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RE : [lwip-users] local connection failed on loopif, race?

From: Frédéric BERNON
Subject: RE : [lwip-users] local connection failed on loopif, race?
Date: Mon, 26 Mar 2007 09:10:03 +0200 
The workaround you have find is "something like" the one I proposed in 
https://savannah.nongnu.org/bugs/?19157 ("lwip_close problems"). It would be 
good to add a netconn_close in your code. Follow information for bug #19157 : 
lwip_close problems, I will propose a patch, like (not yet tested like this) :

err_t
netconn_close(struct netconn *conn)
{
  struct api_msg msg;

  if (conn == NULL) {
    return ERR_VAL;
  }

  conn->state = NETCONN_CLOSE;
 again:
  msg.type = API_MSG_CLOSE;
  msg.msg.conn = conn;
  api_msg_post(&msg);
  if (conn->err == ERR_MEM && conn->sem != SYS_SEM_NULL) {
    sys_sem_wait(conn->sem);
    goto again;
  }
  if (conn->type==NETCONN_TCP) {
    if (((sock->conn->pcb.tcp->unacked!=NULL) || 
(sock->conn->pcb.tcp->unsent!=NULL)) && (sock->conn->err==ERR_OK)) {
      sys_msleep(1);//I don't like that, but...
      goto again:
  }
  conn->state = NETCONN_NONE;
  return conn->err;
}

  
====================================
Frédéric BERNON 
HYMATOM SA 
Chef de projet informatique 
Microsoft Certified Professional 
Tél. : +33 (0)4-67-87-61-10 
Fax. : +33 (0)4-67-70-85-44 
Email : address@hidden 
Web Site : http://www.hymatom.fr 
====================================
P Avant d'imprimer, penser à l'environnement
 


-----Message d'origine-----
De : address@hidden [mailto:address@hidden De la part de Tai-hwa Liang
Envoyé : lundi 26 mars 2007 08:28
À : Mailing list for lwIP users
Objet : Re: [lwip-users] local connection failed on loopif, race?


