mac80211: always synchronize_net() during station removal

If there are keys left during station removal, then a
synchronize_net() will be done (for each key, I have a
patch to address this for 3.10), otherwise it won't be
done at all which causes issues because the station
could be used for TX while it's being removed from the
driver -- that might confuse the driver.

Fix this by always doing synchronize_net() if no key
was present any more.

Cc: stable@vger.kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.c

@@ -766,6 +766,7 @@ int __must_check __sta_info_destroy(struct sta_info *sta)
 	struct ieee80211_local *local;
 	struct ieee80211_sub_if_data *sdata;
 	int ret, i;
+	bool have_key = false;
 
 	might_sleep();
 
@@ -793,12 +794,19 @@ int __must_check __sta_info_destroy(struct sta_info *sta)
 	list_del_rcu(&sta->list);
 
 	mutex_lock(&local->key_mtx);
-	for (i = 0; i < NUM_DEFAULT_KEYS; i++)
+	for (i = 0; i < NUM_DEFAULT_KEYS; i++) {
 		__ieee80211_key_free(key_mtx_dereference(local, sta->gtk[i]));
-	if (sta->ptk)
+		have_key = true;
+	}
+	if (sta->ptk) {
 		__ieee80211_key_free(key_mtx_dereference(local, sta->ptk));
+		have_key = true;
+	}
 	mutex_unlock(&local->key_mtx);
 
+	if (!have_key)
+		synchronize_net();
+
 	sta->dead = true;
 
 	local->num_sta--;