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SubjectRe: [PATCH v2 2/2] perf/arm-ccn: Remove broken race mitigation
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Hi Robin,

On 03/04/2019 18:10, Robin Murphy wrote:
> Like arm-cci, arm-ccn has the same issue of disabling preemption around
> operations which can take mutexes. Again, remove the definite bug by
> simply not trying to fight the theoretical races. And since we are
> touching the hotplug handling code, take the opportunity to streamline
> it, as there's really no need to store a full-sized cpumask to keep
> track of a single CPU ID.
>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> drivers/perf/arm-ccn.c | 23 +++++++++++------------
> 1 file changed, 11 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/perf/arm-ccn.c b/drivers/perf/arm-ccn.c
> index 2ae76026e947..a0214308b0cd 100644
> --- a/drivers/perf/arm-ccn.c
> +++ b/drivers/perf/arm-ccn.c

> /* Pick one CPU which we will use to collect data from CCN... */
> - cpumask_set_cpu(get_cpu(), &ccn->dt.cpu);
> + ccn->dt.cpu = raw_smp_processor_id();
>
> /* Also make sure that the overflow interrupt is handled by this CPU */
> if (ccn->irq) {
> - err = irq_set_affinity_hint(ccn->irq, &ccn->dt.cpu);
> + err = irq_set_affinity_hint(ccn->irq, cpumask_of(ccn->dt.cpu));
> if (err) {
> dev_err(ccn->dev, "Failed to set interrupt affinity!\n");
> goto error_set_affinity;
> }
> }
>
> + cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE,
> + &ccn->dt.node);
> +
> err = perf_pmu_register(&ccn->dt.pmu, name, -1);
> if (err)
> goto error_pmu_register;

Should we not remove the above instance, in case we fail to register
the PMU ? Similarly for the CCI driver, we may have to reset the g_cci_pmu
if we fail.

Cheers
Suzuki


>
> - cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE,
> - &ccn->dt.node);
> - put_cpu();
> return 0;
>
> error_pmu_register:
> error_set_affinity:
> - put_cpu();
> error_choose_name:
> ida_simple_remove(&arm_ccn_pmu_ida, ccn->dt.id);
> for (i = 0; i < ccn->num_xps; i++)
>

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