kref: minor cleanup
- make warning smp-safe
- result of atomic _unless_zero functions should be checked by caller
to avoid use-after-free error
- trivial whitespace fix.
Link: https://lkml.org/lkml/2013/4/12/391
Tested: compile x86, boot machine and run xfstests
Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com>
[ Removed line-break, changed to use WARN_ON_ONCE() - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/kref.h b/include/linux/kref.h
index 4972e6e..e15828f 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -39,8 +39,11 @@
*/
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 freeing by some other thread right now.
+ * In this case one should use kref_get_unless_zero()
+ */
+ WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
}
/**
@@ -100,7 +103,7 @@
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..b7e29a6 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -529,7 +529,7 @@
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;