[PATCH] perf/arm-dmc620: Reverse locking order in dmc620_pmu_get_irq()

[Waiman Long]

The following circular locking dependency was reported when running
cpus online/offline test on an arm64 system.

[   84.195923] Chain exists of:
                 dmc620_pmu_irqs_lock --> cpu_hotplug_lock --> cpuhp_state-down

[   84.207305]  Possible unsafe locking scenario:

[   84.213212]        CPU0                    CPU1
[   84.217729]        ----                    ----
[   84.222247]   lock(cpuhp_state-down);
[   84.225899]                                lock(cpu_hotplug_lock);
[   84.232068]                                lock(cpuhp_state-down);
[   84.238237]   lock(dmc620_pmu_irqs_lock);
[   84.242236]
                *** DEADLOCK ***

The problematic locking order seems to be

	lock(dmc620_pmu_irqs_lock) --> lock(cpu_hotplug_lock)

This locking order happens when dmc620_pmu_get_irq() is called from
dmc620_pmu_device_probe(). Fix this possible deadlock scenario by
reversing the locking order.

Also export __cpuhp_state_add_instance_cpuslocked() so that it can be
accessed by kernel modules.

Signed-off-by: Waiman Long <longman at redhat.com>
---
 drivers/perf/arm_dmc620_pmu.c | 4 +++-
 kernel/cpu.c                  | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/perf/arm_dmc620_pmu.c b/drivers/perf/arm_dmc620_pmu.c
index 54aa4658fb36..78d3bfbe96a6 100644
--- a/drivers/perf/arm_dmc620_pmu.c
+++ b/drivers/perf/arm_dmc620_pmu.c
@@ -425,7 +425,7 @@ static struct dmc620_pmu_irq *__dmc620_pmu_get_irq(int irq_num)
 	if (ret)
 		goto out_free_irq;
 
-	ret = cpuhp_state_add_instance_nocalls(cpuhp_state_num, &irq->node);
+	ret = cpuhp_state_add_instance_nocalls_cpuslocked(cpuhp_state_num, &irq->node);
 	if (ret)
 		goto out_free_irq;
 
@@ -445,9 +445,11 @@ static int dmc620_pmu_get_irq(struct dmc620_pmu *dmc620_pmu, int irq_num)
 {
 	struct dmc620_pmu_irq *irq;
 
+	cpus_read_lock();
 	mutex_lock(&dmc620_pmu_irqs_lock);
 	irq = __dmc620_pmu_get_irq(irq_num);
 	mutex_unlock(&dmc620_pmu_irqs_lock);
+	cpus_read_unlock();
 
 	if (IS_ERR(irq))
 		return PTR_ERR(irq);
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6c0a92ca6bb5..05daaef362e6 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2036,6 +2036,7 @@ int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state,
 	mutex_unlock(&cpuhp_state_mutex);
 	return ret;
 }
+EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance_cpuslocked);
 
 int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
 			       bool invoke)
-- 
2.31.1