linux-kernel - Re: Boot regression caused by kauditd

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Message-ID: <CAM_iQpWSJ3eqY7Lnts4L+U_Cp9+wQ1Y2T4ZZvdaVod1Es7tRxg@mail.gmail.com>
Date:   Thu, 27 Apr 2017 14:35:04 -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 Thu, Apr 27, 2017 at 1:31 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> 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.

The attached patch seems working for me, I tried to boot my
VM for 4 times, so far no crash or warning.

Please let me know if it looks reasonable to you.

View attachment "auditd-rcu.diff" of type "text/plain" (8231 bytes)