1 files changed, 128 insertions, 0 deletions
diff --git a/lib/lockref.c b/lib/lockref.c
new file mode 100644
index 00000000000..9d76f404ce9
--- /dev/null
+++ b/lib/lockref.c
@@ -0,0 +1,128 @@
+#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;						\
+		}								\
+		cpu_relax();							\
+	}									\
+} while (0)
+
+#else
+
+#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
+
+#endif
+
+/**
+ * lockref_get - Increments reference count unconditionally
+ * @lockcnt: pointer to lockref structure
+ *
+ * This operation is only valid if you already hold a reference
+ * to the object, so you know the count cannot be zero.
+ */
+void lockref_get(struct lockref *lockref)
+{
+	CMPXCHG_LOOP(
+		new.count++;
+	,
+		return;
+	);
+
+	spin_lock(&lockref->lock);
+	lockref->count++;
+	spin_unlock(&lockref->lock);
+}
+EXPORT_SYMBOL(lockref_get);
+
+/**
+ * lockref_get_not_zero - Increments count unless the count is 0
+ * @lockcnt: pointer to lockref structure
+ * Return: 1 if count updated successfully or 0 if count was zero
+ */
+int lockref_get_not_zero(struct lockref *lockref)
+{
+	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;
+	}
+	spin_unlock(&lockref->lock);
+	return retval;
+}
+EXPORT_SYMBOL(lockref_get_not_zero);
+
+/**
+ * lockref_get_or_lock - Increments count unless the count is 0
+ * @lockcnt: pointer to lockref structure
+ * Return: 1 if count updated successfully or 0 if count was zero
+ * and we got the lock instead.
+ */
+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;
+	lockref->count++;
+	spin_unlock(&lockref->lock);
+	return 1;
+}
+EXPORT_SYMBOL(lockref_get_or_lock);
+
+/**
+ * lockref_put_or_lock - decrements count unless count <= 1 before decrement
+ * @lockcnt: pointer to lockref structure
+ * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
+ */
+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;
+	lockref->count--;
+	spin_unlock(&lockref->lock);
+	return 1;
+}
+EXPORT_SYMBOL(lockref_put_or_lock);