iwlwifi: mvm: synchronize TID queue removal

When we mark a TID as no longer having a queue, there's no
guarantee the TX path isn't using this txq_id right now,
having accessed it just before we reset the value. To fix
this, add synchronize_net() when we change the TIDs from
having a queue to not having one, so that we can then be
sure that the TX path is no longer accessing that queue.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

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

@@ -545,6 +545,16 @@ static int iwl_mvm_remove_sta_queue_marking(struct iwl_mvm *mvm, int queue)
 
 	rcu_read_unlock();
 
+	/*
+	 * The TX path may have been using this TXQ_ID from the tid_data,
+	 * so make sure it's no longer running so that we can safely reuse
+	 * this TXQ later. We've set all the TIDs to IWL_MVM_INVALID_QUEUE
+	 * above, but nothing guarantees we've stopped using them. Thus,
+	 * without this, we could get to iwl_mvm_disable_txq() and remove
+	 * the queue while still sending frames to it.
+	 */
+	synchronize_net();
+
 	return disable_agg_tids;
 }