[PATCH v2 1/3 gnumach] vm_map: Add comment and assert for vm_map_delete

[Damien Zammit]

This will prevent calling vm_map_delete without the map locked
unless ref_count is zero.
---
 vm/vm_map.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/vm/vm_map.c b/vm/vm_map.c
index e454bb2a..f221c532 100644
--- a/vm/vm_map.c
+++ b/vm/vm_map.c
@@ -551,10 +551,12 @@ void vm_map_deallocate(vm_map_t map)
        c = --map->ref_count;
        simple_unlock(&map->ref_lock);
 
+       /* Check the refcount */
        if (c > 0) {
                return;
        }
 
+       /* If no more references, call vm_map_delete without locking the map */
        projected_buffer_collect(map);
        (void) vm_map_delete(map, map->min_offset, map->max_offset);
 
@@ -2028,6 +2030,11 @@ kern_return_t vm_map_delete(
        if (map->pmap == kernel_pmap && (start < kernel_virtual_start || end > 
kernel_virtual_end))
                panic("vm_map_delete(%lx-%lx) falls in physical memory 
area!\n", (unsigned long) start, (unsigned long) end);
 
+       /*
+        *      Must be called with map lock taken unless refcount is zero
+        */
+       assert((map->ref_count > 0 && map->lock.want_write) || (map->ref_count 
== 0));
+
        /*
         *      Find the start of the region, and clip it
         */
-- 
2.43.0