[d-kernel] [PATCH 3/2] wifi: mt76: mt7921: fix potential deadlock in mt7921_roc_abort_sync

[Ajrat Makhmutov <rauty@altlinux.org>]

From: Sean Wang <sean.wang@mediatek.com>

roc_abort_sync() can deadlock with roc_work(). roc_work() holds
dev->mt76.mutex, while cancel_work_sync() waits for roc_work()
to finish. If the caller already owns the same mutex, both
sides block and no progress is possible.

This deadlock can occur during station removal when
mt76_sta_state() -> mt76_sta_remove() -> mt7921_mac_sta_remove() ->
mt7921_roc_abort_sync() invokes cancel_work_sync() while
roc_work() is still running and holding dev->mt76.mutex.

This avoids the mutex deadlock and preserves exactly-once
work ownership.

Fixes: 352d966126e6 ("wifi: mt76: mt7921: fix a potential association failure upon resuming")
Co-developed-by: Quan Zhou <quan.zhou@mediatek.com>
Signed-off-by: Quan Zhou <quan.zhou@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Link: https://patch.msgid.link/20260126180013.8167-1-sean.wang@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
(cherry picked from commit d5059e52fd8bc624ec4255c9fa01a266513d126b)

[ALT: keep del_timer_sync() instead of timer_delete_sync() — the
 timer API rename is not present in 6.12.y. ]
---
Дополнение к ранее присланной серии из двух патчей.

Саша Левин на ревью запроса в stable@ указал, что patch 2/2 (5ed54896,
"fix a potential scan no APs") в одиночку вносит достижимый self-deadlock
по dev->mt76.mutex: путь удаления станции идёт под этим mutex (его берёт
ядровая mt76_sta_remove()), а добавленный там roc_abort_sync() делает
cancel_work_sync() по roc_work(), который тоже хочет этот mutex.

Этот коммит (d5059e52) — обязательное лечение, применять вместе с 2/2.
Таким образом серия теперь из трёх патчей.

 drivers/net/wireless/mediatek/mt76/mt7921/main.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/main.c b/drivers/net/wireless/mediatek/mt76/mt7921/main.c
index f2fffca868b51..99561094640f1 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7921/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7921/main.c
@@ -365,12 +365,15 @@ void mt7921_roc_abort_sync(struct mt792x_dev *dev)
 {
 	struct mt792x_phy *phy = &dev->phy;

+	if (!test_and_clear_bit(MT76_STATE_ROC, &phy->mt76->state))
+		return;
+
 	del_timer_sync(&phy->roc_timer);
-	cancel_work_sync(&phy->roc_work);
-	if (test_and_clear_bit(MT76_STATE_ROC, &phy->mt76->state))
-		ieee80211_iterate_interfaces(mt76_hw(dev),
-					     IEEE80211_IFACE_ITER_RESUME_ALL,
-					     mt7921_roc_iter, (void *)phy);
+	cancel_work(&phy->roc_work);
+
+	ieee80211_iterate_interfaces(mt76_hw(dev),
+				     IEEE80211_IFACE_ITER_RESUME_ALL,
+				     mt7921_roc_iter, (void *)phy);
 }
 EXPORT_SYMBOL_GPL(mt7921_roc_abort_sync);

--
2.50.1