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

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Message-ID: <CANRm+Cywhi1p5gYLfG=JcyTdYuWK+9bGqF6HD-LiBJM9Q5ykNQ@mail.gmail.com>
Date:   Wed, 29 Jul 2020 09:00:22 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Nitesh Narayan Lal <nitesh@...hat.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 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.

I still can reproduce this after removing the ipi/timer fastpath
codes, anyway, I will have a look.