mac80211: disentangle iflist_mtx and chanctx_mtx

At least on iwlwifi, sometimes lockdep complains that we can
lock
 chanctx_mtx -> mvm.mutex -> iflist_mtx
 (due to iterate_interfaces)
and
 iflist_mtx -> chanctx_mtx

Remove the latter dependency in mac80211 by using the RTNL
that we already hold in one case, and can relatively easily
achieve in the other case.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -739,11 +739,8 @@ static int ieee80211_set_monitor_channel(struct wiphy *wiphy,
 		return 0;
 
 	mutex_lock(&local->mtx);
-	mutex_lock(&local->iflist_mtx);
 	if (local->use_chanctx) {
-		sdata = rcu_dereference_protected(
-				local->monitor_sdata,
-				lockdep_is_held(&local->iflist_mtx));
+		sdata = rtnl_dereference(local->monitor_sdata);
 		if (sdata) {
 			ieee80211_vif_release_channel(sdata);
 			ret = ieee80211_vif_use_channel(sdata, chandef,
@@ -756,7 +753,6 @@ static int ieee80211_set_monitor_channel(struct wiphy *wiphy,
 
 	if (ret == 0)
 		local->monitor_chandef = *chandef;
-	mutex_unlock(&local->iflist_mtx);
 	mutex_unlock(&local->mtx);
 
 	return ret;

net/mac80211/main.c

@@ -253,6 +253,7 @@ static void ieee80211_restart_work(struct work_struct *work)
 	WARN(test_bit(SCAN_HW_SCANNING, &local->scanning),
 	     "%s called with hardware scan in progress\n", __func__);
 
+	flush_work(&local->radar_detected_work);
 	rtnl_lock();
 	list_for_each_entry(sdata, &local->interfaces, list)
 		flush_delayed_work(&sdata->dec_tailroom_needed_wk);
@@ -1187,6 +1188,7 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
 	cancel_work_sync(&local->reconfig_filter);
 	cancel_work_sync(&local->tdls_chsw_work);
 	flush_work(&local->sched_scan_stopped_work);
+	flush_work(&local->radar_detected_work);
 
 	ieee80211_clear_tx_pending(local);
 	rate_control_deinitialize(local);

net/mac80211/util.c

@@ -2791,8 +2791,10 @@ void ieee80211_dfs_cac_cancel(struct ieee80211_local *local)
 	struct ieee80211_sub_if_data *sdata;
 	struct cfg80211_chan_def chandef;
 
+	/* for interface list, to avoid linking iflist_mtx and chanctx_mtx */
+	ASSERT_RTNL();
+
 	mutex_lock(&local->mtx);
-	mutex_lock(&local->iflist_mtx);
 	list_for_each_entry(sdata, &local->interfaces, list) {
 		/* it might be waiting for the local->mtx, but then
 		 * by the time it gets it, sdata->wdev.cac_started
@@ -2809,7 +2811,6 @@ void ieee80211_dfs_cac_cancel(struct ieee80211_local *local)
 					   GFP_KERNEL);
 		}
 	}
-	mutex_unlock(&local->iflist_mtx);
 	mutex_unlock(&local->mtx);
 }
 
@@ -2831,7 +2832,9 @@ void ieee80211_dfs_radar_detected_work(struct work_struct *work)
 	}
 	mutex_unlock(&local->chanctx_mtx);
 
+	rtnl_lock();
 	ieee80211_dfs_cac_cancel(local);
+	rtnl_unlock();
 
 	if (num_chanctx > 1)
 		/* XXX: multi-channel is not supported yet */
@@ -2846,7 +2849,7 @@ void ieee80211_radar_detected(struct ieee80211_hw *hw)
 
 	trace_api_radar_detected(local);
 
-	ieee80211_queue_work(hw, &local->radar_detected_work);
+	schedule_work(&local->radar_detected_work);
 }
 EXPORT_SYMBOL(ieee80211_radar_detected);