ocfs2: remove ocfs2_is_o2cb_active()

Remove ocfs2_is_o2cb_active().  We have similar functions to identify
which cluster stack is being used via osb->osb_cluster_stack.

Secondly, the current implementation of ocfs2_is_o2cb_active() is not
totally safe.  Based on the design of stackglue, we need to get
ocfs2_stack_lock before using ocfs2_stack related data structures, and
that active_stack pointer can be NULL in the case of mount failure.

Link: http://lkml.kernel.org/r/1495441079-11708-1-git-send-email-ghe@suse.com
Signed-off-by: Gang He <ghe@suse.com>
Reviewed-by: Joseph Qi <jiangqi903@gmail.com>
Reviewed-by: Eric Ren <zren@suse.com>
Acked-by: Changwei Ge <ge.changwei@h3c.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/dlmglue.c

@@ -3603,7 +3603,7 @@ static int ocfs2_downconvert_lock(struct ocfs2_super *osb,
 	 * we can recover correctly from node failure. Otherwise, we may get
 	 * invalid LVB in LKB, but without DLM_SBF_VALNOTVALID being set.
 	 */
-	if (!ocfs2_is_o2cb_active() &&
+	if (ocfs2_userspace_stack(osb) &&
 	    lockres->l_ops->flags & LOCK_TYPE_USES_LVB)
 		lvb = 1;