linux-kernel - Re: [PATCH -next v3 3/3] rcu/nocb: Extract nocb_defer_wakeup

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Message-ID: <cb21423d-6781-45de-84b5-5c1f475848eb@paulmck-laptop>
Date: Thu, 22 Jan 2026 13:59:30 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>,
	rcu@...r.kernel.org, Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang@...ux.dev>
Subject: Re: [PATCH -next v3 3/3] rcu/nocb: Extract
 nocb_defer_wakeup_cancel() helper

On Mon, Jan 19, 2026 at 06:12:23PM -0500, Joel Fernandes wrote:
> The pattern of checking nocb_defer_wakeup and deleting the timer is
> duplicated in __wake_nocb_gp() and nocb_gp_wait(). Extract this into a
> common helper function nocb_defer_wakeup_cancel().
> 
> This removes code duplication and makes it easier to maintain.
> 
> Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>

Good eyes!

Reviewed-by: Paul E. McKenney <paulmck@...nel.org>

> ---
>  kernel/rcu/tree_nocb.h | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index 64a8ff350f92..b3337c7231cc 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -190,6 +190,15 @@ static void rcu_init_one_nocb(struct rcu_node *rnp)
>  	init_swait_queue_head(&rnp->nocb_gp_wq[1]);
>  }
>  
> +/* Clear any pending deferred wakeup timer (nocb_gp_lock must be held). */
> +static void nocb_defer_wakeup_cancel(struct rcu_data *rdp_gp)
> +{
> +	if (rdp_gp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
> +		WRITE_ONCE(rdp_gp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
> +		timer_delete(&rdp_gp->nocb_timer);
> +	}
> +}
> +
>  static bool __wake_nocb_gp(struct rcu_data *rdp_gp,
>  			   struct rcu_data *rdp,
>  			   unsigned long flags)
> @@ -204,10 +213,7 @@ static bool __wake_nocb_gp(struct rcu_data *rdp_gp,
>  		return false;
>  	}
>  
> -	if (rdp_gp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
> -		WRITE_ONCE(rdp_gp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
> -		timer_delete(&rdp_gp->nocb_timer);
> -	}
> +	nocb_defer_wakeup_cancel(rdp_gp);
>  
>  	if (READ_ONCE(rdp_gp->nocb_gp_sleep)) {
>  		WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
> @@ -788,10 +794,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
>  		if (rdp_toggling)
>  			my_rdp->nocb_toggling_rdp = NULL;
>  
> -		if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
> -			WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
> -			timer_delete(&my_rdp->nocb_timer);
> -		}
> +		nocb_defer_wakeup_cancel(my_rdp);
>  		WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
>  		raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
>  	} else {
> -- 
> 2.34.1
>