mac80211: Fix tx queue handling during scans

Scans currently work by stopping the netdev tx queues but leaving the
mac80211 queues active. This stops the flow of incoming packets while
still allowing mac80211 to transmit nullfunc and probe request frames to
facilitate scanning. However, the driver may try to wake the mac80211
queues while in this state, which will also wake the netdev queues.

To prevent this, add a new queue stop reason,
IEEE80211_QUEUE_STOP_REASON_OFFCHANNEL, to be used when stopping the tx
queues for off-channel operation. This prevents the netdev queues from
waking when a driver wakes the mac80211 queues.

This also stops all frames from being transmitted, even those meant to
be sent off-channel. Add a new tx control flag,
IEEE80211_TX_CTL_OFFCHAN_TX_OK, which allows frames to be transmitted
when the queues are stopped only for the off-channel stop reason. Update
all locations transmitting off-channel frames to use this flag.
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -399,6 +399,9 @@ struct ieee80211_bss_conf {
  * @IEEE80211_TX_CTL_RATE_CTRL_PROBE: internal to mac80211, can be
  *	set by rate control algorithms to indicate probe rate, will
  *	be cleared for fragmented frames (except on the last fragment)
+ * @IEEE80211_TX_INTFL_OFFCHAN_TX_OK: Internal to mac80211. Used to indicate
+ *	that a frame can be transmitted while the queues are stopped for
+ *	off-channel operation.
  * @IEEE80211_TX_INTFL_NEED_TXPROCESSING: completely internal to mac80211,
  *	used to indicate that a pending frame requires TX processing before
  *	it can be sent out.
@@ -464,6 +467,7 @@ enum mac80211_tx_control_flags {
 	IEEE80211_TX_STAT_AMPDU			= BIT(10),
 	IEEE80211_TX_STAT_AMPDU_NO_BACK		= BIT(11),
 	IEEE80211_TX_CTL_RATE_CTRL_PROBE	= BIT(12),
+	IEEE80211_TX_INTFL_OFFCHAN_TX_OK	= BIT(13),
 	IEEE80211_TX_INTFL_NEED_TXPROCESSING	= BIT(14),
 	IEEE80211_TX_INTFL_RETRIED		= BIT(15),
 	IEEE80211_TX_INTFL_DONT_ENCRYPT		= BIT(16),

net/mac80211/cfg.c

@@ -2749,7 +2749,8 @@ static int ieee80211_mgmt_tx(struct wiphy *wiphy, struct wireless_dev *wdev,
 		goto out_unlock;
 	}
 
-	IEEE80211_SKB_CB(skb)->flags |= IEEE80211_TX_CTL_TX_OFFCHAN;
+	IEEE80211_SKB_CB(skb)->flags |= IEEE80211_TX_CTL_TX_OFFCHAN |
+					IEEE80211_TX_INTFL_OFFCHAN_TX_OK;
 	if (local->hw.flags & IEEE80211_HW_QUEUE_CONTROL)
 		IEEE80211_SKB_CB(skb)->hw_queue =
 			local->hw.offchannel_tx_hw_queue;

net/mac80211/ieee80211_i.h

@@ -809,6 +809,7 @@ enum queue_stop_reason {
 	IEEE80211_QUEUE_STOP_REASON_AGGREGATION,
 	IEEE80211_QUEUE_STOP_REASON_SUSPEND,
 	IEEE80211_QUEUE_STOP_REASON_SKB_ADD,
+	IEEE80211_QUEUE_STOP_REASON_OFFCHANNEL,
 };
 
 #ifdef CONFIG_MAC80211_LEDS

net/mac80211/mlme.c

@@ -685,7 +685,8 @@ void ieee80211_send_nullfunc(struct ieee80211_local *local,
 	if (powersave)
 		nullfunc->frame_control |= cpu_to_le16(IEEE80211_FCTL_PM);
 
-	IEEE80211_SKB_CB(skb)->flags |= IEEE80211_TX_INTFL_DONT_ENCRYPT;
+	IEEE80211_SKB_CB(skb)->flags |= IEEE80211_TX_INTFL_DONT_ENCRYPT |
+					IEEE80211_TX_INTFL_OFFCHAN_TX_OK;
 	if (ifmgd->flags & (IEEE80211_STA_BEACON_POLL |
 			    IEEE80211_STA_CONNECTION_POLL))
 		IEEE80211_SKB_CB(skb)->flags |= IEEE80211_TX_CTL_USE_MINRATE;

net/mac80211/offchannel.c

@@ -113,6 +113,10 @@ void ieee80211_offchannel_stop_vifs(struct ieee80211_local *local)
 	 * notify the AP about us leaving the channel and stop all
 	 * STA interfaces.
 	 */
+
+	ieee80211_stop_queues_by_reason(&local->hw,
+					IEEE80211_QUEUE_STOP_REASON_OFFCHANNEL);
+
 	mutex_lock(&local->iflist_mtx);
 	list_for_each_entry(sdata, &local->interfaces, list) {
 		if (!ieee80211_sdata_running(sdata))
@@ -133,12 +137,9 @@ void ieee80211_offchannel_stop_vifs(struct ieee80211_local *local)
 				sdata, BSS_CHANGED_BEACON_ENABLED);
 		}
 
