wifi: mac80211: always hold sdata lock in chanctx assign/unassign

Due to all the multi-link handling, we now expose the fact that
the sdata/vif is locked to drivers, e.g. when the driver uses
ieee80211_set_monitor_channel(). This was true when a chanctx
is added to or removed from a link, _except_ in monitor mode
with the virtual sdata/vif. Change that, so that drivers can
make that assumption.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230619161906.a5cf7534beda.I5b51664231abee27e02f222083df7ccf88722929@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -913,24 +913,30 @@ static int ieee80211_set_monitor_channel(struct wiphy *wiphy,
 	if (cfg80211_chandef_identical(&local->monitor_chandef, chandef))
 		return 0;
 
-	mutex_lock(&local->mtx);
 	if (local->use_chanctx) {
 		sdata = wiphy_dereference(local->hw.wiphy,
 					  local->monitor_sdata);
 		if (sdata) {
+			sdata_lock(sdata);
+			mutex_lock(&local->mtx);
 			ieee80211_link_release_channel(&sdata->deflink);
 			ret = ieee80211_link_use_channel(&sdata->deflink,
 							 chandef,
 							 IEEE80211_CHANCTX_EXCLUSIVE);
+			mutex_unlock(&local->mtx);
+			sdata_unlock(sdata);
+		}
+	} else {
+		mutex_lock(&local->mtx);
+		if (local->open_count == local->monitors) {
+			local->_oper_chandef = *chandef;
+			ieee80211_hw_config(local, 0);
 		}
-	} else if (local->open_count == local->monitors) {
-		local->_oper_chandef = *chandef;
-		ieee80211_hw_config(local, 0);
+		mutex_unlock(&local->mtx);
 	}
 
 	if (ret == 0)
 		local->monitor_chandef = *chandef;
-	mutex_unlock(&local->mtx);
 
 	return ret;
 }

net/mac80211/iface.c

@@ -1133,6 +1133,7 @@ int ieee80211_add_virtual_monitor(struct ieee80211_local *local)
 	snprintf(sdata->name, IFNAMSIZ, "%s-monitor",
 		 wiphy_name(local->hw.wiphy));
 	sdata->wdev.iftype = NL80211_IFTYPE_MONITOR;
+	mutex_init(&sdata->wdev.mtx);
 
 	ieee80211_sdata_init(local, sdata);
 
@@ -1157,16 +1158,19 @@ int ieee80211_add_virtual_monitor(struct ieee80211_local *local)
 	rcu_assign_pointer(local->monitor_sdata, sdata);
 	mutex_unlock(&local->iflist_mtx);
 
+	sdata_lock(sdata);
 	mutex_lock(&local->mtx);
 	ret = ieee80211_link_use_channel(&sdata->deflink, &local->monitor_chandef,
 					 IEEE80211_CHANCTX_EXCLUSIVE);
 	mutex_unlock(&local->mtx);
+	sdata_unlock(sdata);
 	if (ret) {
 		mutex_lock(&local->iflist_mtx);
 		RCU_INIT_POINTER(local->monitor_sdata, NULL);
 		mutex_unlock(&local->iflist_mtx);
 		synchronize_net();
 		drv_remove_interface(local, sdata);
+		mutex_destroy(&sdata->wdev.mtx);
 		kfree(sdata);
 		return ret;
 	}
@@ -1202,12 +1206,15 @@ void ieee80211_del_virtual_monitor(struct ieee80211_local *local)
 
 	synchronize_net();
 
+	sdata_lock(sdata);
 	mutex_lock(&local->mtx);
 	ieee80211_link_release_channel(&sdata->deflink);
 	mutex_unlock(&local->mtx);
+	sdata_unlock(sdata);
 
 	drv_remove_interface(local, sdata);
 
+	mutex_destroy(&sdata->wdev.mtx);
 	kfree(sdata);
 }