From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH v2 6/8] kvm tools: Add rwlock wrapper
Date: Fri, 3 Jun 2011 09:34:27 +0200
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Cc: Avi Kivity <avi@redhat.com>,
	Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>,
	Pekka Enberg <penberg@kernel.org>, kvm@vger.kernel.org,
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To: Sasha Levin <levinsasha928@gmail.com>,
	Yinghai Lu <yinghai@kernel.org>
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* Sasha Levin <levinsasha928@gmail.com> wrote:

> > with no apparent progress being made.
> 
> Since it's something that worked in 2.6.37, I've looked into it to 
> find what might have caused this issue.
> 
> I've bisected guest kernels and found that the problem starts with:
> 
> a26ac2455ffcf3be5c6ef92bc6df7182700f2114 is the first bad commit
> commit a26ac2455ffcf3be5c6ef92bc6df7182700f2114
> Author: Paul E. McKenney <paul.mckenney@linaro.org>
> Date:   Wed Jan 12 14:10:23 2011 -0800
> 
>     rcu: move TREE_RCU from softirq to kthread
> 
> Ingo, could you confirm that the problem goes away for you when you 
> use an earlier commit?

testing will have to wait, but there's a recent upstream fix:

  d72bce0e67e8: rcu: Cure load woes

That *might* perhaps address this problem too.

If not then this appears to be some sort of RCU related livelock with 
brutally overcommitted vcpus. On native this would show up too, in a 
less drastic form, as a spurious bootup delay.

Thanks,

	Ingo