[PATCH] arm: Use arch_spin_lock for unwind to avoid lockdep deadlock

[tglx@linutronix.de (Thomas Gleixner)]

On Tue, 17 May 2011, Thomas Gleixner wrote:

> On Tue, 17 May 2011, Peter Zijlstra wrote:
> 
> > On Tue, 2011-05-17 at 16:11 +0200, Thomas Gleixner wrote:
> > > When lockdep traces a lock taken in a module the arm unwinder takes
> > > unwind_lock which causes a recursive lockdep call deadlocking itself
> > > on the unwind_lock.
> > > 
> > > Make unwind_lock an arch_spin_lock to avoid the lockdep call and use
> > > the raw_local_irq_save/restore() variants to avoid irq tracing as
> > > well. 
> > 
> > That doesn't parse, lockdep has recursion protection, this shouldn't
> > happen.
> 
> Gah, misread the splat. The problem is 
> 
>      unwind() -> lock() -> lock_acquired() -> unwind() -> lock()

Grmpf, no. That does not make sense as the stack trace is taken in
lock_aquire() which happens before lock(). Ignore that for now until I
have it reproduced.

Thanks,

	tglx