linux-kernel - Re: [PATCH] mm/init: cpu_hotplug_init() must be initialized before SLAB

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Date:	Tue, 23 Jun 2009 12:59:14 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Sachin Sant <sachinp@...ibm.com>
Subject: Re: [PATCH] mm/init: cpu_hotplug_init() must be initialized before
 SLAB

On Mon, 2009-06-22 at 19:29 -0700, Linus Torvalds wrote:
> 
> On Tue, 23 Jun 2009, Benjamin Herrenschmidt wrote:
> 
> > +	/*
> > +	 * This initializes the mutex used by get/put_online_cpus()
> > +	 * which is used by SLAB
> > +	 */
> > +	cpu_hotplug_init();
> 
> Oh fudge it.
> 
> Why not get rid of that stupid thing, rather than have that subtle 
> dependency and a comment for it.
> 
> IOW, does this simpler alternative also work?

You mean static init ? Sure, it should do.

> When given the choice of simplifying and removing code, always do so. 

Yup. Agreed. Thought about it... got shy :-)

> Static initializers are much nicer than having to worry about when 
> something gets initialized, no?

I'll test that asap.

> 		Linus
> 
> ---
>  include/linux/cpu.h |    5 -----
>  init/main.c         |    1 -
>  kernel/cpu.c        |   13 +++++--------
>  3 files changed, 5 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 2643d84..4d668e0 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -69,7 +69,6 @@ static inline void unregister_cpu_notifier(struct notifier_block *nb)
>  
>  int cpu_up(unsigned int cpu);
>  void notify_cpu_starting(unsigned int cpu);
> -extern void cpu_hotplug_init(void);
>  extern void cpu_maps_update_begin(void);
>  extern void cpu_maps_update_done(void);
>  
> @@ -84,10 +83,6 @@ static inline void unregister_cpu_notifier(struct notifier_block *nb)
>  {
>  }
>  
> -static inline void cpu_hotplug_init(void)
> -{
> -}
> -
>  static inline void cpu_maps_update_begin(void)
>  {
>  }
> diff --git a/init/main.c b/init/main.c
> index 09131ec..4870dfe 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -678,7 +678,6 @@ asmlinkage void __init start_kernel(void)
>  #endif
>  	page_cgroup_init();
>  	enable_debug_pagealloc();
> -	cpu_hotplug_init();
>  	kmemtrace_init();
>  	kmemleak_init();
>  	debug_objects_mem_init();
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 395b697..8ce1004 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -34,14 +34,11 @@ static struct {
>  	 * an ongoing cpu hotplug operation.
>  	 */
>  	int refcount;
> -} cpu_hotplug;
> -
> -void __init cpu_hotplug_init(void)
> -{
> -	cpu_hotplug.active_writer = NULL;
> -	mutex_init(&cpu_hotplug.lock);
> -	cpu_hotplug.refcount = 0;
> -}
> +} cpu_hotplug = {
> +	.active_writer = NULL,
> +	.lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
> +	.refcount = 0,
> +};
>  
>  #ifdef CONFIG_HOTPLUG_CPU
>  

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