On Thu, 27 Jul 2017, Thomas Gleixner wrote: > On Thu, 27 Jul 2017, Michael Ellerman wrote: > > Thomas Gleixner <t...@linutronix.de> writes: > > > > > 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() > > > > Great thanks. > > > > Patch on the way. > > Hmm. Second thoughts. The issue is the stability of the CPUs. Surely the > boot CPU can't go away at that point, but the debug stuff does not know > about it. maybe I'm missing something ....
Ok. Now seeing your patch I know what I was missing :)