Regardless of future of "struct utrace utrace;" patch looks like there is another race: engine's flags and ops settings in utrace_detach() and acting on them in report_quiescent(): utrace_detach() report_quiescent() --------------- ------------------ [utrace lock held] [utrace lock is not held] engine->flags = UTRACE_EVENT(QUIESCE) | UTRACE_ACTION_QUIESCE; if (engine->flags & UTRACE_EVENT(QUIESCE)) REPORT(report_quiesce); rcu_assign_pointer(engine->ops, &dead_engine_ops); At the moment of REPORT call engine's ops are still "live" ptrace ops which do not have ->report_quiesce callback. So, there will oops while calling function at NULL address. "Dead" ptrace engine ops do have dummy callback but it wasn't yet glued. I hit this once with "struct utrace utrace;" patch applied, but this bug is also present in stock utrace, I'm sure. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/