mac80211: improve locking around the txq scheduling / airtime fairness API

Signed-off-by: Felix Fietkau <[email protected]>

package/kernel/mac80211/patches/subsys/352-mac80211-rework-locking-for-txq-scheduling-airtime-f.patch

@@ -0,0 +1,214 @@
+From: Felix Fietkau <[email protected]>
+Date: Wed, 13 Mar 2019 19:09:22 +0100
+Subject: [PATCH] mac80211: rework locking for txq scheduling / airtime
+ fairness
+
+Holding the lock around the entire duration of tx scheduling can create
+some nasty lock contention, especially when processing airtime information
+from the tx status or the rx path.
+Improve locking by only holding the active_txq_lock for lookups / scheduling
+list modifications.
+
+Signed-off-by: Felix Fietkau <[email protected]>
+---
+
+--- a/include/net/mac80211.h
++++ b/include/net/mac80211.h
+@@ -6069,8 +6069,6 @@ struct sk_buff *ieee80211_tx_dequeue(str
+  * @hw: pointer as obtained from ieee80211_alloc_hw()
+  * @ac: AC number to return packets from.
+  *
+- * Should only be called between calls to ieee80211_txq_schedule_start()
+- * and ieee80211_txq_schedule_end().
+  * Returns the next txq if successful, %NULL if no queue is eligible. If a txq
+  * is returned, it should be returned with ieee80211_return_txq() after the
+  * driver has finished scheduling it.
+@@ -6078,51 +6076,41 @@ struct sk_buff *ieee80211_tx_dequeue(str
+ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac);
+ 
+ /**
+- * ieee80211_return_txq - return a TXQ previously acquired by ieee80211_next_txq()
+- *
+- * @hw: pointer as obtained from ieee80211_alloc_hw()
+- * @txq: pointer obtained from station or virtual interface
+- *
+- * Should only be called between calls to ieee80211_txq_schedule_start()
+- * and ieee80211_txq_schedule_end().
+- */
+-void ieee80211_return_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq);
+-
+-/**
+- * ieee80211_txq_schedule_start - acquire locks for safe scheduling of an AC
++ * ieee80211_txq_schedule_start - start new scheduling round for TXQs
+  *
+  * @hw: pointer as obtained from ieee80211_alloc_hw()
+  * @ac: AC number to acquire locks for
+  *
+- * Acquire locks needed to schedule TXQs from the given AC. Should be called
+- * before ieee80211_next_txq() or ieee80211_return_txq().
++ * Should be called before ieee80211_next_txq() or ieee80211_return_txq().
+  */
+-void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac)
+-	__acquires(txq_lock);
++void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac);
++
++/* (deprecated) */
++static inline void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
++{
++}
+ 
+ /**
+- * ieee80211_txq_schedule_end - release locks for safe scheduling of an AC
++ * ieee80211_schedule_txq - schedule a TXQ for transmission
+  *
+  * @hw: pointer as obtained from ieee80211_alloc_hw()
+- * @ac: AC number to acquire locks for
++ * @txq: pointer obtained from station or virtual interface
+  *
+- * Release locks previously acquired by ieee80211_txq_schedule_end().
++ * Schedules a TXQ for transmission if it is not already scheduled.
+  */
+-void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
+-	__releases(txq_lock);
++void ieee80211_schedule_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq);
+ 
+ /**
+- * ieee80211_schedule_txq - schedule a TXQ for transmission
++ * ieee80211_return_txq - return a TXQ previously acquired by ieee80211_next_txq()
+  *
+  * @hw: pointer as obtained from ieee80211_alloc_hw()
+  * @txq: pointer obtained from station or virtual interface
+- *
+- * Schedules a TXQ for transmission if it is not already scheduled. Takes a
+- * lock, which means it must *not* be called between
+- * ieee80211_txq_schedule_start() and ieee80211_txq_schedule_end()
+  */
+-void ieee80211_schedule_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq)
