ocfs2: fix a tiny race case when fire callbacks

index 42252bf..af5cd3b 100644
@@ -641,16 +641,9 @@ static void o2hb_fire_callbacks(struct o2hb_callback *hbcall,
 /* Will run the list in order until we process the passed event */
 static void o2hb_run_event_list(struct o2hb_node_event *queued_event)
 {
-	int empty;
 	struct o2hb_callback *hbcall;
 	struct o2hb_node_event *event;
 
-	spin_lock(&o2hb_live_lock);
-	empty = list_empty(&queued_event->hn_item);
-	spin_unlock(&o2hb_live_lock);
-	if (empty)
-		return;
-
 	/* Holding callback sem assures we don't alter the callback
 	 * lists when doing this, and serializes ourselves with other
 	 * processes wanting callbacks. */

@@ -709,6 +702,7 @@ static void o2hb_shutdown_slot(struct o2hb_disk_slot *slot)
 	struct o2hb_node_event event =
 		{ .hn_item = LIST_HEAD_INIT(event.hn_item), };
 	struct o2nm_node *node;
+	int queued = 0;
 
 	node = o2nm_get_node_by_num(slot->ds_node_num);
 	if (!node)

@@ -726,11 +720,13 @@ static void o2hb_shutdown_slot(struct o2hb_disk_slot *slot)
 
 			o2hb_queue_node_event(&event, O2HB_NODE_DOWN_CB, node,
 					      slot->ds_node_num);
+			queued = 1;
 		}
 	}
 	spin_unlock(&o2hb_live_lock);
 
-	o2hb_run_event_list(&event);
+	if (queued)
+		o2hb_run_event_list(&event);
 
 	o2nm_node_put(node);
 }

@@ -790,6 +786,7 @@ static int o2hb_check_slot(struct o2hb_region *reg,
 	unsigned int dead_ms = o2hb_dead_threshold * O2HB_REGION_TIMEOUT_MS;
 	unsigned int slot_dead_ms;
 	int tmp;
+	int queued = 0;
 
 	memcpy(hb_block, slot->ds_raw_block, reg->hr_block_bytes);
 

@@ -883,6 +880,7 @@ fire_callbacks:
 					      slot->ds_node_num);
 
 			changed = 1;
+			queued = 1;
 		}
 
 		list_add_tail(&slot->ds_live_item,

@@ -934,6 +932,7 @@ fire_callbacks:
 					      node, slot->ds_node_num);
 
 			changed = 1;
+			queued = 1;
 		}
 
 		/* We don't clear this because the node is still

@@ -949,7 +948,8 @@ fire_callbacks:
 out:
 	spin_unlock(&o2hb_live_lock);
 
-	o2hb_run_event_list(&event);
+	if (queued)
+		o2hb_run_event_list(&event);
 
 	if (node)
 		o2nm_node_put(node);