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

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:

quoted

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.

quoted

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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