Index: sys/riscv/include/cpu.h
===================================================================
--- sys/riscv/include/cpu.h
+++ sys/riscv/include/cpu.h
@@ -46,7 +46,7 @@
 
 #define	cpu_getstack(td)	((td)->td_frame->tf_sp)
 #define	cpu_setstack(td, sp)	((td)->td_frame->tf_sp = (sp))
-#define	cpu_spinwait()		/* nothing */
+#define	cpu_spinwait()		__asm __volatile("nop")
 #define	cpu_lock_delay()	DELAY(1)
 
 #ifdef _KERNEL