Hi Florian,
2017-04-24 21:37 GMT+08:00 Florian Westphal <fw@xxxxxxxxx>:
> nf_log_unregister() (which is what gets called in the logger backends
> module exit paths) does a (required, module is removed) synchronize_rcu().
>
> But nf_log_unset() is only called from pernet exit handlers. It doesn't
> free any memory so there appears to be no need to call synchronize_rcu.
If I did not miss something, maybe there's an exception here, in
the nfnetlink_log.ko's module exit routine, nf_log_unregister
is invoked before unregister_pernet_subsys, i.e. _log_unregister
will be done before _log_unset.
So removing the synchronize_rcu in _log_unset will become unsafe
when uninstalling the nfnetlink_log.ko:
static void __exit nfnetlink_log_fini(void)
{
nf_log_unregister(&nfulnl_logger); --> synchronize_rcu here.
nfnetlink_subsys_unregister(&nfulnl_subsys);
netlink_unregister_notifier(&nfulnl_rtnl_notifier);
unregister_pernet_subsys(&nfnl_log_net_ops); --> _log_unset
without synchronize_rcu.
}
So I think after dropping the synchronize_rcu in _log_unset, we
should also put the "nf_log_unregister(&nfulnl_logger);" to the
end, just like other nf_log_X modules do.
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