linux-kernel - Re: [PATCH tip/core/rcu 05/23] rcu: Prevent offline CPUs from executing RCU core code

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Date:	Sat, 1 Sep 2012 18:45:45 -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, sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 05/23] rcu: Prevent offline CPUs from
 executing RCU core code

On Thu, Aug 30, 2012 at 11:18:20AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> 
> 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@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

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

>  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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