Fix deadlock in JSON cache migration and prevent same storage selection

- Snapshot JSON data before yielding batches
- Release lock during batch processing
- Exclude source type from target selection
- Add detailed docstring for lock behavior
- Filter available storage types properly

lightrag/tools/migrate_llm_cache.py

@@ -561,20 +561,33 @@ class MigrationTool:
 
         Yields:
             Dictionary batches of cache entries
+
+        Note:
+            This method creates a snapshot of matching items while holding the lock,
+            then releases the lock before yielding batches. This prevents deadlock
+            when the target storage (also JsonKVStorage) tries to acquire the same
+            lock during upsert operations.
         """
+        # Create a snapshot of matching items while holding the lock
         async with storage._storage_lock:
-            batch = {}
-            for key, value in storage._data.items():
-                if key.startswith("default:extract:") or key.startswith(
-                    "default:summary:"
-                ):
-                    batch[key] = value
-                    if len(batch) >= batch_size:
-                        yield batch
-                        batch = {}
-            # Yield remaining items
-            if batch:
+            matching_items = [
+                (key, value)
+                for key, value in storage._data.items()
+                if key.startswith("default:extract:")
+                or key.startswith("default:summary:")
+            ]
+
+        # Now iterate over snapshot without holding lock
+        batch = {}
+        for key, value in matching_items:
+            batch[key] = value
+            if len(batch) >= batch_size:
                 yield batch
+                batch = {}
+
+        # Yield remaining items
+        if batch:
+            yield batch
 
     async def stream_default_caches_redis(self, storage, batch_size: int):
         """Stream default caches from RedisKVStorage - yields batches
@@ -829,13 +842,17 @@ class MigrationTool:
             print(f"✗ Invalid choice, please enter one of: {', '.join(valid_choices)}")
 
     async def setup_storage(
-        self, storage_type: str, use_streaming: bool = False
+        self,
+        storage_type: str,
+        use_streaming: bool = False,
+        exclude_storage_name: str = None,
     ) -> tuple:
         """Setup and initialize storage
 
         Args:
             storage_type: Type label (source/target)
             use_streaming: If True, only count records without loading. If False, load all data (legacy mode)
+            exclude_storage_name: Storage type to exclude from selection (e.g., to prevent selecting same as source)
 
         Returns:
             Tuple of (storage_instance, storage_name, workspace, total_count)
@@ -843,11 +860,27 @@ class MigrationTool:
         """
         print(f"\n=== {storage_type} Storage Setup ===")
 
+        # Filter available storage types if exclusion is specified
+        available_types = STORAGE_TYPES.copy()
+        if exclude_storage_name:
+            # Remove the excluded storage type from available options
+            available_types = {
+                k: v for k, v in STORAGE_TYPES.items() if v != exclude_storage_name
+            }
+
+            # Print available types
+            print("\nAvailable Storage Types for Target:")
+            for key, value in available_types.items():
+                print(f"[{key}] {value}")
+        else:
+            # Print all storage types for source
+            self.print_storage_types()
+
         # Get storage type choice - allow exit for source storage
         allow_exit = storage_type == "Source"
         choice = self.get_user_choice(
             f"Select {storage_type} storage type (1-4)",
-            list(STORAGE_TYPES.keys()),
+            list(available_types.keys()),
             allow_exit=allow_exit,
         )
 
@@ -1162,12 +1195,15 @@ class MigrationTool:
                 return
 
             # Setup target storage with streaming (only count, don't load all data)
+            # Exclude source storage type from target selection
             (
                 self.target_storage,
                 target_storage_name,
                 self.target_workspace,
                 target_count,
-            ) = await self.setup_storage("Target", use_streaming=True)
+            ) = await self.setup_storage(
+                "Target", use_streaming=True, exclude_storage_name=source_storage_name
+            )
 
             if not self.target_storage:
                 print("\n✗ Target storage setup failed")