Patch "bus: arm-cci: Fix use of smp_processor_id() in preemptible context" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

bus: arm-cci: Fix use of smp_processor_id() in preemptible context

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
bus-arm-cci-fix-use-of-smp_processor_id-in-preemptible-context.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Marc Zyngier <[email protected]>
Date: Tue, 3 Oct 2017 18:14:13 +0100
Subject: bus: arm-cci: Fix use of smp_processor_id() in preemptible context

From: Marc Zyngier <[email protected]>

commit 4608af8aa53e7f3922ddee695d023b7bcd5cb35b upstream.

The ARM CCI driver seem to be using smp_processor_id() in a preemptible context, which is likely to make a DEBUG_PREMPT kernel scream at boot time.

Turn this into a get_cpu()/put_cpu() that extends over the CPU hotplug registration, making sure that we don't race against a CPU down operation.

---
 drivers/bus/arm-cci.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

@@ -1755,14 +1755,17 @@ static int cci_pmu_probe(struct platform
 	raw_spin_lock_init(&cci_pmu->hw_events.pmu_lock);
 	mutex_init(&cci_pmu->reserve_mutex);
 	atomic_set(&cci_pmu->active_events, 0);
-	cpumask_set_cpu(smp_processor_id(), &cci_pmu->cpus);
+	cpumask_set_cpu(get_cpu(), &cci_pmu->cpus);
 
 	ret = cci_pmu_init(cci_pmu, pdev);
-	if (ret)
+	if (ret) {
+		put_cpu();
 		return ret;
+	}
 
 	cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCI_ONLINE,
 					 &cci_pmu->node);
+	put_cpu();
 	pr_info("ARM %s PMU driver probed", cci_pmu->model->name);
 	return 0;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/arm-kvm-fix-vttbr_baddr_mask-bug_on-off-by-one.patch queue-4.9/kvm-arm-arm64-vgic-its-check-result-of-allocation-before-use.patch queue-4.9/kvm-arm-arm64-vgic-irqfd-fix-msi-entry-allocation.patch queue-4.9/bus-arm-cci-fix-use-of-smp_processor_id-in-preemptible-context.patch queue-4.9/arm64-kvm-fix-vttbr_baddr_mask-bug_on-off-by-one.patch queue-4.9/bus-arm-ccn-fix-use-of-smp_processor_id-in-preemptible-context.patch