linux-kernel - Re: [PATCH v6 2/8] debugfs: prevent access to removed files' private data

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Message-ID: <20160518160520.GA5407@kroah.com>
Date:	Wed, 18 May 2016 09:05:20 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Nicolai Stange <nicstange@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jonathan Corbet <corbet@....net>, Jan Kara <jack@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	Gilles Muller <Gilles.Muller@...6.fr>,
	Nicolas Palix <nicolas.palix@...g.fr>,
	Michal Marek <mmarek@...e.com>, linux-kernel@...r.kernel.org,
	cocci@...teme.lip6.fr
Subject: Re: [PATCH v6 2/8] debugfs: prevent access to removed files' private
 data

On Wed, May 18, 2016 at 11:18:16AM -0400, Sasha Levin wrote:
> On 05/18/2016 11:01 AM, Nicolai Stange wrote:
> > Thanks a million for reporting!
> > 
> > 1.) Do you have lockdep enabled?
> 
> Yup, nothing there.
> 
> > 2.) Does this happen before or after userspace init has been spawned,
> >     i.e. does the lockup happen at debugfs file creation time or
> >     possibly at usage time?
> 
> So I looked closer, and it seems to happen after starting syzkaller, which
> as far as I know tries to open many different debugfs files.
> 
> Is there debug code I can add it that'll help us figure out what's up?

Trying to figure out _which_ debugfs file is causing this would be
great, if at all possible.  strace?