Index: sys/uvm/uvm_map.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_map.c,v
retrieving revision 1.360
diff -p -u -r1.360 uvm_map.c
--- sys/uvm/uvm_map.c	8 Jun 2019 23:48:33 -0000	1.360
+++ sys/uvm/uvm_map.c	2 Jul 2019 06:13:33 -0000
@@ -4446,9 +4446,11 @@ uvm_mapent_forkcopy(struct vm_map *new_m
 		if (old_entry->aref.ar_amap &&
 		    !UVM_ET_ISNEEDSCOPY(old_entry)) {
 			if (old_entry->max_protection & VM_PROT_WRITE) {
+				uvm_map_lock_entry(old_entry);
 				pmap_protect(old_map->pmap,
 				    old_entry->start, old_entry->end,
 				    old_entry->protection & ~VM_PROT_WRITE);
+				uvm_map_unlock_entry(old_entry);
 			}
 			old_entry->etype |= UVM_ET_NEEDSCOPY;
 		}

.