linux-kernel - Re: [PATCH tip/core/rcu 12/14] rcu: Prevent __call_rcu() from invoking RCU core on offline CPUs

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Date:	Fri, 15 Jun 2012 14:04:45 -0700
From:	Josh Triplett <josh@...htriplett.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, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 12/14] rcu: Prevent __call_rcu() from
 invoking RCU core on offline CPUs

On Fri, Jun 15, 2012 at 01:13:13PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> 
> The __call_rcu() function will invoke the RCU core, for example, if
> it detects that the current CPU has too many callbacks.  However, this
> can happen on an offline CPU that is on its way to the idle loop, in
> which case it is an error to invoke the RCU core, and the excess callbacks
> will be adopted in any case.  This commit therefore adds checks to
> __call_rcu() for running on an offline CPU, refraining from invoking
> the RCU core in this case.
> 
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@...htriplett.org>

>  kernel/rcutree.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 7720177..9419ebf 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1901,11 +1901,11 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
>  	 * If called from an extended quiescent state, invoke the RCU
>  	 * core in order to force a re-evaluation of RCU's idleness.
>  	 */
> -	if (rcu_is_cpu_idle())
> +	if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
>  		invoke_rcu_core();
>  
> -	/* If interrupts were disabled, don't dive into RCU core. */
> -	if (irqs_disabled_flags(flags)) {
> +	/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
> +	if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) {
>  		local_irq_restore(flags);
>  		return;
>  	}
> -- 
> 1.7.8
> 
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