Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <ece36eb1-253a-8ec6-c183-309c10bb35d5@redhat.com>
In-Reply-To: <ece36eb1-253a-8ec6-c183-309c10bb35d5@redhat.com>
From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Wed, 29 Jul 2020 09:00:22 +0800
Message-ID: <CANRm+Cywhi1p5gYLfG=JcyTdYuWK+9bGqF6HD-LiBJM9Q5ykNQ@mail.gmail.com>
Subject: Re: WARNING: suspicious RCU usage - while installing a VM on a CPU
 listed under nohz_full
To:     Nitesh Narayan Lal <nitesh@redhat.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        KVM list <kvm@vger.kernel.org>,
        Wanpeng Li <wanpengli@tencent.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Liran Alon <liran.alon@oracle.com>,
        "frederic@kernel.org" <frederic@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Juri Lelli <juri.lelli@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 28 Jul 2020 at 22:40, Nitesh Narayan Lal <nitesh@redhat.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.