[PATCH mt76] wifi: mt76: mt792x: drop redundant napi_disable() in unregister path

[Mikhail Gavrilov]

Commit 13b7e6a96a00 ("wifi: mt76: Disable napi when removing device")
made mt76_dma_cleanup() disable every RX NAPI instance before deleting
it.  mt7921e_unregister_device() and mt7925e_unregister_device() already
disable the very same instances and only afterwards call
mt792x_dma_cleanup() -> mt76_dma_cleanup(), so each instance is now
disabled twice.

napi_disable() is not idempotent: on return it leaves NAPIF_STATE_SCHED
and NAPIF_STATE_NPSVC set, so a second call without an intervening
napi_enable() spins in usleep_range() forever, waiting for bits that
nobody will clear:

  task:modprobe        state:D stack:25720 pid:7954  tgid:7954
  Call Trace:
   <TASK>
   __schedule+0x11b8/0x26d0
   schedule+0xe7/0x2f0
   schedule_hrtimeout_range_clock+0x218/0x330
   usleep_range_state+0x133/0x1b0
   napi_disable_locked+0x37d/0x5f0
   napi_disable+0x43/0x80
   mt76_dma_cleanup+0x2b4/0x860 [mt76]
   mt7921_pci_remove+0x17f/0x350 [mt7921e]
   pci_device_remove+0xb6/0x1e0
   device_release_driver_internal+0x38d/0x540
   driver_detach+0xd0/0x1b0
   bus_remove_driver+0x127/0x2d0
   pci_unregister_driver+0x2a/0x280
   __do_sys_delete_module+0x36a/0x5b0
   do_syscall_64+0x11c/0x6d0
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
   </TASK>

mt7921_pci_shutdown() and mt7925_pci_shutdown() reuse the remove path,
so the same deadlock is hit on every reboot and poweroff.  It is silent:
the stuck task keeps sleeping and rescheduling, so neither the hung task
detector nor the lockup detectors fire, and the last line on the console
is "systemd-shutdown[1]: Rebooting."

Drop the driver-side loops and rely on mt76_dma_cleanup() instead.
mt792x_dma_cleanup() stops and resets the WFDMA engine before calling
it, so RX is already quiesced when the NAPI instances are disabled
there.

Fixes: 13b7e6a96a00 ("wifi: mt76: Disable napi when removing device")
Reported-by: Bert Karwatzki <spasswolf@xxxxxx>
Closes: https://lore.kernel.org/all/20260724151419.26014-1-spasswolf@xxxxxx/
Suggested-by: Nicolas Cavallari <nicolas.cavallari@xxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
---

I hit the same hang on an ASRock B650I Lightning WiFi with MT7922
(mt7921e) and bisected it to the same commit.  mt7921e has the same
duplicated napi_disable() as mt7925e, so this covers both; it is
Nicolas' suggestion from [1] extended to mt7921e and with the now
unused 'int i' removed.
 
Tested on 7.2.0-rc5 with KASAN and lockdep enabled, MT7922 / mt7921e.
Before the patch 'modprobe -r mt7921e' hangs (backtrace above, taken
with sysrq-w) and the machine never gets past "Rebooting.".  With the
patch 'modprobe -r mt7921e' and 'modprobe mt7921e' both complete and
the interface comes back up, reboot and poweroff work again, and no
__netif_napi_del_locked() or page_pool_disable_direct_recycling()
warnings are logged.
 
[1] https://lore.kernel.org/all/59c03ab1-ec4a-411b-9b7e-8183ecf3e02b@xxxxxxxxxxxxxxxxxxxxxxx/

 drivers/net/wireless/mediatek/mt76/mt7921/pci.c | 3 ---
 drivers/net/wireless/mediatek/mt76/mt7925/pci.c | 3 ---
 2 files changed, 6 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/pci.c b/drivers/net/wireless/mediatek/mt76/mt7921/pci.c
index 7728c5ae6791..65d09d13304f 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7921/pci.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7921/pci.c
@@ -43,7 +43,6 @@ static int mt7921e_init_reset(struct mt792x_dev *dev)
 
 static void mt7921e_unregister_device(struct mt792x_dev *dev)
 {
-	int i;
 	struct mt76_connac_pm *pm = &dev->pm;
 	struct ieee80211_hw *hw = mt76_hw(dev);
 
@@ -52,8 +51,6 @@ static void mt7921e_unregister_device(struct mt792x_dev *dev)
 
 	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);
diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/pci.c b/drivers/net/wireless/mediatek/mt76/mt7925/pci.c
index ea64303283ed..eb1bd60e3d9f 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/pci.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/pci.c
@@ -36,7 +36,6 @@ static int mt7925e_init_reset(struct mt792x_dev *dev)
 
 static void mt7925e_unregister_device(struct mt792x_dev *dev)
 {
-	int i;
 	struct mt76_connac_pm *pm = &dev->pm;
 	struct ieee80211_hw *hw = mt76_hw(dev);
 
@@ -45,8 +44,6 @@ static void mt7925e_unregister_device(struct mt792x_dev *dev)
 
 	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);
-- 
2.55.0