+
+/*
+ * Based on [1], __sync_lock_test_and_set() is not a full barrier, but
+ * instead only an acquire barrier. Given that uatomic_xchg() acts as
+ * both release and acquire barriers, we therefore need to have our own
+ * release barrier before this operation.
+ *
+ * [1] https://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Atomic-Builtins.html
+ */
+#define uatomic_xchg(addr, v) \
+ ({ \
+ cmm_smp_mb(); \
+ __sync_lock_test_and_set(addr, v); \
+ })