Re: [PATCH v10 2/4] mac80211: multiple bssid support in interface handling

On 2021-06-23 08:57, Johannes Berg wrote:

On Mon, 2021-04-26 at 12:05 -0700, Aloka Dixit wrote:

quoted

Hm wait, didn't I see the same code in cfg80211 - maybe cfg80211 should
just pass the pointer?

quoted

 static int ieee80211_del_iface(struct wiphy *wiphy, struct 
wireless_dev *wdev)
 {
+	struct ieee80211_sub_if_data *sdata = 
IEEE80211_WDEV_TO_SUB_IF(wdev);
+	struct ieee80211_local *local;
+	struct ieee80211_vif *vif;
+
+	if (!sdata)
+		return 0;
+
+	local = sdata->local;
+	vif = &sdata->vif;
+	if (vif->type == NL80211_IFTYPE_AP &&
+	    ieee80211_hw_check(&local->hw, SUPPORTS_MBSSID_AP)) {
+		if (vif->mbssid.flags & IEEE80211_VIF_MBSSID_TX) {
+			struct ieee80211_sub_if_data *child, *tmpsdata;
+
+			wiphy_unlock(local->hw.wiphy);
+			mutex_lock(&local->iflist_mtx);

I really don't think you can drop the locking like that in the middle 
of
something. That's almost always a recipe for disaster.

quoted

@@ -375,6 +375,18 @@ static void ieee80211_do_stop(struct 

ieee80211_sub_if_data *sdata, bool going_do
 	struct cfg80211_chan_def chandef;
 	bool cancel_scan;
 	struct cfg80211_nan_func *func;
+	struct ieee80211_sub_if_data *parent;
+
+	if (sdata->vif.type == NL80211_IFTYPE_AP &&
+	    ieee80211_hw_check(&local->hw, SUPPORTS_MBSSID_AP) &&
+	    sdata->vif.mbssid.flags & IEEE80211_VIF_MBSSID_NON_TX) {
+		parent = vif_to_sdata(sdata->vif.mbssid.parent);
+		if (parent && ieee80211_sdata_running(parent)) {
+			wiphy_unlock(local->hw.wiphy);
+			dev_close(parent->wdev.netdev);
+			wiphy_lock(local->hw.wiphy);

Same here.

johannes

Hi Johannes,

Thanks for the comments, will go through all, but need your help with 
this particular one -

I'm not able to come up with a different solution which does not cause a 
deadlock by continuing to hold wiphy_lock() as we discussed last time 
that dev_close() will in turn call into cfg80211.

You had suggested looking at dev_close() for VLAN, that code also 
doesn't lock wiphy_lock hence I did same here but locked 
'local->iflist_mtx'. Dropping both won't be good for sure.

Can you please suggest a better way? I'm really not able to come up with 
one.

Thanks.