On Wed, 26 Jul 2017, Michael Ellerman wrote:
> Hi Thomas,
>
> I'm seeing the lockdep barf below on some bare metal Power8 machines.
>
> This seems to be caused by our smp_cpus_done(), which does:
>
> void __init smp_cpus_done(unsigned int max_cpus)
> {
> /*
> * We want the setup_cpu() here to be called on the boot CPU, but
> * init might run on any CPU, so make sure it's invoked on the boot
> * CPU.
> */
> if (smp_ops && smp_ops->setup_cpu)
> work_on_cpu_safe(boot_cpuid, smp_setup_cpu_workfn, NULL);
>
>
> I don't think CPU hotplug can happen at this point, so I don't think
> there's really a bug.
>
> But it looks like the work_on_cpu_safe() call could just go away, since
> you pinned init to the boot CPU in 8fb12156b8db ("init: Pin init task to
> the boot CPU, initially"). Though I can't see where init is unpinned, so
> maybe we do still need to do it?
It's undone in sched_init_smp(). So it looks safe. The call order is:
smp_init()
...
smp_cpus_done()
sched_init_smp()
Thanks,
tglx
