linux-kernel - Re: Q: a bogus task_running() check in try_to_wake

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Date:	Tue, 17 Jul 2007 21:05:48 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org
Subject: Re: Q: a bogus task_running() check in try_to_wake_up() ?


* Oleg Nesterov <oleg@...sign.ru> wrote:

> try_to_wake_up:
> 	
> 	if (p->se.on_rq)
> 		goto out_running;
> 
> 	...
> 
> 	if (unlikely(task_running(rq, p)))
> 		goto out_activate;
> 
> How it possible that rq->curr has on_rq == 0 ?
> 
> AFAICS, this can only happen if this task is rq->idle. But idle 
> threads should not sleep, we have a special "scheduling from the idle 
> thread!" check in schedule().

it's also possible if an arch uses __ARCH_WANT_INTERRUPTS_ON_CTXSW, 
right?

[ btw., we dont have a special "scheduling from the idle thread" check
  in schedule() anymore, it's now in kernel/sched_idletask.c :-) ]

	Ingo
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