Re: [GIT pull] smp/hotplug: Removal of notifiers

From: Borislav Petkov
Date: Mon Dec 26 2016 - 16:00:33 EST

On Mon, Dec 26, 2016 at 07:21:44PM +0100, Thomas Gleixner wrote:
> Is there anything interesting error message before the BUG hits? I'll try
> to reproduce on a AMD box tomorrow.

Hmm, so lemme see if I see it correctly:

threshold_create_bank() does kobject_create_and_add(name, &dev->kobj);
and that dev thing is

struct device *dev = per_cpu(mce_device, cpu);

BUT(!), those mce_device per-CPU things get initialized in

|-> mce_device_create(cpu);

With a CONFIG_HOTPLUG_CPU=n .config that doesn't happen, right?

Oh, and I see what could've changed that:

8c0eeac819c8 ("x86/mcheck: Move CPU_ONLINE and CPU_DOWN_PREPARE to hotplug state machine")

And before that, we did call mce_device_create(cpu) in
mcheck_init_device() which is a device initcall and not dependent on CPU

And frankly, flipping back to the for_each_online_cpu(i) is yucky as
hell but I don't see any other/better solution besides pulling up
mce_device_create() into mcheck_init_device()...



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