Fix unloading of LoRAs when xformers attention procs are in use (#4179)

src/diffusers/loaders.py

@@ -26,6 +26,7 @@ from huggingface_hub import hf_hub_download
 from torch import nn
 
 from .models.attention_processor import (
+    LORA_ATTENTION_PROCESSORS,
     AttnAddedKVProcessor,
     AttnAddedKVProcessor2_0,
     AttnProcessor,
@@ -1293,22 +1294,21 @@ class LoraLoaderMixin:
         >>> ...
         ```
         """
-        is_unet_lora = all(
-            isinstance(processor, (LoRAAttnProcessor2_0, LoRAAttnProcessor, LoRAAttnAddedKVProcessor))
-            for _, processor in self.unet.attn_processors.items()
-        )
+        unet_attention_classes = {type(processor) for _, processor in self.unet.attn_processors.items()}
+
+        if unet_attention_classes.issubset(LORA_ATTENTION_PROCESSORS):
             # Handle attention processors that are a mix of regular attention and AddedKV
             # attention.
-        if is_unet_lora:
-            is_attn_procs_mixed = all(
-                isinstance(processor, (LoRAAttnProcessor2_0, LoRAAttnProcessor))
-                for _, processor in self.unet.attn_processors.items()
-            )
-            if not is_attn_procs_mixed:
-                unet_attn_proc_cls = AttnProcessor2_0 if hasattr(F, "scaled_dot_product_attention") else AttnProcessor
-                self.unet.set_attn_processor(unet_attn_proc_cls())
-            else:
+            if len(unet_attention_classes) > 1 or LoRAAttnAddedKVProcessor in unet_attention_classes:
                 self.unet.set_default_attn_processor()
+            else:
+                regular_attention_classes = {
+                    LoRAAttnProcessor: AttnProcessor,
+                    LoRAAttnProcessor2_0: AttnProcessor2_0,
+                    LoRAXFormersAttnProcessor: XFormersAttnProcessor,
+                }
+                [attention_proc_class] = unet_attention_classes
+                self.unet.set_attn_processor(regular_attention_classes[attention_proc_class]())
 
         # Safe to call the following regardless of LoRA.
         self._remove_text_encoder_monkey_patch()

src/diffusers/models/attention_processor.py

@@ -167,7 +167,7 @@ class Attention(nn.Module):
     ):
         is_lora = hasattr(self, "processor") and isinstance(
             self.processor,
-            (LoRAAttnProcessor, LoRAAttnProcessor2_0, LoRAXFormersAttnProcessor, LoRAAttnAddedKVProcessor),
+            LORA_ATTENTION_PROCESSORS,
         )
         is_custom_diffusion = hasattr(self, "processor") and isinstance(
             self.processor, (CustomDiffusionAttnProcessor, CustomDiffusionXFormersAttnProcessor)
@@ -1623,6 +1623,13 @@ AttentionProcessor = Union[
     CustomDiffusionXFormersAttnProcessor,
 ]
 
+LORA_ATTENTION_PROCESSORS = (
+    LoRAAttnProcessor,
+    LoRAAttnProcessor2_0,
+    LoRAXFormersAttnProcessor,
+    LoRAAttnAddedKVProcessor,
+)
+
 
 class SpatialNorm(nn.Module):
     """

tests/models/test_lora_layers.py

@@ -464,6 +464,14 @@ class LoraLoaderMixinTests(unittest.TestCase):
                 if isinstance(module, Attention):
                     self.assertIsInstance(module.processor, LoRAXFormersAttnProcessor)
 
+            # unload lora weights
+            sd_pipe.unload_lora_weights()
+
+            # check if attention processors are reverted back to xFormers
+            for _, module in sd_pipe.unet.named_modules():
+                if isinstance(module, Attention):
+                    self.assertIsInstance(module.processor, XFormersAttnProcessor)
+
     @unittest.skipIf(torch_device != "cuda", "This test is supposed to run on GPU")
     def test_lora_save_load_with_xformers(self):
         pipeline_components, lora_components = self.get_dummy_components()