1 files changed, 59 insertions, 1 deletions

diff --git a/lib/lockref.c b/lib/lockref.c
index a9a4f4e1eff5..7819c2d1d315 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;