ocfs2: cluster: fix potential deadlock on &qs->qs_lock

&qs->qs_lock is acquired by timer o2net_idle_timer() along the following
call chain. Thus the acquisition of the lock under process context should
disable bottom half, otherwise deadlock could happen if the timer happens
to preempt the execution while the lock is held in process context on the
same CPU.

<timer interrupt>
-> o2net_idle_timer()
-> o2quo_conn_err()
-> spin_lock(&qs->qs_lock)

Several lock acquisition of &qs->qs_lock under process contex do not
disable irq or bottom half. The patch fixes these potential deadlocks
scenerio by using spin_lock_bh() on &qs->qs_lock.

This flaw was found by an experimental static analysis tool I am
developing for irq-related deadlock. x86_64 allmodconfig using gcc shows
no new warning.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Chengfeng Ye <[e-mail]>
Cc: Mark Fasheh <[e-mail]>
Cc: Joel Becker <[e-mail]>
Cc: Junxiao Bi <[e-mail]>
Cc: Joseph Qi <[e-mail]>
Cc: Gang He <[e-mail]>
Cc: Jun Piao <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

fs/ocfs2/cluster/quorum.c

···
 	int lowest_hb, lowest_reachable = 0, fence = 0;
 	struct o2quo_state *qs = &o2quo_state;
 
-	spin_lock(&qs->qs_lock);
+	spin_lock_bh(&qs->qs_lock);
 
 	lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES);
 	if (lowest_hb != O2NM_MAX_NODES)
···
 
 out:
 	if (fence) {
-		spin_unlock(&qs->qs_lock);
+		spin_unlock_bh(&qs->qs_lock);
 		o2quo_fence_self();
 	} else {
 		mlog(ML_NOTICE, "not fencing this node, heartbeating: %d, "
 			"connected: %d, lowest: %d (%sreachable)\n",
 			qs->qs_heartbeating, qs->qs_connected, lowest_hb,
 			lowest_reachable ? "" : "un");
-		spin_unlock(&qs->qs_lock);
+		spin_unlock_bh(&qs->qs_lock);
 
 	}
 
···
 {
 	struct o2quo_state *qs = &o2quo_state;
 
-	spin_lock(&qs->qs_lock);
+	spin_lock_bh(&qs->qs_lock);
 
 	qs->qs_heartbeating++;
 	mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES,
···
 	else
 		o2quo_clear_hold(qs, node);
 
-	spin_unlock(&qs->qs_lock);
+	spin_unlock_bh(&qs->qs_lock);
 }
 
 /* hb going down releases any holds we might have had due to this node from
···
 {
 	struct o2quo_state *qs = &o2quo_state;
 
-	spin_lock(&qs->qs_lock);
+	spin_lock_bh(&qs->qs_lock);
 
 	qs->qs_heartbeating--;
 	mlog_bug_on_msg(qs->qs_heartbeating < 0,
···
 
 	o2quo_clear_hold(qs, node);
 
-	spin_unlock(&qs->qs_lock);
+	spin_unlock_bh(&qs->qs_lock);
 }
 
 /* this tells us that we've decided that the node is still heartbeating
···
 {
 	struct o2quo_state *qs = &o2quo_state;
 
-	spin_lock(&qs->qs_lock);
+	spin_lock_bh(&qs->qs_lock);
 
 	mlog(0, "node %u\n", node);
 
 	qs->qs_pending = 1;
 	o2quo_clear_hold(qs, node);
 
-	spin_unlock(&qs->qs_lock);
+	spin_unlock_bh(&qs->qs_lock);
 }
 
 /* This is analogous to hb_up.  as a node's connection comes up we delay the
···
 {
 	struct o2quo_state *qs = &o2quo_state;
 
-	spin_lock(&qs->qs_lock);
+	spin_lock_bh(&qs->qs_lock);
 
 	qs->qs_connected++;
 	mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES,
···
 	else
 		o2quo_clear_hold(qs, node);
 
-	spin_unlock(&qs->qs_lock);
+	spin_unlock_bh(&qs->qs_lock);
 }
 
 /* we've decided that we won't ever be connecting to the node again.  if it's
···
 {
 	struct o2quo_state *qs = &o2quo_state;
 
-	spin_lock(&qs->qs_lock);
+	spin_lock_bh(&qs->qs_lock);
 
 	if (test_bit(node, qs->qs_conn_bm)) {
 		qs->qs_connected--;
···
 	mlog(0, "node %u, %d total\n", node, qs->qs_connected);
 
 
-	spin_unlock(&qs->qs_lock);
+	spin_unlock_bh(&qs->qs_lock);
 }
 
 void o2quo_init(void)