linux-kernel - Re: [PATCH] lockdep: lockdep_depth vs. debug_locks Re: [2.6.20] BUG: workqueue leaked lock

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Date:	Thu, 22 Mar 2007 08:06:44 +0100
From:	Jarek Poplawski <jarkao2@...pl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>, Neil Brown <neilb@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Folkert van Heusden <folkert@...heusden.com>,
	linux-kernel@...r.kernel.org,
	"J\. Bruce Fields" <bfields@...ldses.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] lockdep: lockdep_depth vs. debug_locks Re: [2.6.20] BUG: workqueue leaked lock

On Wed, Mar 21, 2007 at 10:28:02PM -0800, Andrew Morton wrote:
> On Thu, 22 Mar 2007 07:11:19 +0100 Jarek Poplawski <jarkao2@...pl> wrote:
> 
> > 
> > Here is some joke:
> > 
> > [PATCH] lockdep: lockdep_depth vs. debug_locks
> > 
> > lockdep really shouldn't be used when debug_locks == 0!
> > 
> 
> This isn't a very good changelog.
> 
> > 
> > Reported-by: Folkert van Heusden <folkert@...heusden.com>
> > Inspired-by: Oleg Nesterov <oleg@...sign.ru>
> > Signed-off-by: Jarek Poplawski <jarkao2@...pl>
> > 
> > ---
> > 
> > diff -Nurp 2.6.21-rc4-git4-/include/linux/lockdep.h 2.6.21-rc4-git4/include/linux/lockdep.h
> > --- 2.6.21-rc4-git4-/include/linux/lockdep.h	2007-03-20 20:24:17.000000000 +0100
> > +++ 2.6.21-rc4-git4/include/linux/lockdep.h	2007-03-21 22:32:41.000000000 +0100
> > @@ -245,7 +245,7 @@ extern void lock_release(struct lockdep_
> >  
> >  # define INIT_LOCKDEP				.lockdep_recursion = 0,
> >  
> > -#define lockdep_depth(tsk)	((tsk)->lockdep_depth)
> > +#define lockdep_depth(tsk)	(debug_locks ? (tsk)->lockdep_depth : 0)
> >  
> >  #else /* !LOCKDEP */
> >  
> 
> What problem does this solve, and how does it solve it?
> 
> I assume that some codepath is incrementing ->lockdep_depth even when
> debug_locks==0.  Isn't that wrong of it?
> 

This should definitely solve this problem - as it was said
a few times before lockdep stops registering locks after
a bug, so even the lock which caused the warning isn't
reported. Here lockdep found a bug in a workqueue function,
so after this no lock or unlock isn't counted nor reported.

I think Ingo can tell more.

Regards,
Jarek P.
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