[PATCH] Support lockref reference count if enable LOCK_STAT

[yongli-oc]

Swap the positions of lock and count to support CMPXCHG_LOCKREF
if SPINLOCK_SIZE > 4 when enable LOCK_STAT. The reference count
can always be used regardless of the spinlock_t size.

Signed-off-by: yongli-oc <yongli-oc@xxxxxxxxxxx>
---
 include/linux/lockref.h | 17 ++++++++++++++++-
 lib/lockref.c           | 26 ++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/include/linux/lockref.h b/include/linux/lockref.h
index c3a1f78bc884..44ac754a029b 100644
--- a/include/linux/lockref.h
+++ b/include/linux/lockref.h
@@ -22,15 +22,30 @@
 	(IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \
 	 IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4)
 
+#define USE_CMPXCHG_LOCKREF_ALTERNATIVE \
+	(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;
 		};
+#elif USE_CMPXCHG_LOCKREF_ALTERNATIVE
+		aligned_u64 lock_count;
+		struct {
+			int count;
+			spinlock_t lock;
+		} __packed;
+#else
+		struct {
+			spinlock_t lock;
+			int count;
+		};
+#endif
 	};
 };
 
diff --git a/lib/lockref.c b/lib/lockref.c
index 2afe4c5d8919..e92606f66e9b 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -26,6 +26,32 @@
 	}									\
 } while (0)
 
+#elif USE_CMPXCHG_LOCKREF_ALTERNATIVE
+
+/*
+ * Note that the "cmpxchg()" reloads the "old" value for the
+ * failure case.
+ */
+#define CMPXCHG_LOOP(CODE, SUCCESS) do {					\
+	int retry = 100;							\
+	struct lockref old;							\
+	BUILD_BUG_ON(offsetof(struct lockref, lock) != 4);			\
+	BUILD_BUG_ON(offsetof(spinlock_t, rlock) != 0);				\
+	BUILD_BUG_ON(offsetof(raw_spinlock_t, raw_lock) != 0);			\
+	old.lock_count = READ_ONCE(lockref->lock_count);			\
+	while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) {	\
+		struct lockref new = old;					\
+		CODE								\
+		if (likely(try_cmpxchg64_relaxed(&lockref->lock_count,		\
+						 &old.lock_count,		\
+						 new.lock_count))) {		\
+			SUCCESS;						\
+		}								\
+		if (!--retry)							\
+			break;							\
+	}									\
+} while (0)
+
 #else
 
 #define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
-- 
2.34.1