linux-kernel - Re: [PATCH] rcu: remove lock acquirement when very eary boot

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Message-ID: <20100328041724.GR2343@linux.vnet.ibm.com>
Date:	Sat, 27 Mar 2010 21:17:24 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rcu: remove lock acquirement when very eary boot

On Sun, Mar 28, 2010 at 11:14:13AM +0800, Lai Jiangshan wrote:
> 
> cleanup: remove lock acquirement when very eary boot

This is indeed a safe change, however, I am keeping this lock acquisition
and release for documentation purposes.  Call me paranoid, but...

							Thanx, Paul

> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 112edb5..e6014e1 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1646,13 +1646,10 @@ EXPORT_SYMBOL_GPL(rcu_barrier_sched);
>  static void __init
>  rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
>  {
> -	unsigned long flags;
>  	int i;
>  	struct rcu_data *rdp = rsp->rda[cpu];
> -	struct rcu_node *rnp = rcu_get_root(rsp);
> 
>  	/* Set up local state, ensuring consistent view of global state. */
> -	raw_spin_lock_irqsave(&rnp->lock, flags);
>  	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
>  	rdp->nxtlist = NULL;
>  	for (i = 0; i < RCU_NEXT_SIZE; i++)
> @@ -1662,7 +1659,6 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
>  	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
>  #endif /* #ifdef CONFIG_NO_HZ */
>  	rdp->cpu = cpu;
> -	raw_spin_unlock_irqrestore(&rnp->lock, flags);
>  }
> 
>  /*
> 
--
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