3 files changed, 138 insertions, 0 deletions

diff --git a/lib/Kconfig b/lib/Kconfig
index 71d9f81f6eed..65561716c16c 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -48,6 +48,16 @@ config STMP_DEVICE
 config PERCPU_RWSEM
         boolean
 
+config ARCH_USE_CMPXCHG_LOCKREF
+        bool
+
+config CMPXCHG_LOCKREF
+        def_bool y if ARCH_USE_CMPXCHG_LOCKREF
+        depends on SMP
+        depends on !GENERIC_LOCKBREAK
+        depends on !DEBUG_SPINLOCK
+        depends on !DEBUG_LOCK_ALLOC
+
 config CRC_CCITT
         tristate "CRC-CCITT functions"
         help
diff --git a/lib/Makefile b/lib/Makefile
index 7baccfd8a4e9..f2cb3082697c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -20,6 +20,7 @@ lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o
 
 lib-y   += kobject.o klist.o
+obj-y   += lockref.o
 
 obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
          bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
diff --git a/lib/lockref.c b/lib/lockref.c
new file mode 100644
index 000000000000..7819c2d1d315
--- /dev/null
+++ b/lib/lockref.c
@@ -0,0 +1,127 @@
+#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
+ *
+ * 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);