Re: [B.A.T.M.A.N.] [PATCH v2 6/7] batman-adv: ELP - use tp meter to estimate the throughput if otherwise not available

On Fri, May 18, 2018 at 09:47:53AM +0800, Marek Lindner wrote:

+/**

• • batadv_v_elp_tp_start() - start a tp meter session for a neighbor
• • @neigh: neighbor to run tp meter on
• */

+static void batadv_v_elp_tp_start(struct batadv_hardif_neigh_node *neigh) +{

• struct batadv_hard_iface *hard_iface = neigh->if_incoming;
• struct batadv_priv *bat_priv = netdev_priv(hard_iface->soft_iface);
• neigh->bat_v.tp_meter_running = true;
• batadv_tp_start(bat_priv, neigh->addr, neigh, 10, NULL, BATADV_TP_ELP);

+}

This seems racy here? We have no ordering constraints between the assigment and batadv_tp_start() which might lead to...

@@ -152,6 +192,25 @@ static u32 batadv_v_elp_get_throughput(struct batadv_hardif_neigh_node *neigh) return throughput * 10; }

+fallback_throughput:

• last_tp_run_jiffies = jiffies - neigh->bat_v.last_tp_meter_run;
• last_tp_run_msecs = jiffies_to_msecs(last_tp_run_jiffies);
• /* check the tp_meter_running flag before checking the timestamp to

• * avoid a race condition where a new tp meter session is scheduled
  

• * right after the previous tp meter session has completed
  

• */
  

• if (!neigh->bat_v.tp_meter_running &&

•    last_tp_run_msecs > BATADV_ELP_TP_RUN_INTERVAL)
  

• batadv_v_elp_tp_start(neigh);
  

...multiple instances potentially being started at the same time here?