smb: client: fix DFS failover in multiuser mounts

For sessions and tcons created on behalf of new users accessing a
multiuser mount, matching their sessions in tcon_super_cb() with
master tcon will always lead to false as every new user will have its
own session and tcon.

All multiuser sessions, however, will inherit ->dfs_root_ses from
master tcon, so match it instead.
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/misc.c

@@ -1111,7 +1111,8 @@ static void tcon_super_cb(struct super_block *sb, void *arg)
 	t2 = cifs_sb_master_tcon(cifs_sb);
 
 	spin_lock(&t2->tc_lock);
-	if (t1->ses == t2->ses &&
+	if ((t1->ses == t2->ses ||
+	     t1->ses->dfs_root_ses == t2->ses->dfs_root_ses) &&
 	    t1->ses->server == t2->ses->server &&
 	    t2->origin_fullpath &&
 	    dfs_src_pathname_equal(t2->origin_fullpath, t1->origin_fullpath))