On Mon, 19 Mar 2007, Tai-hwa Liang wrote:
> Hi,
>
>  Is there anyone having success on using loopif in a multi-threaded 
> application?  The attached is a modified unix/proj/unixsim/simhost.c. 
> Basically it is a self-contained server/client which binds/connects to 
> 127.0.0.2 through loopif.
>
>  The problem is that this program failed to run indefinitely and hung 
> after a few client <-> server transactions(lwIP CVS version, with 
> LWIP_HAVE_LOOPIF = 1, running on FreeBSD-CURRENT):
>
> freebsd> ./simhost -d
> Host at 127.0.0.2 mask 255.0.0.0 gateway 127.0.0.1
> System initialized.
> TCP/IP initialized.
> netif_set_ipaddr: netif address being changed
> netif: IP address of interface API message 0x8065a28
> cli connecting...
> tcpip_thread: API message 0x8065a28
> tcp_bind: bind to port 80
> tcpip_thread: API message 0x8065a3c
> tcp_connect to port 80
> tcp_enqueue(pcb=0x8065300, arg=0x0, len=0, flags=2, copy=0)
> tcp_enqueue: queuelen: 0
> tcp_enqueue: queueing 6509:6510 (0x2)
> tcp_enqueue: 1 (after enqueued)
> tcp_output: snd_wnd 8096, cwnd 1, wnd 1, effwnd 0, seq 6509, ack 6509
> tcp_output: snd_wnd 8096, cwnd 1, wnd 1, effwnd 0, seq 6509, ack 6509, 
> i 0
> tcp_output_segment: rtseq 6509
> tcp_output_segment: 6509:6509
> ip_output_if: lo0
> IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        44     | (v, hl, tos, len)
> +-------------------------------+
> |        0      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc7     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> netif->output()tcpip_thread: API message 0x8065a3c
> srv listening return, proceed to accept
> tcp_slowtmr: processing active pcb
> tcp_slowtmr: processing active pcb
> tcp_slowtmr: processing active pcb
> tcp_slowtmr: processing active pcb
> tcp_slowtmr: polling application
> tcp_output: nothing to send (0x0)
> tcp_output: snd_wnd 8096, cwnd 1, wnd 1, seg == NULL, ack 6509
> tcp_slowtmr: processing active pcb
> tcp_slowtmr: processing active pcb
> tcp_slowtmr: rtime 6 pcb->rto 6
> tcp_slowtmr: cwnd 1024 ssthresh 2048
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, effwnd 0, seq 6509, ack 
> 6509
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, effwnd 0, seq 6509, ack 6509, 
> i 0
> tcp_output_segment: rtseq 6509
> tcp_output_segment: 6509:6509
> ip_output_if: lo0
> IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        44     | (v, hl, tos, len)
> +-------------------------------+
> |        1      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc6     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> netif->output()tcpip_thread: IP packet 0x8065a3c
> ip_input: iphdr->dest 0x200007f netif->ip_addr 0x200007f (0x7f, 0x7f,
> 0x2000000)
> ip_input: packet accepted on interface lo
> ip_input: IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        44     | (v, hl, tos, len)
> +-------------------------------+
> |        1      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc6     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> ip_input: p->len 44 p->tot_len 44
> TCP header:
> +-------------------------------+
> |     4097      |       80      | (src port, dest port)
> +-------------------------------+
> |           0000006509          | (seq no)
> +-------------------------------+
> |           0000000000          | (ack no)
> +-------------------------------+
> |  6 |   |000010|      8096     | (hdrlen, flags (SYN ), win)
> +-------------------------------+
> |    0x5278     |         0     | (chksum, urgp)
> +-------------------------------+
> tcp_input: packed for LISTENing connection.
> TCP connection request 4097 -> 80.
> tcp_enqueue(pcb=0x80653a4, arg=0x0, len=0, flags=12, copy=0)
> tcp_enqueue: queuelen: 0
> tcp_enqueue: queueing 6516:6517 (0x12)
> tcp_enqueue: 1 (after enqueued)
> tcp_output: snd_wnd 8096, cwnd 1, wnd 1, effwnd 0, seq 6516, ack 6516
> tcp_output: snd_wnd 8096, cwnd 1, wnd 1, effwnd 0, seq 6516, ack 6516, 
> i 0
> tcp_output_segment: rtseq 6516
> tcp_output_segment: 6516:6516
> ip_output_if: lo0
> IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        44     | (v, hl, tos, len)
> +-------------------------------+
> |        2      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc5     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> netif->output()tcpip_thread: IP packet 0x8065a3c
> ip_input: iphdr->dest 0x200007f netif->ip_addr 0x200007f (0x7f, 0x7f,
> 0x2000000)
> ip_input: packet accepted on interface lo
> ip_input: IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        44     | (v, hl, tos, len)
> +-------------------------------+
