Pull vfs dentry reference count fix from Al Viro.
This fixes a possible inode_permission NULL pointer dereference (and
other problems) that were due to the root dentry count being decremented
too much. In commit 48a066e72d97 ("RCU'd vfsmounts") the placement of
clearing the LOOKUP_RCU bit changed, and we then returned failure of
incrementing the lockref on the parent dentry with LOOKUP_RCU cleared.
But that meant we needed to go through the same cleanup routines that
the later failures did wrt LOOKUP_ROOT and nd->root.
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
fix bogus path_put() of nd->root after some unlazy_walk() failures
b01537bfbc