Commit ace2e92e authored Oct 16, 2007 by Jeremy Fitzhardinge Committed by Jeremy Fitzhardinge Oct 16, 2007

xfs: eagerly remove vmap mappings to avoid upsetting Xen



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.  David Chinner says this shouldn't
have any performance impact on filesystems with default block sizes;
it will only affect filesystems with large block sizes.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: David Chinner <dgc@sgi.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: XFS masters <xfs-masters@oss.sgi.com>
Cc: Stable kernel <stable@kernel.org>
Cc: Morten =?utf-8?q?B=C3=B8geskov?= <xen-users@morten.bogeskov.dk>
Cc: Mark Williamson <mark.williamson@cl.cam.ac.uk>

parent a122d623

fs/xfs/linux-2.6/xfs_buf.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -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);