Re: [PATCH tip/core/rcu 05/23] rcu: Prevent offline CPUs fromexecuting RCU core code

[Josh Triplett]

On Thu, Aug 30, 2012 at 11:18:20AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@xxxxxxxxxx>
> 
> Earlier versions of RCU invoked the RCU core from the CPU_DYING notifier
> in order to note a quiescent state for the outgoing CPU.  Because the
> CPU is marked "offline" during the execution of the CPU_DYING notifiers,
> the RCU core had to tolerate being invoked from an offline CPU.  However,
> commit b1420f1c (Make rcu_barrier() less disruptive) left only tracing
> code in the CPU_DYING notifier, so the RCU core need no longer execute
> on offline CPUs.  This commit therefore enforces this restriction.
> 
> Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>

>  kernel/rcutree.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 300aba6..84a6f55 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1892,6 +1892,8 @@ static void rcu_process_callbacks(struct softirq_action *unused)
>  {
>  	struct rcu_state *rsp;
>  
> +	if (cpu_is_offline(smp_processor_id()))
> +		return;
>  	trace_rcu_utilization("Start RCU core");
>  	for_each_rcu_flavor(rsp)
>  		__rcu_process_callbacks(rsp);
> -- 
> 1.7.8
> 
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