Revert "kernfs: remove kernfs_addrm_cxt"

This reverts commit 99177a3411.

Tejun writes:
        I'm sorry but can you please revert the whole series?
        get_active() waiting while a node is deactivated has potential
        to lead to deadlock and that deactivate/reactivate interface is
        something fundamentally flawed and that cgroup will have to work
        with the remove_self() like everybody else.  IOW, I think the
        first posting was correct.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/kernfs.h

@@ -89,6 +89,10 @@ struct kernfs_node {
 
 	struct rb_node		rb;
 
+	union {
+		struct kernfs_node	*removed_list;
+	} u;
+
 	const void		*ns;	/* namespace tag */
 	unsigned int		hash;	/* ns + name hash */
 	union {