Index: head/sys/vm/vm_object.c
===================================================================
--- head/sys/vm/vm_object.c
+++ head/sys/vm/vm_object.c
@@ -2278,7 +2278,7 @@
 vm_object_unwire(vm_object_t object, vm_ooffset_t offset, vm_size_t length,
     uint8_t queue)
 {
-	vm_object_t tobject;
+	vm_object_t tobject, t1object;
 	vm_page_t m, tm;
 	vm_pindex_t end_pindex, pindex, tpindex;
 	int depth, locked_depth;
@@ -2292,6 +2292,7 @@
 		return;
 	pindex = OFF_TO_IDX(offset);
 	end_pindex = pindex + atop(length);
+again:
 	locked_depth = 1;
 	VM_OBJECT_RLOCK(object);
 	m = vm_page_find_least(object, pindex);
@@ -2325,16 +2326,26 @@
 			m = TAILQ_NEXT(m, listq);
 		}
 		vm_page_lock(tm);
+		if (vm_page_xbusied(tm)) {
+			for (tobject = object; locked_depth >= 1;
+			    locked_depth--) {
+				t1object = tobject->backing_object;
+				VM_OBJECT_RUNLOCK(tobject);
+				tobject = t1object;
+			}
+			vm_page_busy_sleep(tm, "unwbo", true);
+			goto again;
+		}
 		vm_page_unwire(tm, queue);
 		vm_page_unlock(tm);
 next_page:
 		pindex++;
 	}
 	/* Release the accumulated object locks. */
-	for (depth = 0; depth < locked_depth; depth++) {
-		tobject = object->backing_object;
-		VM_OBJECT_RUNLOCK(object);
-		object = tobject;
+	for (tobject = object; locked_depth >= 1; locked_depth--) {
+		t1object = tobject->backing_object;
+		VM_OBJECT_RUNLOCK(tobject);
+		tobject = t1object;
 	}
 }