Re: [lwip-devel] communication hangs after single ACK

[Albert Bartel]

Finally we found the bug that was responsible for the communication hang for 60sec after a single ack.

It could be easy reproduced with fast and short requests, much more often with vista than with xp (because tcp/ip with vista is faster than with xp).

 

The request was received, correctly processed and a NETCONN_EVT_RCVPLUS should be sent by calling API_EVENT() but because of speed problems the conn->socket (that is prior also stored in the local variable s) is invalid after the first try.

After the sys_sem_wait(socksem) it is checked again. If it is still invalid, there is a return.

But if we now got a valid conn->socket we get the socket with sock = get_socket(s), but s is still invalid.

 

Because s is used later, s should be set to conn->socket after we get a valid conn->socket. (see comment)

 

 

 

static void

event_callback(struct netconn *conn, enum netconn_evt evt, u16_t len)

{

  int s;

  struct lwip_socket *sock;

  struct lwip_select_cb *scb;

 

  LWIP_UNUSED_ARG(len);

 

  if (conn) {

    s = conn->socket;

    if (s < 0) {

      sys_sem_wait(socksem);

      if (conn->socket < 0) {

        if (evt == NETCONN_EVT_RCVPLUS) {

          conn->socket--;

        }

        sys_sem_signal(socksem);

        return;

      }

      // set s to conn->socket because now conn->socket is valid

      // and s (old conn->socket) is still invalid

      s = conn->socket;

 

      sys_sem_signal(socksem);

    }

 

    sock = get_socket(s);

    if (!sock) {

      return;

    }

  } else {

    return;

  }

 

...

 

}