linux-kernel - Re: [PATCH 1/2] Add for_each

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Message-ID: <20100922141432.GB30730@Krystal>
Date:	Wed, 22 Sep 2010 10:14:32 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	jbaron@...hat.com, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, hpa@...or.com,
	tglx@...utronix.de, roland@...hat.com, rth@...hat.com,
	mhiramat@...hat.com, fweisbec@...il.com, avi@...hat.com,
	davem@...emloft.net, vgoyal@...hat.com, sam@...nborg.org,
	tony@...eyournoodle.com, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] Add for_each_module iterator function v2

* Andi Kleen (andi@...stfloor.org) wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> This is a generic function to iterate over all modules.
> To be used in the next patch.
> 
> v2: Use module_mutex instead of preempt disabling
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  include/linux/module.h |    1 +
>  kernel/module.c        |   10 ++++++++++
>  2 files changed, 11 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 403ac26..809b6db 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -410,6 +410,7 @@ struct module *__module_address(unsigned long addr);
>  bool is_module_address(unsigned long addr);
>  bool is_module_percpu_address(unsigned long addr);
>  bool is_module_text_address(unsigned long addr);
> +void for_each_module(void (*op)(struct module *, void *arg), void *arg);
>  
>  static inline int within_module_core(unsigned long addr, struct module *mod)
>  {
> diff --git a/kernel/module.c b/kernel/module.c
> index eba1341..9e2a561 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -384,6 +384,16 @@ struct module *find_module(const char *name)
>  }
>  EXPORT_SYMBOL_GPL(find_module);
>  
> +void for_each_module(void (*op)(struct module *, void *arg), void *arg)
> +{
> +	struct module *mod;
> +
> +	mutex_lock(&module_mutex);

I'm concerned about the following mutex dependency chain:

module_mutex -> jump_label_mutex (on module load)
jump_label_mutex -> module_mutex (on jump_label_update)

Actually, I think your module notifier is missing in your version. This
is why you don't see this dependency problem.

Mathieu

> +	list_for_each_entry_rcu(mod, &modules, list)
> +		op(mod, arg);
> +	mutex_unlock(&module_mutex);
> +}
> +
>  #ifdef CONFIG_SMP
>  
>  static inline void __percpu *mod_percpu(struct module *mod)
> -- 
> 1.7.1
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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