linux-kernel - Re: [PATCH 1/3] rcu: Remove unnecessary condition check in rcu_qsctr

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Date:	Wed, 11 Feb 2015 08:09:24 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] rcu: Remove unnecessary condition check in
 rcu_qsctr_help()

On Wed, Feb 11, 2015 at 03:42:37PM +0100, Alexander Gordeev wrote:
> In cases ->curtail and ->donetail pointers differ ->rcucblist
> always points to the beginning of the current list and thus
> can not be NULL. Therefore, the check ->rcucblist != NULL is
> redundant and could be removed.
> 
> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Alexander Gordeev <agordeev@...hat.com>

Good point, queued for 3.21.

							Thanx, Paul

> ---
>  kernel/rcu/tiny.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
> index cc9ceca..d4e7fe5 100644
> --- a/kernel/rcu/tiny.c
> +++ b/kernel/rcu/tiny.c
> @@ -103,8 +103,7 @@ EXPORT_SYMBOL(__rcu_is_watching);
>  static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
>  {
>  	RCU_TRACE(reset_cpu_stall_ticks(rcp));
> -	if (rcp->rcucblist != NULL &&
> -	    rcp->donetail != rcp->curtail) {
> +	if (rcp->donetail != rcp->curtail) {
>  		rcp->donetail = rcp->curtail;
>  		return 1;
>  	}
> -- 
> 1.8.3.1
> 

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