linux-kernel - Re: [RFC PATCH 48/86] rcu: handle quiescent states for PREEMPT

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Date:   Wed, 6 Dec 2023 21:10:22 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     paulmck@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        torvalds@...ux-foundation.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com,
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        krypton@...ich-teichert.org, David.Laight@...lab.com,
        richard@....at, mjguzik@...il.com
Subject: Re: [RFC PATCH 48/86] rcu: handle quiescent states for
 PREEMPT_RCU=n

On Wed, 06 Dec 2023 17:31:30 -0800
Ankur Arora <ankur.a.arora@...cle.com> wrote:

> ---
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 9aa6358a1a16..d8139cda8814 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -226,9 +226,11 @@ do { \
>  #ifdef CONFIG_PREEMPTION
>  #define preempt_enable() \
>  do { \
>  	barrier(); \
>  	if (unlikely(preempt_count_dec_and_test())) \
>  		__preempt_schedule(); \
> +	else if (unlikely(raw_cpu_read(rcu_data.rcu_urgent_qs))) \

Shouldn't this still have the:

	else if (!IS_ENABLED(CONFIG_PREEMPT_RCU) && \

That is, is it needed when PREEMPT_RCU is set?

-- Steve


> +		rcu_all_qs_check();
>  } while (0)
> 
>  #define preempt_enable_notrace() \