> |        2      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc5     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> ip_input: p->len 44 p->tot_len 44
> TCP header:
> +-------------------------------+
> |       80      |     4097      | (src port, dest port)
> +-------------------------------+
> |           0000006516          | (seq no)
> +-------------------------------+
> |           0000006510          | (ack no)
> +-------------------------------+
> |  6 |   |010010|      8096     | (hdrlen, flags (SYN ACK ), win)
> +-------------------------------+
> |    0x38f3     |         0     | (chksum, urgp)
> +-------------------------------+
> +-+-+-+-+-+-+-+-+-+-+-+-+-+- tcp_input: flags SYN ACK
> -+-+-+-+-+-+-+-+-+-+-+-+-+-+
> State: SYN_SENT
> SYN-SENT: ackno 6510 pcb->snd_nxt 6510 unacked 6509
> tcp_process: SYN-SENT --queuelen 0
> tcp_output: nothing to send (0x0)
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, seg == NULL, ack 6510
> State: ESTABLISHED
> cli writing HTTP request....
> netconn_write: writing 29 bytes (0)
> tcpip_thread: API message 0x8065a3c
> tcp_write(pcb=0x8065300, arg=0x80623f0, len=29, copy=0) 
> tcp_enqueue(pcb=0x8065300, arg=0x80623f0, len=29, flags=0, copy=0)
> tcp_enqueue: queuelen: 0
> tcp_enqueue: queueing 6510:6539 (0x0)
> tcp_enqueue: 2 (after enqueued)
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, effwnd 29, seq 6510, 
> ack 6510
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, effwnd 29, seq 6510, ack 6510, 
> i 0
> tcp_output_segment: 6510:6539
> ip_output_if: lo0
> IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        69     | (v, hl, tos, len)
> +-------------------------------+
> |        3      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dab     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> netif->output()cli deleting connection
> tcpip_thread: API message 0x8065a3c
> tcp_close: closing in State: ESTABLISHED tcp_enqueue(pcb=0x8065300, 
> arg=0x0, len=0, flags=1, copy=1)
> tcp_enqueue: queuelen: 2
> tcp_enqueue: queueing 6539:6540 (0x1)
> tcp_enqueue: 3 (after enqueued)
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, effwnd 29, seq 6539, 
> ack 6510
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, effwnd 29, seq 6539, ack 6510, 
> i 0
> tcp_output_segment: 6539:6539
> ip_output_if: lo0
> IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        40     | (v, hl, tos, len)
> +-------------------------------+
> |        4      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc7     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> netif->output()tcpip_thread: IP packet 0x8065a3c
> ip_input: iphdr->dest 0x200007f netif->ip_addr 0x200007f (0x7f, 0x7f,
> 0x2000000)
> ip_input: packet accepted on interface lo
> ip_input: IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        69     | (v, hl, tos, len)
> +-------------------------------+
> |        3      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dab     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> ip_input: p->len 69 p->tot_len 69
> TCP header:
> +-------------------------------+
> |     4097      |       80      | (src port, dest port)
> +-------------------------------+
> |           0000006510          | (seq no)
> +-------------------------------+
> |           0000006517          | (ack no)
> +-------------------------------+
> |  5 |   |011000|      8096     | (hdrlen, flags (PSH ACK ), win)
> +-------------------------------+
> |    0x8d1b     |         0     | (chksum, urgp)
> +-------------------------------+
> +-+-+-+-+-+-+-+-+-+-+-+-+-+- tcp_input: flags PSH ACK
> -+-+-+-+-+-+-+-+-+-+-+-+-+-+
> State: SYN_RCVD
> TCP connection established 4097 -> 80.
> State: ESTABLISHED
> tcp_receive: window update 8096
> tcp_receive: slow start cwnd 1025
> tcp_receive: ACK for 6517, unacked->seqno 6516:6517
> tcp_receive: removing 6516:6517 from pcb->unacked
> tcp_receive: queuelen 1 ... 0 (after freeing unacked)
> tcp_receive: pcb->rttest 6 rtseq 6516 ackno 6517
> tcp_receive: experienced rtt 0 ticks (0 msec).
> tcp_receive: RTO 5 (2500 milliseconds)
> tcp_output: nothing to send (0x0)
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, seg == NULL, ack 6517
> State: ESTABLISHED
> cli (re)creating connection...
> srv receiving HTTP request ....
> tcpip_thread: API message 0x8065a3c
> tcpip_thread: API message 0x8065a28
> tcp_output: sending ACK for 6539
> ip_output_if: lo0
> IP header:
> +-------------------------------+
> cli connecting...
> | 4 | 5 |  0x00 |        40     | (v, hl, tos, len)
> +-------------------------------+
