linux-kernel - Re: [Xen-devel] [PATCH] xen/x86: Don't BUG on CPU0 offlining

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Message-ID: <877ezwvzsw.fsf@vitty.brq.redhat.com>
Date:   Wed, 28 Jun 2017 18:31:59 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     xen-devel@...ts.xenproject.org, Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] xen/x86: Don't BUG on CPU0 offlining

Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> writes:

> On Mon, Jun 26, 2017 at 06:39:30PM +0200, Vitaly Kuznetsov wrote:
>> CONFIG_BOOTPARAM_HOTPLUG_CPU0 allows to offline CPU0 but Xen HVM guests
>> BUG() in xen_teardown_timer(). Remove the BUG_ON(), this is probably a
>> leftover from ancient times when CPU0 hotplug was impossible, it works
>> just fine for HVM.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>
> Perhaps:
>
> BUG_ON(cpu == 0 && xen_pv_domain()); 
>

Linus says no BUG_ONs :-)

xen_pv_cpu_disable() has the following:

    if (cpu == 0)
            return -EBUSY;

as a protection so we won't get to xen_teardown_timer() but if you think
additional BUG_ON() protection is justified I'm definitely not against
adding it.

-- 
  Vitaly