Re: module: Optimize search_module_extables()

[Jessica Yu]

+++ Peter Zijlstra [08/02/17 15:48 +0100]:
> 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@xxxxxxxxxxxxx>

Applied, thanks.

Hm. A quick scan through module.c still shows a couple of places that use
similar linear lookups, and may benefit from the same __module_address
optimization. But I'll save that for a separate patch..

Jessica

> ---
> 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;
> }