[Fix] Fix loss parse in val_step

mmseg/models/segmentors/base.py

@@ -145,15 +145,22 @@ def train_step(self, data_batch, optimizer, **kwargs):
 
         return outputs
 
-    def val_step(self, data_batch, **kwargs):
+    def val_step(self, data_batch, optimizer=None, **kwargs):
         """The iteration step during validation.
 
         This method shares the same signature as :func:`train_step`, but used
         during val epochs. Note that the evaluation after training epochs is
         not implemented with this method, but an evaluation hook.
         """
-        output = self(**data_batch, **kwargs)
-        return output
+        losses = self(**data_batch)
+        loss, log_vars = self._parse_losses(losses)
+
+        outputs = dict(
+            loss=loss,
+            log_vars=log_vars,
+            num_samples=len(data_batch['img_metas']))
+
+        return outputs
 
     @staticmethod
     def _parse_losses(losses):