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Date: Wed, 7 Oct 2015 14:03:37 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
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        Thomas Gleixner <tglx@linutronix.de>, rostedt <rostedt@goodmis.org>,
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        fweisbec@gmail.com, oleg@redhat.com,
        bobby prani <bobby.prani@gmail.com>
Subject: Re: [PATCH tip/core/rcu 02/18] rcu: Move rcu_report_exp_rnp() to
 allow consolidation
Message-ID: <20151007120337.GL11639@twins.programming.kicks-ass.net>
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On Wed, Oct 07, 2015 at 01:50:46PM +0200, Peter Zijlstra wrote:
> @@ -1512,10 +1554,8 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
>  	 * hold it, acquire the root rcu_node structure's lock in order to
>  	 * start one (if needed).
>  	 */
> -	if (rnp != rnp_root) {
> -		raw_spin_lock(&rnp_root->lock);
> -		smp_mb__after_unlock_lock();
> -	}
> +	if (rnp != rnp_root)
> +		raw_spin_lock_rcu_node(rnp);

					rnp_root


> @@ -2312,8 +2343,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
>  	gps = rnp->gpnum;
>  	mask = rnp->grpmask;
>  	raw_spin_unlock(&rnp->lock);	/* irqs remain disabled. */
> -	raw_spin_lock(&rnp_p->lock);	/* irqs already disabled. */
> -	smp_mb__after_unlock_lock();
> +	raw_spin_lock_rcu_node(rnp);	/* irqs already disabled. */

				rnp_p