wifi: iwlwifi: mvm: protect TXQ list manipulation

Some recent upstream debugging uncovered the fact that in
iwlwifi, the TXQ list manipulation is racy.

Introduce a new state bit for when the TXQ is completely
ready and can be used without locking, and if that's not
set yet acquire the lock to check everything correctly.

Reviewed-by: Benjamin Berg <[e-mail]>
Tested-by: Jose Ignacio Tornos Martinez <[e-mail]>
Signed-off-by: Johannes Berg <[e-mail]>

drivers/net/wireless/intel/iwlwifi/mvm/mac80211.c

···
 	struct iwl_mvm *mvm = IWL_MAC80211_GET_MVM(hw);
 	struct iwl_mvm_txq *mvmtxq = iwl_mvm_txq_from_mac80211(txq);
 
-	/*
-	 * Please note that racing is handled very carefully here:
-	 * mvmtxq->txq_id is updated during allocation, and mvmtxq->list is
-	 * deleted afterwards.
-	 * This means that if:
-	 * mvmtxq->txq_id != INVALID_QUEUE && list_empty(&mvmtxq->list):
-	 *	queue is allocated and we can TX.
-	 * mvmtxq->txq_id != INVALID_QUEUE && !list_empty(&mvmtxq->list):
-	 *	a race, should defer the frame.
-	 * mvmtxq->txq_id == INVALID_QUEUE && list_empty(&mvmtxq->list):
-	 *	need to allocate the queue and defer the frame.
-	 * mvmtxq->txq_id == INVALID_QUEUE && !list_empty(&mvmtxq->list):
-	 *	queue is already scheduled for allocation, no need to allocate,
-	 *	should defer the frame.
-	 */
-
-	/* If the queue is allocated TX and return. */
-	if (!txq->sta || mvmtxq->txq_id != IWL_MVM_INVALID_QUEUE) {
-		/*
-		 * Check that list is empty to avoid a race where txq_id is
-		 * already updated, but the queue allocation work wasn't
-		 * finished
-		 */
-		if (unlikely(txq->sta && !list_empty(&mvmtxq->list)))
-			return;
-
+	if (likely(test_bit(IWL_MVM_TXQ_STATE_READY, &mvmtxq->state)) ||
+	    !txq->sta) {
 		iwl_mvm_mac_itxq_xmit(hw, txq);
 		return;
 	}
 
-	/* The list is being deleted only after the queue is fully allocated. */
-	if (!list_empty(&mvmtxq->list))
-		return;
+	/* iwl_mvm_mac_itxq_xmit() will later be called by the worker
+	 * to handle any packets we leave on the txq now
+	 */
 
-	list_add_tail(&mvmtxq->list, &mvm->add_stream_txqs);
-	schedule_work(&mvm->add_stream_wk);
+	spin_lock_bh(&mvm->add_stream_lock);
+	/* The list is being deleted only after the queue is fully allocated. */
+	if (list_empty(&mvmtxq->list) &&
+	    /* recheck under lock */
+	    !test_bit(IWL_MVM_TXQ_STATE_READY, &mvmtxq->state)) {
+		list_add_tail(&mvmtxq->list, &mvm->add_stream_txqs);
+		schedule_work(&mvm->add_stream_wk);
+	}
+	spin_unlock_bh(&mvm->add_stream_lock);
 }
 
 #define CHECK_BA_TRIGGER(_mvm, _trig, _tid_bm, _tid, _fmt...)		\

drivers/net/wireless/intel/iwlwifi/mvm/mvm.h

···
 	atomic_t tx_request;
 #define IWL_MVM_TXQ_STATE_STOP_FULL	0
 #define IWL_MVM_TXQ_STATE_STOP_REDIRECT	1
+#define IWL_MVM_TXQ_STATE_READY		2
 	unsigned long state;
 };
 
···
 		struct iwl_mvm_tvqm_txq_info tvqm_info[IWL_MAX_TVQM_QUEUES];
 	};
 	struct work_struct add_stream_wk; /* To add streams to queues */
+	spinlock_t add_stream_lock;
 
 	const char *nvm_file_name;
 	struct iwl_nvm_data *nvm_data;

drivers/net/wireless/intel/iwlwifi/mvm/ops.c

···
 	INIT_DELAYED_WORK(&mvm->scan_timeout_dwork, iwl_mvm_scan_timeout_wk);
 	INIT_WORK(&mvm->add_stream_wk, iwl_mvm_add_new_dqa_stream_wk);
 	INIT_LIST_HEAD(&mvm->add_stream_txqs);
+	spin_lock_init(&mvm->add_stream_lock);
 
 	init_waitqueue_head(&mvm->rx_sync_waitq);
 

drivers/net/wireless/intel/iwlwifi/mvm/sta.c

···
 		struct iwl_mvm_txq *mvmtxq =
 			iwl_mvm_txq_from_tid(sta, tid);
 
-		mvmtxq->txq_id = IWL_MVM_INVALID_QUEUE;
+		spin_lock_bh(&mvm->add_stream_lock);
 		list_del_init(&mvmtxq->list);
+		clear_bit(IWL_MVM_TXQ_STATE_READY, &mvmtxq->state);
+		mvmtxq->txq_id = IWL_MVM_INVALID_QUEUE;
+		spin_unlock_bh(&mvm->add_stream_lock);
 	}
 
 	/* Regardless if this is a reserved TXQ for a STA - mark it as false */
···
 			disable_agg_tids |= BIT(tid);
 		mvmsta->tid_data[tid].txq_id = IWL_MVM_INVALID_QUEUE;
 
-		mvmtxq->txq_id = IWL_MVM_INVALID_QUEUE;
+		spin_lock_bh(&mvm->add_stream_lock);
 		list_del_init(&mvmtxq->list);
+		clear_bit(IWL_MVM_TXQ_STATE_READY, &mvmtxq->state);
+		mvmtxq->txq_id = IWL_MVM_INVALID_QUEUE;
+		spin_unlock_bh(&mvm->add_stream_lock);
 	}
 
 	mvmsta->tfd_queue_msk &= ~BIT(queue); /* Don't use this queue anymore */
···
 		 * a queue in the function itself.
 		 */
 		if (iwl_mvm_sta_alloc_queue(mvm, txq->sta, txq->ac, tid)) {
+			spin_lock_bh(&mvm->add_stream_lock);
 			list_del_init(&mvmtxq->list);
+			spin_unlock_bh(&mvm->add_stream_lock);
 			continue;
 		}
 
-		list_del_init(&mvmtxq->list);
+		/* now we're ready, any remaining races/concurrency will be
+		 * handled in iwl_mvm_mac_itxq_xmit()
+		 */
+		set_bit(IWL_MVM_TXQ_STATE_READY, &mvmtxq->state);
+
 		local_bh_disable();
+		spin_lock(&mvm->add_stream_lock);
+		list_del_init(&mvmtxq->list);
+		spin_unlock(&mvm->add_stream_lock);
+
 		iwl_mvm_mac_itxq_xmit(mvm->hw, txq);
 		local_bh_enable();
 	}
···
 		struct iwl_mvm_txq *mvmtxq =
 			iwl_mvm_txq_from_mac80211(sta->txq[i]);
 
+		spin_lock_bh(&mvm->add_stream_lock);
 		mvmtxq->txq_id = IWL_MVM_INVALID_QUEUE;
 		list_del_init(&mvmtxq->list);
+		clear_bit(IWL_MVM_TXQ_STATE_READY, &mvmtxq->state);
+		spin_unlock_bh(&mvm->add_stream_lock);
 	}
 }