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

Jason Baron
2011-10-10T15:36:50Z

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);
> + 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
>

Hi,

I just realized that the early call to jump_label_inc(), isn't being
honored with this patch until later when we invoke jump_label_init().
That strikes me as being inconsistent. When jump_label_inc() returns we
should expect the branch to be updated.

Thus, I think what probably want is to add a new 'int jump_label_init'
flag. If its not set we can call 'jump_label_init()' from
jump_label_inc()/dec(). And jump_label_init() can avoid initialization
if its already set.

Thanks,

-Jason