Fix race condition bug in poll() for backlogged connections

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@2032 42af7a65-404d-4744-a932-0658087f49c3

ChangeLog

@@ -856,3 +856,7 @@
 	  extra two bytes of length cause the driver to sometimes read one too many
 	  words from the received FIFO (corrupting the next queued receive packet,
 	  if any).
+	* net/net_poll.c and net/uip/uip_tcpbacklog.c.  Fixed an important race condition
+	  bug in polling for connections.  The logic worked if the poll was inplace
+	  before the connection was received; but the poll failed to awaken if the
+	  connection was already pending in the backlog when poll() was called.

Documentation/NuttX.html

@@ -8,7 +8,7 @@
   <tr align="center" bgcolor="#e4e4e4">
     <td>
       <h1><big><font color="#3c34ec"><i>NuttX RTOS</i></font></big></h1>
-      <p>Last Updated: September 09, 2009</p>
+      <p>Last Updated: September 10, 2009</p>
     </td>
   </tr>
 </table>
@@ -1517,6 +1517,10 @@ nuttx-0.4.11 2009-xx-xx Gregory Nutt &lt;spudmonkey@racsa.co.cr&gt;
 	  extra two bytes of length cause the driver to sometimes read one too many
 	  words from the received FIFO (corrupting the next queued receive packet,
 	  if any).
+	* net/net_poll.c and net/uip/uip_tcpbacklog.c.  Fixed an important race condition
+	  bug in polling for connections.  The logic worked if the poll was inplace
+	  before the connection was received; but the poll failed to awaken if the
+	  connection was already pending in the backlog when poll() was called.
 
 pascal-0.1.3 2009-xx-xx Gregory Nutt &lt;spudmonkey@racsa.co.cr&gt;
 

include/net/uip/uip-tcp.h

@@ -400,6 +400,11 @@ extern int uip_backlogdestroy(FAR struct uip_conn *conn);
 /* APIs to manage individual backlog actions */
 
 extern int uip_backlogadd(FAR struct uip_conn *conn, FAR struct uip_conn *blconn);
+#ifndef CONFIG_DISABLE_POLL
+extern boolean uip_backlogavailable(FAR struct uip_conn *conn);
+#else
+#  define uip_backlogavailable(conn)   (FALSE);
+#endif
 extern FAR struct uip_conn *uip_backlogremove(FAR struct uip_conn *conn);
 extern int uip_backlogdelete(FAR struct uip_conn *conn, FAR struct uip_conn *blconn);
 
@@ -407,6 +412,7 @@ extern int uip_backlogdelete(FAR struct uip_conn *conn, FAR struct uip_conn *blc
 #  define uip_backlogcreate(conn,nblg) (-ENOSYS)
 #  define uip_backlogdestroy(conn)     (-ENOSYS)
 #  define uip_backlogadd(conn,blconn)  (-ENOSYS)
+#  define uip_backlogavailable(conn)   (FALSE);
 #  define uip_backlogremove(conn)      (NULL)
 #endif
 

net/net_poll.c

@@ -201,9 +201,15 @@ static inline int net_pollsetup(FAR struct socket *psock, struct pollfd *fds)
 
   fds->priv    = (FAR void *)cb;
 
+#ifdef CONFIG_NET_TCPBACKLOG
+  /* Check for read data or backlogged connection availability now */
+
+  if (!sq_empty(&conn->readahead) || uip_backlogavailable(conn))
+#else
   /* Check for read data availability now */
 
   if (!sq_empty(&conn->readahead))
+#endif
     {
       fds->revents = fds->events & POLLIN;
       if (fds->revents != 0)

net/uip/uip_tcpbacklog.c

@@ -261,6 +261,25 @@ int uip_backlogadd(FAR struct uip_conn *conn, FAR struct uip_conn *blconn)
   return ret;
 }
 
+/****************************************************************************
+ * Function: uip_backlogremove
+ *
+ * Description:
+ *  Called from poll().  Before waiting for a new connection, poll will
+ *  call this API to see if there are pending connections in the backlog.
+ *
+ * Assumptions:
+ *   Called from normal user code, but with interrupts disabled,
+ *
+ ****************************************************************************/
+
+#ifndef CONFIG_DISABLE_POLL
+boolean uip_backlogavailable(FAR struct uip_conn *conn)
+{
+  return (conn && conn->backlog && !sq_empty(&conn->backlog->bl_pending));
+}
+#endif
+
 /****************************************************************************
  * Function: uip_backlogremove
  *