RE: [lwip-users] netconn_delete and _recv not thread safe

[Krueger, Don]

> 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

====================================================================== 
 This electronic message transmission and any attachments are 
 confidential and/or proprietary and may constitute legally privileged 
information of 
 Meso Scale Diagnostics, LLC. The information is intended for solely 
 the use of Mailing list for lwIP users (address@hidden).  If you are not 
 the intended recipient, you are hereby notified that any 
 disclosure, copying, distribution or the taking of any action in 
 reliance of this information is strictly prohibited. You are not 
 authorized to retain it in any form nor to re-transmit it, and 
 you should destroy this email immediately. 

 If you have received this electronic transmission in error, 
 please notify us by telephone (240-631-2522) or by electronic 
 mail to the sender of this email, Krueger, Don (address@hidden),
 immediately. 
 =====================================================================