linux-kernel - Re: [PATCH tip/core/urgent 1/7] rcu: decrease rcu_report_exp

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Date:	Wed, 20 Jul 2011 04:40:18 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...aro.org,
	greearb@...delatech.com, edt@....ca
Subject: Re: [PATCH tip/core/urgent 1/7] rcu: decrease rcu_report_exp_rnp
 coupling with scheduler

On Tue, 2011-07-19 at 17:18 -0700, Paul E. McKenney wrote:
> +++ b/kernel/rcutree_plugin.h
> @@ -696,8 +696,10 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
>         raw_spin_lock_irqsave(&rnp->lock, flags);
>         for (;;) {
>                 if (!sync_rcu_preempt_exp_done(rnp))
> +                       raw_spin_unlock_irqrestore(&rnp->lock, flags);
>                         break;

I bet that'll all work much better if you wrap it in curly braces like:

		if (!sync_rcu_preempt_exp_done(rnp)) {
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
			break;
		}

That might also explain those explosions Ed and Ben have been seeing.

>                 if (rnp->parent == NULL) {
> +                       raw_spin_unlock_irqrestore(&rnp->lock, flags);
>                         wake_up(&sync_rcu_preempt_exp_wq);
>                         break;
>                 }
> @@ -707,7 +709,6 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
>                 raw_spin_lock(&rnp->lock); /* irqs already disabled */
>                 rnp->expmask &= ~mask;
>         }
> -       raw_spin_unlock_irqrestore(&rnp->lock, flags);
>  } 
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