[PATCH wireless] wifi: mt76: usb: keep the tx worker parked through a reset or teardown

[Devin Wittmayer]

The mt792x USB reset and disconnect paths park the tx worker and then
stop tx. If frames are still queued when the wait runs out, stopping tx
parks the worker a second time, which warns. It then unparks the worker,
which runs again during the chip reset or the teardown:

  WARNING: kernel/kthread.c:710 at kthread_park+0x8c/0xc0, CPU#2: kworker/u16:1/100
  Workqueue: mt76 mt7925_mac_reset_work [mt7925_common]
  Call Trace:
   mt7925u_mac_reset.part.0+0x73/0x1e0 [mt7925u]
   mt7925u_mac_reset+0x3c/0x50 [mt7925u]
   mt7925_mac_reset_work+0xb5/0x1f0 [mt7925_common]

Remember that a worker is disabled, and leave the worker to the caller
that parked it.

Fixes: 0d2afe09fad5 ("mt76: mt7921: add mt7921u driver")
Fixes: 7910bd565d8b ("wifi: mt76: mt792x: quiesce USB paths on disconnect")
Signed-off-by: Devin Wittmayer <lucid_duck at justthetip.ca>
---
Making the disable call skip an already parked worker is not enough on
its own: stopping tx would still unpark the worker at its end.

Viktor Pashaiev's mt792x USB hardening patch avoided the same warning on
disconnect by not parking the worker there:
https://lore.kernel.org/linux-wireless/20260927180415.1498019-1-w.paszajew@gmail.com/
This keeps the park and fixes the stop path, which also covers the reset.

 drivers/net/wireless/mediatek/mt76/usb.c  | 10 ++++++++--
 drivers/net/wireless/mediatek/mt76/util.h |  9 ++++++++-
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
index be48a88a3ad0..47106ed6bb94 100644
--- a/drivers/net/wireless/mediatek/mt76/usb.c
+++ b/drivers/net/wireless/mediatek/mt76/usb.c
@@ -1068,6 +1068,7 @@ void mt76u_stop_tx(struct mt76_dev *dev)
 	ret = wait_event_timeout(dev->tx_wait, !mt76_has_tx_pending(&dev->phy),
 				 HZ / 5);
 	if (!ret) {
+		bool parked = mt76_worker_disabled(&dev->tx_worker);
 		struct mt76_queue_entry entry;
 		struct mt76_queue *q;
 		int i, j;
@@ -1083,7 +1084,11 @@ void mt76u_stop_tx(struct mt76_dev *dev)
 				usb_kill_urb(q->entry[j].urb);
 		}
 
-		mt76_worker_disable(&dev->tx_worker);
+		/* The mt792x disconnect and reset paths park the worker
+		 * before they get here. Leave it parked for them.
+		 */
+		if (!parked)
+			mt76_worker_disable(&dev->tx_worker);
 
 		/* On device removal we maight queue skb's, but mt76u_tx_kick()
 		 * will fail to submit urb, cleanup those skb's manually.
@@ -1100,7 +1105,8 @@ void mt76u_stop_tx(struct mt76_dev *dev)
 			}
 		}
 
-		mt76_worker_enable(&dev->tx_worker);
+		if (!parked)
+			mt76_worker_enable(&dev->tx_worker);
 	}
 
 	cancel_work_sync(&dev->usb.stat_work);
diff --git a/drivers/net/wireless/mediatek/mt76/util.h b/drivers/net/wireless/mediatek/mt76/util.h
index 617966e8de76..71f3aa42bb82 100644
--- a/drivers/net/wireless/mediatek/mt76/util.h
+++ b/drivers/net/wireless/mediatek/mt76/util.h
@@ -21,6 +21,7 @@ struct mt76_worker
 enum {
 	MT76_WORKER_SCHEDULED,
 	MT76_WORKER_RUNNING,
+	MT76_WORKER_DISABLED,
 };
 
 #define MT76_INCR(_var, _size) \
@@ -91,7 +92,7 @@ static inline void mt76_worker_disable(struct mt76_worker *w)
 		return;
 
 	kthread_park(w->task);
-	WRITE_ONCE(w->state, 0);
+	WRITE_ONCE(w->state, BIT(MT76_WORKER_DISABLED));
 }
 
 static inline void mt76_worker_enable(struct mt76_worker *w)
@@ -99,10 +100,16 @@ static inline void mt76_worker_enable(struct mt76_worker *w)
 	if (!w->task)
 		return;
 
+	clear_bit(MT76_WORKER_DISABLED, &w->state);
 	kthread_unpark(w->task);
 	mt76_worker_schedule(w);
 }
 
+static inline bool mt76_worker_disabled(struct mt76_worker *w)
+{
+	return test_bit(MT76_WORKER_DISABLED, &w->state);
+}
+
 static inline void mt76_worker_teardown(struct mt76_worker *w)
 {
 	if (!w->task)
-- 
2.56.0