linux-kernel - Re: Boot regression caused by kauditd

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Message-ID: <CAM_iQpXon89v+5Ce=LQZ5NLcVXLYawr=6xJRg-jY2pWGe6pJzw@mail.gmail.com>
Date:   Thu, 27 Apr 2017 13:31:10 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: Boot regression caused by kauditd

On Wed, Apr 26, 2017 at 2:20 PM, Paul Moore <paul@...l-moore.com> wrote:
> Thanks for the report, this is the only one like it that I've seen.
> I'm looking at the code in Linus' tree and I'm not seeing anything
> obvious ... looking at the trace above it appears that the problem is
> when get_net() goes to bump the refcount and the passed net pointer is
> NULL; unless I'm missing something, the only way this would happen in
> kauditd_thread() is if the auditd_conn.pid value is non-zero but the
> auditd_conn.net pointer is NULL.
>
> That shouldn't happen.
>

Looking at the code that reads/writes the global auditd_conn,
I don't see how it even works with RCU+spinlock, RCU plays
with pointers and you have to make a copy as its name implies.
But it looks like you simply use RCU+spinlock as a traditional
rwlock, it doesn't work.