Add delay-init quirk for Corsair K70 RGB keyboards

[pandora-kernel.git] / include / linux / kref.h

diff --git a/include/linux/kref.h b/include/linux/kref.h
index d4a62ab..d064502 100644 (file)
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -16,6 +16,7 @@
 #define _KREF_H_
 
 #include <linux/types.h>
+#include <linux/atomic.h>
 
 struct kref {
        atomic_t refcount;
@@ -27,4 +28,24 @@ int kref_put(struct kref *kref, void (*release) (struct kref *kref));
 int kref_sub(struct kref *kref, unsigned int count,
             void (*release) (struct kref *kref));
 
+/**
+ * kref_get_unless_zero - Increment refcount for object unless it is zero.
+ * @kref: object.
+ *
+ * Return non-zero if the increment succeeded. Otherwise return 0.
+ *
+ * This function is intended to simplify locking around refcounting for
+ * objects that can be looked up from a lookup structure, and which are
+ * removed from that lookup structure in the object destructor.
+ * Operations on such objects require at least a read lock around
+ * lookup + kref_get, and a write lock around kref_put + remove from lookup
+ * structure. Furthermore, RCU implementations become extremely tricky.
+ * With a lookup followed by a kref_get_unless_zero *with return value check*
+ * locking in the kref_put path can be deferred to the actual removal from
+ * the lookup structure and RCU lookups become trivial.
+ */
+static inline int __must_check kref_get_unless_zero(struct kref *kref)
+{
+       return atomic_add_unless(&kref->refcount, 1, 0);
+}
 #endif /* _KREF_H_ */