On Fri, Apr 19, 2013 at 06:33:54PM -0700, Anatol Pomozov wrote:
> Follow-up for https://lkml.org/lkml/2013/4/12/391
>
> * make warning smp-safe
> * result of atomic _unless_zero functions should be checked by caller
> to avoid use-after-free error
>
> Signed-off-by: Anatol Pomozov <anatol.pomo...@gmail.com>
> ---
> include/linux/kref.h | 9 ++++++---
> lib/kobject.c | 3 ++-
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/kref.h b/include/linux/kref.h
> index 4972e6e..092529a 100644
> --- a/include/linux/kref.h
> +++ b/include/linux/kref.h
> @@ -39,8 +39,11 @@ static inline void kref_init(struct kref *kref)
> */
> static inline void kref_get(struct kref *kref)
> {
> - WARN_ON(!atomic_read(&kref->refcount));
> - atomic_inc(&kref->refcount);
> + /* If refcount was 0 before incrementing then we have a race
> + * condition when this kref is freing by some other thread right now.
> + * In this case one should use kref_get_unless_zero()
> + */
> + WARN_ON(atomic_inc_return(&kref->refcount) < 2);
What happens if you disable WARN_ON(), does the atomic_inc_return() go
away as well? Or did we fix that?
> }
>
> /**
> @@ -100,7 +103,7 @@ static inline int kref_put_mutex(struct kref *kref,
> struct mutex *lock)
> {
> WARN_ON(release == NULL);
> - if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) {
> + if (unlikely(!atomic_add_unless(&kref->refcount, -1, 1))) {
> mutex_lock(lock);
> if (unlikely(!atomic_dec_and_test(&kref->refcount))) {
> mutex_unlock(lock);
> diff --git a/lib/kobject.c b/lib/kobject.c
> index a654866..bbd7362 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -529,7 +529,8 @@ struct kobject *kobject_get(struct kobject *kobj)
> return kobj;
> }
>
> -static struct kobject *kobject_get_unless_zero(struct kobject *kobj)
> +static struct kobject *__must_check kobject_get_unless_zero(
> + struct kobject *kobj)
__must_check needs to be in the .h file, not the .c file.
thanks,
greg k-h
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