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Date: Mon, 21 Feb 2011 15:30:23 +0100
From: Andrea Arcangeli <aarcange@redhat.com>
To: Johannes Weiner <jweiner@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        Jeremy Fitzhardinge <jeremy@goop.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
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        Ian Campbell <Ian.Campbell@citrix.com>,
        Jan Beulich <JBeulich@novell.com>, Larry Woodman <lwoodman@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andi Kleen <andi@firstfloor.org>, Hugh Dickins <hughd@google.com>,
        Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH] fix pgd_lock deadlock
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On Thu, Feb 17, 2011 at 11:19:41AM +0100, Johannes Weiner wrote:
> So Xen needs all page tables protected when pinning/unpinning and
> extended page_table_lock to cover kernel range, which it does nowhere
> else AFAICS.  But the places it extended are also taking the pgd_lock,
> so I wonder if Xen could just take the pgd_lock itself in these paths
> and we could revert page_table_lock back to cover user va only?
> Jeremy, could this work?  Untested.

If this works for Xen, I definitely prefer this.

Still there's no point to insist on _irqsave if nothing takes the
pgd_lock from irq, so my patch probably should be applied anyway or
it's confusing and there's even a comment saying pgd_dtor is called
from irq, if it's not it should be corrected. But then it becomes a
cleanup notafix.