Fix MultiWorkerMirroredStrategy validation in Model.fit

PiperOrigin-RevId: 299150128
Change-Id: Ie0ef99dcbd1afc91ad1a0e19c56638c5e48a7865

tensorflow/python/keras/distribute/multi_worker_callback_tf2_test.py

@@ -94,6 +94,8 @@ class KerasCallbackMultiProcessTest(parameterized.TestCase, test.TestCase):
           x=train_ds,
           epochs=num_epoch,
           steps_per_epoch=steps,
+          validation_data=train_ds,
+          validation_steps=steps,
           callbacks=[
               callbacks.ModelCheckpoint(
                   filepath=saving_filepath, save_weights_only=save_weights_only)

tensorflow/python/keras/engine/training.py

@@ -21,6 +21,7 @@ from __future__ import print_function
 import copy
 
 from tensorflow.python.distribute import distribute_coordinator as dc
+from tensorflow.python.distribute import distribute_coordinator_context as dc_context
 from tensorflow.python.distribute import distribution_strategy_context as ds_context
 from tensorflow.python.distribute import values as ds_values
 from tensorflow.python.eager import backprop
@@ -63,6 +64,10 @@ def enable_multi_worker(method):
     if not self._in_multi_worker_mode():  # pylint: disable=protected-access
       return method(self, *args, **kwargs)
 
+    # Running inside `run_distribute_coordinator` already.
+    if dc_context.get_current_worker_context():
+      return method(self, *args, **kwargs)
+
     return dc.run_distribute_coordinator(
         lambda _: method(self, *args, **kwargs),
         self.distribute_strategy,