Code agents are increasingly used in debugging workflows, where fault localization (FL) is often evaluated as endpoint retrieval: whether a model names the faulty code location. This view is inadequate for Linux kernel debugging, where failure logs may expose downstream symptoms while the erroneous state is introduced earlier and propagates through various dependences. We introduce KernelPath, a 200-instance Linux 5.10 function-level FL benchmark that pairs each root cause function with a source-grounded state propagation path and a dependence layer. KernelPath evaluates both endpoint localization and ordered diagnostic process recovery. Experiments with SOTA agents show that agents often retrieve plausible candidates but remain unreliable at recovering the diagnostic process, with performance degrading sharply under complex dependence relations. Further diagnostic probes show that agents can use explicit state-transition evidence, yet fail to infer how functions affect the erroneous state, drifting toward neighboring objectives such as repair-site selection, or up stream suspicious function retrieval. These findings reveal an unstable task model for kernel FL in current code agents.