Peter Zijlstra <pet...@infradead.org> wrote: > On Mon, Nov 06, 2017 at 11:51:07AM +0100, Florian Westphal wrote: > > @@ -180,6 +164,12 @@ int __rtnl_register(int protocol, int msgtype, > > rcu_assign_pointer(rtnl_msg_handlers[protocol], tab); > > } > > > > + WARN_ON(tab[msgindex].owner && tab[msgindex].owner != owner); > > + > > + tab[msgindex].owner = owner; > > + /* make sure owner is always visible first */ > > + smp_wmb(); > > + > > if (doit) > > tab[msgindex].doit = doit; > > if (dumpit) > > > @@ -235,6 +279,9 @@ int rtnl_unregister(int protocol, int msgtype) > > handlers[msgindex].doit = NULL; > > handlers[msgindex].dumpit = NULL; > > handlers[msgindex].flags = 0; > > + /* make sure we clear owner last */ > > + smp_wmb(); > > + handlers[msgindex].owner = NULL; > > rtnl_unlock(); > > > > return 0; > > These wmb()'s don't make sense; and the comments are incomplete. What do > they pair with? Who cares about this ordering?
rtnetlink_rcv_msg: 4406 dumpit = READ_ONCE(handlers[type].dumpit); 4407 if (!dumpit) 4408 goto err_unlock; 4409 owner = READ_ONCE(handlers[type].owner); 4410 } .. 4417 if (!try_module_get(owner)) 4418 err = -EPROTONOSUPPORT; 4419 I don't want dumpit function address to be visible before owner. Does that make sense?
