linux-kernel - Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at kernel/locking/lockdep.c:2017 __lock

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Date:	Sun, 27 Mar 2016 14:23:51 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Sedat Dilek <sedat.dilek@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at
 kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260

On Sun, Mar 27, 2016 at 05:03:44AM -0700, Linus Torvalds wrote:
> 
> Unless you're using overlayfs or per-file encryption, I'm not seeing
> that any of that should make any difference (but it's entirely
> possible I'm missing something).
> 
> Was it entirely repeatable before? Maybe it just happened to happen
> without that update, and then happened to _not_ happen after you
> rebooted with that 'dev' branch pulled in?
> 
> Anyway, I don't think that DEBUG_LOCKS_WARN_ON() in
> 
>   kernel/locking/lockdep.c:2017 __lock_acquire
> 
> would be an ext4 issue, it looks more like an internal lockdep issue.

That's my guess.  I've been doing a lot of regression testing with
lockdep enabled, and I haven't seen the problem which Sedat has
reported.

At the moment I'm testing my ext4 bug fixes on top of 243d5067858310
(Merge branch 'overlayfs-linus'....) dating from March 22nd, and the
lockdep merges came much earlier than that, on March 15th, just two
days after v4.5 was released, and I'm not noticing any lockdep issues
with ext4 while running all of my regression tests.

     	  		       	  - Ted