netdev - Re: [PATCH net] rxrpc: use rcu protection while reading sk->sk_user

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Message-ID: <8142.1571268276@warthog.procyon.org.uk>
Date:   Thu, 17 Oct 2019 00:24:36 +0100
From:   David Howells <dhowells@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     dhowells@...hat.com, "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: Re: [PATCH net] rxrpc: use rcu protection while reading sk->sk_user_data

Eric Dumazet <edumazet@...gle.com> wrote:

> We need to extend the rcu_read_lock() section in rxrpc_error_report()
> and use rcu_dereference_sk_user_data() instead of plain access
> to sk->sk_user_data to make sure all rules are respected.

Should I take it that the caller won't be guaranteed to be holding the RCU
read lock?

Looking at __udp4_lib_err(), that calls __udp4_lib_err_encap(), which calls
__udp4_lib_err_encap_no_sk(), which should throw a warning if the RCU read
lock is not held.

Similarly, icmp_socket_deliver() and icmpv6_notify() should also throw a
warning before calling ->err_handler().

Does that mean something further up the CPU stack is going to be holding the
RCU read lock?

David