netdev - Re: Crash due to mutex genl_lock called from RCU context

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Date:   Sat, 26 Nov 2016 18:08:28 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     subashab@...eaurora.org, Thomas Graf <tgraf@...g.ch>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Crash due to mutex genl_lock called from RCU context

On Fri, Nov 25, 2016 at 8:54 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> Oh well, this wont work, since sk->sk_destruct will be called from RCU
> callback.
>
> Grabbing the mutex should not be done from netlink_sock_destruct() but
> from netlink_release()

But you also change the behavior of cb.done(), currently it is called when the
last sock ref is gone, with your patch it is called when the first
sock is closed.
No?

I don't see why we need to get genl_lock in ->done() here, because we are
already the last sock using it and module ref protects the ops from being
removed via module, seems we are pretty safe without any lock.