linux-kernel - Re: [PATCH] sched/fair: Fix RCU stall upon ENOMEM atsched_create

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Message-Id: <201501062345.IGG21352.SQFHJOOOVtMFFL@I-love.SAKURA.ne.jp>
Date:	Tue, 6 Jan 2015 23:45:29 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	peterz@...radead.org
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Fix RCU stall upon ENOMEM atsched_create_group().

Peter Zijlstra wrote:
> On Thu, Dec 25, 2014 at 10:10:45PM +0900, Tetsuo Handa wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index ef2b104..586ee15 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7756,8 +7756,12 @@ static void task_move_group_fair(struct task_struct *p, int queued)
> >  void free_fair_sched_group(struct task_group *tg)
> >  {
> >  	int i;
> > +	struct cfs_bandwidth *cfs_b;
> >  
> > -	destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));
> > +	/* Check whether init_cfs_bandwidth() was called. */
> > +	cfs_b = tg_cfs_bandwidth(tg);
> > +	if (cfs_b->throttled_cfs_rq.next)
> > +		destroy_cfs_bandwidth(cfs_b);
> >  
> >  	for_each_possible_cpu(i) {
> >  		if (tg->cfs_rq)
> 
> This doesn't actually compile for !CONFIG_CFS_BANDWIDTH, how about:
> 
> ---
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4005,6 +4005,10 @@ void __start_cfs_bandwidth(struct cfs_ba
>  
>  static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
>  {
> +	/* init_cfs_bandwidth() was not called */
> +	if (!cfs_b->throttled_cfs_rq.next)
> +		return;
> +
>  	hrtimer_cancel(&cfs_b->period_timer);
>  	hrtimer_cancel(&cfs_b->slack_timer);
>  }
> 
I posted "#ifdef CONFIG_CFS_BANDWIDTH" version 7 minutes ago.
But I'm fine with your patch. Thank you.
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