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);
}
/**
@@ -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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