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Date:   Sat, 29 Jun 2019 09:15:17 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Feng Tang <feng.tang@intel.com>
cc:     "Chen, Rong A" <rong.a.chen@intel.com>,
        "tipbuild@zytor.com" <tipbuild@zytor.com>,
        Ingo Molnar <mingo@kernel.org>, "lkp@01.org" <lkp@01.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org
Subject: Re: [LKP] [x86/hotplug] e1056a25da:
 WARNING:at_arch/x86/kernel/apic/apic.c:#setup_local_APIC
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Feng,

On Fri, 28 Jun 2019, Thomas Gleixner wrote:
> On Fri, 28 Jun 2019, Feng Tang wrote:
> > On Tue, Jun 25, 2019 at 07:32:03PM +0800, Thomas Gleixner wrote:
> > > the head of that branch is:
> > > 
> > >       4f3f6d6a7f8e ("x86/apic/x2apic: Add conditional IPI shorthands support")
> > > 
> > > This is WIP and force pushed. There are no incremental changes. Could you
> > > please check again?
> > 
> > Since you can't reproduce it yet, we've added some debug hook to get more
> > info, like dmesg below:
> > 
> > [  288.866069] IRR[7]: 0x1000
> > [  289.890274] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/apic/apic.c:1502 setup_local_APIC+0x2d1/0x4f0
> 
> > [  290.182418] queued = 0x1000 acked = 0
> > [  290.189159] IRR[7]: 0x1000
> > 
> > Which shows the IRR[7] was set 0x1000, IIUC, it means vector
> > 0xec, which is for LAPIC timer, and ISRs are all 0 before and
> > after the loop.
> 
> Ahhhh. That makes a lot of sense now.
> 
> That interrupt is in the IRR, but not in the ISR. So the acknowledge
> attempts are useless because the ack only clears an pending ISR and the IRR
> is not propagated because in the state in which this happens the entry is
> masked.
> 
> That function just 'works' by chance not by design. I'll stare into it and
> fix it up for real.
> 
> Thank you very much for that information. Your debug was spot on!

I rewrote that function so it actually handles that case correctly along
with some other things which were broken and force pushed the WIP.x86/ipi
branch.

Can you please run exactly that test again against that new version and
verify that this is fixed now?

Thanks,

	tglx