background_threads 588 tools/testing/selftests/vm/userfaultfd.c pthread_t background_threads[nr_cpus]; background_threads 607 tools/testing/selftests/vm/userfaultfd.c if (pthread_create(&background_threads[cpu], &attr, background_threads 612 tools/testing/selftests/vm/userfaultfd.c if (pthread_join(background_threads[cpu], NULL))