linux-kernel - Re: [GIT PULL rcu/next] rcu commits for 2.6.40

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Date:	Mon, 16 May 2011 00:01:17 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40

On Sat, May 14, 2011 at 11:34:53AM -0700, Paul E. McKenney wrote:
>  rcutree.c |   91 +++++++++++++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 75 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index a4a2ef0..0b541bd 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -308,23 +308,25 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
>  
>  #ifdef CONFIG_NO_HZ
>  
> -/**
> - * rcu_enter_nohz - inform RCU that current CPU is entering nohz
> +/*
> + * __rcu_enter_nohz - inform RCU that current CPU is entering nohz
>   *
>   * Enter nohz mode, in other words, -leave- the mode in which RCU
>   * read-side critical sections can occur.  (Though RCU read-side
>   * critical sections can occur in irq handlers in nohz mode, a possibility
>   * handled by rcu_irq_enter() and rcu_irq_exit()).
> + *
> + * This variant should only be called from rcu_irq_exit() because it
> + * assumes perfect nesting.  The caller must have irqs disabled.
>   */
> -void rcu_enter_nohz(void)
> +void __rcu_enter_nohz(void)
>  {
> -	unsigned long flags;
>  	struct rcu_dynticks *rdtp;
>  
> -	local_irq_save(flags);
>  	rdtp = &__get_cpu_var(rcu_dynticks);
> +	WARN_ON_ONCE(rdtp->dynticks_nesting <= 0);

But this warning will always trigger if it's called from rcu_irq_enter()
after rcu_enter_nohz(). Right?
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