How task_struct.rt.time_slice is initialized?

[Simon Guo]

Hi, 

On Sat, Jun 06, 2015 at 06:53:22PM +0800, Simon Guo wrote:
> Dear alias,
> 
> I noticed there is a time_slice variable for SCHED_RR policy in
> task_struct.rt member (I am using 4.1.0 kernel):
>         struct sched_rt_entity {
>                 ...
>                 unsigned int time_slice;
>                 ...
>         };
> 
> Per my understanding, the task_struct.rt.time_slice should be
> initialized to sched_rr_timeslice or RR_TIMESLICE . Like what process 0 has done:
> #define INIT_TASK(tsk)  \
> {   
>         ...
>                 .rt             = { \
>                                 .run_list       = LIST_HEAD_INIT(tsk.rt.run_list), \
>                                 .time_slice     = RR_TIMESLICE, \
>                 },
>         ...
> }
> 
> However I didn't see somewhere in copy_process() to set time_slice
> value for a new forked SCHED_RR process.
> 
> If time_slice is not initialized, time_slice will be with value 0 and
> will be overflow to a big value in following "if (--p->rt.time_slice)" statement:
> static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
> {
>         ...
> 	/*
> 	 * RR tasks need a special form of timeslice management.
> 	 * FIFO tasks have no timeslices.
> 	 */
> 	if (p->policy != SCHED_RR)
> 		return;
> 
> 	if (--p->rt.time_slice)                          
> 		return;
> 
> 	p->rt.time_slice = sched_rr_timeslice;
>         ...
> }
> 
> Is it a bug? Please correct me if I am wrong.
Looks the initialization logic is in arch_dup_task_struct(). Please
ignore my previous question.

Thanks,
Simon