[PATCH] Bluetooth: fix kernel null pointer dereference error on suspend

[Vamshi K Sthambamkadi]

BUG Call Trace:
  queue_work_on+0x39/0x40
  hci_adv_monitors_clear+0x71/0x90 [bluetooth]
  hci_unregister_dev+0x18a/0x2f0 [bluetooth]
  btusb_disconnect+0x68/0x150 [btusb]
  usb_unbind_interface+0x7f/0x260
  device_release_driver_internal+0xec/0x1b0
  device_release_driver+0x12/0x20
  bus_remove_device+0xe1/0x150
  device_del+0x17d/0x3e0
  usb_disable_device+0x9f/0x250
  usb_disconnect+0xc6/0x270
  hub_event+0x6da/0x18d0
  process_one_work+0x20c/0x400
  worker_thread+0x34/0x400

RIP: 0010:__queue_work+0x92/0x3f0

NULL deference occurs in hci_update_background_scan() while it tries
to queue_work on already destroyed workqueues.

Change hci_unregister_dev() to invoke destroy_workqueues after the
call to hci_adv_monitors_clear().

Signed-off-by: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@xxxxxxxxx>
---
 net/bluetooth/hci_core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 7959b85..5577cf9 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -3795,9 +3795,6 @@ void hci_unregister_dev(struct hci_dev *hdev)
 	kfree_const(hdev->hw_info);
 	kfree_const(hdev->fw_info);
 
-	destroy_workqueue(hdev->workqueue);
-	destroy_workqueue(hdev->req_workqueue);
-
 	hci_dev_lock(hdev);
 	hci_bdaddr_list_clear(&hdev->blacklist);
 	hci_bdaddr_list_clear(&hdev->whitelist);
@@ -3815,6 +3812,9 @@ void hci_unregister_dev(struct hci_dev *hdev)
 	hci_blocked_keys_clear(hdev);
 	hci_dev_unlock(hdev);
 
+	destroy_workqueue(hdev->workqueue);
+	destroy_workqueue(hdev->req_workqueue);
+
 	hci_dev_put(hdev);
 
 	ida_simple_remove(&hci_index_ida, id);
-- 
2.7.4