Re: [PATCH 1/2] powerpc/rtas: use device model APIs and serialization during LPM

Nathan Lynch [off-list ref] writes:

During LPAR migration, cpu hotplug and migration operations can
interleave like so:

cd /sys/devices/system/cpu/cpu7/ | drmgr -m -c pmig -p pre \
echo 0 > online                  | -s 0xd7a884f83d830e6d -t 19 \
echo 1 > online                  | -n -d 1 5
---------------------------------+-------------------------------------------
online_store() {                 |
  device_offline() {             |
    cpu_subsys_offline() {       |
      cpu_down(7);               |
    }                            |
    dev->offline = true;         |
  }                              | migration_store() {
}                                |   rtas_ibm_suspend_me() {
                                 |     rtas_online_cpus_mask() {
                                 |       cpu_up(7);
				 |     }
                                 |     cpu_hotplug_disable();
                                 |     on_each_cpu(rtas_percpu_suspend_me());
                                 |     cpu_hotplug_enable();
online_store() {                 |
  device_online() {              |
    cpu_subsys_online() {        |
      cpu_up(7);                 |
    }                            |
    dev->offline = false;        |
  }                              |     rtas_offline_cpus_mask() {
}                                |       rtas_cpu_state_change_mask() {
                                 |         cpu_down(7);
				 |       }
				 |     }
				 |   }
				 | }

Actually I think this isn't a correct depiction of the race. I'll
rewrite and resend.