[Bugfix] Fix Engine Failing After Invalid Request - AsyncEngineDeadError

[robertgshaw2-redhat]

Sending invalid logit_bias parameter can put the server into a bad state:

curl http://localhost:8000/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "meta-llama/Meta-Llama-3-8B-Instruct",
    "logit_bias": {
        "AI": -100
    },
    "messages": [
        {
            "role": "system",
            "content": "You are a a helpful assistant."
        },
        {
            "role": "user",
            "content": "What can I do with AI? Provide a very short answer."
        }
    ]
}'

• In the logits_processor, we call int(token_id) from the logit_bias
• If the token_id cannot be converted to an int, python throws a value error. However, this error will not arise until the request is already in the LLMEngine, since the logits_processor is used during sampling
• The fix is to validate that the logits_bias is well formed before we add it into the LLMEngine such that we can throw the value error at the OpenAI layer and avoid throwing the error in LLMEngine

Launch Server:

python3 -m vllm.entrypoints.openai.api_server --model meta-llama/Meta-Llama-3-8B-Instruct --enforce-eager

Send Requests:

curl http://localhost:8000/v1/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "meta-llama/Meta-Llama-3-8B-Instruct",
    "logit_bias": {
        "AI": -100
    },
    "prompt": "Hello my name is"
}'

^ this fails, but subsequent requests will work

curl http://localhost:8000/v1/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "meta-llama/Meta-Llama-3-8B-Instruct",
    "prompt": "Hello my name is"
}'

^ this works after the fix!

FIX #5822 (link existing issues this PR will resolve)

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[DarkLight1337]

Thanks for the fix! Just a few comments

[robertgshaw2-redhat]

@DarkLight1337 addressed

[robertgshaw2-redhat]

Sorry, fixed

[DarkLight1337]

Sorry, just noticed this

[DarkLight1337]

To speed up the CI queue for #5905, I've cancelled the distributed tests for the latest CI run in this PR since they won't pass anyway until #5905 has been merged. Please merge main into your branch after that happens so that the CI can pass once again.

[DarkLight1337]

Looks like you accidentally included parts of your other PR here

[robertgshaw2-redhat]

shoot. Will undo