Re: xfs readdir hang on for-next (3.15.0-rc1)

From: Peter Zijlstra <peterz@infradead.org>
To: Brian Foster <bfoster@redhat.com>
Cc: xfs@oss.sgi.com
Subject: Re: xfs readdir hang on for-next (3.15.0-rc1)
Date: Mon, 14 Apr 2014 22:57:37 +0200	[thread overview]
Message-ID: <20140414205737.GI26782@laptop.programming.kicks-ass.net> (raw)
In-Reply-To: <20140414190834.GB62307@bfoster.bfoster>

On Mon, Apr 14, 2014 at 03:08:36PM -0400, Brian Foster wrote:
> On Mon, Apr 14, 2014 at 12:43:14PM -0400, Brian Foster wrote:
> > Hi all,
> > 
> > This is a heads up that I'm seeing a blatant readdir hang on the current
> > for-next with selinux enabled. To reproduce, I format a clean fs, mount
> > and attempt an ls.
> > 
> > The problem does not occur with selinux disabled, if I back out the
> > following commit:
> > 
> > 40194ecc6d78 xfs: reinstate the ilock in xfs_readdir
> > 
> > ... or if I remove the locking around xfs_attr_get(), so I suspect this
> > is another instance of a recursive deadlock. I'm getting no output
> > whatsoever in order to confirm this and it also leads to a complete
> > system lockup. It's also interesting that this hasn't been observed
> > until now, given the above commit was introduced in 3.14. So the above
> > commit doesn't appear to be the most recent change that triggers this.
> > 
> > I reproduced on the latest linus tree and do not reproduce on 3.14, so
> > I'm trying to do a bisect to find out what else might have changed to
> > trigger this.
> > 
> 
> This bisected down to:
> 
> commit 6f008e72cd111a119b5d8de8c5438d892aae99eb
> Author: Peter Zijlstra <peterz@infradead.org>
> Date:   Wed Mar 12 13:24:42 2014 +0100
> 
>     locking/mutex: Fix debug checks
> ...
> 
> ... which suggests something down in the mutex debug code. Indeed, the
> problem no longer occurs if I disable kernel debug in my .config. What
> is also interesting is that it didn't return when I reenable
> DEBUG_KERNEL and DEBUG_MUTEXES alone. It does return when I start to
> enable some of the other lock debugging options. FWIW, I also cleared
> out my tree and rebuilt from scratch just to be sure that I didn't have
> anything stale/broken lying around.
> 
> Peter,
> 
> Any insight on this? 

http://lkml.kernel.org/r/tip-a227960fe0cafcc229a8d6bb8b454a3a0b33719d@git.kernel.org

That will make the kernel continue after the lockdep splat. I too see it
on some of my XFS using machines.

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