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authorDavid Herrmann <dh.herrmann@gmail.com>2014-08-09 01:25:25 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2014-08-09 02:57:31 +0400
commit4bb5f5d9395bc112d93a134d8f5b05611eddc9c0 (patch)
tree68af5a8a8cc65375c51c25bff678d0f9825d86af /mm/swap_state.c
parent935e9f02e798051d2923d59f6025cd74f59aa0e1 (diff)
downloadlinux-4bb5f5d9395bc112d93a134d8f5b05611eddc9c0.tar.xz
mm: allow drivers to prevent new writable mappings
This patch (of 6): The i_mmap_writable field counts existing writable mappings of an address_space. To allow drivers to prevent new writable mappings, make this counter signed and prevent new writable mappings if it is negative. This is modelled after i_writecount and DENYWRITE. This will be required by the shmem-sealing infrastructure to prevent any new writable mappings after the WRITE seal has been set. In case there exists a writable mapping, this operation will fail with EBUSY. Note that we rely on the fact that iff you already own a writable mapping, you can increase the counter without using the helpers. This is the same that we do for i_writecount. Signed-off-by: David Herrmann <dh.herrmann@gmail.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ryan Lortie <desrt@desrt.ca> Cc: Lennart Poettering <lennart@poettering.net> Cc: Daniel Mack <zonque@gmail.com> Cc: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap_state.c')
-rw-r--r--mm/swap_state.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index e160151da6b8..3e0ec83d000c 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -39,6 +39,7 @@ static struct backing_dev_info swap_backing_dev_info = {
struct address_space swapper_spaces[MAX_SWAPFILES] = {
[0 ... MAX_SWAPFILES - 1] = {
.page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
+ .i_mmap_writable = ATOMIC_INIT(0),
.a_ops = &swap_aops,
.backing_dev_info = &swap_backing_dev_info,
}