1 files changed, 59 insertions, 1 deletions

diff --git a/lib/lockref.c b/lib/lockref.c
index a9a4f4e..7819c2d 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -1,6 +1,33 @@
 #include <linux/export.h>
 #include <linux/lockref.h>
 
+#ifdef CONFIG_CMPXCHG_LOCKREF
+
+/*
+ * Note that the "cmpxchg()" reloads the "old" value for the
+ * failure case.
+ */
+#define CMPXCHG_LOOP(CODE, SUCCESS) do {					\
+	struct lockref old;							\
+	BUILD_BUG_ON(sizeof(old) != 8);						\
+	old.lock_count = ACCESS_ONCE(lockref->lock_count);			\
+	while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) {  	\
+		struct lockref new = old, prev = old;				\
+		CODE								\
+		old.lock_count = cmpxchg(&lockref->lock_count,			\
+					 old.lock_count, new.lock_count);	\
+		if (likely(old.lock_count == prev.lock_count)) {		\
+			SUCCESS;						\
+		}								\
+	}									\
+} while (0)
+
+#else
+
+#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
+
+#endif
+
 /**
  * lockref_get - Increments reference count unconditionally
  * @lockcnt: pointer to lockref structure
@@ -10,6 +37,12 @@
  */
 void lockref_get(struct lockref *lockref)
 {
+	CMPXCHG_LOOP(
+		new.count++;
+	,
+		return;
+	);
+
 	spin_lock(&lockref->lock);
 	lockref->count++;
 	spin_unlock(&lockref->lock);
@@ -23,9 +56,18 @@ EXPORT_SYMBOL(lockref_get);
  */
 int lockref_get_not_zero(struct lockref *lockref)
 {
-	int retval = 0;
+	int retval;
+
+	CMPXCHG_LOOP(
+		new.count++;
+		if (!old.count)
+			return 0;
+	,
+		return 1;
+	);
 
 	spin_lock(&lockref->lock);
+	retval = 0;
 	if (lockref->count) {
 		lockref->count++;
 		retval = 1;
@@ -43,6 +85,14 @@ EXPORT_SYMBOL(lockref_get_not_zero);
  */
 int lockref_get_or_lock(struct lockref *lockref)
 {
+	CMPXCHG_LOOP(
+		new.count++;
+		if (!old.count)
+			break;
+	,
+		return 1;
+	);
+
 	spin_lock(&lockref->lock);
 	if (!lockref->count)
 		return 0;
@@ -59,6 +109,14 @@ EXPORT_SYMBOL(lockref_get_or_lock);
  */
 int lockref_put_or_lock(struct lockref *lockref)
 {
+	CMPXCHG_LOOP(
+		new.count--;
+		if (old.count <= 1)
+			break;
+	,
+		return 1;
+	);
+
 	spin_lock(&lockref->lock);
 	if (lockref->count <= 1)
 		return 0;