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

[Jason Baron <jbaron@xxxxxxxxxx>]

On Sat, Oct 01, 2011 at 02:55:35PM -0700, Jeremy Fitzhardinge wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> ---
>  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 

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