wasm: make SMP acquire and release accesses atomic

arch/wasm/include/asm/barrier.h

@@ -5,6 +5,56 @@
 #define __smp_rmb() __atomic_thread_fence(__ATOMIC_ACQ_REL)
 #define __smp_wmb() __atomic_thread_fence(__ATOMIC_ACQ_REL)
 
+#define __wasm_atomic_ptr(p)						\
+	((typeof(p))__builtin_assume_aligned((const void *)(p), sizeof(*(p))))
+
+/*
+ * A fence does not make an adjacent plain Wasm memory access atomic.  Use an
+ * atomic instruction for the access itself so that release/acquire pairs
+ * synchronize through shared linear memory.
+ */
+#define __smp_store_release(p, v)					\
+do {									\
+	compiletime_assert_atomic_type(*(p));				\
+	__atomic_store_n(__wasm_atomic_ptr(p), (v), __ATOMIC_RELEASE);	\
+} while (0)
+
+#define __smp_load_acquire(p)						\
+({									\
+	__unqual_scalar_typeof(*(p)) __value;				\
+	compiletime_assert_atomic_type(*(p));				\
+	__value = __atomic_load_n(__wasm_atomic_ptr(p), __ATOMIC_ACQUIRE);\
+	(typeof(*(p)))__value;						\
+})
+
+#define smp_cond_load_relaxed(ptr, cond_expr)				\
+({									\
+	typeof(ptr) __ptr = (ptr);					\
+	__unqual_scalar_typeof(*(ptr)) VAL;				\
+	for (;;) {							\
+		VAL = __atomic_load_n(__wasm_atomic_ptr(__ptr),		\
+				      __ATOMIC_RELAXED);			\
+		if (cond_expr)						\
+			break;						\
+		cpu_relax();						\
+	}								\
+	(typeof(*(ptr)))VAL;						\
+})
+
+#define smp_cond_load_acquire(ptr, cond_expr)				\
+({									\
+	typeof(ptr) __ptr = (ptr);					\
+	__unqual_scalar_typeof(*(ptr)) VAL;				\
+	for (;;) {							\
+		VAL = __atomic_load_n(__wasm_atomic_ptr(__ptr),		\
+				      __ATOMIC_ACQUIRE);			\
+		if (cond_expr)						\
+			break;						\
+		cpu_relax();						\
+	}								\
+	(typeof(*(ptr)))VAL;						\
+})
+
 #include <asm-generic/barrier.h>
 
 #endif