Patch "bus: arm-ccn: Fix use of smp_processor_id() in preemptible context" has been added to the 4.14-stable tree

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

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

to the 4.14-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-ccn-fix-use-of-smp_processor_id-in-preemptible-context.patch
and it can be found in the queue-4.14 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 18:14:12 +0100
Subject: bus: arm-ccn: Fix use of smp_processor_id() in preemptible context

From: Marc Zyngier <[email protected]>

commit b18c2b9487d8e797fc0a757e57ac3645348c5fba upstream.

Booting a DEBUG_PREEMPT enabled kernel on a CCN-based system results in the following splat:

[...]
arm-ccn e8000000.ccn: No access to interrupts, using timer.

BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
caller is debug_smp_processor_id+0x1c/0x28
CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.13.0 #6111
Hardware name: AMD Seattle/Seattle, BIOS 17:08:23 Jun 26 2017
Call trace:
[<ffff000008089e78>] dump_backtrace+0x0/0x278
[<ffff00000808a22c>] show_stack+0x24/0x30
[<ffff000008bc3bc4>] dump_stack+0x8c/0xb0
[<ffff00000852b534>] check_preemption_disabled+0xfc/0x100
[<ffff00000852b554>] debug_smp_processor_id+0x1c/0x28
[<ffff000008551bd8>] arm_ccn_probe+0x358/0x4f0

[...]

as we use smp_processor_id() in the wrong context.

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-ccn.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

@@ -1301,7 +1301,7 @@ static int arm_ccn_pmu_init(struct arm_c
 	}
 
 	/* Pick one CPU which we will use to collect data from CCN... */
-	cpumask_set_cpu(smp_processor_id(), &ccn->dt.cpu);
+	cpumask_set_cpu(get_cpu(), &ccn->dt.cpu);
 
 	/* Also make sure that the overflow interrupt is handled by this CPU */
 	if (ccn->irq) {

@@ -1318,10 +1318,12 @@ static int arm_ccn_pmu_init(struct arm_c
 
 	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++)

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

queue-4.14/arm-kvm-fix-vttbr_baddr_mask-bug_on-off-by-one.patch queue-4.14/kvm-arm-arm64-vgic-its-check-result-of-allocation-before-use.patch queue-4.14/kvm-arm-arm64-vgic-preserve-the-revious-read-from-the-pending-table.patch queue-4.14/kvm-arm-arm64-vgic-irqfd-fix-msi-entry-allocation.patch queue-4.14/bus-arm-cci-fix-use-of-smp_processor_id-in-preemptible-context.patch queue-4.14/arm64-kvm-fix-vttbr_baddr_mask-bug_on-off-by-one.patch queue-4.14/bus-arm-ccn-fix-use-of-smp_processor_id-in-preemptible-context.patch