Index: uvm_swap.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_swap.c,v
retrieving revision 1.180
diff -p -u -r1.180 uvm_swap.c
--- uvm_swap.c	27 Jan 2019 05:22:19 -0000	1.180
+++ uvm_swap.c	31 Aug 2019 10:53:35 -0000
@@ -1778,6 +1778,10 @@ uvm_swap_io(struct vm_page **pps, int st
 	write = (flags & B_READ) == 0;
 	async = (flags & B_ASYNC) != 0;
 
+	/* XXX swap io make take place before the aiodone queue exists */
+	if (uvm.aiodone_queue == NULL)
+		async = 0;
+
 	/*
 	 * allocate a buf for the i/o.
 	 */