't change socket state upon shutdown reception. It changes
>>> just the assoc state, even though it's a TCP-style socket.
>>>
>>> For some cases, if we really need to check sk->sk_state, it's necessary to
>>> fix this issue, at least when we use ss or netstat to dump, we can get a
>>> more exact information.
>>>
>>> As an improvement, we will change sk->sk_state when we change asoc->state
>>> to SHUTDOWN_RECEIVED, and also do it in sctp_shutdown to keep consistent with
>>> sctp_close.
>>>
>>> Signed-off-by: Xin Long <lucien.xin@gmail.com>
>>> ---
>>>  net/sctp/sm_sideeffect.c | 4 +++-
>>>  net/sctp/socket.c        | 1 +
>>>  2 files changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
>>> index aa37122..12d4519 100644
>>> --- a/net/sctp/sm_sideeffect.c
>>> +++ b/net/sctp/sm_sideeffect.c
>>> @@ -806,8 +806,10 @@ static void sctp_cmd_new_state(sctp_cmd_seq_t *cmds,
>>>
>>>               /* Set the RCV_SHUTDOWN flag when a SHUTDOWN is received. */
>>>               if (sctp_state(asoc, SHUTDOWN_RECEIVED) &&
>>> -                 sctp_sstate(sk, ESTABLISHED))
>>> +                 sctp_sstate(sk, ESTABLISHED)) {
>>> +                     sk->sk_state = SCTP_SS_CLOSING;
>>>                       sk->sk_shutdown |= RCV_SHUTDOWN;
>>> +             }
>>>       }
>>>
>>>       if (sctp_state(asoc, COOKIE_WAIT)) {
>>> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
>>> index 67154b8..91a460d 100644
>>> --- a/net/sctp/socket.c
>>> +++ b/net/sctp/socket.c
>>> @@ -4193,6 +4193,7 @@ static void sctp_shutdown(struct sock *sk, int how)
>>>               return;
>>>
>>>       if (how & SEND_SHUTDOWN) {
>>> +             sk->sk_state = SCTP_SS_CLOSING;
>>>               ep = sctp_sk(sk)->ep;
>>>               if (!list_empty(&ep->asocs)) {
>>>                       asoc = list_entry(ep->asocs.next,
>>
>> Oh but I think the removed chunk was important, it just needed fixing.
>>
>> A comment in there said:
>>         /* If the association on the newsk is already closed before
>>          * accept() is called, set RCV_SHUTDOWN flag.
>>          */
>> Meaning that there is a way that it will create a socket in the state
>> you're trying to avoid here, which now is not handled.
> agreed, but it's another problem
> there, we'd better free newsk and assoc after sctp_sock_migrate,
> and let sctp_accept return err. I will think more about it and see if
> I cook another patch for it.

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.

   Marcelo

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

[David Miller]

From: Xin Long <lucien.xin@gmail.com>
Date: Fri,  3 Jun 2016 22:42:45 +0800

> Now sctp doesn't change socket state upon shutdown reception. It changes
> just the assoc state, even though it's a TCP-style socket.
> 
> For some cases, if we really need to check sk->sk_state, it's necessary to
> fix this issue, at least when we use ss or netstat to dump, we can get a
> more exact information.
> 
> As an improvement, we will change sk->sk_state when we change asoc->state
> to SHUTDOWN_RECEIVED, and also do it in sctp_shutdown to keep consistent with
> sctp_close.
> 
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

It looks like some changes are still needed for this.

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

[Xin Long]

On Sat, Jun 4, 2016 at 8:22 PM, Marcelo Ricardo Leitner
<marcelo.leitner@gmail.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.

[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 ?

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 ?

>
>   Marcelo

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

[Marcelo Ricardo Leitner]

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@gmail.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

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

[Xin Long]

On Tue, Jun 7, 2016 at 8:08 PM, Marcelo Ricardo Leitner
<marcelo.leitner@gmail.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@gmail.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
>

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

[Xin Long]

On Tue, Jun 7, 2016 at 7:03 PM, Xin Long <lucien.xin@gmail.com> wrote:
> On Sat, Jun 4, 2016 at 8:22 PM, Marcelo Ricardo Leitner
>
> --- 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;
>
I'm still thinking about this, if we want to get addrs info from
closed assoc, like Adam's requirement. this will make it more
impossible.

case in
sctp_getsockopt_peer_addrs()->sctp_id2assoc():

                if (!sctp_sstate(sk, ESTABLISHED))
                        return NULL;

we can't  get assoc as sstate is SS_CLOSING already.

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

[Marcelo Ricardo Leitner]

Em 08-06-2016 07:42, Xin Long escreveu:
> On Tue, Jun 7, 2016 at 7:03 PM, Xin Long <lucien.xin@gmail.com> wrote:
>> On Sat, Jun 4, 2016 at 8:22 PM, Marcelo Ricardo Leitner
>>
>> --- 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;
>>
> I'm still thinking about this, if we want to get addrs info from
> closed assoc, like Adam's requirement. this will make it more
> impossible.
>
> case in
> sctp_getsockopt_peer_addrs()->sctp_id2assoc():
>
>                 if (!sctp_sstate(sk, ESTABLISHED))
>                         return NULL;
>
> we can't  get assoc as sstate is SS_CLOSING already.
>

We probably can add another state to that if(). So far ESTABLISHED was 
the only reasonable state in there, but SS_CLOSING will make sense too 
then, I guess. A throughout check is necessary for this.

   Marcelo