---
id: pr-flash-attention-2481
repo: Dao-AILab/flash-attention
pr: 2481
title: '[cute,bwd] fix PDL race in bwd_preprocess, which corrupting dpsum on SM90+'
author: geruome
date: '2026-04-21'
url: https://github.com/Dao-AILab/flash-attention/pull/2481
source_category: upstream-code
architectures:
- sm90
tags:
- attention kernel
- cute
- hopper
- sm80
- sm90
techniques: []
hardware_features:
- hopper
- pdl
kernel_types:
- attention
languages:
- cuda-cpp
- cute-dsl
captured_at: '2026-05-16'
status: merged
merge_sha: 3a7694c04748e3ba1cd954eb5dfdfd4b6646a234
inclusion_reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.
changed_paths:
- flash_attn/cute/flash_bwd_preprocess.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2481
head_ref_oid: 21ecd1c323a2bd2838609d40a3d714b9e39e6658
---
# [cute,bwd] fix PDL race in bwd_preprocess, which corrupting dpsum on SM90+

- Repository: `Dao-AILab/flash-attention`
- PR: [2481](https://github.com/Dao-AILab/flash-attention/pull/2481)
- Decision: `Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.`
- Reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.

## Changed Paths

- `flash_attn/cute/flash_bwd_preprocess.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2481`