> |        5      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc6     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> netif->output()tcp_recved: recveived 29 bytes, wnd 8096 (0).
> tcpip_thread: API message 0x8065a3c
> tcp_connect to port 80
> tcp_enqueue(pcb=0x806525c, arg=0x0, len=0, flags=2, copy=0)
> tcp_enqueue: queuelen: 0
> tcp_enqueue: queueing 6527:6528 (0x2)
> tcp_enqueue: 1 (after enqueued)
> tcp_output: snd_wnd 8096, cwnd 1, wnd 1, effwnd 0, seq 6527, ack 6527
> tcp_output: snd_wnd 8096, cwnd 1, wnd 1, effwnd 0, seq 6527, ack 6527, 
> i 0
> tcp_output_segment: rtseq 6527
> tcp_output_segment: 6527:6527
> ip_output_if: lo0
> IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        44     | (v, hl, tos, len)
> +-------------------------------+
> |        6      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc1     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> netif->output()netconn_recv: received 0x806571c (err 0)
> srv: it's a GET method GET /index.html HTTP/1.0
>
>
> srv delete server connection
> tcpip_thread: API message 0x8065a3c
> tcp_close: closing in State: ESTABLISHED tcp_enqueue(pcb=0x80653a4, 
> arg=0x0, len=0, flags=1, copy=1)
> tcp_enqueue: queuelen: 0
> tcp_enqueue: queueing 6517:6518 (0x1)
> tcp_enqueue: 1 (after enqueued)
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, effwnd 0, seq 6517, ack 
> 6517
> tcp_output: snd_wnd 8096, cwnd 1024, wnd 1024, effwnd 0, seq 6517, ack 6517, 
> i 0
> tcp_output_segment: rtseq 6517
> tcp_output_segment: 6517:6517
> ip_output_if: lo0
> IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        40     | (v, hl, tos, len)
> +-------------------------------+
> |        7      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc4     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> netif->output()tcpip_thread: IP packet 0x8065a3c
> ip_input: iphdr->dest 0x200007f netif->ip_addr 0x200007f (0x7f, 0x7f,
> 0x2000000)
> ip_input: packet accepted on interface lo
> ip_input: IP header:
> +-------------------------------+
> | 4 | 5 |  0x00 |        40     | (v, hl, tos, len)
> +-------------------------------+
> |        5      |010|       0   | (id, flags, offset)
> +-------------------------------+
> |  255  |    6  |    0x7dc6     | (ttl, proto, chksum)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (src)
> +-------------------------------+
> |  127  |    0  |    0  |    2  | (dest)
> +-------------------------------+
> ip_input: p->len 40 p->tot_len 40
> TCP header:
> +-------------------------------+
> |       80      |     4097      | (src port, dest port)
> +-------------------------------+
> |           0000006517          | (seq no)
> +-------------------------------+
> |           0000006539          | (ack no)
> +-------------------------------+
> |  5 |   |010000|      8096     | (hdrlen, flags (ACK ), win)
> +-------------------------------+
> |    0x4edf     |         0     | (chksum, urgp)
> +-------------------------------+
> +-+-+-+-+-+-+-+-+-+-+-+-+-+- tcp_input: flags ACK
> -+-+-+-+-+-+-+-+-+-+-+-+-+-+
> State: FIN_WAIT_1
> tcp_receive: window update 8096
> tcp_receive: slow start cwnd 2048
> tcp_receive: ACK for 6539, unacked->seqno 6510:6539
> tcp_receive: removing 6510:6539 from pcb->unacked
> tcp_receive: queuelen 3 ... 1 (after freeing unacked)
> tcp_receive: pcb->rttest 6 rtseq 6509 ackno 6539
> tcp_receive: experienced rtt 0 ticks (0 msec).
> tcp_receive: RTO 5 (2500 milliseconds)
> tcp_output: nothing to send (0x0)
> tcp_output: snd_wnd 8096, cwnd 2048, wnd 2048, seg == NULL, ack 6539
> State: FIN_WAIT_1
> srv listening return, proceed to accept
> [...hanging...]

   I managed to workaround this hanging by adding a 1 second delay between 
netconn_write() and netconn_delete():

        /* pseudo code */
        for (;;) {
                srv = netconn_new(NETCONN_TCP)
                netconn_connect(srv, srv_addr, srv_port);
                netconn_write(srv, buf, len, NETCONN_NOCOPY);
                sleep(1);       /* this is vital! */
                netconn_delete(srv);
        }

   In addition to that, the default setting of MEMP_NUM_SYS_TIMEOUT in unixsim 
still isn't able to cope with the load required in my loopif testing case.  
Raising the default value from 3 to 8 plus the aforementioned 1 second delay 
seems to "resolve" the hanging observed in my case.

   Now the question turns to be: why armed sys_timeout() inside lwIP seems to 
"lost" when the system is heavily stressed?

-- 
Cheers,

Tai-hwa Liang


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