linux-kernel - Re: NULL pointer dereference in autofs4_expire

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Message-ID: <5257FD34.2060406@gmail.com>
Date:	Fri, 11 Oct 2013 07:29:24 -0600
From:	David Ahern <dsahern@...il.com>
To:	Ian Kent <raven@...maw.net>
CC:	autofs@...r.kernel.org, viro@...IV.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: NULL pointer dereference in autofs4_expire_wait

On 10/11/13 3:55 AM, Ian Kent wrote:
> On Fri, 2013-10-11 at 10:06 +0800, Ian Kent wrote:
>> On Thu, 2013-10-10 at 17:22 -0600, David Ahern wrote:
>>> Running 3.12-rc3 just hit BUG in autofs4_expire_wait
>>
>> It doesn't look like this could be due to Al's change to the locking in
>> autos4_wait() and that the only change to autofs that I'm aware of.
>>
>> Could you do a bisect please?
>
> Of course that assumes it's repeatable.
> Is it?
>
> Can you provide any information about the environment and activity that
> was happening at the time of the BUG()?

The system was up and running for 9 days before hitting the BUG. After 
that with 3 cpus on softlockup I had to do a reboot (forced). After the 
reboot I continued the workload again without a repeat incident (yet), 
so I am not sure bisect is going to be possible.

This is a corporate environment where practically everything is in an 
automount. Specific to this problem I was repeatedly building a 
workspace in one window, using cscope in another and checking code 
against a different workspace in a third -- all 3 of those were 
different automounts and different NAS servers.

 From objdump on vmlinux the line in question is fs/autofs4/expire.c:465

     if (ino->flags & AUTOFS_INF_EXPIRING) {

I will be continuing the sequence above today (working through compile 
problems for on OS port). I will bump the kernel to top of tree and see 
if it repeats.

David
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