+-	__acquires(txq_lock) __releases(txq_lock);
++static inline void
++ieee80211_return_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq)
++{
++	ieee80211_schedule_txq(hw, txq);
++}
+ 
+ /**
+  * ieee80211_txq_may_transmit - check whether TXQ is allowed to transmit
+--- a/net/mac80211/tx.c
++++ b/net/mac80211/tx.c
+@@ -3619,16 +3619,17 @@ EXPORT_SYMBOL(ieee80211_tx_dequeue);
+ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
+ {
+ 	struct ieee80211_local *local = hw_to_local(hw);
++	struct ieee80211_txq *ret = NULL;
+ 	struct txq_info *txqi = NULL;
+ 
+-	lockdep_assert_held(&local->active_txq_lock[ac]);
++	spin_lock_bh(&local->active_txq_lock[ac]);
+ 
+  begin:
+ 	txqi = list_first_entry_or_null(&local->active_txqs[ac],
+ 					struct txq_info,
+ 					schedule_order);
+ 	if (!txqi)
+-		return NULL;
++		goto out;
+ 
+ 	if (txqi->txq.sta) {
+ 		struct sta_info *sta = container_of(txqi->txq.sta,
+@@ -3645,21 +3646,25 @@ struct ieee80211_txq *ieee80211_next_txq
+ 
+ 
+ 	if (txqi->schedule_round == local->schedule_round[ac])
+-		return NULL;
++		goto out;
+ 
+ 	list_del_init(&txqi->schedule_order);
+ 	txqi->schedule_round = local->schedule_round[ac];
+-	return &txqi->txq;
++	ret = &txqi->txq;
++
++out:
++	spin_unlock_bh(&local->active_txq_lock[ac]);
++	return ret;
+ }
+ EXPORT_SYMBOL(ieee80211_next_txq);
+ 
+-void ieee80211_return_txq(struct ieee80211_hw *hw,
+-			  struct ieee80211_txq *txq)
++void ieee80211_schedule_txq(struct ieee80211_hw *hw,
++			    struct ieee80211_txq *txq)
+ {
+ 	struct ieee80211_local *local = hw_to_local(hw);
+ 	struct txq_info *txqi = to_txq_info(txq);
+ 
+-	lockdep_assert_held(&local->active_txq_lock[txq->ac]);
++	spin_lock_bh(&local->active_txq_lock[txq->ac]);
+ 
+ 	if (list_empty(&txqi->schedule_order) &&
+ 	    (!skb_queue_empty(&txqi->frags) || txqi->tin.backlog_packets)) {
+@@ -3679,18 +3684,7 @@ void ieee80211_return_txq(struct ieee802
+ 			list_add_tail(&txqi->schedule_order,
+ 				      &local->active_txqs[txq->ac]);
+ 	}
+-}
+-EXPORT_SYMBOL(ieee80211_return_txq);
+ 
+-void ieee80211_schedule_txq(struct ieee80211_hw *hw,
+-			    struct ieee80211_txq *txq)
+-	__acquires(txq_lock) __releases(txq_lock)
+-{
+-	struct ieee80211_local *local = hw_to_local(hw);
+-	struct txq_info *txqi = to_txq_info(txq);
+-
+-	spin_lock_bh(&local->active_txq_lock[txq->ac]);
+-	ieee80211_return_txq(hw, txq);
+ 	spin_unlock_bh(&local->active_txq_lock[txq->ac]);
+ }
+ EXPORT_SYMBOL(ieee80211_schedule_txq);
+@@ -3703,7 +3697,7 @@ bool ieee80211_txq_may_transmit(struct i
+ 	struct sta_info *sta;
+ 	u8 ac = txq->ac;
+ 
+-	lockdep_assert_held(&local->active_txq_lock[ac]);
++	spin_lock_bh(&local->active_txq_lock[ac]);
+ 
+ 	if (!txqi->txq.sta)
+ 		goto out;
+@@ -3733,34 +3727,27 @@ bool ieee80211_txq_may_transmit(struct i
+ 
+ 	sta->airtime[ac].deficit += sta->airtime_weight;
+ 	list_move_tail(&txqi->schedule_order, &local->active_txqs[ac]);
++	spin_unlock_bh(&local->active_txq_lock[ac]);
+ 
+ 	return false;
+ out:
+ 	if (!list_empty(&txqi->schedule_order))
+ 		list_del_init(&txqi->schedule_order);
++	spin_unlock_bh(&local->active_txq_lock[ac]);
+ 
+ 	return true;
+ }
+ EXPORT_SYMBOL(ieee80211_txq_may_transmit);
+ 
+ void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac)
+-	__acquires(txq_lock)
+ {
+ 	struct ieee80211_local *local = hw_to_local(hw);
+ 
+ 	spin_lock_bh(&local->active_txq_lock[ac]);
+ 	local->schedule_round[ac]++;
+-}
+-EXPORT_SYMBOL(ieee80211_txq_schedule_start);
+-
+-void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
+-	__releases(txq_lock)
+-{
+-	struct ieee80211_local *local = hw_to_local(hw);
+-
+ 	spin_unlock_bh(&local->active_txq_lock[ac]);
+ }
+-EXPORT_SYMBOL(ieee80211_txq_schedule_end);
++EXPORT_SYMBOL(ieee80211_txq_schedule_start);
+ 
+ void __ieee80211_subif_start_xmit(struct sk_buff *skb,
+ 				  struct net_device *dev,