[Xen-devel] Re: [PATCH] fix pgd_lock deadlock

To:	Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject:	[Xen-devel] Re: [PATCH] fix pgd_lock deadlock
From:	Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date:	Wed, 16 Feb 2011 10:58:14 +0100
Cc:	Johannes, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, Andrew, maintainers <x86@xxxxxxxxxx>, Hugh Dickins <hughd@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Beulich <JBeulich@xxxxxxxxxx>, Larry Woodman <lwoodman@xxxxxxxxxx>, Jan, Weiner <jweiner@xxxxxxxxxx>, Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, the, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Andi Kleen <ak@xxxxxxx>
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On Wed, 2011-02-16 at 00:17 +0100, Andrea Arcangeli wrote:
> On Wed, Feb 16, 2011 at 12:03:30AM +0100, Thomas Gleixner wrote:
> > I assume you run it with a lockdep enabled kernel as well, right ?
> 
> Yes, I always run with lockdep and prove locking enabled on my test
> box, not sure how it's meant to trigger more bugs in this case, the
> debug check that should be relevant for this is DEBUG_VM and that is
> enabled too of course. I didn't try DEBUG_PAGEALLOC yet.

I think what Thomas tried to tell you is that your
VM_BUG_ON(in_interrupt()) is fully redundant if you have lockdep
enabled.

Lockdep will warn you if a !irqsave lock is taken from IRQ context,
since that is a clear inversion problem.



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[Xen-devel] Re: [PATCH] fix pgd_lock deadlock