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 <[email protected]> [ Removed line-break, changed to use WARN_ON_ONCE() - Linus ] Signed-off-by: Linus Torvalds <[email protected]>
niw · May 7, 2013 · 2d864e4 · 2d864e4
1 parent 292088e
commit 2d864e4
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Showing 2 changed files with 7 additions and 4 deletions.
diff --git 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 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 @@ 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
@@ -529,7 +529,7 @@ 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;