linux-kernel - Re: [PATCH v2 1/2] sched: schedule_tail() should disable preemption

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Message-ID: <20141009145726.GA5604@redhat.com>
Date:	Thu, 9 Oct 2014 16:57:26 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] sched: schedule_tail() should disable preemption

On 10/09, Kirill Tkhai wrote:
>
> В Ср, 08/10/2014 в 21:36 +0200, Oleg Nesterov пишет:
> > @@ -2277,15 +2277,14 @@ static inline void post_schedule(struct rq *rq)
> >  asmlinkage __visible void schedule_tail(struct task_struct *prev)
> >  	__releases(rq->lock)
> >  {
> > -	struct rq *rq = this_rq();
> > +	struct rq *rq;
> >  
> > +	/* finish_task_switch() drops rq->lock and enables preemtion */
> > +	preempt_disable();
> 
> Maybe, the code would look simpler if we change
> init_task_preempt_count() and create new tasks
> with preempt_count() == 2, so this preempt_disable()
> won't be necessary. But it's more or less subjectively.

Yes, yes, I thought about the same.

Except I think we should kill init_task_preempt_count() and change
schedule_tail()

	-	preempt_disable();
	+	preempt_count_set(PREEMPT_DISABLED + 1);

but first we need to remove ->saved_preempt_count.

> Reviewed-by: Kirill Tkhai <ktkhai@...allels.com>

Thanks!

Oleg.

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