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

Josh Triplett
2012-06-15T21:05:04Z

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
>