Fix assertion error when packed_seq_params is passed without proper qkv_format

[tomzw11]

问题描述

即使没有配置 --reset-attention-mask，也会有 packed_seq_params 被传入，但缺少 qkv_format 或 cu_seqlens_q，导致 assertion 错误：AssertionError: Packed sequences are not supported when fla is not available.

修复方案

修改 cu_seqlens 的初始化逻辑，仅在满足以下所有条件时才设置 cu_seqlens：

1. packed_seq_params is not None
2. packed_seq_params 有 qkv_format 属性
3. qkv_format == 'thd'
4. cu_seqlens_q is not None

[gemini-code-assist]

Code Review

This pull request modifies the packed sequence handling in gated_delta_net.py to ensure cu_seqlens is only set when qkv_format is 'thd' and cu_seqlens_q is present. The reviewer suggested using getattr to safely and concisely access these attributes on packed_seq_params to prevent potential AttributeError exceptions.

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[gemini-code-assist]

使用 getattr 可以更安全、更简洁地获取属性。这样不仅能避免多次调用 hasattr 和直接属性访问，还能防止在 packed_seq_params 缺少 cu_seqlens_q 属性时触发 AttributeError 异常。

        # Only use packed sequences when qkv_format is 'thd' and cu_seqlens_q is present
        cu_seqlens = None
        if packed_seq_params is not None and getattr(packed_seq_params, 'qkv_format', None) == 'thd':
            cu_seqlens = getattr(packed_seq_params, 'cu_seqlens_q', None)

[Jintao-Huang]

没懂，什么场景下 packed_seq_params 为非None值，但是没有 cu_seqlens_q