diff -r 8a290103f462 sys/kern/subr_percpu.c
--- a/sys/kern/subr_percpu.c	Thu Aug 27 14:10:36 2020 +0000
+++ b/sys/kern/subr_percpu.c	Thu Aug 27 14:33:10 2020 +0000
@@ -115,7 +115,8 @@ percpu_cpu_swap(void *p1, void *p2)
 		 * copy data to new storage.
 		 */
 
-		memcpy(newpcc->pcc_data, pcc->pcc_data, pcc->pcc_size);
+		if (pcc->pcc_size)
+			memcpy(newpcc->pcc_data, pcc->pcc_data, pcc->pcc_size);
 
 		/*
 		 * this assignment needs to be atomic for percpu_getptr_remote.