linux-kernel - Re: [PATCH] rcu-tasks: Remove unnecessary lazy_jiffies in call_rcu_tasks_generic

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Message-ID: <d3762d8c-1996-4703-8fa2-f0b00febf2fb@paulmck-laptop>
Date: Tue, 12 Mar 2024 15:05:22 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Zqiang <qiang.zhang1211@...il.com>
Cc: frederic@...nel.org, neeraj.upadhyay@...nel.org, joel@...lfernandes.org,
	rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu-tasks: Remove unnecessary lazy_jiffies in
 call_rcu_tasks_generic_timer()

On Tue, Mar 12, 2024 at 07:35:24PM +0800, Zqiang wrote:
> The rcu_tasks_percpu structure's->lazy_timer is queued only when
> the rcu_tasks structure's->lazy_jiffies is not equal to zero in
> call_rcu_tasks_generic(), if the lazy_timer callback is invoked,
> that means the lazy_jiffes is not equal to zero, this commit
> therefore remove lazy_jiffies check in call_rcu_tasks_generic_timer().
> 
> Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
> ---
>  kernel/rcu/tasks.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index b1254cf3c210..439e0b9a2656 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -299,7 +299,7 @@ static void call_rcu_tasks_generic_timer(struct timer_list *tlp)
>  
>  	rtp = rtpcp->rtpp;
>  	raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
> -	if (!rcu_segcblist_empty(&rtpcp->cblist) && rtp->lazy_jiffies) {
> +	if (!rcu_segcblist_empty(&rtpcp->cblist)) {

Good eyes!

But did you test with something like a WARN_ON_ONCE(rtp->lazy_jiffies)?

						Thanx, Paul

>  		if (!rtpcp->urgent_gp)
>  			rtpcp->urgent_gp = 1;
>  		needwake = true;
> -- 
> 2.17.1
>