Repository: huggingface/transformers
Pull request: Fix setting FLASH_ATTENTION_DETERMINISTIC after importing

# What does this PR do?

transformers.enable_full_determinism enables deterministic flash attention using `FLASH_ATTENTION_DETERMINISTIC` https://github.com/huggingface/transformers/blob/800510c67bfc5cedd0bb7635648a07f39719be43/src/transformers/trainer_utils.py#L79

However, current checks use a global variable `deterministic_g`, which will do the environment variable check as soon as importing, this will cause issues as users can call `transformers.enable_full_determinism` after `transformers.modeling_flash_attention_utils` is imported. This behavior is introduced in https://github.com/huggingface/transformers/pull/33932/files#r1806668579 to fix the graph break.

As a result, this PR implement fixes by delaying the environment variable check to the first time when `_flash_attention_forward` is executed, so that we can fix this issue and we won't introduce a graph break.

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Changed files:
filename: src/transformers/modeling_flash_attention_utils.py
patch: @@ -279,7 +279,7 @@ def fa_peft_integration_check(
 
 
 flash_241 = is_flash_attn_greater_or_equal("2.4.1")
-deterministic_g = os.environ.get("FLASH_ATTENTION_DETERMINISTIC", "0") == "1"
+deterministic_g = None
 
 
 def _flash_attention_forward(
@@ -342,6 +342,9 @@ def _flash_attention_forward(
 
     if flash_241:
         if deterministic is None:
+            global deterministic_g
+            if deterministic_g is None:
+                deterministic_g = os.environ.get("FLASH_ATTENTION_DETERMINISTIC", "0") == "1"
             deterministic = deterministic_g
         flash_kwargs["deterministic"] = deterministic