Subject: Re: [mmotm and linux-next][PATCH] irq: enclose irq_desc_lock_class in CONFIG_LOCKDEP

From: Ingo Molnar <[email-masked]>
Date: Tue, 16 Dec 2008 12:20:19 +0100

* KOSAKI Motohiro <[email-masked]> wrote:

> Hi!
> 
> >> > No, lockdep.h (which we forgot to include) already handles that:
> >> >
> >> > # define lockdep_set_class(lock, key)               do { (void)(key); } while (0)
> >> >
> >> > the problem is that the code which references irq_desc_lock_class is
> >> > inside #ifdef CONFIG_SPARSE_IRQ, so this is a better fix:
> >>
> >> agreed that this is the better fix - applied to tip/irq/sparseirq,
> >> thanks!
> >
> > actually, this breaks the build on !SPARSEIRQ because we will use that 
> > class in the non-sparseirq case. So we've converted a build warning to 
> > a build failure ;-)
> 
> Please give me your .config and tell me your arch. my ia64 box (ia64 is 
> !SPARSEIRQ) can build the akpm patch.

The expected build failure is obvious from reading the code:

 #ifdef CONFIG_TRACE_IRQFLAGS
 void early_init_irq_lock_class(void)
 {
 #ifndef CONFIG_SPARSE_IRQ
         struct irq_desc *desc;
         int i;

         for_each_irq_desc(i, desc) {
                 if (!desc)
                         continue;

                 lockdep_set_class(&desc->lock, &irq_desc_lock_class);

Note that it's an #ifndef sparseirq, not an #ifdef sparseirq condition.

	Ingo