diff --git a/arch/um/include/asm/futex.h b/arch/um/include/asm/futex.h
index 785fd6649aa2..07ab81f09281 100644
--- a/arch/um/include/asm/futex.h
+++ b/arch/um/include/asm/futex.h
@@ -12,7 +12,56 @@ int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
 int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 			      u32 oldval, u32 newval);
 #else
+#include <linux/atomic.h>
 #include <asm-generic/futex.h>
-#endif
+
+#ifdef CONFIG_SMP
+static inline int
+arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
+{
+	u32 oldval, newval;
+	u32 *p = (u32 __force *)uaddr;
+
+	do {
+		oldval = READ_ONCE(*p);
+
+		switch (op) {
+		case FUTEX_OP_SET:
+			newval = oparg;
+			break;
+		case FUTEX_OP_ADD:
+			newval = oldval + oparg;
+			break;
+		case FUTEX_OP_OR:
+			newval = oldval | oparg;
+			break;
+		case FUTEX_OP_ANDN:
+			newval = oldval & ~oparg;
+			break;
+		case FUTEX_OP_XOR:
+			newval = oldval ^ oparg;
+			break;
+		default:
+			return -ENOSYS;
+		}
+	} while (!try_cmpxchg(p, &oldval, newval));
+
+	*oval = oldval;
+	return 0;
+}
+
+static inline int
+futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
+			      u32 oldval, u32 newval)
+{
+	u32 *p = (u32 __force *)uaddr;
+
+	*uval = cmpxchg(p, oldval, newval);
+
+	return 0;
+}
+#endif /* CONFIG_SMP */
+
+#endif /* CONFIG_MMU */
 
 #endif