Function _vm_map_lock_upgrade

freebsd/vm/vm_map.c:768–793

* _vm_map_lock_upgrade: [ internal use only ] * * Tries to upgrade a read (shared) lock on the specified map to a write * (exclusive) lock. Returns the value "0" if the upgrade succeeds and a * non-zero value if the upgrade fails. If the upgrade fails, the map is * returned without a read or write lock held. * * Requires that the map be read locked. */

 *	Requires that the map be read locked.
 */
int
_vm_map_lock_upgrade(vm_map_t map, const char *file, int line)
{
	unsigned int last_timestamp;

	if (map->system_map) {
		mtx_assert_(&map->system_mtx, MA_OWNED, file, line);
	} else {
		if (!sx_try_upgrade_(&map->lock, file, line)) {
			last_timestamp = map->timestamp;
			sx_sunlock_(&map->lock, file, line);
			vm_map_process_deferred();
			/*
			 * If the map's timestamp does not change while the
			 * map is unlocked, then the upgrade succeeds.
			 */
			sx_xlock_(&map->lock, file, line);
			if (last_timestamp != map->timestamp) {
				sx_xunlock_(&map->lock, file, line);
				return (1);
			}
		}
	}
	map->timestamp++;
	return (0);
}

void
_vm_map_lock_downgrade(vm_map_t map, const char *file, int line)