crash in ieee80211_wake_txqs

[Stanislaw Gruszka <sgruszka@redhat.com>]

Hi

I have crash in ieee80211_wake_txqs:
https://imgur.com/a/VIrU9yK
when starting mt76x0u driver. Not sure if this is beacuse the driver
do not initalize sta->txq properly, but reverting the

commit 21a5d4c3a45ca608477a083096cfbce76e449a0c
Author: Manikanta Pubbisetty <mpubbise@codeaurora.org>
Date:   Wed Jul 11 00:12:53 2018 +0530

    mac80211: add stop/start logic for software TXQs

make crash gone.

gdb pointed at 'if (ac != txq->ac)' line in the code:

               for (i = 0; i < ARRAY_SIZE(sta->sta.txq); i++) {
                       struct ieee80211_txq *txq = sta->sta.txq[i];

                       txqi = to_txq_info(txq);

                       if (ac != txq->ac)
                               continue;

Looks txq is NULL and referencing txq->ac crashes.

Thanks
Stanislaw