linux-kernel - Re: Interaction between Xen and XFS: stray RW mappings

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Date:	Fri, 12 Oct 2007 10:08:49 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	David Chinner <dgc@....com>
CC:	xfs@....sgi.com, Xen-devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mark Williamson <mark.williamson@...cam.ac.uk>,
	Morten Bøgeskov 
	<xen-users@...ten.bogeskov.dk>, xfs-masters@....sgi.com
Subject: Re: Interaction between Xen and XFS: stray RW mappings

Jeremy Fitzhardinge wrote:
> I guess we could create a special-case interface to do the same thing
> with XFS mappings, but it would be nicer to have something more generic.
>
> Is my analysis correct?  Or should XFS not be holding stray mappings? 
> Or is there already some kind of generic mechanism I can use to get it
> to release its mappings?

This test patch confirms my theory:

diff -r 36a518c1fb4b fs/xfs/linux-2.6/xfs_buf.c
--- a/fs/xfs/linux-2.6/xfs_buf.c	Fri Oct 12 10:03:56 2007 -0700
+++ b/fs/xfs/linux-2.6/xfs_buf.c	Fri Oct 12 10:07:03 2007 -0700
@@ -186,6 +186,11 @@ free_address(
 	void		*addr)
 {
 	a_list_t	*aentry;
+
+#ifdef CONFIG_XEN
+	vunmap(addr);
+	return;
+#endif
 
 	aentry = kmalloc(sizeof(a_list_t), GFP_NOWAIT);
 	if (likely(aentry)) {


With this in place, the problem goes away.

    J
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