ath9k: add txq locking for ath_tx_aggr_start

Prevents race conditions when un-aggregated frames are pending in the
driver.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/xmit.c

@@ -1390,11 +1390,15 @@ int ath_tx_aggr_start(struct ath_softc *sc, struct ieee80211_sta *sta,
 		      u16 tid, u16 *ssn)
 {
 	struct ath_atx_tid *txtid;
+	struct ath_txq *txq;
 	struct ath_node *an;
 	u8 density;
 
 	an = (struct ath_node *)sta->drv_priv;
 	txtid = ATH_AN_2_TID(an, tid);
+	txq = txtid->ac->txq;
+
+	ath_txq_lock(sc, txq);
 
 	/* update ampdu factor/density, they may have changed. This may happen
 	 * in HT IBSS when a beacon with HT-info is received after the station
@@ -1418,6 +1422,8 @@ int ath_tx_aggr_start(struct ath_softc *sc, struct ieee80211_sta *sta,
 	memset(txtid->tx_buf, 0, sizeof(txtid->tx_buf));
 	txtid->baw_head = txtid->baw_tail = 0;
 
+	ath_txq_unlock_complete(sc, txq);
+
 	return 0;
 }