[cherry-pick-2.2]Fix fused_attention_op and fused_feedforward_op bug when pre_layer_norm is false. #36816
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…rm is false. (PaddlePaddle#36793) * Fix bug when pre_layer_norm is false.
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xingfeng01
approved these changes
Oct 28, 2021
zkh2016
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Oct 28, 2021
lanxianghit
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Oct 28, 2021
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PR types
Bug fixes
PR changes
OPs
Describe
问题描述：
fused_attention_op中，当pre_layer_norm为false时，fused_attention_op.cc的GradOpMaker将与pre layer_norm相关的张量也作为了输入和输出（比如，将d_scale，d_bias和d_ln_out作为输出）。此时，模型中调用该op时，梯度更新阶段会更新d_scale, d_bias和d_ln_out。由于这几个张量的值是没有初始化的，会偶发性的引发nan，inf的错误。
同理，fused_feedforwad_op也有类似的问题。
解决：
1.当pre_layer_norm为false时，反向的输入输出中去掉与pre layer_norm相关的张量；
2.为fused_attention_op增加单测，测试pre_layer_norm为true和false的情形。