add: thread->last_time_type = KERNEL_TIME;
context: _create_user_thread_kentry(void){	struct thread *thread = thread_get_current_thread();	// a signal may have been delivered here//	thread_atkernel_exit();	thread->last_time = system_time();	thread->in_kernel = false;	// jump to the entry point in user space	arch_thread_enter_uspace(thread, (addr)thread->entry, thread->args);	// never get here	return 0;}