[PATCH] genirq: Make - vs ?: precedence explicit

[PATCH] genirq: Make - vs ?: precedence explicit

[Kees Cook]

Noticed with a Clang build. This improves the readability of the ?:
expression, as it has lower precedence than the - expression. Show
explicitly that - is evaluated first.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 kernel/irq/matrix.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c
index a3cbbc8191c5..7df2480005f8 100644
--- a/kernel/irq/matrix.c
+++ b/kernel/irq/matrix.c
@@ -384,7 +384,7 @@ unsigned int irq_matrix_available(struct irq_matrix *m, bool cpudown)
 {
 	struct cpumap *cm = this_cpu_ptr(m->maps);
 
-	return m->global_available - cpudown ? cm->available : 0;
+	return (m->global_available - cpudown) ? cm->available : 0;
 }
 
 /**
-- 
2.7.4


-- 
Kees Cook
Pixel Security

[tip:irq/urgent] genirq/matrix: Make - vs ?: Precedence explicit

[tip-bot for Kees Cook]

Commit-ID:  75f1133873d6a1276d3c19918b7c94975840f990
Gitweb:     https://git.kernel.org/tip/75f1133873d6a1276d3c19918b7c94975840f990
Author:     Kees Cook <keescook@chromium.org>
AuthorDate: Wed, 22 Nov 2017 12:56:45 -0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 23 Nov 2017 20:09:31 +0100

genirq/matrix: Make - vs ?: Precedence explicit

Noticed with a Clang build. This improves the readability of the ?:
expression, as it has lower precedence than the - expression. Show
explicitly that - is evaluated first.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20171122205645.GA27125@beast
---
 kernel/irq/matrix.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c
index a3cbbc8..7df2480 100644
--- a/kernel/irq/matrix.c
+++ b/kernel/irq/matrix.c
@@ -384,7 +384,7 @@ unsigned int irq_matrix_available(struct irq_matrix *m, bool cpudown)
 {
 	struct cpumap *cm = this_cpu_ptr(m->maps);
 
-	return m->global_available - cpudown ? cm->available : 0;
+	return (m->global_available - cpudown) ? cm->available : 0;
 }
 
 /**

Re: [PATCH] genirq: Make - vs ?: precedence explicit

[Rasmus Villemoes]

On 2017-11-22 21:56, Kees Cook wrote:
> Noticed with a Clang build. This improves the readability of the ?:
> expression, as it has lower precedence than the - expression. Show
> explicitly that - is evaluated first.
> 
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  kernel/irq/matrix.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c
> index a3cbbc8191c5..7df2480005f8 100644
> --- a/kernel/irq/matrix.c
> +++ b/kernel/irq/matrix.c
> @@ -384,7 +384,7 @@ unsigned int irq_matrix_available(struct irq_matrix *m, bool cpudown)
>  {
>  	struct cpumap *cm = this_cpu_ptr(m->maps);
>  
> -	return m->global_available - cpudown ? cm->available : 0;
> +	return (m->global_available - cpudown) ? cm->available : 0;
>  }

I see that this got applied, and that doesn't change the semantics of
the code. But surely the code is and was buggy, right? From the kernel
doc, I'm pretty sure the idea is to subtract cm->available if cpudown is
true, otherwise subtract 0, i.e.

  return m->global_available - (cpudown ? cm->available : 0);

Rasmus

Re: [PATCH] genirq: Make - vs ?: precedence explicit

[Thomas Gleixner]

On Tue, 28 Nov 2017, Rasmus Villemoes wrote:
> On 2017-11-22 21:56, Kees Cook wrote:
> > Noticed with a Clang build. This improves the readability of the ?:
> > expression, as it has lower precedence than the - expression. Show
> > explicitly that - is evaluated first.
> > 
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  kernel/irq/matrix.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c
> > index a3cbbc8191c5..7df2480005f8 100644
> > --- a/kernel/irq/matrix.c
> > +++ b/kernel/irq/matrix.c
> > @@ -384,7 +384,7 @@ unsigned int irq_matrix_available(struct irq_matrix *m, bool cpudown)
> >  {
> >  	struct cpumap *cm = this_cpu_ptr(m->maps);
> >  
> > -	return m->global_available - cpudown ? cm->available : 0;
> > +	return (m->global_available - cpudown) ? cm->available : 0;
> >  }
> 
> I see that this got applied, and that doesn't change the semantics of
> the code. But surely the code is and was buggy, right? From the kernel
> doc, I'm pretty sure the idea is to subtract cm->available if cpudown is
> true, otherwise subtract 0, i.e.
> 
>   return m->global_available - (cpudown ? cm->available : 0);

Yes, you are right. I completely misread it when I merged that patch. Good
catch!

Thanks,

	tglx