[PATCH] bus: arm-ccn: Handle correctly no-more-cpus case

[PATCH] bus: arm-ccn: Handle correctly no-more-cpus case

[Pawel Moll]

When migrating events the driver picks another cpu using
cpumask_any_but() function, which returns value >= nr_cpu_ids
when there is none available, not a negative value as the code
assumed. Fixed now.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
---
Another day, another arm-ccn.c update...

This time Dan's static checker spotted unsigned int target
being expected to carry negative values. Fixed now.

Interestingly enough, cpumask_any_but() implementation (and its
normal prototype) returns int, but version for NR_CPUS == 1 case,
inlined in linux/cpumask.h returns unsigned int...

 drivers/bus/arm-ccn.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/bus/arm-ccn.c b/drivers/bus/arm-ccn.c
index 7d9879e..cc322fb 100644
--- a/drivers/bus/arm-ccn.c
+++ b/drivers/bus/arm-ccn.c
@@ -1184,7 +1184,7 @@ static int arm_ccn_pmu_cpu_notifier(struct notifier_block *nb,
 		if (!cpumask_test_and_clear_cpu(cpu, &dt->cpu))
 			break;
 		target = cpumask_any_but(cpu_online_mask, cpu);
-		if (target < 0)
+		if (target >= nr_cpu_ids)
 			break;
 		perf_pmu_migrate_context(&dt->pmu, cpu, target);
 		cpumask_set_cpu(target, &dt->cpu);
-- 
2.1.0

[PATCH] bus: arm-ccn: Handle correctly no-more-cpus case

[Mark Rutland]

On Thu, May 14, 2015 at 11:50:24AM +0100, Pawel Moll wrote:
> When migrating events the driver picks another cpu using
> cpumask_any_but() function, which returns value >= nr_cpu_ids
> when there is none available, not a negative value as the code
> assumed. Fixed now.

The fix looks good to me:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Does this need to be CC'd to stable? What does perf_pmu_migrate_context
do when passed a target >= nr_cpus?

The original bug seems to have been copied over from arm-cci.c, which
will need the same fix. That appears to be my fault -- I'd mostly been
following the x86 uncore PMU drivers, but they figure out the target CPU
in a different way for which -1 is a sane error case.

I'll spin a patch for arm-cci.c momentarily.

Thanks,
Mark.

> 
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Pawel Moll <pawel.moll@arm.com>
> ---
> Another day, another arm-ccn.c update...
> 
> This time Dan's static checker spotted unsigned int target
> being expected to carry negative values. Fixed now.
> 
> Interestingly enough, cpumask_any_but() implementation (and its
> normal prototype) returns int, but version for NR_CPUS == 1 case,
> inlined in linux/cpumask.h returns unsigned int...
> 
>  drivers/bus/arm-ccn.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/arm-ccn.c b/drivers/bus/arm-ccn.c
> index 7d9879e..cc322fb 100644
> --- a/drivers/bus/arm-ccn.c
> +++ b/drivers/bus/arm-ccn.c
> @@ -1184,7 +1184,7 @@ static int arm_ccn_pmu_cpu_notifier(struct notifier_block *nb,
>  		if (!cpumask_test_and_clear_cpu(cpu, &dt->cpu))
>  			break;
>  		target = cpumask_any_but(cpu_online_mask, cpu);
> -		if (target < 0)
> +		if (target >= nr_cpu_ids)
>  			break;
>  		perf_pmu_migrate_context(&dt->pmu, cpu, target);
>  		cpumask_set_cpu(target, &dt->cpu);
> -- 
> 2.1.0
> 

[PATCH] bus: arm-ccn: Handle correctly no-more-cpus case

[Mark Rutland]

On Thu, May 14, 2015 at 12:04:28PM +0100, Mark Rutland wrote:
> On Thu, May 14, 2015 at 11:50:24AM +0100, Pawel Moll wrote:
> > When migrating events the driver picks another cpu using
> > cpumask_any_but() function, which returns value >= nr_cpu_ids
> > when there is none available, not a negative value as the code
> > assumed. Fixed now.
> 
> The fix looks good to me:
> 
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> 
> Does this need to be CC'd to stable? What does perf_pmu_migrate_context
> do when passed a target >= nr_cpus?

Never mind, it looks like we can never encounter that case anyway. In
the case of kexec or reset we won't notify CPU_DOWN_PREPARE on the final
CPU, and we can't hotplug the final CPU.

Which means that the target check is irrelevant as we should always get
a valid cpu back from cpumask_any_but in the cases we'll call it. So we
could just delete it entirely, assuming I haven't missed a
CPU_DOWN_PREPARE notification path...

Mark.

> > diff --git a/drivers/bus/arm-ccn.c b/drivers/bus/arm-ccn.c
> > index 7d9879e..cc322fb 100644
> > --- a/drivers/bus/arm-ccn.c
> > +++ b/drivers/bus/arm-ccn.c
> > @@ -1184,7 +1184,7 @@ static int arm_ccn_pmu_cpu_notifier(struct notifier_block *nb,
> >  		if (!cpumask_test_and_clear_cpu(cpu, &dt->cpu))
> >  			break;
> >  		target = cpumask_any_but(cpu_online_mask, cpu);
> > -		if (target < 0)
> > +		if (target >= nr_cpu_ids)
> >  			break;
> >  		perf_pmu_migrate_context(&dt->pmu, cpu, target);
> >  		cpumask_set_cpu(target, &dt->cpu);
> > -- 
> > 2.1.0
> > 
> 
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