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

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Date:	Mon, 04 Aug 2008 18:38:55 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrea Arcangeli <andrea@...ranet.com>
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, 2008-08-04 at 18:26 +0200, Andrea Arcangeli wrote:
> 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

You also need CONFIG_PROVE_LOCKING, but I'll assume that's set too.

> 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).

Dave Jones just handed me:

  https://bugzilla.redhat.com/show_bug.cgi?id=457779


> 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.

David Miller just did a patch that might fix that.

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