-		if (sdata->vif.type != NL80211_IFTYPE_MONITOR) {
-			netif_tx_stop_all_queues(sdata->dev);
-			if (sdata->vif.type == NL80211_IFTYPE_STATION &&
-			    sdata->u.mgd.associated)
-				ieee80211_offchannel_ps_enable(sdata);
-		}
+		if (sdata->vif.type == NL80211_IFTYPE_STATION &&
+		    sdata->u.mgd.associated)
+			ieee80211_offchannel_ps_enable(sdata);
 	}
 	mutex_unlock(&local->iflist_mtx);
 }
@@ -166,20 +167,6 @@ void ieee80211_offchannel_return(struct ieee80211_local *local)
 		    sdata->u.mgd.associated)
 			ieee80211_offchannel_ps_disable(sdata);
 
-		if (sdata->vif.type != NL80211_IFTYPE_MONITOR) {
-			/*
-			 * This may wake up queues even though the driver
-			 * currently has them stopped. This is not very
-			 * likely, since the driver won't have gotten any
-			 * (or hardly any) new packets while we weren't
-			 * on the right channel, and even if it happens
-			 * it will at most lead to queueing up one more
-			 * packet per queue in mac80211 rather than on
-			 * the interface qdisc.
-			 */
-			netif_tx_wake_all_queues(sdata->dev);
-		}
-
 		if (test_and_clear_bit(SDATA_STATE_OFFCHANNEL_BEACON_STOPPED,
 				       &sdata->state)) {
 			sdata->vif.bss_conf.enable_beacon = true;
@@ -188,6 +175,9 @@ void ieee80211_offchannel_return(struct ieee80211_local *local)
 		}
 	}
 	mutex_unlock(&local->iflist_mtx);
+
+	ieee80211_wake_queues_by_reason(&local->hw,
+					IEEE80211_QUEUE_STOP_REASON_OFFCHANNEL);
 }
 
 void ieee80211_handle_roc_started(struct ieee80211_roc_work *roc)

net/mac80211/scan.c

@@ -382,6 +382,11 @@ static void ieee80211_scan_state_send_probe(struct ieee80211_local *local,
 	int i;
 	struct ieee80211_sub_if_data *sdata;
 	enum ieee80211_band band = local->hw.conf.channel->band;
+	u32 tx_flags;
+
+	tx_flags = IEEE80211_TX_INTFL_OFFCHAN_TX_OK;
+	if (local->scan_req->no_cck)
+		tx_flags |= IEEE80211_TX_CTL_NO_CCK_RATE;
 
 	sdata = rcu_dereference_protected(local->scan_sdata,
 					  lockdep_is_held(&local->mtx));
@@ -393,9 +398,7 @@ static void ieee80211_scan_state_send_probe(struct ieee80211_local *local,
 			local->scan_req->ssids[i].ssid_len,
 			local->scan_req->ie, local->scan_req->ie_len,
 			local->scan_req->rates[band], false,
-			local->scan_req->no_cck ?
-				IEEE80211_TX_CTL_NO_CCK_RATE : 0,
-			local->hw.conf.channel, true);
+			tx_flags, local->hw.conf.channel, true);
 
 	/*
 	 * After sending probe requests, wait for probe responses

net/mac80211/tx.c

@@ -1230,6 +1230,21 @@ static bool ieee80211_tx_frags(struct ieee80211_local *local,
 		spin_lock_irqsave(&local->queue_stop_reason_lock, flags);
 		if (local->queue_stop_reasons[q] ||
 		    (!txpending && !skb_queue_empty(&local->pending[q]))) {
+			if (unlikely(info->flags &
+					IEEE80211_TX_INTFL_OFFCHAN_TX_OK &&
+				     local->queue_stop_reasons[q] &
+					~BIT(IEEE80211_QUEUE_STOP_REASON_OFFCHANNEL))) {
+				/*
+				 * Drop off-channel frames if queues are stopped
+				 * for any reason other than off-channel
+				 * operation. Never queue them.
+				 */
+				spin_unlock_irqrestore(
+					&local->queue_stop_reason_lock, flags);
+				ieee80211_purge_tx_queue(&local->hw, skbs);
+				return true;
+			}
+
 			/*
 			 * Since queue is stopped, queue up frames for later
 			 * transmission from the tx-pending tasklet when the