linux-kernel - Re: [PATCH -tip/core/rcu 2/6] Introduce cpu_notifier() to handle !HOTPLUG

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Date:	Mon, 17 Aug 2009 10:21:59 -0700
From:	Josh Triplett <josht@...ux.vnet.ibm.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	hugh.dickins@...cali.co.uk, benh@...nel.crashing.org
Subject: Re: [PATCH -tip/core/rcu 2/6] Introduce cpu_notifier() to handle
 !HOTPLUG_CPU case

On Sat, 2009-08-15 at 09:53 -0700, Paul E. McKenney wrote:
> From: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> This patch introduces a new cpu_notifier() API that is similar to
> hotcpu_notifier(), but which also notifies of CPUs coming online during
> boot in the !HOTPLUG_CPU case.
[...]
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -48,6 +48,15 @@ struct notifier_block;
> 
>  #ifdef CONFIG_SMP
>  /* Need to know about CPUs going up/down? */
> +#if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE)
> +#define cpu_notifier(fn, pri) {					\
> +	static struct notifier_block fn##_nb __cpuinitdata =	\
> +		{ .notifier_call = fn, .priority = pri };	\
> +	register_cpu_notifier(&fn##_nb);			\
> +}
> +#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */
> +#define cpu_notifier(fn, pri)	do { (void)(fn); } while (0)
> +#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */

These two definitions seem inconsistent.  I think the first one needs to
change to use do { ... } while(0) as well, so it eats the subsequent
semicolon.

Does this really want to live under defined(CONFIG_HOTPLUG_CPU)?  What
happens when onlining CPUs during the !define(CONFIG_HOTPLUG_CPU) case?
This seems somewhat inconsistent with the explanation in your commit
message; can you clarify?

Also, why !defined(MODULE)?

- Josh Triplett

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