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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
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