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

Jarek Poplawski
2007-03-22T07:02:13Z

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@o2.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@vanheusden.com>
> > Inspired-by: Oleg Nesterov <oleg@tv-sign.ru>
> > Signed-off-by: Jarek Poplawski <jarkao2@o2.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.