RDS: Move loop-only function to loop.c

Also, try to better-document the locking around the
rm and its m_inc in loop.c.
Signed-off-by: Andy Grover <andy.grover@oracle.com>

net/rds/loop.c

@@ -64,7 +64,8 @@ static int rds_loop_xmit(struct rds_connection *conn, struct rds_message *rm,
 	BUG_ON(hdr_off || sg || off);
 
 	rds_inc_init(&rm->m_inc, conn, conn->c_laddr);
-	rds_message_addref(rm); /* for the inc */
+	/* For the embedded inc. Matching put is in loop_inc_free() */
+	rds_message_addref(rm);
 
 	rds_recv_incoming(conn, conn->c_laddr, conn->c_faddr, &rm->m_inc,
 			  GFP_KERNEL, KM_USER0);
@@ -77,6 +78,16 @@ static int rds_loop_xmit(struct rds_connection *conn, struct rds_message *rm,
 	return sizeof(struct rds_header) + be32_to_cpu(rm->m_inc.i_hdr.h_len);
 }
 
+/*
+ * See rds_loop_xmit(). Since our inc is embedded in the rm, we
+ * make sure the rm lives at least until the inc is done.
+ */
+static void rds_loop_inc_free(struct rds_incoming *inc)
+{
+        struct rds_message *rm = container_of(inc, struct rds_message, m_inc);
+        rds_message_put(rm);
+}
+
 static int rds_loop_xmit_cong_map(struct rds_connection *conn,
 				  struct rds_cong_map *map,
 				  unsigned long offset)
@@ -176,6 +187,6 @@ struct rds_transport rds_loop_transport = {
 	.conn_connect		= rds_loop_conn_connect,
 	.conn_shutdown		= rds_loop_conn_shutdown,
 	.inc_copy_to_user	= rds_message_inc_copy_to_user,
-	.inc_free		= rds_message_inc_free,
+	.inc_free		= rds_loop_inc_free,
 	.t_name			= "loopback",
 };

net/rds/message.c

@@ -89,12 +89,6 @@ void rds_message_put(struct rds_message *rm)
 }
 EXPORT_SYMBOL_GPL(rds_message_put);
 
-void rds_message_inc_free(struct rds_incoming *inc)
-{
-	struct rds_message *rm = container_of(inc, struct rds_message, m_inc);
-	rds_message_put(rm);
-}
-
 void rds_message_populate_header(struct rds_header *hdr, __be16 sport,
 				 __be16 dport, u64 seq)
 {