Remove direct freeing of sessions

Sessions are now always freed by releasing the last reference to it.

include/maxscale/session.h

@@ -204,7 +204,6 @@ typedef struct session
 
 SESSION *session_alloc(struct service *, struct dcb *);
 SESSION *session_set_dummy(struct dcb *);
-bool session_free(SESSION *);
 int session_isvalid(SESSION *);
 int session_reply(void *inst, void *session, GWBUF *data);
 char *session_get_remote(SESSION *);
@@ -347,10 +346,22 @@ static inline bool session_set_autocommit(SESSION* ses, bool autocommit)
  * @param id Unique session ID
  * @return Reference to a SESSION or NULL if the session was not found
  *
- * @note The caller must free the session reference by passing it to the
+ * @note The caller must free the session reference by calling session_put_ref
- * @c session_put_ref function
  */
-SESSION* session_get_ref(int id);
+SESSION* session_get_by_id(int id);
+
+/**
+ * @brief Get a session reference
+ *
+ * This creates an additional reference to a session which allows it to live
+ * as long as it is needed.
+ *
+ * @param session Session reference to get
+ * @return Reference to a SESSION
+ *
+ * @note The caller must free the session reference by calling session_put_ref
+ */
+SESSION* session_get_ref(SESSION *sessoin);
 
 /**
  * @brief Release a session reference

server/core/dcb.c

@@ -348,7 +348,7 @@ dcb_final_free(DCB *dcb)
             bool is_client_dcb = (DCB_ROLE_CLIENT_HANDLER == dcb->dcb_role ||
                                   DCB_ROLE_INTERNAL == dcb->dcb_role);
 
-            session_free(local_session);
+            session_put_ref(local_session);
 
             if (is_client_dcb)
             {
@@ -1714,7 +1714,7 @@ dcb_maybe_add_persistent(DCB *dcb)
             CHK_SESSION(local_session);
             if (SESSION_STATE_DUMMY != local_session->state)
             {
-                session_free(local_session);
+                session_put_ref(local_session);
             }
         }
         spinlock_acquire(&dcb->cb_lock);

server/core/modulecmd.c

@@ -277,7 +277,7 @@ static bool process_argument(modulecmd_arg_type_t *type, const void* value,
                 break;
 
             case MODULECMD_ARG_SESSION:
-                if ((arg->value.session = session_get_ref(atoi(value))))
+                if ((arg->value.session = session_get_by_id(atoi(value))))
                 {
                     arg->type.type = MODULECMD_ARG_SESSION;
                 }

server/core/session.c

@@ -336,31 +336,14 @@ session_simple_free(SESSION *session, DCB *dcb)
  *
  * @param session       The session to deallocate
  */
-bool
+static void session_free(SESSION *session)
-session_free(SESSION *session)
 {
-    if (NULL == session || SESSION_STATE_DUMMY == session->state)
-    {
-        return true;
-    }
     CHK_SESSION(session);
+    ss_dassert(session->refcount == 0);
 
-    /*
-     * Remove one reference. If there are no references left,
-     * free session.
-     */
-    if (atomic_add(&session->refcount, -1) > 1)
-    {
-        /* Must be one or more references left */
-        return false;
-    }
     session->state = SESSION_STATE_TO_BE_FREED;
-
     atomic_add(&session->service->stats.n_current, -1);
 
-    /***
-     *
-     */
     if (session->client_dcb)
     {
         dcb_free_all_memory(session->client_dcb);
@@ -396,9 +379,7 @@ session_free(SESSION *session)
         MXS_FREE(session->filters);
     }
 
-    MXS_INFO("Stopped %s client session [%lu]",
+    MXS_INFO("Stopped %s client session [%lu]", session->service->name, session->ses_id);
-             session->service->name,
-             session->ses_id);
 
     /** Disable trace and decrease trace logger counter */
     session_disable_log_priority(session, LOG_INFO);
@@ -409,7 +390,6 @@ session_free(SESSION *session)
         session->state = SESSION_STATE_FREE;
         session_final_free(session);
     }
-    return true;
 }
 
 static void
@@ -925,17 +905,14 @@ static bool ses_find_id(DCB *dcb, void *data)
 
     if (dcb->session->ses_id == *id)
     {
-        /** We need to increment the reference count of the session to prevent it
+        *ses = session_get_ref(dcb->session);
-         * from being freed while it's in use. */
-        atomic_add(&dcb->session->refcount, 1);
-        *ses = dcb->session;
         rval = false;
     }
 
     return rval;
 }
 
-SESSION* session_get_ref(int id)
+SESSION* session_get_by_id(int id)
 {
     SESSION *session = NULL;
     void *params[] = {&session, &id};
@@ -945,10 +922,20 @@ SESSION* session_get_ref(int id)
     return session;
 }
 
+SESSION* session_get_ref(SESSION *session)
+{
+    atomic_add(&session->refcount, 1);
+    return session;
+}
+
 void session_put_ref(SESSION *session)
 {
-    if (session)
+    if (session && session->state != SESSION_STATE_DUMMY)
     {
-        session_free(session);
+        /** Remove one reference. If there are no references left, free session */
+        if (atomic_add(&session->refcount, -1) == 1)
+        {
+            session_free(session);
+        }
     }
 }

server/modules/filter/tee/tee.c

@@ -701,7 +701,7 @@ freeSession(FILTER *instance, void *session)
 
         if (state == SESSION_STATE_ROUTER_READY)
         {
-            session_free(ses);
+            session_put_ref(ses);
         }
         else if (state == SESSION_STATE_TO_BE_FREED)
         {