-----"Jason Gunthorpe" <jgg@xxxxxxxx> wrote: ----- >To: "Bernard Metzler" <BMT@xxxxxxxxxxxxxx> >From: "Jason Gunthorpe" <jgg@xxxxxxxx> >Date: 08/26/2019 05:14PM >Cc: linux-rdma@xxxxxxxxxxxxxxx, bvanassche@xxxxxxx, >dledford@xxxxxxxxxx >Subject: [EXTERNAL] Re: Re: [PATCH] RDMA/siw: Fix IPv6 addr_list >locking > >On Mon, Aug 26, 2019 at 03:12:20PM +0000, Bernard Metzler 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. > >I'm not sure, I thought it was the case that rtnl protected the >address lists on write. > >> 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()). > >That uses rtnl_derference which calls into rcu_dereference_protected >which is saying 'this RCU protected data is being read outside RCU >because we are holding the write side lock' > >Which means it is locked by RTNL > OK, makes sense. So this is probably really overdone. Thanks, Bernard.
