Re: [PATCH v2 2/5] preempt/dynamic: Introduce preempt mode accessors

From: Marco Elver <elver@google.com>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
	linuxppc-dev@lists.ozlabs.org, linux-kbuild@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Mike Galbraith <efault@gmx.de>,
	Dmitry Vyukov <dvyukov@google.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH v2 2/5] preempt/dynamic: Introduce preempt mode accessors
Date: Thu, 11 Nov 2021 09:54:05 +0100	[thread overview]
Message-ID: <YYzaLTtf1tFbqDSn@elver.google.com> (raw)
In-Reply-To: <20211110202448.4054153-3-valentin.schneider@arm.com>

On Wed, Nov 10, 2021 at 08:24PM +0000, Valentin Schneider wrote:
[...]
> +#ifdef CONFIG_PREEMPT_DYNAMIC
> +
> +extern bool is_preempt_none(void);
> +extern bool is_preempt_voluntary(void);
> +extern bool is_preempt_full(void);
> +
> +#else
> +
> +#define is_preempt_none() IS_ENABLED(CONFIG_PREEMPT_NONE)
> +#define is_preempt_voluntary() IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)
> +#define is_preempt_full() IS_ENABLED(CONFIG_PREEMPT)
> +
> +#endif
> +
> +#define is_preempt_rt() IS_ENABLED(CONFIG_PREEMPT_RT)
> +

Can these callables be real functions in all configs, making the
!DYNAMIC ones just static inline bool ones? That'd catch invalid use in
#if etc. in all configs.

>  /*
>   * Does a critical section need to be broken due to another
>   * task waiting?: (technically does not depend on CONFIG_PREEMPTION,
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 97047aa7b6c2..9db7f77e53c3 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6638,6 +6638,17 @@ static void __init preempt_dynamic_init(void)
>  	}
>  }
>  
> +#define PREEMPT_MODE_ACCESSOR(mode) \
> +	bool is_preempt_##mode(void)						 \
> +	{									 \
> +		WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
> +		return preempt_dynamic_mode == preempt_dynamic_##mode;		 \
> +	}

This needs an EXPORT_SYMBOL, so it's usable from modules like the
kcsan_test module.