RE: netconn_delete and _recv not thread safe

> I have most of the lwip stack running in a "tcpip" thread, and stack
> users in various threads synchronise with it using the netconn* API.
But
> there is a problem with netconn_delete and netconn_recv when they
delete
> mboxes. A packet, or a connection to a listening socket, may arrive in
> the gap between removing mbox items, and deleting the mboxes. For
> example:
> 
>    /* Drain the recvmbox. */
>    if (conn->recvmbox != SYS_MBOX_NULL) {
>      while (sys_arch_mbox_fetch(conn->recvmbox, &mem, 1) !=
SYS_ARCH_TIMEOUT) {
>        if (conn->type == NETCONN_TCP) {
>          if(mem != NULL)
>            pbuf_free((struct pbuf *)mem);
>        } else {
>          netbuf_delete((struct netbuf *)mem);
>        }
>      }
> 
> *** PACKET CAN ARRIVE HERE ***
>      sys_mbox_free(conn->recvmbox);
>      conn->recvmbox = SYS_MBOX_NULL;
>    }
> 
> In that case a sys_mbox_free can be called on a non-empty mbox. This
may
> either leak a pbuf, or cause an assertion in the OS from the
underlying
> mbox implementation. I've been thinking about how to fix this. Either
> new sys_arch primitives could be added. Or, better, we could try to
use
> SYS_LIGHTWEIGHT_PROT, but this seems a bit dubious as we need to
protect
> from before the sys_arch_mbox_fetch, until the conn->recvmbox =
> SYS_MBOX_NULL.

Doesn't the API_MSG_DELCONN message posted just prior to the above code
already prevent any further packets from being placed in the recvmbox?

Don Krueger

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