:Fix host task whole graph update bug

Author: fabiomestre

sycl/source/detail/graph_impl.cpp

@@ -1398,6 +1398,14 @@ void exec_graph_impl::update(
             this, Nodes, AllocaQueue, UpdateRequirements, MExecutionEvents);
 
     MExecutionEvents.push_back(UpdateEvent);
+
+    // If the graph has HostTasks, the update has to be blocking. This is
+    // needed because HostTasks are scheduled using a separate thread
+    // which can execute at an arbitrary point in the program (e.g. after
+    // resources have been freed).
+    if (MContainsHostTask) {
+      UpdateEvent->wait(UpdateEvent);
+    }
   } else {
     // For each partition in the executable graph, call UR update on the
     // command-buffer with the nodes to update.