preempt_enable();
void exit_thread(void){	if (last_task_used_math == current)		last_task_used_math = NULL;	if (last_task_used_altivec == current)		last_task_used_altivec = NULL;#ifdef CONFIG_SPE	if (last_task_used_spe == current)		last_task_used_spe = NULL;#endif}