Re: [PATCH v5 4/4] wifi: ath12k: implement custom wake_tx_queue with flow control

[Jeff Johnson <jeff.johnson@oss.qualcomm.com>]

On 8/11/2026 4:14 AM, Jose Ignacio Tornos Martinez wrote:
> Keeping rcu_read_lock() for the entire function is intentional. 
> ath12k_wifi7_mac_op_tx() calls rcu_dereference() internally (on ahvif->link[]
> and ahsta->link[]), and with CONFIG_DEBUG_LOCK_ALLOC, rcu_dereference() checks
> lock_is_held(&rcu_lock_map) via rcu_read_lock_held(). 
> Only an explicit rcu_read_lock() sets rcu_lock_map and spin_lock_bh() does not,
> so releasing early would trigger lockdep warnings.

hmm, so some of the following commits are broken?
https://lore.kernel.org/all/20250916044735.2316171-1-dolinux.peng@gmail.com/

In particular the one that I merged into ath9k:
https://lore.kernel.org/all/20250916044735.2316171-15-dolinux.peng@gmail.com/

diff --git a/drivers/net/wireless/ath/ath9k/xmit.c
b/drivers/net/wireless/ath/ath9k/xmit.c
index 0ac9212e42f7..4a0f465aa2fe 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -1993,7 +1993,6 @@ void ath_txq_schedule(struct ath_softc *sc, struct
ath_txq *txq)

 	ieee80211_txq_schedule_start(hw, txq->mac80211_qnum);
 	spin_lock_bh(&sc->chan_lock);
-	rcu_read_lock();

 	if (sc->cur_chan->stopped)
 		goto out;
@@ -2011,7 +2010,6 @@ void ath_txq_schedule(struct ath_softc *sc, struct
ath_txq *txq)
 	}

 out:
-	rcu_read_unlock();
 	spin_unlock_bh(&sc->chan_lock);
 	ieee80211_txq_schedule_end(hw, txq->mac80211_qnum);
 }

I fed that into my review agent and it confirms your observation:
  The change works correctly on production kernels without
  CONFIG_DEBUG_LOCK_ALLOC. It will produce a false lockdep splat on debug
  kernels with CONFIG_PROVE_RCU because rcu_dereference() checks
  rcu_read_lock_held() which requires an explicit rcu_read_lock(), not just a
  spinlock.

I have a fixup for ath9k which does:
      171 -  ratetbl = rcu_dereference(sta->rates);
      171 +  ratetbl = rcu_dereference_bh(sta->rates);

Should ath12k also use rcu_dereference_bh()?

/jeff