[BUG] fix crash on flashinfer backend with cudagraph disabled, when attention group_size not in [1,2,4,8] (#7509)

tests/kernels/test_flashinfer.py

@@ -4,7 +4,7 @@ import flashinfer
 import pytest
 import torch
 
-NUM_HEADS = [(16, 16), (32, 8), (64, 8)]
+NUM_HEADS = [(16, 16), (32, 8), (64, 8), (6, 1)]
 HEAD_SIZES = [128, 256]
 BLOCK_SIZES = [16, 32]
 DTYPES = [torch.float16, torch.bfloat16]
@@ -123,7 +123,10 @@ def test_flashinfer_decode_with_paged_kv(kv_lens: List[int],
 
     workspace_buffer = torch.empty(128 * 1024 * 1024, dtype=torch.int8)
     wrapper = flashinfer.\
-        BatchDecodeWithPagedKVCacheWrapper(workspace_buffer, "NHD")
+        BatchDecodeWithPagedKVCacheWrapper(workspace_buffer, "NHD",
+                use_tensor_cores=(
+                    (num_query_heads//num_kv_heads) not in (1, 2, 4, 8))
+                )
     wrapper.begin_forward(kv_indptr,
                           kv_indices,
                           kv_last_page_lens,