linux-kernel - Re: [RFC][PATCH RT 1/6] rt,rcu: Have rcu_read_lock_sched() use locks for PREEMPT

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Date:	Thu, 27 Jun 2013 05:52:14 +0200
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Clark Williams <clark.williams@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH RT 1/6] rt,rcu: Have rcu_read_lock_sched() use
 locks for PREEMPT_RT

On Wed, 2013-06-26 at 15:28 -0400, Steven Rostedt wrote:

> @@ -2491,6 +2491,31 @@ static inline int rcu_blocking_is_gp(voi
>  	return ret;
>  }
>  
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +DEFINE_LOCAL_IRQ_LOCK(rcu_sched_lock);
> +/*
> + * Real-time allows for synchronize sched to sleep but not migrate.
> + * This is done via the local locks. When calling synchronize_sched(),
> + * all the local locks need to be taken and released. This will ensure
> + * that all users of rcu_read_lock_sched() will be out of their critical
> + * sections at the completion of this function. synchronize_sched() will
> + * still perform the normal RCU sched operations to synchronize with
> + * locations that use disabling preemption or interrupts.
> + */
> +static void rcu_synchronize_sched_rt(void)
> +{
> +	int cpu;
> +
> +	for_each_possible_cpu(cpu) {
> +		spin_lock(&per_cpu(rcu_sched_lock, cpu).lock);
> +		spin_unlock(&per_cpu(rcu_sched_lock, cpu).lock);
> +	}
> +}

Does that have to be possible vs online?

-Mike

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