Re: lockdep oddity

Heiko Carstens
2006-09-06T06:55:29Z

> > > > The reason is that the BUILD_LOCK_OPS macros in kernel/lockdep.c
> > > > don't contain any of the *_acquire calls, while all of the _unlock
> > > > functions contain a *_release call. Hence I get immediately
> > > > unbalanced locks.
> > >
> > > hmmm ... that sounds like a bug. Weird - i recently ran
> > > PREEMPT+SMP+LOCKDEP kernels and didnt notice this.
> >
> > ok, the reason i didnt find this problem is because this is fixed in
> > my tree, but i didnt realize that it's a fix also for upstream ...
>
> actually ... it works fine in the upstream kernel due to this:
>
> * If lockdep is enabled then we use the non-preemption spin-ops
> * even on CONFIG_PREEMPT, because lockdep assumes that interrupts are
> * not re-enabled during lock-acquire (which the preempt-spin-ops do):
> */
> #if !defined(CONFIG_PREEMPT) || !defined(CONFIG_SMP) || \
> defined(CONFIG_DEBUG_LOCK_ALLOC)
>
> so i'm wondering, how did you you manage to get into the
> BUILD_LOCK_OPS() branch?

That seems to be code that isn't upstream. 2.6.18-rc5-mm1 as well as
Linus' current git tree have this:

/*
* If lockdep is enabled then we use the non-preemption spin-ops
* even on CONFIG_PREEMPT, because lockdep assumes that interrupts are
* not re-enabled during lock-acquire (which the preempt-spin-ops do):
*/
#if !defined(CONFIG_PREEMPT) || !defined(CONFIG_SMP) || \
defined(CONFIG_PROVE_LOCKING)

And yes, using CONFIG_DEBUG_LOCK_ALLOC instead of CONFIG_PROVE_LOCKING fixes
this for me :)