MNT_UNBINDABLE fix

Some time ago ( http://lkml.org/lkml/2007/6/19/128 ) I wrote about
MNT_UNBINDABLE that it felt like a bug that it is not reset by "mount
--make-private".

Today I happened to see mount(8) and Documentation/sharedsubtree.txt and
both document the version obtained by applying the little patch given in
the above (and again below).

So, the present kernel code is not according to specs and must be regarded
as buggy.

Specification in Documentation/sharedsubtree.txt:
See state diagram: unbindable should become private upon make-private.

Specification in mount(8):
    ...  It's
    also possible to  set  up  uni-directional  propagation  (with  --make-
    slave),  to  make  a  mount  point unavailable for --bind/--rbind (with
    --make-unbindable), and to undo any  of  these  (with  --make-private).

Repeat of old fix-shared-subtrees-make-private.patch
(due to Dirk Gerrits, René Gabriëls, Peter Kooijmans):

Acked-by: Ram Pai <linuxram@us.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/pnode.c b/fs/pnode.c
index 89940f243fc235d2f2f8d9abf27e5b0f6862cd52..05ba692bc540ade3b63c5f5af72e1987556bd9fe 100644 (file)
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -83,6 +83,8 @@ void change_mnt_propagation(struct vfsmount *mnt, int type)
                mnt->mnt_master = NULL;
                if (type == MS_UNBINDABLE)
                        mnt->mnt_flags |= MNT_UNBINDABLE;
+               else
+                       mnt->mnt_flags &= ~MNT_UNBINDABLE;
        }
 }