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

[Josh Triplett <josh@joshtriplett.org>]

On Fri, Jun 15, 2012 at 01:13:13PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@linaro.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@linaro.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@joshtriplett.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
>