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Date:   Thu, 6 Sep 2018 22:31:45 +0200
From:   Olaf Hering <olaf@aepfle.de>
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc:     xen-devel@lists.xenproject.org, Juergen Gross <jgross@suse.com>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] xen: avoid crash in disable_hotplug_cpu
Message-ID: <20180906223145.37f7009b.olaf@aepfle.de>
In-Reply-To: <b7306d7f-e827-6556-e1bb-4b934a162e46@oracle.com>
References: <20180906063712.28639-1-olaf@aepfle.de>
        <b7306d7f-e827-6556-e1bb-4b934a162e46@oracle.com>
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Am Thu, 6 Sep 2018 14:45:57 -0400
schrieb Boris Ostrovsky <boris.ostrovsky@oracle.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() !=3D 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.

Olaf

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