netdev - Re: [RFC] ifa_list needs proper rcu protection

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Message-ID: <20190504180139.ftpnwgefjvukda7w@breakpoint.cc>
Date:   Sat, 4 May 2019 20:01:39 +0200
From:   Florian Westphal <fw@...len.de>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Networking <netdev@...r.kernel.org>,
        David Ahern <dsahern@...il.com>,
        Florian Westphal <fw@...len.de>
Subject: Re: [RFC] ifa_list needs proper rcu protection

Eric Dumazet <eric.dumazet@...il.com> wrote:

Sorry for late reply.

> It looks that unless RTNL is held, accessing ifa_list needs proper RCU protection ?
> 
> indev->ifa_list can be changed under us by another cpu (which owns RTNL)
> 
> Lets took an example.
> 
> (A proper rcu_dereference() with an happy sparse support would require adding __rcu attribute,
>  I put a READ_ONCE() which should be just fine in this particular context)

I don't see e.g. __inet_insert_ifa() use rcu_assign_pointer() or similar
primitive, so I don't think its enough to change readers.

Same for __inet_del_ifa(), i see freeing gets dealyed via call_rcu, but
it uses normal assignemts instead of a rcu helper.

So, I am afraid we will have to sprinkle some rcu_assign_/derefence in
several places.