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


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