Fix resuming partial msg reading on TCP

When conn rebalancing or parallel processing is enabled for TCP, a read operation may start (partial reading) in one process and be completed in a different one. So the con_req (buffer for partial reading) must be in shm mem and also it must survive a conn release (passing the conn back to MAIN).
Many thanks to @liviuchircu for reporting and helping with the troubleshooting
This issue was found during the TCP performance tests done for the 3.4 release

(cherry picked from commit e0fe732)

net/net_tcp.c

@@ -711,6 +711,9 @@ static void _tcpconn_rm(struct tcp_connection* c, int no_event)
 		c->async = NULL;
 	}
 
+	if (c->con_req)
+		shm_free(c->con_req);
+
 	if (protos[c->type].net.conn_clean)
 		protos[c->type].net.conn_clean(c);
 

net/net_tcp_proc.c

@@ -69,14 +69,6 @@ static void tcpconn_release(struct tcp_connection* c, long state, int writer,
 			c, state, c->fd, c->id);
 	LM_DBG(" extra_data %p\n", c->extra_data);
 
-	/* if we are in a writer context, do not touch the buffer contain read packets per connection
-	might be in a completely different process
-	even if in our process we shouldn't touch it, since it might currently be in use, when we've read multiple SIP messages in one try*/
-	if (!writer && c->con_req) {
-		pkg_free(c->con_req);
-		c->con_req = NULL;
-	}
-
 	/* release req & signal the parent */
 	if (!writer)
 		c->proc_id = -1;

net/proto_tcp/proto_tcp.c

@@ -676,9 +676,9 @@ static int tcp_read_req(struct tcp_connection* con, int* bytes_read)
 
 	if (con->con_req) {
 		req=con->con_req;
-		LM_DBG("Using the per connection buff \n");
+		LM_DBG("Using the per connection buff for conn %p\n",con);
 	} else {
-		LM_DBG("Using the global ( per process ) buff \n");
+		LM_DBG("Using the global ( per process ) buff for conn %p\n",con);
 		init_tcp_req(&tcp_current_req, 0);
 		req=&tcp_current_req;
 	}
@@ -741,7 +741,7 @@ static int tcp_read_req(struct tcp_connection* con, int* bytes_read)
 			goto error;
 	}
 
-	LM_DBG("tcp_read_req end\n");
+	LM_DBG("tcp_read_req end for conn %p, req is %p\n",con,con->con_req);
 done:
 	if (bytes_read) *bytes_read=total_bytes;
 	/* connection will be released */

net/proto_tcp/tcp_common.h

@@ -449,7 +449,7 @@ static inline int tcp_handle_req(struct tcp_req *req,
 		if (req != &_tcp_common_current_req) {
 			/* if we no longer need this tcp_req
 			 * we can free it now */
-			pkg_free(req);
+			shm_free(req);
 			con->con_req = NULL;
 		}
 	} else {
@@ -469,8 +469,8 @@ static inline int tcp_handle_req(struct tcp_req *req,
 		if (req == &_tcp_common_current_req) {
 			/* let's duplicate this - most likely another conn will come in */
 
-			LM_DBG("We didn't manage to read a full request\n");
-			con->con_req = pkg_malloc(sizeof(struct tcp_req));
+			LM_ERR("We didn't manage to read a full request on con %p\n",con);
+			con->con_req = shm_malloc(sizeof(struct tcp_req));
 			if (con->con_req == NULL) {
 				LM_ERR("No more mem for dynamic con request buffer\n");
 				goto error;