Re: [PATCH] irqdomain: protect macro variable in domain iterators

[Dave Martin <dave.martin-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Fri, Dec 02, 2011 at 02:53:17PM +0100, Nicolas Ferre wrote:
> Signed-off-by: Nicolas Ferre <nicolas.ferre-AIFe0yeh4nAAvxtiuMwx3w@public.gmane.org>
> ---
> Error found while using those iterators in an irq controller
> initialization function.
> 
> May also need protection around irq and hwirq macro variables
> but those values are usually plain "int" anyway... Tell me if you
> feel that it should be done.
> 
>  include/linux/irqdomain.h |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
> index 99834e58..a553004 100644
> --- a/include/linux/irqdomain.h
> +++ b/include/linux/irqdomain.h
> @@ -82,12 +82,12 @@ static inline unsigned int irq_domain_to_irq(struct irq_domain *d,
>  }
>  
>  #define irq_domain_for_each_hwirq(d, hw) \
> -	for (hw = d->hwirq_base; hw < d->hwirq_base + d->nr_irq; hw++)
> +	for (hw = (d)->hwirq_base; hw < (d)->hwirq_base + (d)->nr_irq; hw++)
>  
>  #define irq_domain_for_each_irq(d, hw, irq) \
> -	for (hw = d->hwirq_base, irq = irq_domain_to_irq(d, hw); \
> -	     hw < d->hwirq_base + d->nr_irq; \
> -	     hw++, irq = irq_domain_to_irq(d, hw))
> +	for (hw = (d)->hwirq_base, irq = irq_domain_to_irq((d), hw); \
> +	     hw < (d)->hwirq_base + (d)->nr_irq; \
> +	     hw++, irq = irq_domain_to_irq((d), hw))

I suggest just putting all the brackets in -- if having spotted this
problem you only half-fix the macros, an opportunity is being missed;
someone have to come and fix it again later:


#define irq_domain_for_each_hwirq(d, hw) \
	for ((hw) = (d)->hwirq_base; (hw) < (d)->hwirq_base + (d)->nr_irq; (hw)++)

#define irq_domain_for_each_irq(d, hw, irq) \
	for ((hw) = (d)->hwirq_base, (irq) = irq_domain_to_irq(d, hw); \
	     (hw) < (d)->hwirq_base + (d)->nr_irq; \
	     (hw)++, (irq) = irq_domain_to_irq(d, hw))


If you feel happier though, you can harmlessly add the extra brackets round
the arguments to irq_domain_to_irq(), without changing the behaviour.
Arguably the "always add brackets" rule is simpler to understand.

In fact, where a macro argument is not part of a larger expression, or is an
operand to a comma-expression, there's no need for extra brackets -- all
possible operators parse at higher priority than commas.  A macro argument
which itself is a comma-expression whould have to be explicitly bracketed
in the macro invocation anyway, so there is no extra risk of the macro
expansion being parsed in an unexpected way in that case.

Cheers
---Dave