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 following locking order happens when dmc620_pmu_get_irq() calls
cpuhp_state_add_instance_nocalls().

	lock(dmc620_pmu_irqs_lock) --> lock(cpu_hotplug_lock)

On the other hand, the calling sequence

  cpuhp_thread_fun()
    => cpuhp_invoke_callback()
      => dmc620_pmu_cpu_teardown()

leads to the locking sequence

	lock(cpuhp_state-down) => lock(dmc620_pmu_irqs_lock)

Here dmc620_pmu_irqs_lock protects both the dmc620_pmu_irqs and the
pmus_node lists in various dmc620_pmu instances. dmc620_pmu_get_irq()
requires protected access to dmc620_pmu_irqs whereas
dmc620_pmu_cpu_teardown() needs protection to the pmus_node lists.
Break this circular locking dependency by using two separate locks to
protect dmc620_pmu_irqs list and the pmus_node lists respectively.
Suggested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20230812235549.494174-1-longman@redhat.comSigned-off-by: Will Deacon <will@kernel.org>