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vLLM bug allows incompatible LoRA adapters to load silently

By PulseAugur Editorial · [1 sources] ·

A bug in the vLLM library allows users to load LoRA adapters that are not compatible with the specified model architecture, leading to the model defaulting to its base version without any errors or warnings. The issue stems from vLLM performing two separate checks for LoRA module compatibility: one permissive check against `supported_lora_modules` and a stricter check against `lora_config.target_modules`. If the adapter's target modules do not align with the model's architecture, the permissive check passes, but the stricter check fails to apply the adapter, resulting in the base model being used. This behavior was observed with vLLM version 0.28.0 and the Qwen/Qwen2.5-0.5B-Instruct model. AI

IMPACT This bug could lead to incorrect model outputs if users are unaware that their LoRA adapters are not being applied, potentially impacting fine-tuning and inference accuracy.

RANK_REASON Bug report about a specific software library's functionality.

Read on dev.to — LLM tag →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

vLLM bug allows incompatible LoRA adapters to load silently

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COVERAGE [1]

  1. dev.to — LLM tag TIER_1 English(EN) · The Homelab Postmortem ·

    vLLM accepts a LoRA it will never apply, and answers with the base model instead

    <p><strong>TL;DR</strong>: <code>vllm serve --lora-target-modules qkv_proj</code> plus an adapter that only touches <code>down_proj</code> is a combination vLLM accepts. It loads the adapter, compiles the LoRA kernels, and then wraps zero layers with it — every request comes back…

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