ocfs2/cluster: close a race that fence can't be triggered

When some nodes of cluster face with TCP connection fault, ocfs2 will
pick up a quorum to continue to work and other nodes will be fenced by
resetting host.

In order to decide which node should be fenced, ocfs2 leverages
o2quo_state::qs_holds.  If that variable is reduced to zero, then a try
to decide if fence local node is performed.  However, under a specific
scenario that local node is not disconnected from others at the same
time, above method has a problem to reduce ::qs_holds to zero.

Because, o2net 90s idle timer corresponding to different nodes is
triggered one after another.

  node 2			node 3
  90s idle timer elapses
  clear ::qs_conn_bm
  set hold
				40s is passed
				90 idle timer elapses
				clear ::qs_conn_bm
				set hold
  still up timer elapses
  clear hold (NOT to zero )
  90s idle timer elapses AGAIN
				still up timer elapses.
				clear hold
				still up timer elapses

To solve this issue, a node which has already be evicted from
::qs_conn_bm can't set hold again and again invoked from idle timer.

Link: http://lkml.kernel.org/r/63ADC13FD55D6546B7DECE290D39E373F1F3F93B@H3CMLB12-EX.srv.huawei-3com.com
Signed-off-by: Yang Zhang <zhang.yangB@h3c.com>
Signed-off-by: Changwei Ge <ge.changwei@h3c.com>
Cc: Mark Fasheh <mfasheh@versity.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/cluster/quorum.c

@@ -314,12 +314,13 @@ void o2quo_conn_err(u8 node)
 				node, qs->qs_connected);
 
 		clear_bit(node, qs->qs_conn_bm);
+
+		if (test_bit(node, qs->qs_hb_bm))
+			o2quo_set_hold(qs, node);
 	}
 
 	mlog(0, "node %u, %d total\n", node, qs->qs_connected);
 
-	if (test_bit(node, qs->qs_hb_bm))
-		o2quo_set_hold(qs, node);
 
 	spin_unlock(&qs->qs_lock);
 }