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    Subject[PATCH] kref: minor cleanup
    Date
    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.pomozov@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);
    }

    /**
    @@ -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)
    {
    if (!kref_get_unless_zero(&kobj->kref))
    kobj = NULL;
    --
    1.8.2.1


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