linux-kernel - Re: [PATCH v2 4/5] kscan: Use preemption model accessors

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Date:   Thu, 11 Nov 2021 10:11:21 +0100
From:   Marco Elver <elver@...gle.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kbuild@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mike Galbraith <efault@....de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 4/5] kscan: Use preemption model accessors

Subject s/kscan/kcsan/

On Wed, Nov 10, 2021 at 08:24PM +0000, Valentin Schneider wrote:
> Per PREEMPT_DYNAMIC, checking CONFIG_PREEMPT doesn't tell you the actual
> preemption model of the live kernel. Use the newly-introduced accessors
> instead.
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@....com>

Reviewed-by: Marco Elver <elver@...gle.com>

Though it currently doesn't compile as a module due to missing
EXPORT_SYMBOL of is_preempt*().

> ---
>  kernel/kcsan/kcsan_test.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
> index dc55fd5a36fc..14d811eb9a21 100644
> --- a/kernel/kcsan/kcsan_test.c
> +++ b/kernel/kcsan/kcsan_test.c
> @@ -1005,13 +1005,13 @@ static const void *nthreads_gen_params(const void *prev, char *desc)
>  	else
>  		nthreads *= 2;
>  
> -	if (!IS_ENABLED(CONFIG_PREEMPT) || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) {
> +	if (!is_preempt_full() || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) {
>  		/*
>  		 * Without any preemption, keep 2 CPUs free for other tasks, one
>  		 * of which is the main test case function checking for
>  		 * completion or failure.
>  		 */
> -		const long min_unused_cpus = IS_ENABLED(CONFIG_PREEMPT_NONE) ? 2 : 0;
> +		const long min_unused_cpus = is_preempt_none() ? 2 : 0;
>  		const long min_required_cpus = 2 + min_unused_cpus;
>  
>  		if (num_online_cpus() < min_required_cpus) {
> -- 
> 2.25.1