linux-kernel - Re: Boot regression caused by kauditd

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Message-ID: <CAM_iQpVf+vt+bfM3y1UrB2NR7YS_DyqfgFU5F1niPTqFHWxcHw@mail.gmail.com>
Date:   Thu, 27 Apr 2017 14:45:44 -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 2:35 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> 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.
>

Or even better, save a memory allocation for reset path...

View attachment "auditd-rcu.diff" of type "text/plain" (6715 bytes)