mac80211: fix a kernel panic when TXing after TXQ teardown

Recently TXQ teardown was moved earlier in ieee80211_unregister_hw(),
to avoid a use-after-free of the netdev data. However, interfaces
aren't fully removed at the point, and cfg80211_shutdown_all_interfaces
can for example, TX a deauth frame. Move the TXQ teardown to the
point between cfg80211_shutdown_all_interfaces and the free of
netdev queues, so we can be sure they are torn down before netdev
is freed, but after there is no ongoing TX.

Fixes: 77cfaf52 ("mac80211: Run TXQ teardown code before de-registering interfaces")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/iface.c

@@ -7,6 +7,7 @@
  * Copyright 2008, Johannes Berg <johannes@sipsolutions.net>
  * Copyright 2013-2014  Intel Mobile Communications GmbH
  * Copyright (c) 2016        Intel Deutschland GmbH
+ * Copyright (C) 2018 Intel Corporation
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -1951,6 +1952,8 @@ void ieee80211_remove_interfaces(struct ieee80211_local *local)
 	WARN(local->open_count, "%s: open count remains %d\n",
 	     wiphy_name(local->hw.wiphy), local->open_count);
 
+	ieee80211_txq_teardown_flows(local);
+
 	mutex_lock(&local->iflist_mtx);
 	list_for_each_entry_safe(sdata, tmp, &local->interfaces, list) {
 		list_del(&sdata->list);

net/mac80211/main.c

@@ -1262,7 +1262,6 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
 	rtnl_unlock();
 	ieee80211_led_exit(local);
 	ieee80211_wep_free(local);
-	ieee80211_txq_teardown_flows(local);
  fail_flows:
 	destroy_workqueue(local->workqueue);
  fail_workqueue:
@@ -1288,7 +1287,6 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
 #if IS_ENABLED(CONFIG_IPV6)
 	unregister_inet6addr_notifier(&local->ifa6_notifier);
 #endif
-	ieee80211_txq_teardown_flows(local);
 
 	rtnl_lock();