[PATCH 1/2] nl80211: add support to enable/disable bss color collision detection

[Lorenzo Bianconi]

> On 19/01/2023 15:02, Johannes Berg wrote:
> > On Mon, 2022-12-26 at 14:03 +0530, Rameshkumar Sundaram wrote:
> > > As per 802.11ax-2021, STAs shall process BSS Color Change Announcement
> > > (BCCA) from AP and switch to new color, but some STAs aren't processing
> > > BCCA from AP and not doing color switch, causing them to drop data
> > > frames from AP post color change.
> > > 
> > > Provide an option to disable color collision detection and therefore
> > > not to do BCCA to mitigate the same from AP. If it's required in case
> > > where STA supports BCCA handling, then it can enabled in AP using this
> > > option.
> > > 
> > 
> > You should probably split this into cfg80211 and mac80211.
> > 
> > Also, this doesn't really seem to make a lot of _sense_ since nothing in
> > the kernel actually acts on detection of a color collision - hostapd is
> > acting on that.
> > 
> > So since you can easily make hostapd ignore the event, why do you even
> > need this?
> 
> This may not be related, but the software color collision detection sends a
> netlink message for every colliding frame and it can hose up the system if
> the other network is very active.
> 
> Also, cfg80211_bss_color_notify() complains that the wdev lock isn't held.

Hi Nicolas,

I agree, I think we can ratelimit netlink messages sent by the kernel to
userspace (e.g. to hostapd), I would say every 500ms is ok.
I guess we can move cfg80211_obss_color_collision_notify() in a dedicated
delayed_work so we can grab wdev mutex (cfg80211_obss_color_collision_notify is
currently running in interrupt context).
To give an idea, what do you think about patch below? (please note it is just
compiled tested so far).

Regards,
Lorenzo

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index f5d43f42f6d8..0aefaca989aa 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -4652,6 +4652,20 @@ void ieee80211_color_change_finalize_work(struct work_struct *work)
 	sdata_unlock(sdata);
 }
 
+void ieee80211_color_collision_detection_work(struct work_struct *work)
+{
+	struct delayed_work *delayed_work = to_delayed_work(work);
+	struct ieee80211_link_data *link =
+		container_of(delayed_work, struct ieee80211_link_data,
+			     dfs_cac_timer_work);
+	struct ieee80211_sub_if_data *sdata = link->sdata;
+
+	sdata_lock(sdata);
+	cfg80211_obss_color_collision_notify(sdata->dev, link->color_bitmap,
+					     GFP_KERNEL);
+	sdata_unlock(sdata);
+}
+
 void ieee80211_color_change_finish(struct ieee80211_vif *vif)
 {
 	struct ieee80211_sub_if_data *sdata = vif_to_sdata(vif);
@@ -4666,11 +4680,21 @@ ieee80211_obss_color_collision_notify(struct ieee80211_vif *vif,
 				       u64 color_bitmap, gfp_t gfp)
 {
 	struct ieee80211_sub_if_data *sdata = vif_to_sdata(vif);
+	struct ieee80211_link_data *link = &sdata->deflink;
 
 	if (sdata->vif.bss_conf.color_change_active || sdata->vif.bss_conf.csa_active)
 		return;
 
-	cfg80211_obss_color_collision_notify(sdata->dev, color_bitmap, gfp);
+	if (delayed_work_pending(&link->color_collision_detect_work))
+		return;
+
+	link->color_bitmap = color_bitmap;
+	/* queue the color collision detection event every 500 ms in order to
+	 * avoid sending too much netlink messages to userspace.
+	 */
+	ieee80211_queue_delayed_work(&sdata->local->hw,
+				     &link->color_collision_detect_work,
+				     msecs_to_jiffies(500)); /* 500 ms */
 }
 EXPORT_SYMBOL_GPL(ieee80211_obss_color_collision_notify);
 
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index d16606e84e22..7ca9bde3c6d2 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -974,6 +974,8 @@ struct ieee80211_link_data {
 	struct cfg80211_chan_def csa_chandef;
 
 	struct work_struct color_change_finalize_work;
+	struct delayed_work color_collision_detect_work;
+	u64 color_bitmap;
 
 	/* context reservation -- protected with chanctx_mtx */
 	struct ieee80211_chanctx *reserved_chanctx;
@@ -1929,6 +1931,7 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
 
 /* color change handling */
 void ieee80211_color_change_finalize_work(struct work_struct *work);
+void ieee80211_color_collision_detection_work(struct work_struct *work);
 
 /* interface handling */
 #define MAC80211_SUPPORTED_FEATURES_TX	(NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM | \
diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 23ed13f15067..1ef970b457d1 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -541,6 +541,7 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata, bool going_do
 	cancel_work_sync(&sdata->deflink.color_change_finalize_work);
 
 	cancel_delayed_work_sync(&sdata->deflink.dfs_cac_timer_work);
+	cancel_delayed_work_sync(&sdata->deflink.color_collision_detect_work);
 
 	if (sdata->wdev.cac_started) {
 		chandef = sdata->vif.bss_conf.chandef;
diff --git a/net/mac80211/link.c b/net/mac80211/link.c
index d1f5a9f7c647..acab8309d2d6 100644
--- a/net/mac80211/link.c
+++ b/net/mac80211/link.c
@@ -39,6 +39,8 @@ void ieee80211_link_init(struct ieee80211_sub_if_data *sdata,
 		  ieee80211_csa_finalize_work);
 	INIT_WORK(&link->color_change_finalize_work,
 		  ieee80211_color_change_finalize_work);
+	INIT_DELAYED_WORK(&link->color_collision_detect_work,
+			  ieee80211_color_collision_detection_work);
 	INIT_LIST_HEAD(&link->assigned_chanctx_list);
 	INIT_LIST_HEAD(&link->reserved_chanctx_list);
 	INIT_DELAYED_WORK(&link->dfs_cac_timer_work,
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