[Bugfix][V1] Fix FlashInfer V1 backend using the wrong VllmConfig

[mgoin]

FIX #17483 (comment)

Thanks to @chenyang78 for reporting and @heheda12345 for the fix.

The global vllm config may not be set by set_current_vllm_config, so we should read it from runner directly so self.vllm_config = runner.vllm_config. This is already what FlashInfer V0 does so this was likely just an oversight

vllm/vllm/attention/backends/flashinfer.py

Line 200 in 19324d6

self.vllm_config = self.runner.vllm_config

Before:

VLLM_USE_V1=1 VLLM_ATTENTION_BACKEND=FLASHINFER lm_eval --model vllm --model_args pretrained=meta-llama/Llama-3.1-8B-Instruct --trust_remote_code --tasks gsm8k --num_fewshot 5 --batch_size auto 

assert len(per_layer_params) > 0, "No attention layers found in the model."

After:

VLLM_USE_V1=1 VLLM_ATTENTION_BACKEND=FLASHINFER lm_eval --model vllm --model_args pretrained=meta-llama/Llama-3.1-8B-Instruct --trust_remote_code --tasks gsm8k --num_fewshot 5 --batch_size auto 

vllm (pretrained=meta-llama/Llama-3.1-8B-Instruct,trust_remote_code=True), gen_kwargs: (None), limit: None, num_fewshot: 5, batch_size: auto
|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.7892|±  |0.0112|
|     |       |strict-match    |     5|exact_match|↑  |0.7635|±  |0.0117|

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