[PATCH wireless-next] wifi: mt76: use wait_event_interruptible in worker thread for PREEMPT_RT

[PATCH wireless-next] wifi: mt76: use wait_event_interruptible in worker thread for PREEMPT_RT

[Joshua Klinesmith]

The mt76 worker thread uses a manual set_current_state(TASK_INTERRUPTIBLE)
/ schedule() loop. On PREEMPT_RT kernels, this pattern triggers:

  BUG: scheduling while atomic: mt76-usb-rx phy/2852/0x00000002

The manual task state manipulation interacts poorly with RT's preemption
model, where different locking and state transition semantics apply.

Replace the open-coded sleep loop with wait_event_interruptible() on a
new wait_queue_head embedded in struct mt76_worker. The schedule point
becomes an RT-safe wait_event that properly handles the task state
transitions. Update mt76_worker_schedule() to use wake_up() to signal
the wait queue.

This follows the standard kernel pattern for kthread wait loops and
eliminates the need for manual set_current_state() calls entirely.

Link: https://github.com/openwrt/mt76/issues/1053
Signed-off-by: Joshua Klinesmith <joshuaklinesmith@gmail.com>
---
 drivers/net/wireless/mediatek/mt76/util.c | 8 ++++----
 drivers/net/wireless/mediatek/mt76/util.h | 5 ++++-
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/util.c b/drivers/net/wireless/mediatek/mt76/util.c
index 83d3dc42e534..452c303d8a68 100644
--- a/drivers/net/wireless/mediatek/mt76/util.c
+++ b/drivers/net/wireless/mediatek/mt76/util.c
@@ -111,20 +111,20 @@ int __mt76_worker_fn(void *ptr)
 	struct mt76_worker *w = ptr;
 
 	while (!kthread_should_stop()) {
-		set_current_state(TASK_INTERRUPTIBLE);
-
 		if (kthread_should_park()) {
 			kthread_parkme();
 			continue;
 		}
 
 		if (!test_and_clear_bit(MT76_WORKER_SCHEDULED, &w->state)) {
-			schedule();
+			wait_event_interruptible(w->wq,
+				test_bit(MT76_WORKER_SCHEDULED, &w->state) ||
+				kthread_should_stop() ||
+				kthread_should_park());
 			continue;
 		}
 
 		set_bit(MT76_WORKER_RUNNING, &w->state);
-		set_current_state(TASK_RUNNING);
 		w->fn(w);
 		cond_resched();
 		clear_bit(MT76_WORKER_RUNNING, &w->state);
diff --git a/drivers/net/wireless/mediatek/mt76/util.h b/drivers/net/wireless/mediatek/mt76/util.h
index 617966e8de76..a1ac52753a3f 100644
--- a/drivers/net/wireless/mediatek/mt76/util.h
+++ b/drivers/net/wireless/mediatek/mt76/util.h
@@ -9,12 +9,14 @@
 #include <linux/skbuff.h>
 #include <linux/bitops.h>
 #include <linux/bitfield.h>
+#include <linux/wait.h>
 #include <net/mac80211.h>
 
 struct mt76_worker
 {
 	struct task_struct *task;
 	void (*fn)(struct mt76_worker *);
+	wait_queue_head_t wq;
 	unsigned long state;
 };
 
@@ -63,6 +65,7 @@ mt76_worker_setup(struct ieee80211_hw *hw, struct mt76_worker *w,
 
 	if (fn)
 		w->fn = fn;
+	init_waitqueue_head(&w->wq);
 	w->task = kthread_run(__mt76_worker_fn, w,
 			      "mt76-%s %s", name, dev_name);
 
@@ -82,7 +85,7 @@ static inline void mt76_worker_schedule(struct mt76_worker *w)
 
 	if (!test_and_set_bit(MT76_WORKER_SCHEDULED, &w->state) &&
 	    !test_bit(MT76_WORKER_RUNNING, &w->state))
-		wake_up_process(w->task);
+		wake_up(&w->wq);
 }
 
 static inline void mt76_worker_disable(struct mt76_worker *w)
-- 
2.43.0