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Re: 4.5.0+ panic when setup loop device

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: 4.5.0+ panic when setup loop device
Date 2016-03-18 09:00 +0100
Message-ID <rdXua-2C8-7@gated-at.bofh.it> (permalink)
References <rddrk-53G-5@gated-at.bofh.it> <rdlyy-2jP-3@gated-at.bofh.it> <rdvod-yw-1@gated-at.bofh.it> <rdCSL-5Ht-39@gated-at.bofh.it> <rdU3g-vw-5@gated-at.bofh.it>
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On Fri, Mar 18, 2016 at 05:11:54AM +0100, Mike Galbraith wrote:
> On Thu, 2016-03-17 at 10:52 +0100, Peter Zijlstra wrote:
> 
> > Andreas; Borislav said to Cc you since you wrote all this.
> > The issue is that Linux assumes:
> > 
> > 	> nr_logical_cpus = nr_cores * nr_siblings
> 
> It also seems to now assume that if SMT is possible, it's enabled.

Urgh..

What I think, with my pre wakeup brain, happens is that the CPUID
topology muck still reports 2 siblings (it tends to do that).

But the BIOS only reports APIC-IDs for all your cores, so our
nr_cpu_ids is reduced, while the nr_siblings count it not.

And them *boom*.

This is the same old problem that is nearly impossible to tell if HT is
enabled or not -- complete and utter trainwreck :/

I need to go make wake-up-juice and ponder wth to do about this.

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Thread

Re: 4.5.0+ panic when setup loop device Thomas Gleixner <tglx@linutronix.de> - 2016-03-16 16:30 +0100
  Re: 4.5.0+ panic when setup loop device Peter Zijlstra <peterz@infradead.org> - 2016-03-17 11:00 +0100
  Re: 4.5.0+ panic when setup loop device Peter Zijlstra <peterz@infradead.org> - 2016-03-17 11:00 +0100
    Re: 4.5.0+ panic when setup loop device Thomas Gleixner <tglx@linutronix.de> - 2016-03-17 11:30 +0100
      Re: 4.5.0+ panic when setup loop device Peter Zijlstra <peterz@infradead.org> - 2016-03-17 11:30 +0100
        Re: 4.5.0+ panic when setup loop device Thomas Gleixner <tglx@linutronix.de> - 2016-03-17 12:50 +0100
          Re: 4.5.0+ panic when setup loop device Peter Zijlstra <peterz@infradead.org> - 2016-03-17 13:00 +0100
            Re: 4.5.0+ panic when setup loop device Borislav Petkov <bp@alien8.de> - 2016-03-17 13:00 +0100
            Re: 4.5.0+ panic when setup loop device Thomas Gleixner <tglx@linutronix.de> - 2016-03-17 13:10 +0100
              Re: 4.5.0+ panic when setup loop device Jens Axboe <axboe@kernel.dk> - 2016-03-17 17:50 +0100
                Re: 4.5.0+ panic when setup loop device Jens Axboe <axboe@kernel.dk> - 2016-03-17 19:30 +0100
                Re: 4.5.0+ panic when setup loop device Jens Axboe <axboe@kernel.dk> - 2016-03-17 21:30 +0100
                Re: 4.5.0+ panic when setup loop device Thomas Gleixner <tglx@linutronix.de> - 2016-03-17 21:40 +0100
                Re: 4.5.0+ panic when setup loop device Jens Axboe <axboe@kernel.dk> - 2016-03-17 21:50 +0100
                Re: 4.5.0+ panic when setup loop device Thomas Gleixner <tglx@linutronix.de> - 2016-03-17 21:30 +0100
          Re: 4.5.0+ panic when setup loop device Xiong Zhou <jencce.kernel@gmail.com> - 2016-03-18 03:40 +0100
    Re: 4.5.0+ panic when setup loop device Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-18 05:20 +0100
      Re: 4.5.0+ panic when setup loop device Peter Zijlstra <peterz@infradead.org> - 2016-03-18 09:00 +0100
      Re: 4.5.0+ panic when setup loop device Peter Zijlstra <peterz@infradead.org> - 2016-03-18 11:20 +0100
        Re: 4.5.0+ panic when setup loop device Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-18 13:40 +0100
          Re: 4.5.0+ panic when setup loop device Peter Zijlstra <peterz@infradead.org> - 2016-03-18 14:40 +0100
            Re: 4.5.0+ panic when setup loop device Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-18 15:10 +0100
      Re: 4.5.0+ panic when setup loop device Thomas Gleixner <tglx@linutronix.de> - 2016-03-18 13:00 +0100
        Re: 4.5.0+ panic when setup loop device Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-03-18 13:50 +0100
        [tip:x86/urgent] x86/topology: Use total_cpus not nr_cpu_ids for  logical packages tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2016-03-19 10:40 +0100
    [tip:x86/urgent] x86/topology: Fix AMD core count tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2016-03-29 10:50 +0200

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