Date: Wed, 16 Feb 2011 00:03:30 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Andrea Arcangeli <aarcange@redhat.com>
cc: Jeremy Fitzhardinge <jeremy@goop.org>, "H. Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        "Xen-devel@lists.xensource.com" <Xen-devel@lists.xensource.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ian Campbell <Ian.Campbell@citrix.com>,
        Jan Beulich <JBeulich@novell.com>, Larry Woodman <lwoodman@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>, Andi Kleen <ak@suse.de>,
        Johannes Weiner <jweiner@redhat.com>, Hugh Dickins <hughd@google.com>,
        Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH] fix pgd_lock deadlock
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On Tue, 15 Feb 2011, Andrea Arcangeli wrote:

> On Tue, Feb 15, 2011 at 09:26:35PM +0100, Thomas Gleixner wrote:
> > Another thing. You check for in_interrupt(), but what makes sure that
> > the code which takes pgd_lock is never taken with interrupts disabled
> > except during early boot ?
> 
> It's perfectly fine to take pgd_lock with irq disabled, as long as you
> don't pretend to take the page_table_lock too after that. So that's
> not a concern.
> 
> I removed _irqsave from all pgd_lock, and I doubt there's any code
> protected by pgd_lock that runs with irq disabled, but if there is,
> it's still ok and it especially shouldn't have used _irqsave.
> 
> The only real issue here to sort out, is if pgd_lock is ever taken
> from irq or not, and to me it looks like in_interrupt() should trigger
> if it is ever taken from irq, so it won't go unnoticed for long if
> this isn't ok.

I assume you run it with a lockdep enabled kernel as well, right ?

Thanks,

	tglx

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