v4.19.13 snapshot.
diff --git a/lib/lockref.c b/lib/lockref.c
new file mode 100644
index 0000000..3d468b5
--- /dev/null
+++ b/lib/lockref.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+#include <linux/lockref.h>
+
+#if USE_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 = READ_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 = cmpxchg64_relaxed(&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
+ * @lockref: 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 or dead
+ * @lockref: 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 <= 0)
+ return 0;
+ ,
+ return 1;
+ );
+
+ spin_lock(&lockref->lock);
+ retval = 0;
+ if (lockref->count > 0) {
+ lockref->count++;
+ retval = 1;
+ }
+ spin_unlock(&lockref->lock);
+ return retval;
+}
+EXPORT_SYMBOL(lockref_get_not_zero);
+
+/**
+ * lockref_put_not_zero - Decrements count unless count <= 1 before decrement
+ * @lockref: pointer to lockref structure
+ * Return: 1 if count updated successfully or 0 if count would become zero
+ */
+int lockref_put_not_zero(struct lockref *lockref)
+{
+ int retval;
+
+ CMPXCHG_LOOP(
+ new.count--;
+ if (old.count <= 1)
+ return 0;
+ ,
+ return 1;
+ );
+
+ spin_lock(&lockref->lock);
+ retval = 0;
+ if (lockref->count > 1) {
+ lockref->count--;
+ retval = 1;
+ }
+ spin_unlock(&lockref->lock);
+ return retval;
+}
+EXPORT_SYMBOL(lockref_put_not_zero);
+
+/**
+ * lockref_get_or_lock - Increments count unless the count is 0 or dead
+ * @lockref: 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 <= 0)
+ break;
+ ,
+ return 1;
+ );
+
+ spin_lock(&lockref->lock);
+ if (lockref->count <= 0)
+ return 0;
+ lockref->count++;
+ spin_unlock(&lockref->lock);
+ return 1;
+}
+EXPORT_SYMBOL(lockref_get_or_lock);
+
+/**
+ * lockref_put_return - Decrement reference count if possible
+ * @lockref: pointer to lockref structure
+ *
+ * Decrement the reference count and return the new value.
+ * If the lockref was dead or locked, return an error.
+ */
+int lockref_put_return(struct lockref *lockref)
+{
+ CMPXCHG_LOOP(
+ new.count--;
+ if (old.count <= 0)
+ return -1;
+ ,
+ return new.count;
+ );
+ return -1;
+}
+EXPORT_SYMBOL(lockref_put_return);
+
+/**
+ * lockref_put_or_lock - decrements count unless count <= 1 before decrement
+ * @lockref: 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);
+
+/**
+ * lockref_mark_dead - mark lockref dead
+ * @lockref: pointer to lockref structure
+ */
+void lockref_mark_dead(struct lockref *lockref)
+{
+ assert_spin_locked(&lockref->lock);
+ lockref->count = -128;
+}
+EXPORT_SYMBOL(lockref_mark_dead);
+
+/**
+ * lockref_get_not_dead - Increments count unless the ref is dead
+ * @lockref: pointer to lockref structure
+ * Return: 1 if count updated successfully or 0 if lockref was dead
+ */
+int lockref_get_not_dead(struct lockref *lockref)
+{
+ int retval;
+
+ CMPXCHG_LOOP(
+ new.count++;
+ if (old.count < 0)
+ return 0;
+ ,
+ return 1;
+ );
+
+ spin_lock(&lockref->lock);
+ retval = 0;
+ if (lockref->count >= 0) {
+ lockref->count++;
+ retval = 1;
+ }
+ spin_unlock(&lockref->lock);
+ return retval;
+}
+EXPORT_SYMBOL(lockref_get_not_dead);