linux-kernel - Re: Deadlock related to file permissions and/or cgroup, 4.4.6+

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Date:	Wed, 13 Apr 2016 15:00:25 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Deadlock related to file permissions and/or cgroup, 4.4.6+

Hello,

On Thu, Apr 07, 2016 at 02:59:41PM -0700, Ben Greear wrote:
> This is from a modified 4.4.6+ kernel, with local patches.  Git tree found
> below, but I don't think this lockup is related to any local changes we have made.
> 
> http://dmz2.candelatech.com/?p=linux-4.4.dev.y/.git;a=summary
> 
> The test case involves using a libcurl based application that
> is making an ftp request to a second port on the same machine.
> vsftp is serving up the ftp file.
> The ports are looped together with an ethernet cable, and routing rules
> are set up so that traffic flows over the external interface.
> 
> The key change from a working solution and kernel deadlock, is that
> with the file-to-be-read has permissions 700, it fails, but 600
> does not.  (As I was writing this up, our system-test guy managed to
> lock it up with 600 permissions as well, so it is not *just* related to
> permission 700).
> 
> This is very repeatable permissions 700.
> 
> The tainting probably comes from a warning in another (GPL, but out-of-tree module that we write),
> but very unlikely that has anything to do with this issue.

Can you please try to reproduce the problem with lockdep turned on and
without the out-of-tree module?  Lockdep should be able to point to
where the actual deadlock is happening.

Thanks.

-- 
tejun