[Bugfix] fix bf16 multimodal model hash (vllm-project#23623)

Signed-off-by: Yuekai Zhang <zhangyuekai@foxmail.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Roger Wang <hey@rogerw.io>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>
Signed-off-by: Xiao Yu <xiao.yu@amd.com>

Author: 4 people

vllm/multimodal/hasher.py

@@ -43,7 +43,19 @@ def serialize_item(cls, obj: object) -> Union[bytes, memoryview]:
             return cls.item_to_bytes(
                 "image", np.asarray(convert_image_mode(obj, "RGBA")))
         if isinstance(obj, torch.Tensor):
-            return cls.item_to_bytes("tensor", obj.cpu().numpy())
+            tensor_obj: torch.Tensor = obj.cpu()
+            tensor_dtype = tensor_obj.dtype
+            if tensor_dtype == torch.bfloat16:
+                tensor_obj = tensor_obj.contiguous()
+                tensor_obj = tensor_obj.view(
+                    (tensor_obj.numel(), )).view(torch.uint8)
+                return cls.item_to_bytes(
+                    "tensor", {
+                        "original_dtype": str(tensor_dtype),
+                        "original_shape": tuple(tensor_obj.shape),
+                        "data": tensor_obj.numpy()
+                    })
+            return cls.item_to_bytes("tensor", tensor_obj.numpy())
         if isinstance(obj, np.ndarray):
             # If the array is non-contiguous, we need to copy it first
             arr_data = obj.data if obj.flags.c_contiguous else obj.tobytes()