linux-kernel - Re: [PATCH 0/4] KVM: srcu-less dirty logging

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Message-ID: <4F4CA66F.8090109@redhat.com>
Date:	Tue, 28 Feb 2012 12:03:27 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
	mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 0/4] KVM: srcu-less dirty logging

On 02/23/2012 03:25 PM, Peter Zijlstra wrote:
> On Thu, 2012-02-23 at 20:33 +0900, Takuya Yoshikawa wrote:
> > - Stop allocating extra dirty bitmap buffer area
> > 
> >   According to Peter, mmu_notifier has become preemptible.  If we can
> >   change mmu_lock from spin_lock to mutex_lock, as Avi said before, this
> >   would be staightforward because we can use __put_user() right after
> >   xchg() with the mmu_lock held 
>
> So the 'only' thing to consider is running the end result with lockdep
> enabled since the mmu locks are rather deep in the nesting tree its very
> easy to accidentally cause inversions.

There will be an inversion for sure, if __put_user() faults and triggers
an mmu notifier (perhaps directly, perhaps through an allocation that
triggers a swap).

-- 
error compiling committee.c: too many arguments to function

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