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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com,
	rostedt@goodmis.org
Subject: Re: [PATCH 3/8] refscale: Add local_bh_disable() readers
Message-ID: <20251111153803.5_08_ro2@linutronix.de>
References: <19fae851-0c49-43d2-9bbf-913424641ff4@paulmck-laptop>
 <20251102224948.3906224-3-paulmck@kernel.org>
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In-Reply-To: <20251102224948.3906224-3-paulmck@kernel.org>

On 2025-11-02 14:49:43 [-0800], Paul E. McKenney wrote:
> --- a/kernel/rcu/refscale.c
> +++ b/kernel/rcu/refscale.c
> @@ -636,6 +636,37 @@ static const struct ref_scale_ops jiffies_ops = {
>  	.name		= "jiffies"
>  };
>  
> +static void ref_bh_section(const int nloops)
> +{
> +	int i;
> +
> +	preempt_disable();
> +	for (i = nloops; i >= 0; i--) {
> +		local_bh_disable();

This (preempt off followed by bh off) may cause warnings. That would be
bh is disabled on the CPU, it gets preempted by _this_ which disables
first preemption and then bh. 
I hid the code under CONFIG_PREEMPT_RT_NEEDS_BH_LOCK so it shouldn't be
a problem in the long term I think. So just if you see a warning here
under RT you know why :)

> +		local_bh_enable();
> +	}
> +	preempt_enable();
> +}

Sebastian