linux-kernel - Re: [PATCH v2] xen: avoid crash in disable_hotplug

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Message-ID: <a1248fa4-793e-5aef-bd5d-4691d289a114@suse.com>
Date:   Fri, 7 Sep 2018 07:15:22 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Olaf Hering <olaf@...fle.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     xen-devel@...ts.xenproject.org,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] xen: avoid crash in disable_hotplug_cpu

On 06/09/18 22:31, Olaf Hering wrote:
> Am Thu, 6 Sep 2018 14:45:57 -0400
> schrieb Boris Ostrovsky <boris.ostrovsky@...cle.com>:
> 
>> On 09/06/2018 02:37 AM, Olaf Hering wrote:
>>> The command 'xl vcpu-set 0 0', issued in dom0, will crash dom0:
> 
>>> This happens because handle_vcpu_hotplug_event is called twice. In the
>>> first iteration cpu_present is still true, in the second iteration
>>> cpu_present is false which causes get_cpu_device to return NULL.
>>> In case of cpu#0, cpu_online is apparently always true.
> 
>> I think we should check both this and num_online_cpus() != 0.
> 
> This can not possibly help. cpu#0 is the first one that goes offline.
> IF cpu0_hotpluggable is broken, then only "if (!cpu) return;" can help.

We should add the Xen PV guest test to arch_register_cpu() and switch
cpu0_hotpluggable off.


Juergen