mac80211: only alloc mem if a station doesn't exist yet

This speeds up the function in case a station already exists by avoiding
calling an expensive kzalloc just to free it again after the next check.
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.c

@@ -513,23 +513,23 @@ static int sta_info_insert_finish(struct sta_info *sta) __acquires(RCU)
 {
 	struct ieee80211_local *local = sta->local;
 	struct ieee80211_sub_if_data *sdata = sta->sdata;
-	struct station_info *sinfo;
+	struct station_info *sinfo = NULL;
 	int err = 0;
 
 	lockdep_assert_held(&local->sta_mtx);
 
-	sinfo = kzalloc(sizeof(struct station_info), GFP_KERNEL);
-	if (!sinfo) {
-		err = -ENOMEM;
-		goto out_err;
-	}
-
 	/* check if STA exists already */
 	if (sta_info_get_bss(sdata, sta->sta.addr)) {
 		err = -EEXIST;
 		goto out_err;
 	}
 
+	sinfo = kzalloc(sizeof(struct station_info), GFP_KERNEL);
+	if (!sinfo) {
+		err = -ENOMEM;
+		goto out_err;
+	}
+
 	local->num_sta++;
 	local->sta_generation++;
 	smp_mb();