1 files changed, 65 insertions, 0 deletions
diff --git a/include/linux/lockref.h b/include/linux/lockref.h
new file mode 100644
index 000000000000..815d871fadfc
--- /dev/null
+++ b/include/linux/lockref.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_LOCKREF_H
+#define __LINUX_LOCKREF_H
+
+/*
+ * Locked reference counts.
+ *
+ * These are different from just plain atomic refcounts in that they
+ * are atomic with respect to the spinlock that goes with them.  In
+ * particular, there can be implementations that don't actually get
+ * the spinlock for the common decrement/increment operations, but they
+ * still have to check that the operation is done semantically as if
+ * the spinlock had been taken (using a cmpxchg operation that covers
+ * both the lock and the count word, or using memory transactions, for
+ * example).
+ */
+
+#include <linux/spinlock.h>
+#include <generated/bounds.h>
+
+#define USE_CMPXCHG_LOCKREF \
+	(IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \
+	 IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4)
+
+struct lockref {
+	union {
+#if USE_CMPXCHG_LOCKREF
+		aligned_u64 lock_count;
+#endif
+		struct {
+			spinlock_t lock;
+			int count;
+		};
+	};
+};
+
+/**
+ * lockref_init - Initialize a lockref
+ * @lockref: pointer to lockref structure
+ *
+ * Initializes @lockref->count to 1.
+ */
+static inline void lockref_init(struct lockref *lockref)
+{
+	spin_lock_init(&lockref->lock);
+	lockref->count = 1;
+}
+
+void lockref_get(struct lockref *lockref);
+int lockref_put_return(struct lockref *lockref);
+bool lockref_get_not_zero(struct lockref *lockref);
+bool lockref_put_or_lock(struct lockref *lockref);
+#define lockref_put_or_lock(_lockref) \
+	(!__cond_lock((_lockref)->lock, !lockref_put_or_lock(_lockref)))
+
+void lockref_mark_dead(struct lockref *lockref);
+bool lockref_get_not_dead(struct lockref *lockref);
+
+/* Must be called under spinlock for reliable results */
+static inline bool __lockref_is_dead(const struct lockref *l)
+{
+	return ((int)l->count < 0);
+}
+
+#endif /* __LINUX_LOCKREF_H */