[T5 fp16] Fix fp16 in T5 (#4436)

* fix fp16 in t5

* make style

* refactor invert_attention_mask fn

* fix typo

src/transformers/modeling_t5.py

@@ -149,8 +149,12 @@ class T5LayerNorm(nn.Module):
         self.variance_epsilon = eps
 
     def forward(self, x):
-        variance = x.pow(2).mean(-1, keepdim=True)
+        # layer norm should always be calculated in float32
+        variance = x.to(torch.float32).pow(2).mean(-1, keepdim=True)
         x = x / torch.sqrt(variance + self.variance_epsilon)
+
+        if self.weight.dtype == torch.float16:
+            x = x.to(torch.float16)
         return self.weight * x
 
 
@@ -691,7 +695,9 @@ class T5Stack(T5PreTrainedModel):
             attention_mask = torch.ones(batch_size, mask_seq_length).to(inputs_embeds.device)
         if self.is_decoder and encoder_attention_mask is None and encoder_hidden_states is not None:
             encoder_seq_length = encoder_hidden_states.shape[1]
-            encoder_attention_mask = torch.ones(batch_size, encoder_seq_length).to(inputs_embeds.device)
+            encoder_attention_mask = torch.ones(
+                batch_size, encoder_seq_length, device=inputs_embeds.device, dtype=torch.long
+            )
 
         # initialize past_key_value_states with `None` if past does not exist
         if past_key_value_states is None:
@@ -733,6 +739,7 @@ class T5Stack(T5PreTrainedModel):
             # layer_outputs is a tuple with:
             # hidden-states, key-value-states, (self-attention weights), (self-attention position bias), (cross-attention weights), (cross-attention position bias)
             hidden_states, present_key_value_state = layer_outputs[:2]
+
             if i == 0:
                 # We share the position biases between the layers - the first layer store them
                 # layer_outputs = hidden-states, key-value-states (self-attention weights), (self-attention position bias), (cross-attention weights), (cross-attention position bias)

src/transformers/modeling_utils.py

@@ -128,7 +128,18 @@ class ModuleUtilsMixin:
         # encoder_extended_attention_mask = (encoder_extended_attention_mask ==
         # encoder_extended_attention_mask.transpose(-1, -2))
         encoder_extended_attention_mask = encoder_extended_attention_mask.to(dtype=self.dtype)  # fp16 compatibility
+
+        if self.dtype == torch.float16:
+            encoder_extended_attention_mask = (1.0 - encoder_extended_attention_mask) * -1e4
+        elif self.dtype == torch.float32:
             encoder_extended_attention_mask = (1.0 - encoder_extended_attention_mask) * -1e9
+        else:
+            raise ValueError(
+                "{} not recognized. `dtype` should be set to either `torch.float32` or `torch.float16`".format(
+                    self.dtype
+                )
+            )
+
         return encoder_extended_attention_mask
 
     def get_extended_attention_mask(self, attention_mask: Tensor, input_shape: tuple, device: device):

tests/test_modeling_t5.py

@@ -304,6 +304,16 @@ class T5ModelTest(ModelTesterMixin, unittest.TestCase):
             output_with_past_cache = model.generate(input_ids[:1], num_beams=2, max_length=5, do_sample=True)
             self.parent.assertTrue(torch.all(output_with_past_cache == output_without_past_cache))
 
+        def create_and_check_t5_model_fp16_forward(
+            self, config, input_ids, decoder_input_ids, attention_mask, decoder_attention_mask, lm_labels,
+        ):
+            model = T5Model(config=config)
+            model.to(torch_device)
+            model.half()
+            model.eval()
+            output = model(input_ids, decoder_input_ids=input_ids, attention_mask=attention_mask)[0]
+            self.parent.assertFalse(torch.isnan(output).any().item())
+
         def prepare_config_and_inputs_for_common(self):
             config_and_inputs = self.prepare_config_and_inputs()
             (
@@ -355,6 +365,11 @@ class T5ModelTest(ModelTesterMixin, unittest.TestCase):
         config_and_inputs = self.model_tester.prepare_config_and_inputs()
         self.model_tester.create_t5_and_check_t5_generate_with_past_key_value_states(*config_and_inputs)
 
+    @unittest.skipIf(torch_device == "cpu", "Cant do half precision")
+    def test_t5_model_fp16_forward(self):
+        config_and_inputs = self.model_tester.prepare_config_and_inputs()
+        self.model_tester.create_and_check_t5_model_fp16_forward(*config_and_inputs)
+
     @slow
     def test_model_from_pretrained(self):
         for model_name in list(T5_PRETRAINED_MODEL_ARCHIVE_MAP.keys())[:1]: