mac80211: warn if unexpectedly removing stations

When an interface is brought down it must have been
disconnected (or similar) in all modes other than WDS,
so warn if any stations were removed in other modes.
Tested-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/iface.c

@@ -747,7 +747,7 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata,
 	unsigned long flags;
 	struct sk_buff *skb, *tmp;
 	u32 hw_reconf_flags = 0;
-	int i;
+	int i, flushed;
 
 	clear_bit(SDATA_STATE_RUNNING, &sdata->state);
 
@@ -772,11 +772,13 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata,
 	 * (because if we remove a STA after ops->remove_interface()
 	 * the driver will have removed the vif info already!)
 	 *
-	 * This is relevant only in AP, WDS and mesh modes, since in
-	 * all other modes we've already removed all stations when
-	 * disconnecting etc.
+	 * This is relevant only in WDS mode, in all other modes we've
+	 * already removed all stations when disconnecting or similar,
+	 * so warn otherwise.
 	 */
-	sta_info_flush(sdata);
+	flushed = sta_info_flush(sdata);
+	WARN_ON_ONCE((sdata->vif.type != NL80211_IFTYPE_WDS && flushed > 0) ||
+		     (sdata->vif.type == NL80211_IFTYPE_WDS && flushed != 1));
 
 	/*
 	 * Don't count this interface for promisc/allmulti while it