-----"Jason Gunthorpe" <jgg@xxxxxxxx> wrote: ----- >To: "Bernard Metzler" <bmt@xxxxxxxxxxxxxx> >From: "Jason Gunthorpe" <jgg@xxxxxxxx> >Date: 08/26/2019 04:25PM >Cc: linux-rdma@xxxxxxxxxxxxxxx, bvanassche@xxxxxxx, >dledford@xxxxxxxxxx >Subject: [EXTERNAL] Re: [PATCH] RDMA/siw: Fix IPv6 addr_list locking > >On Mon, Aug 26, 2019 at 04:17:40PM +0200, Bernard Metzler wrote: >> Walking the address list of an inet6_dev requires >> appropriate locking. Since the called function >> siw_listen_address() may sleep, we have to use >> rtnl_lock() + rcu_read_lock_bh() instead of >> read_lock_bh(). > >What is the RCU for if you have RTNL? > Frankly, I looked around in net/ipv6 and found, if not rwlocked, addr_list walking to be rcu protected, even if rtnl_lock()'d (e.g. addrconf_verify_rtnl()). You are saying this is useless and overdone, since all changes to that list are rtnl_lock protected right? I was not sure about that. For the IPv4 case further up, we also take the rtnl_lock, and RCU-deref the address pointer (via in_dev_for_each_ifa_rtnl()). Hmmm. Thanks for your help, Bernard.
