linux-kernel - Re: Oops from calibrate_delay_is_known on qemu machine with Linux v4.5-1523-g271ecc5253e2

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Date:	Thu, 17 Mar 2016 18:30:38 +0000
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	Josh Boyer <jwboyer@...oraproject.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, x86 <x86@...nel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: Oops from calibrate_delay_is_known on qemu machine with Linux
 v4.5-1523-g271ecc5253e2

On Thu, Mar 17, 2016 at 01:54:36PM -0400, Josh Boyer wrote:
> Hi Thomas,
> 
> We've had a report [1] of the mainline kernel crashing on a single-cpu
> QEMU machine (not kvm) in Fedora.  It looks as if the emulated machine
> is failing to provide a TSC and the calibrate_delay_is_known function
> is passing NULL to cpumask_any_but for the mask parameter.  At least
> that's all I've been able to discern thus far.
> 
> I was wondering if you had any insight into this issue, given your
> recent commit to change calibrate_delay_is_known to use
> topology_core_cpumask.  The backtrace is below.

Thanks for reporting this upstream Josh.

I've added to the bug a simple test script that reproduces the issue,
not 100% reliably by any means, but some of the time.  See:

  https://bugzilla.redhat.com/show_bug.cgi?id=1318596#c6

Rich.

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