Re: [PATCH] module: Optimize search_module_extables()

From: Mark Rutland
Date: Wed Feb 08 2017 - 11:08:54 EST


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@xxxxxxxxxxxxx>

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@xxxxxxx>

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;
> }
>