Linux Virtualization - Nov 2007 - [patch 14/19] xfs: eagerly remove vmap mappings to avoid upsetting Xen

-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Jeremy Fitzhardinge <jeremy@goop.org>

patch ace2e92e193126711cb3a83a3752b2c5b8396950 in mainline.

XFS leaves stray mappings around when it vmaps memory to make it
virtually contigious.  This upsets Xen if one of those pages is being
recycled into a pagetable, since it finds an extra writable mapping of
the page.

This patch solves the problem in a brute force way, by making XFS
always eagerly unmap its mappings.

[ Stable: This works around a bug in 2.6.23.  We may come up with a
better solution for mainline, but this seems like a low-impact fix for
the stable kernel. ]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: XFS masters <xfs-masters@oss.sgi.com>
Cc: Morten =?utf-8?q?B=C3=B8geskov?= <xen-users@morten.bogeskov.dk>
Cc: Mark Williamson <mark.williamson@cl.cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>


---
 fs/xfs/linux-2.6/xfs_buf.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -187,6 +187,19 @@ free_address(
 {
 	a_list_t	*aentry;
 
+#ifdef CONFIG_XEN
+	/*
+	 * Xen needs to be able to make sure it can get an exclusive
+	 * RO mapping of pages it wants to turn into a pagetable.  If
+	 * a newly allocated page is also still being vmap()ed by xfs,
+	 * it will cause pagetable construction to fail.  This is a
+	 * quick workaround to always eagerly unmap pages so that Xen
+	 * is happy.
+	 */
+	vunmap(addr);
+	return;
+#endif
+
 	aentry = kmalloc(sizeof(a_list_t), GFP_NOWAIT);
 	if (likely(aentry)) {
 		spin_lock(&as_lock);

--