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

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Date:   Mon, 26 Dec 2016 22:00:15 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Markus Trippelsdorf <markus@...ppelsdorf.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [GIT pull] smp/hotplug: Removal of notifiers

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_cpu_online()
|-> 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
hotplug.

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()...

Hmmm.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--