--- zzzz-none-000/linux-4.4.60/drivers/net/wireless/ath/ath9k/tx99.c	2017-04-08 07:53:53.000000000 +0000
+++ scorpion-1750e-727/linux-4.4.60/drivers/net/wireless/ath/ath9k/tx99.c	2021-02-04 17:41:59.000000000 +0000
@@ -190,22 +190,27 @@
 	if (strtobool(buf, &start))
 		return -EINVAL;
 
+	mutex_lock(&sc->mutex);
+
 	if (start == sc->tx99_state) {
 		if (!start)
-			return count;
+			goto out;
 		ath_dbg(common, XMIT, "Resetting TX99\n");
 		ath9k_tx99_deinit(sc);
 	}
 
 	if (!start) {
 		ath9k_tx99_deinit(sc);
-		return count;
+		goto out;
 	}
 
 	r = ath9k_tx99_init(sc);
-	if (r)
+	if (r) {
+		mutex_unlock(&sc->mutex);
 		return r;
-
+	}
+out:
+	mutex_unlock(&sc->mutex);
 	return count;
 }