Fri, Aug 25, 2017 at 11:18:50AM CEST, f...@strlen.de wrote: >Jiri Pirko <j...@resnulli.us> wrote: >> Fri, Aug 25, 2017 at 01:51:29AM CEST, xiyou.wangc...@gmail.com wrote: >> >For TC classes, their ->get() and ->put() are always paired, and the >> >reference counting is completely useless, because: >> > >> >1) For class modification and dumping paths, we already hold RTNL lock, >> > so all of these ->get(),->change(),->put() are atomic. >> >> There is ongoing initiative by Florian to avoid taking RTNL for some >> rtnetlink calls. I think that for dumping it could be done in tc as well. >> Don't we need the refcnt then? > >Dumping is a problem at this time because several places depend on RTNL >to ensure we get a consistent state, even "simple" functions like >rtnl_fill_ifinfo, see e.g. 2907c35ff64708065e5a7fd54e8ded8263eb3074 >(net: hold rtnl again in dump callbacks). > >So for these places we already need some other way (e.g. seqlock) >to ensure we don't put garbage in netlink skb. > >At this time I think that it is better if Congs patches go in >(Unless there are other problems of course) as they simplify >things quite a bit, and I am not sure that we need refcount. > >It might be enough to use rcu and detect when the class we just read >from might have been in inconsistent state (so we can retry). > >Does that make sense to you?
It does. Thanks!
