Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out

Jason Baron
2011-10-03T15:03:07Z

Hi,

(Sorry for the late reply - I was away for a few days).

The early enable is really nice - it means there are not restrictions on
when jump_label_inc()/dec() can be called which is nice.

comments below.

On Sat, Oct 01, 2011 at 02:55:35PM -0700, Jeremy Fitzhardinge wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>
> If a key has been enabled before jump_label_init() is called, don't
> nop it out.
>
> This removes arch_jump_label_text_poke_early() (which can only nop
> out a site) and uses arch_jump_label_transform() instead.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> ---
> include/linux/jump_label.h | 3 ++-
> kernel/jump_label.c | 20 ++++++++------------
> 2 files changed, 10 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
> index 1213e9d..c8fb1b3 100644
> --- a/include/linux/jump_label.h
> +++ b/include/linux/jump_label.h
> @@ -45,7 +45,8 @@ extern void jump_label_lock(void);
> extern void jump_label_unlock(void);
> extern void arch_jump_label_transform(struct jump_entry *entry,
> enum jump_label_type type);
> -extern void arch_jump_label_text_poke_early(jump_label_t addr);
> +extern void arch_jump_label_transform_early(struct jump_entry *entry,
> + enum jump_label_type type);
> extern int jump_label_text_reserved(void *start, void *end);
> extern void jump_label_inc(struct jump_label_key *key);
> extern void jump_label_dec(struct jump_label_key *key);
> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> index a8ce450..059202d5 100644
> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -121,13 +121,6 @@ static void __jump_label_update(struct jump_label_key *key,
> }
> }
>
> -/*
> - * Not all archs need this.
> - */
> -void __weak arch_jump_label_text_poke_early(jump_label_t addr)
> -{
> -}
> -
> static __init int jump_label_init(void)
> {
> struct jump_entry *iter_start = __start___jump_table;
> @@ -139,12 +132,15 @@ static __init int jump_label_init(void)
> jump_label_sort_entries(iter_start, iter_stop);
>
> for (iter = iter_start; iter < iter_stop; iter++) {
> - arch_jump_label_text_poke_early(iter->code);
> - if (iter->key == (jump_label_t)(unsigned long)key)
> + struct jump_label_key *iterk;
> +
> + iterk = (struct jump_label_key *)(unsigned long)iter->key;
> + arch_jump_label_transform(iter, jump_label_enabled(iterk) ?
> + JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);

The only reason I called this at boot-time was that the 'ideal' x86
no-op isn't known until boot time. Thus, in the enabled case we could
skip the the arch_jump_label_transform() call. ie:

if (!enabled)
arch_jump_label_transform(iter, JUMP_LABEL_DISABLE);

> + if (iterk == key)
> continue;
>
> - key = (struct jump_label_key *)(unsigned long)iter->key;
> - atomic_set(&key->enabled, 0);
> + key = iterk;
> key->entries = iter;
> #ifdef CONFIG_MODULES
> key->next = NULL;
> @@ -212,7 +208,7 @@ void jump_label_apply_nops(struct module *mod)
> return;
>
> for (iter = iter_start; iter < iter_stop; iter++)
> - arch_jump_label_text_poke_early(iter->code);
> + arch_jump_label_transform(iter, JUMP_LABEL_DISABLE);
> }
>
> static int jump_label_add_module(struct module *mod)
> --
> 1.7.6.2
>

hmmm...this is used on module load in smp - so this would introduce a number of
calls to stop_machine() where we didn't have them before. Yes, module
load is a very slow path to begin with, but I think its at least worth
pointing out...

thanks,

-Jason