Fix SDPA dispatch & make SDPA CI compatible with torch<2.1.1 (#27940)

fix sdpa dispatch

Author: fxmarty

src/transformers/modeling_utils.py

@@ -1244,6 +1244,7 @@ def _autoset_attn_implementation(
         # Here we use config._attn_implementation_internal to check whether the attention implementation was explicitely set by the user.
         # The property `PretrainedConfig._attn_implementation` is never `None`, for backward compatibility (always fall back on "eager").
         # The `hasattr` here is used as some Transformers tests for some reason do not call PretrainedConfig __init__ (e.g. test_no_super_init_config_and_model)
+        requested_attn_implementation = None
         if hasattr(config, "_attn_implementation_internal") and config._attn_implementation_internal is not None:
             if config._attn_implementation != "flash_attention_2" and use_flash_attention_2:
                 raise ValueError(
@@ -1260,9 +1261,7 @@ def _autoset_attn_implementation(
                 raise ValueError(message + ".")
 
             # If a config is passed with a preset attn_implementation, we skip the automatic dispatch and use the user-provided config, with hard checks that the requested attention implementation is available.
-            hard_check_only = True
-        else:
-            hard_check_only = False
+            requested_attn_implementation = config._attn_implementation_internal
 
         if use_flash_attention_2:
             logger.warning_once(
@@ -1275,13 +1274,15 @@ def _autoset_attn_implementation(
                 config,
                 torch_dtype=torch_dtype,
                 device_map=device_map,
-                hard_check_only=hard_check_only,
+                hard_check_only=False,
                 check_device_map=check_device_map,
             )
-        elif cls._supports_sdpa or config._attn_implementation == "sdpa":
+        elif requested_attn_implementation in [None, "sdpa"]:
             # use_flash_attention_2 takes priority over SDPA, hence SDPA treated in this elif.
-            config = cls._check_and_enable_sdpa(config, hard_check_only=hard_check_only)
-        elif not hard_check_only:
+            config = cls._check_and_enable_sdpa(
+                config, hard_check_only=False if requested_attn_implementation is None else True
+            )
+        else:
             config._attn_implementation = "eager"
 
         return config

tests/test_modeling_common.py

@@ -83,6 +83,7 @@
     is_flax_available,
     is_tf_available,
     is_torch_fx_available,
+    is_torch_sdpa_available,
 )
 from transformers.utils.generic import ModelOutput
 
@@ -778,7 +779,7 @@ def _create_and_check_torchscript(self, config, inputs_dict):
         configs_no_init.torchscript = True
         for model_class in self.all_model_classes:
             for attn_implementation in ["eager", "sdpa"]:
-                if attn_implementation == "sdpa" and not model_class._supports_sdpa:
+                if attn_implementation == "sdpa" and (not model_class._supports_sdpa or not is_torch_sdpa_available()):
                     continue
 
                 configs_no_init._attn_implementation = attn_implementation