linux-kernel - Re: [PATCH tip/core/rcu 02/18] rcu: Move rcu_report_exp

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Date:	Tue, 6 Oct 2015 22:29:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 02/18] rcu: Move rcu_report_exp_rnp() to
 allow consolidation

On Tue, Oct 06, 2015 at 09:29:21AM -0700, Paul E. McKenney wrote:
> +static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
> +					      struct rcu_node *rnp, bool wake)
> +{
> +	unsigned long flags;
> +	unsigned long mask;
> +
> +	raw_spin_lock_irqsave(&rnp->lock, flags);

Normally we require a comment with barriers, explaining the order and
the pairing etc.. :-)

> +	smp_mb__after_unlock_lock();
> +	for (;;) {
> +		if (!sync_rcu_preempt_exp_done(rnp)) {
> +			raw_spin_unlock_irqrestore(&rnp->lock, flags);
> +			break;
> +		}
> +		if (rnp->parent == NULL) {
> +			raw_spin_unlock_irqrestore(&rnp->lock, flags);
> +			if (wake) {
> +				smp_mb(); /* EGP done before wake_up(). */
> +				wake_up(&rsp->expedited_wq);
> +			}
> +			break;
> +		}
> +		mask = rnp->grpmask;
> +		raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
> +		rnp = rnp->parent;
> +		raw_spin_lock(&rnp->lock); /* irqs already disabled */
> +		smp_mb__after_unlock_lock();
> +		rnp->expmask &= ~mask;
> +	}
> +}
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