Re: [PATCH 22/22] sched: Remove TASK_WAKING

[Frank Rowand]

On 03/02/11 09:38, Peter Zijlstra wrote:
> With the new locking TASK_WAKING has become obsolete, remove it.
> 
> Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> LKML-Reference: <new-submission>
> ---

< snip >

> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -2175,7 +2175,7 @@ void set_task_cpu(struct task_struct *p,
>  	 * We should never call set_task_cpu() on a blocked task,
>  	 * ttwu() will sort out the placement.
>  	 */
> -	WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING &&
> +	WARN_ON_ONCE(p->state != TASK_RUNNING &&
>  			!(task_thread_info(p)->preempt_count & PREEMPT_ACTIVE));
>  
>  #ifdef CONFIG_LOCKDEP
> @@ -2613,7 +2613,7 @@ try_to_wake_up(struct task_struct *p, un
>  	smp_rmb();
>  
>  	p->sched_contributes_to_load = !!task_contributes_to_load(p);
> -	p->state = TASK_WAKING;
> +	p->state = TASK_RUNNING;
>  
>  	if (p->sched_class->task_waking)
>  		p->sched_class->task_waking(p);

No harm if the coded as in the patch, but an alternate suggestion
if you like it:

The only reason left for "p->state = TASK_RUNNING;" here is when
cpu is remote.  If cpu is not remote then p->state will be set by:

   ttwu_queue()
      ttwu_do_activate()
         ttwu_do_wakeup()
            p->state = TASK_RUNNING;

It would be more clear that setting state to TASK_RUNNING is protecting
the process until it has been removed from the wake_list by
sched_ttwu_pending() by setting p->state = TASK_RUNNING in ttwu_queue_remote().

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