only allow nonlinear vmas for ram backed filesystems
authorMiklos Szeredi <mszeredi@suse.cz>
Thu, 19 Jul 2007 08:47:24 +0000 (01:47 -0700)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Thu, 19 Jul 2007 17:04:41 +0000 (10:04 -0700)
commit3ee6dafc677a68e461a7ddafc94a580ebab80735
tree6a92c9f5bd24ff80c52c944327c3b065234f7ad2
parentbb2d5ce16409efcdf94017a6b6fecd468226e29c
only allow nonlinear vmas for ram backed filesystems

page_mkclean() doesn't re-protect ptes for non-linear mappings, so a later
re-dirty through such a mapping will not generate a fault, PG_dirty will
not reflect the dirty state and the dirty count will be skewed.  This
implies that msync() is also currently broken for nonlinear mappings.

The easiest solution is to emulate remap_file_pages on non-linear mappings
with simple mmap() for non ram-backed filesystems.  Applications continue
to work (albeit slower), as long as the number of remappings remain below
the maximum vma count.

However all currently known real uses of non-linear mappings are for ram
backed filesystems, which this patch doesn't affect.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/fremap.c