[PATCH v4 2/2] Bluetooth: btusb: Fix leaked runtime PM reference in btusb_reset

[Jiajia Liu <liujiajia@kylinos.cn>]

btusb_reset calls usb_autopm_get_interface to resume the device
before queuing a reset of it, but never calls the matching
usb_autopm_put_interface.

usb_queue_reset_device ends up in usb_reset_device(), and since
btusb provides no pre_reset/post_reset callbacks the interface is
merely unbound and rebound: the interface device object survives
this cycle, and so does its PM usage count, which is not cleared
when the driver is unbound.

As a result every reset permanently leaks a PM usage reference,
preventing the interface from being runtime suspended again until
it is unbound.

Set BTUSB_RESET flag before usb_queue_reset_device so that
btusb_disconnect drops the reference. If the flag is already set,
drop one reference.

Fixes: c9209b269afd ("Bluetooth: btusb: Introduce generic USB reset")
Assisted-by: Claude:qwen3.8-max
Signed-off-by: Jiajia Liu <liujiajia@kylinos.cn>
---

Changes in v4:
- do not return if BTUSB_RESET is set in case the first reset failed.
  (sashiko)

Changes in v3:
- handle multiple reset requests int btusb_reset (sashiko)
  set BTUSB_RESET after usb_autopm_get_interface. If the flag is
  already set, drop newly acquired reference and return.

Changes in v2:
- Fix the race window (sashiko)
  set BTUSB_USB_RESET_ACTIVE flag before usb_queue_reset_device.

Changes in v1:
- add usb_autopm_put_interface after usb_queue_reset_device

---
 drivers/bluetooth/btusb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
index c95f72484fc0f..f92ea1178bc26 100644
--- a/drivers/bluetooth/btusb.c
+++ b/drivers/bluetooth/btusb.c
@@ -1033,13 +1033,15 @@ static void btusb_reset(struct hci_dev *hdev)
 	int err;
 
 	data = hci_get_drvdata(hdev);
-	/* This is not an unbalanced PM reference since the device will reset */
 	err = usb_autopm_get_interface(data->intf);
 	if (err) {
 		bt_dev_err(hdev, "Failed usb_autopm_get_interface: %d", err);
 		return;
 	}
 
+	if (test_and_set_bit(BTUSB_RESET, &data->flags))
+		usb_autopm_put_interface_no_suspend(data->intf);
+
 	bt_dev_err(hdev, "Resetting usb device.");
 	usb_queue_reset_device(data->intf);
 }
-- 
2.53.0