linux-kernel - Re: [PANIC, hyperv] BUG: unable to handle kernel paging request at ffff880077800004 (hv_ringbuffer

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Date:	Wed, 20 Aug 2014 12:40:14 +0100
From:	Sitsofe Wheeler <sitsofe@...il.com>
To:	Dexuan Cui <decui@...rosoft.com>
Cc:	KY Srinivasan <kys@...rosoft.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	Kylie Liang <kyliel@...rosoft.com>
Subject: Re: [PANIC, hyperv] BUG: unable to handle kernel paging request at
 ffff880077800004 (hv_ringbuffer_write)

Hi,

On Wed, Aug 20, 2014 at 11:15:39AM +0000, Dexuan Cui wrote:
> > -----Original Message-----
> > From: Sitsofe Wheeler
> > Sent: Wednesday, August 20, 2014 17:27 PM
> > To: Dexuan Cui
> > Cc: KY Srinivasan; Greg Kroah-Hartman; Haiyang Zhang;
> > devel@...uxdriverproject.org; linux-kernel@...r.kernel.org; Jean-Christophe
> > Plagniol-Villard; linux-fbdev@...r.kernel.org
> > 
> > While booting a Hyper-V 3.17.0-rc1 guest on a 2012 R2 host a BUG was
> > triggered while registering hyperv_fb which in turn caused a panic.
> > Various kernel debugging options (CONFIG_DEBUG_PAGEALLOC,
> > CONFIG_SLUB_DEBUG=y...) were on at the time. This only seems to happen
> > if the guest is being booted with only one CPU allocated to it.
> > 
> > [    7.645526] hv_vmbus: registering driver hyperv_fb
> > [    7.657553] BUG: unable to handle kernel paging request at
> > ffff880077800004
> > [    7.658224] IP: [<ffffffff8159a7ac>] hv_ringbuffer_write+0x7c/0x150
> > [    7.658224] PGD 2da9067 PUD 2dac067 PMD 7fa27067 PTE
> > 8000000077800060
> > [    7.658224] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
>
> Thanks for reporting the issue!

You're welcome!

> I suppose you're using  the latest mainline v3.17-rc1(7d1311b9).

That's right - Linux 3.17-rc1
(7d1311b93e58ed55f3a31cc8f94c4b8fe988a2b9).

> Can you please attach your kernel config file so that I can try to reproduce
> the issue more easily?

Sure (it's pretty much the same one mentioned in
https://lkml.org/lkml/2014/8/19/101 and
https://lkml.org/lkml/2014/8/19/708 but those don't seem framebuffer
related) but just in case I'll attach it to this mail.

> Do you mean the issue only happens to UP guest and doesn't happen to
> SMP guest?

Yes - if in Windows I go to Hyper-V Manager, press the right mouse
button over the guest and go to Settings..., click on Processor at the
left and set the Number of virtual processors to 1 on the right then
this issue occurs. If the number is greater than 1 then this does not
seem to occur.

-- 
Sitsofe | http://sucs.org/~sits/

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