netcls_cgroup: introduce netcls_mutex

Introduce netcls_mutex to synchronize modifications to
cgroup_cls_state.  New cgrp now inherits classid from ->css_online()
and write_classid() updates classid while holdin netcls_mutex.

As write_classid() doesn't propagate new configuration downwards, this
currently doesn't make any userland-visible difference, but will help
implementing proper hierarchy support.

Signed-off-by: Tejun Heo <tj@kernel.org>
1 file changed