[Bugfix] Fix weight_loader v1 block scale (#31103)

Signed-off-by: Kyuyeun Kim <kyuyeunk@google.com>

vllm/model_executor/layers/linear.py

@@ -80,6 +80,14 @@ def adjust_marlin_shard(param, shard_size, shard_offset):
     return shard_size * marlin_tile_size, shard_offset * marlin_tile_size
 
 
+def adjust_block_scale_shard(weight_block_size, shard_size, shard_offset):
+    assert weight_block_size is not None
+    block_n = weight_block_size[0]
+    shard_offset = (shard_offset + block_n - 1) // block_n
+    shard_size = (shard_size + block_n - 1) // block_n
+    return shard_size, shard_offset
+
+
 def adjust_bitsandbytes_4bit_shard(
     param: Parameter, shard_offsets: dict[str, tuple[int, int]], loaded_shard_id: str
 ) -> tuple[int, int]:
@@ -763,8 +771,18 @@ class MergedColumnParallelLinear(ColumnParallelLinear):
 
         assert loaded_shard_id < len(self.output_sizes)
         if output_dim is not None:
-            shard_offset = sum(self.output_sizes[:loaded_shard_id]) // self.tp_size
-            shard_size = self.output_sizes[loaded_shard_id] // self.tp_size
+            shard_offset = sum(self.output_sizes[:loaded_shard_id])
+            shard_size = self.output_sizes[loaded_shard_id]
+
+            if isinstance(param, BlockQuantScaleParameter):
+                weight_block_size = getattr(self, "weight_block_size", None)
+                shard_size, shard_offset = adjust_block_scale_shard(
+                    weight_block_size, shard_size, shard_offset
+                )
+
+            shard_offset //= self.tp_size
+            shard_size //= self.tp_size
+
             # Special case for quantization.
             # If quantized, we need to adjust the offset and size to account
             # for the packing.
@@ -867,24 +885,17 @@ class MergedColumnParallelLinear(ColumnParallelLinear):
 
         assert loaded_shard_id < len(self.output_sizes)
 
+        shard_offset = sum(self.output_sizes[:loaded_shard_id])
+        shard_size = self.output_sizes[loaded_shard_id]
+
         if isinstance(param, BlockQuantScaleParameter):
-            assert self.quant_method is not None
-            # Assume the weight block size has been set by quant method
-            assert hasattr(self, "weight_block_size")
-            weight_block_size = self.weight_block_size
-            assert weight_block_size is not None
-            block_n, _ = weight_block_size[0], weight_block_size[1]
-            shard_offset = (
-                (sum(self.output_sizes[:loaded_shard_id]) + block_n - 1) // block_n
-            ) // self.tp_size
-            shard_size = (
-                (self.output_sizes[loaded_shard_id] + block_n - 1)
-                // block_n
-                // self.tp_size
+            weight_block_size = getattr(self, "weight_block_size", None)
+            shard_size, shard_offset = adjust_block_scale_shard(
+                weight_block_size, shard_size, shard_offset
             )
-        else:
-            shard_offset = sum(self.output_sizes[:loaded_shard_id]) // self.tp_size
-            shard_size = self.output_sizes[loaded_shard_id] // self.tp_size
+
+        shard_offset //= self.tp_size
+        shard_size //= self.tp_size
 
         param.load_merged_column_weight(
             loaded_weight=loaded_weight,
@@ -1066,16 +1077,11 @@ class QKVParallelLinear(ColumnParallelLinear):
         shard_offset = self._get_shard_offset_mapping(loaded_shard_id)
         shard_size = self._get_shard_size_mapping(loaded_shard_id)
 
-        # Note(simon): This is needed for Qwen3's fp8 quantization.
         if isinstance(param, BlockQuantScaleParameter):
-            assert self.quant_method is not None
-            # Assume the weight block size has been set by quant method
-            assert hasattr(self, "weight_block_size")
-            weight_block_size = self.weight_block_size
-            assert weight_block_size is not None
-            block_n, _ = weight_block_size[0], weight_block_size[1]
-            shard_offset = (shard_offset + block_n - 1) // block_n
-            shard_size = (shard_size + block_n - 1) // block_n
+            weight_block_size = getattr(self, "weight_block_size", None)
+            shard_size, shard_offset = adjust_block_scale_shard(
+                weight_block_size, shard_size, shard_offset
+            )
 
         param.load_qkv_weight(
             loaded_weight=loaded_weight,
@@ -1208,6 +1214,13 @@ class QKVParallelLinear(ColumnParallelLinear):
             elif loaded_shard_id == "v":
                 shard_offset = (self.num_heads + self.num_kv_heads) * self.head_size
                 shard_size = self.num_kv_heads * self.v_head_size
+
+            if isinstance(param, BlockQuantScaleParameter):
+                weight_block_size = getattr(self, "weight_block_size", None)
+                shard_size, shard_offset = adjust_block_scale_shard(
+                    weight_block_size, shard_size, shard_offset
+                )
+
             # Special case for Quantized Weights.
             # If quantized, we need to adjust the offset and size to account
             # for the packing.