linux-kernel - Re: [PATCH] fix pgd

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Message-ID: <1297850294.2413.30.camel@twins>
Date:	Wed, 16 Feb 2011 10:58:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Jan Beulich <JBeulich@...ell.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, Johannes Weiner <jweiner@...hat.com>,
	Hugh Dickins <hughd@...gle.com>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH] fix pgd_lock deadlock

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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