linux-kernel - Re: 2.6.35 hangs on early boot in KVM

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Message-ID: <201008040909.31853.tvrtko.ursulin@sophos.com>
Date:	Wed, 4 Aug 2010 09:09:31 +0100
From:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Avi Kivity <avi@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: 2.6.35 hangs on early boot in KVM

On Tuesday 03 Aug 2010 21:37:06 Eric W. Biederman wrote:
> Tvrtko Ursulin <tvrtko.ursulin@...hos.com> writes:
> > On Tuesday 03 Aug 2010 16:17:20 Tvrtko Ursulin wrote:
> >> On Tuesday 03 Aug 2010 15:57:03 Tvrtko Ursulin wrote:
> >> > On Tuesday 03 Aug 2010 15:51:08 Avi Kivity wrote:
> >> > >   On 08/03/2010 12:28 PM, Tvrtko Ursulin wrote:
> >> > > > I have basically built 2.6.35 with make oldconfig from a working
> >> > > > 2.6.34. Latter works fine in kvm while 2.6.35 hangs very early. I
> >> > > > see nothing after grub (have early printk and verbose bootup
> >> > > > enabled), just a blinking VGA cursor and CPU at 100%.
> >> > >
> >> > > Please copy kvm@...r.kernel.org on kvm issues.
> >> > >
> >> > > > CONFIG_PRINTK_TIME=y
> >> > >
> >> > > Try disabling this as a workaround.
> >> >
> >> > I am in the middle of a bisect run with five builds left to go,
> >> > currently I have:
> >> >
> >> > bad 537b60d17894b7c19a6060feae40299d7109d6e7
> >> > good 93c9d7f60c0cb7715890b1f9e159da6f4d1f5a65
> >>
> >> Bisect is looking good, narrowed it to ten revisions, but I am not sure
> >> to make it to the end today:
> >>
> >> bad cb41838bbc4403f7270a94b93a9a0d9fc9c2e7ea
> >> good 41d59102e146a4423a490b8eca68a5860af4fe1c
> >
> > Bisect points the finger to "x86, ioapic: In mpparse use
> > mp_register_ioapic" (cf7500c0ea133d66f8449d86392d83f840102632), so I am
> > copying Eric. No idea whether this commit is solely to blame or it is a
> > combined interaction with KVM, but I am sure you guys will know.
> >
> > If you want me to test something else please shout.
>
> Interesting.  This is the second report I have heard of no VGA output
> and a hang early in boot, that was bisected to this commit.  Since I
> could not reproduce it I was hoping it was a fluke with a single piece
> of hardware, but it appears not.
>
> There was in fact an off by one bug in that commit, but if that had
> been the issue 2.6.35 would have booted ok.  There was nothing in that
> commit that should have prevented early output, and in fact I can boot
> with a very similar configuration. So I am trying to figure out what
> pieces are interacting to cause this failure mode to happen.
>
> What version of kvm are you running on your host (in case that matters)?
>
> I want to reproduce this myself so I can start guessing what weird
> interactions are going on.

Host is stock openSUSE 11.3 with kvm-0.12.3-2.9.x86_64 and kernel-
desktop-2.6.34-12.3.x86_64. Plus a repeat of my .config if it helps.

Tvrtko



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