Fix cypclass locking logic

Cython/Compiler/CypclassTransforms.py

@@ -425,16 +425,13 @@ class CypclassLockTransform(Visitor.EnvTransform):
         # that the receiver object will only be read, not that
         # __all__ the reachable subobjects will only be read.
         locally_writing = (field_access and node.is_target) or method_call
+        writing = self.writing | locally_writing
         if objtype.is_qualified_cyp_class and objtype.qualifier == 'lock':
-            old_writing = self.writing
-            self.writing = locally_writing
+            self.writing = False
             self.visitchildren(node)
             if field_access or (method_call and not nodetype.self_qualifier == 'lock'):
-                node.obj = ExprNodes.CoerceToLockedNode(node.obj, exclusive=self.writing)
-            self.writing = old_writing
-        elif objtype.is_cyp_class:
-            old_writing = self.writing
-            self.writing |= locally_writing
+                node.obj = ExprNodes.CoerceToLockedNode(node.obj, exclusive=writing)
+        else:
+            self.writing = writing
             self.visitchildren(node)
-            self.writing = old_writing
         return node