operating system testers

Abstract: Detecting data races in the Linux kernel requires exploring both the input space and the thread-interleaving space. Existing kernel concurrency fuzzers couple these two searches by exploring interleavings during fuzzing, often spending substantial scheduling effort on inputs with little potential to trigger real races. In this paper, we present a new concurrency fuzzing paradigm that decouples concurrent-input generation from thread-interleaving exploration, enabling expensive scheduling to focus on promising inputs. To identify inputs that warrant targeted scheduling, we introduce May Race Pairs (MRPs), which represent conflicting memory-access pairs observed within a dynamically determined time threshold. Our framework first generates and executes concurrent syscall groups without controlled scheduling, collecting MRPs to guide further input mutation and identify schedule-worthy inputs. It then uses a separate scheduling instance to explore targeted interleavings and confirm real data races. To improve the effectiveness of both stages, we incorporate LLM-assisted semantic mutation for generating diverse syscall groups, backpressure-guided dynamic threshold control for balancing candidate production and scheduling consumption, and history-aware context recovery, context-aware interleaving scheduling, and candidate MRP prioritization for efficient race confirmation. We implement our framework for the Linux kernel and evaluate it on eight common kernel modules in Linux 6.17. It discovers 187 unique real-world data races, including 59 harmful races. Under the same testing budget, our approach detects substantially more data races than existing kernel concurrency fuzzers, including SegFuzz and CONZZER. These results demonstrate the effectiveness of decoupling concurrent-input generation from interleaving exploration and concentrating scheduling effort on promising candidates.