[PATCH] wifi: mt76: mt7925: Fix unregister deadlock

[PATCH] wifi: mt76: mt7925: Fix unregister deadlock

[JB Tsai]

During device shutdown or removal, a deadlock can occur between the
PCIe remove path and the driver's asynchronous reset work.

The unregistration path calls napi_disable() before cancelling the
reset work. If the reset work runs concurrently, it may re-enable NAPI
and schedule it. Because the device is being unregistered, this can
lead to NAPI state corruption where NAPI is marked as scheduled but
never polled, causing subsequent napi_disable() calls to hang forever.

Fix this by:
1. Moving cancel_work_sync(&dev->reset_work) to the very start of
   mt7925e_unregister_device(), ensuring it is stopped before NAPI
   is disabled.
2. Setting the MT76_REMOVED flag early in the PCI remove path to
   prevent new reset work from being queued.
3. Checking MT76_REMOVED in mt7925_mac_reset_work() and aborting the
   reset early if the device is being removed.

Co-developed-by: Fei Shao <fshao@google.com>
Signed-off-by: JB Tsai <jb.tsai@mediatek.com>
---
 drivers/net/wireless/mediatek/mt76/mt7925/mac.c | 7 +++++++
 drivers/net/wireless/mediatek/mt76/mt7925/pci.c | 4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
index 0641a7131d7c..1c6d43b162c0 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
@@ -1319,6 +1319,9 @@ void mt7925_mac_reset_work(struct work_struct *work)
 	cancel_work_sync(&pm->wake_work);
 
 	for (i = 0; i < 10; i++) {
+		if (test_bit(MT76_REMOVED, &dev->mt76.phy.state))
+			goto out;
+
 		mutex_lock(&dev->mt76.mutex);
 		ret = mt792x_dev_reset(dev);
 		mutex_unlock(&dev->mt76.mutex);
@@ -1338,8 +1341,12 @@ void mt7925_mac_reset_work(struct work_struct *work)
 		ieee80211_scan_completed(dev->mphy.hw, &info);
 	}
 
+out:
 	dev->hw_full_reset = false;
 	pm->suspended = false;
+	if (test_bit(MT76_REMOVED, &dev->mt76.phy.state))
+		return;
+
 	ieee80211_wake_queues(hw);
 	ieee80211_iterate_active_interfaces(hw,
 					    IEEE80211_IFACE_ITER_RESUME_ALL,
diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/pci.c b/drivers/net/wireless/mediatek/mt76/mt7925/pci.c
index ea64303283ed..978a3f08e080 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/pci.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/pci.c
@@ -43,13 +43,13 @@ static void mt7925e_unregister_device(struct mt792x_dev *dev)
 	if (dev->phy.chip_cap & MT792x_CHIP_CAP_WF_RF_PIN_CTRL_EVT_EN)
 		wiphy_rfkill_stop_polling(hw->wiphy);
 
+	cancel_work_sync(&dev->reset_work);
 	cancel_work_sync(&dev->init_work);
 	mt76_unregister_device(&dev->mt76);
 	mt76_for_each_q_rx(&dev->mt76, i)
 		napi_disable(&dev->mt76.napi[i]);
 	cancel_delayed_work_sync(&pm->ps_work);
 	cancel_work_sync(&pm->wake_work);
-	cancel_work_sync(&dev->reset_work);
 
 	mt7925_tx_token_put(dev);
 	__mt792x_mcu_drv_pmctrl(dev);
@@ -498,8 +498,8 @@ static void mt7925_pci_remove(struct pci_dev *pdev)
 	struct mt76_dev *mdev = pci_get_drvdata(pdev);
 	struct mt792x_dev *dev = container_of(mdev, struct mt792x_dev, mt76);
 
-	mt7925e_unregister_device(dev);
 	set_bit(MT76_REMOVED, &mdev->phy.state);
+	mt7925e_unregister_device(dev);
 	devm_free_irq(&pdev->dev, pdev->irq, dev);
 	mt76_free_device(&dev->mt76);
 	pci_free_irq_vectors(pdev);
-- 
2.45.2

Re: [PATCH] wifi: mt76: mt7925: Fix unregister deadlock

[Rafael Passos]

I was having issues with the MT7925 on the ASRock B850M with Bluetooth.
I tested this and other patches in my investigation.
My issue was a platform bug causing a failure in USB enumeration
before the driver path (unrelated to the patch).

I can confirm this patch does not introduce regressions on this platform.
I tested system power cycling and suspension, BT/Wifi adapter enable/disable,
and also modprobing in/out mt7925{e/u}
Patch applied on top of mailine (7.2 rc1).

Tested-by: Rafael Passos <rafael@rcpassos.me>

Thanks,
Rafael Passos