linux-kernel - Re: [PATCH] module: Optimize search_module

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Date:   Wed, 8 Feb 2017 15:44:34 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     jeyu@...hat.com, rusty@...tcorp.com.au,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] module: Optimize search_module_extables()

On Wed, Feb 08, 2017 at 03:48:01PM +0100, Peter Zijlstra wrote:
> 
> While looking through the __ex_table stuff I found that we do a linear
> lookup of the module. Also fix up a comment.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

I'm not all that familiar with the module code, but from a quick scan of
__module_address() this looks sane to me. FWIW:

Acked-by: Mark Rutland <mark.rutland@....com>

Mark.

> ---
>  kernel/module.c | 27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 3d8f126208e3..7bcdc35dbf95 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -4165,22 +4165,23 @@ const struct exception_table_entry *search_module_extables(unsigned long addr)
>  	struct module *mod;
>  
>  	preempt_disable();
> -	list_for_each_entry_rcu(mod, &modules, list) {
> -		if (mod->state == MODULE_STATE_UNFORMED)
> -			continue;
> -		if (mod->num_exentries == 0)
> -			continue;
> +	mod = __module_address(addr);
> +	if (!mod)
> +		goto out;
>  
> -		e = search_extable(mod->extable,
> -				   mod->extable + mod->num_exentries - 1,
> -				   addr);
> -		if (e)
> -			break;
> -	}
> +	if (!mod->num_exentries)
> +		goto out;
> +
> +	e = search_extable(mod->extable,
> +			   mod->extable + mod->num_exentries - 1,
> +			   addr);
> +out:
>  	preempt_enable();
>  
> -	/* Now, if we found one, we are running inside it now, hence
> -	   we cannot unload the module, hence no refcnt needed. */
> +	/*
> +	 * Now, if we found one, we are running inside it now, hence
> +	 * we cannot unload the module, hence no refcnt needed.
> +	 */
>  	return e;
>  }
>