linux-kernel - Re: [RFC][PATCH 7/7] lockdep: spin_lock_nest

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Date:	Mon, 4 Aug 2008 18:26:57 +0200
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Dave Jones <davej@...hat.com>, Roland Dreier <rdreier@...co.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, jeremy@...p.org,
	hugh@...itas.com, mingo@...e.hu, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 7/7] lockdep: spin_lock_nest_lock()

On Mon, Aug 04, 2008 at 04:56:03PM +0200, Peter Zijlstra wrote:
> My guess is that the kvm thing attaches before there are any vma, and
> leaves after all the vma are gone. So it would never actually trigger.

Yes, lockdep seems to be fine with kvm in kernel mainline in my
current and past testing. Andrew asked me to check this long ago.

vmx ~ # zgrep LOCKDEP /proc/config.gz 
CONFIG_LOCKDEP_SUPPORT=y
CONFIG_LOCKDEP=y
CONFIG_DEBUG_LOCKDEP=y

CPA self-test:
 4k 26112 large 1997 gb 0 x 2652[ffff880000000000-ffff8800bffff000]
 miss 262144
 4k 186880 large 1683 gb 0 x 43021[ffff880000000000-ffff8800bffff000]
 miss 262144
 4k 186880 large 1683 gb 0 x 43021[ffff880000000000-ffff8800bffff000]
 miss 262144
ok.
loaded kvm module ()
apic write: bad size=1 fee00030
Ignoring de-assert INIT to vcpu 0
Ignoring de-assert INIT to vcpu 0
kvm: emulating exchange as write
apic write: bad size=1 fee00030
Ignoring de-assert INIT to vcpu 0
Ignoring de-assert INIT to vcpu 0
apic write: bad size=1 fee00030
Ignoring de-assert INIT to vcpu 0
Ignoring de-assert INIT to vcpu 0
apic write: bad size=1 fee00030
Ignoring de-assert INIT to vcpu 0
apic write: bad size=1 fee00030
Ignoring de-assert INIT to vcpu 0
apic write: bad size=1 fee00030
Ignoring de-assert INIT to vcpu 0
Ignoring de-assert INIT to vcpu 0
Ignoring de-assert INIT to vcpu 0

I can't see lockdep errors in dmesg starting one more multiple VM in a
loop (all run on a quadcore).

GRU is likely the same.

The only real place where lockdep is unusable in my experience is
preempt-RT, it grinds it to an halt during boot on 8-way before
reaching the shell.
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