Date: Mon, 26 Dec 2016 22:16:26 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Borislav Petkov <bp@alien8.de>
cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Markus Trippelsdorf <markus@trippelsdorf.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [GIT pull] smp/hotplug: Removal of notifiers
In-Reply-To: <20161226210015.GA2945@nazgul.tnic>
Message-ID: <alpine.DEB.2.20.1612262215130.3687@nanos>
References: <alpine.DEB.2.20.1612251431340.3605@nanos> <20161226074530.GA297@x4> <20161226110600.GB297@x4> <20161226154502.GA287@x4> <53e3b52b-f353-63c8-f96f-649d754596bc@oracle.com> <alpine.DEB.2.20.1612261918360.3605@nanos>
 <20161226210015.GA2945@nazgul.tnic>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1253
Lines: 37

On Mon, 26 Dec 2016, Borislav Petkov wrote:
> 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()...

The hotplug callbacks are invoked even with HOTPLUG=n. So that's not the
problem. I can reproduce it. Will post info once I understand it.

Thanks,

	tglx