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

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Message-ID: <11c26286-cd13-f922-9113-580483181d26@suse.com>
Date:   Thu, 29 Jun 2017 09:02:53 +0200
From:   Juergen Groß <jgross@...e.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     xen-devel@...ts.xenproject.org,
        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

On 06/28/2017 06:31 PM, Vitaly Kuznetsov wrote:
> 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.

No, I don't think its needed. This should be handled at the appropriate
level, not down in the timer handling.

So:

Acked-by: Juergen Gross <jgross@...e.com>


Juergen