[Bug Fix] Fix some bugs

[ming1753]

Motivation

💡 If this PR is a Cherry Pick, the PR title needs to follow the format by adding the [Cherry-Pick] label at the very beginning and appending the original PR ID at the end. For example, [Cherry-Pick][CI] Add check trigger and logic(#5191)

💡 如若此PR是Cherry Pick，PR标题需遵循格式，在最开始加上[Cherry-Pick]标签，以及最后面加上原PR ID，例如[Cherry-Pick][CI] Add check trigger and logic(#5191)

Modifications

Usage or Command

Accuracy Tests

Checklist

• Add at least a tag in the PR title.
  • Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
  • You can add new tags based on the PR content, but the semantics must be clear.
• Format your code, run pre-commit before commit.
• Add unit tests. Please write the reason in this PR if no unit tests.
• Provide accuracy results.
• If the current PR is submitting to the release branch, make sure the PR has been submitted to the develop branch, then cherry-pick it to the release branch with the [Cherry-Pick] PR tag.

[paddle-bot]

Thanks for your contribution!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (develop@334b02c). Learn more about missing BASE report.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #7221   +/-   ##
==========================================
  Coverage           ?   73.87%           
==========================================
  Files              ?      376           
  Lines              ?    52938           
  Branches           ?     8264           
==========================================
  Hits               ?    39106           
  Misses             ?    11095           
  Partials           ?     2737           

Flag	Coverage Δ
GPU	73.87% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[fastdeploy-bot]

🤖 AI Code Review | 2026-04-08

📋 Review 摘要

PR 概述：修复 CUDA 操作中的同步和边界检查 bug

变更范围：custom_ops/gpu_ops/append_attn/、custom_ops/gpu_ops/flash_mask_attn/

影响面 Tag：[OP]

---

📝 PR 规范检查

PR 描述中的 Motivation 和 Modifications 部分未填写，仅保留了模板占位符。请补充描述：

Motivation（建议填写）：

修复两个 bug：1) DtoH 复制后未同步导致 CPU 可能读取到旧数据；2) KV 块未清零无效位置的共享内存，可能导致越界读取未初始化数据。

Modifications（建议填写）：

• get_block_shape_and_split_kv_block.cu: 在 DtoH 复制后添加 cudaStreamSynchronize 确保数据一致性
• mainloop_attn.hpp: 添加 KV 块边界检查，清零无效位置的共享内存

另外，PR 标题使用了 [Bug Fix] 标签（带空格），官方规范中是 [BugFix]（无空格），建议确认团队使用的标签格式。

---

问题

级别	文件	概述
🟡 建议	PR 描述	Motivation 和 Modifications 未填写
🟡 建议	PR 标题	标签格式使用 [Bug Fix]，建议确认应为 [BugFix]

---

总体评价

代码修改整体合理：

1. get_block_shape_and_split_kv_block.cu：

   • 添加 cudaStreamSynchronize(stream) 修复了 DtoH 复制后立即读取 CPU 数据的潜在数据竞争问题
   • 函数末尾的同步确保所有 GPU 操作和内存复制完成

2. mainloop_attn.hpp：

   • 添加 KV 块边界检查逻辑，当 seq_len 不是 kBlockN 整数倍时，正确清零无效位置的共享内存，避免读取未初始化数据

未发现阻塞性问题，但 PR 描述需要完善以帮助后续代码审查和维护。