linux-kernel - Re: WARNING: suspicious RCU usage - while installing a VM on a CPU listed under nohz

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Message-ID: <57ea501b-bf54-3fc0-4a8f-2820df623b14@redhat.com>
Date:   Wed, 29 Jul 2020 08:34:02 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>,
        Wanpeng Li <wanpengli@...cent.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Liran Alon <liran.alon@...cle.com>,
        "frederic@...nel.org" <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: WARNING: suspicious RCU usage - while installing a VM on a CPU
 listed under nohz_full


On 7/28/20 10:38 PM, Wanpeng Li wrote:
> Hi Nitesh，
> On Wed, 29 Jul 2020 at 09:00, Wanpeng Li <kernellwp@...il.com> wrote:
>> On Tue, 28 Jul 2020 at 22:40, Nitesh Narayan Lal <nitesh@...hat.com> wrote:
>>> Hi,
>>>
>>> I have recently come across an RCU trace with the 5.8-rc7 kernel that has the
>>> debug configs enabled while installing a VM on a CPU that is listed under
>>> nohz_full.
>>>
>>> Based on some of the initial debugging, my impression is that the issue is
>>> triggered because of the fastpath that is meant to optimize the writes to x2APIC
>>> ICR that eventually leads to a virtual IPI in fixed delivery mode, is getting
>>> invoked from the quiescent state.
> Could you try latest linux-next tree? I guess maybe some patches are
> pending in linux-next tree, I can't reproduce against linux-next tree.

Sure, I will try this today.

>
-- 
Nitesh



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