Fix FP4 inference corruption issue in glm4.5-air model (#9346)

sgl-kernel/python/sgl_kernel/gemm.py

@@ -205,9 +205,15 @@ def scaled_fp4_quant(
     rounded_m = ((m + 128 - 1) // 128) * 128
     scale_n = n // block_size
     rounded_n = ((scale_n + 4 - 1) // 4) * 4
-    output_scale = torch.empty(
-        (rounded_m, rounded_n // 4), device=device, dtype=torch.int32
-    )
+    # padded part should be zeroed out
+    if rounded_n > scale_n:
+        output_scale = torch.zeros(
+            (rounded_m, rounded_n // 4), device=device, dtype=torch.int32
+        )
+    else:
+        output_scale = torch.empty(
+            (rounded_m, rounded_n // 4), device=device, dtype=torch.int32
+        )
 
     torch.ops.sgl_kernel.scaled_fp4_quant.default(
         output, input, output_scale, input_global_scale
@@ -338,12 +344,21 @@ def scaled_fp4_experts_quant(
     output = torch.empty(
         m_numtopk, k // 2, device=input_tensor.device, dtype=torch.uint8
     )
-    output_scales = torch.empty(
-        MAX_TOKENS_PER_EXPERT * topk,
-        padded_k,
-        dtype=torch.int32,
-        device=input_tensor.device,
-    )
+    # padded part should be zeroed out
+    if padded_k > scales_k:
+        output_scales = torch.zeros(
+            MAX_TOKENS_PER_EXPERT * topk,
+            padded_k,
+            dtype=torch.int32,
+            device=input_tensor.device,
+        )
+    else:
+        output_scales = torch.empty(
+            MAX_TOKENS_PER_EXPERT * topk,
+            padded_k,
+            dtype=torch.int32,
+            device=input_tensor.device,
+        )
     torch.ops.sgl_kernel.scaled_fp4_experts_quant.default(
         output,
         output_scales,