diff mbox series

[V3,17/17] Bluetooth: hci_qca: Fix the teardown problem for real

Message ID 20221123201625.435907114@linutronix.de
State New
Headers
Series timers: Provide timer_shutdown[_sync]() |

Commit Message

Thomas Gleixner Nov. 23, 2022, 8:18 p.m. UTC 
  While discussing solutions for the teardown problem which results from
circular dependencies between timers and workqueues, where timers schedule
work from their timer callback and workqueues arm the timers from work
items, it was discovered that the recent fix to the QCA code is incorrect.

That commit fixes the obvious problem of using del_timer() instead of
del_timer_sync() and reorders the teardown calls to

   destroy_workqueue(wq);
   del_timer_sync(t);

This makes it less likely to explode, but it's still broken:

   destroy_workqueue(wq);
   /* After this point @wq cannot be touched anymore */

   ---> timer expires
         queue_work(wq) <---- Results in a NULl pointer dereference
			      deep in the work queue core code.
   del_timer_sync(t);

Use the new timer_shutdown_sync() function to ensure that the timers are
disarmed, no timer callbacks are running and the timers cannot be armed
again. This restores the original teardown sequence:

   timer_shutdown_sync(t);
   destroy_workqueue(wq);

which is now correct because the timer core silently ignores potential
rearming attempts which can happen when destroy_workqueue() drains pending
work before mopping up the workqueue.

Fixes: 72ef98445aca ("Bluetooth: hci_qca: Use del_timer_sync() before freeing")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: Johan Hedberg <johan.hedberg@gmail.com>
Cc: linux-bluetooth@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: netdev@vger.kernel.org
Link: https://lore.kernel.org/all/87iljhsftt.ffs@tglx
---
 drivers/bluetooth/hci_qca.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Comments

Anna-Maria Behnsen Nov. 24, 2022, 1:56 p.m. UTC | #1 
On Wed, 23 Nov 2022, Thomas Gleixner wrote:

> While discussing solutions for the teardown problem which results from
> circular dependencies between timers and workqueues, where timers schedule
> work from their timer callback and workqueues arm the timers from work
> items, it was discovered that the recent fix to the QCA code is incorrect.
> 
> That commit fixes the obvious problem of using del_timer() instead of
> del_timer_sync() and reorders the teardown calls to
> 
>    destroy_workqueue(wq);
>    del_timer_sync(t);
> 
> This makes it less likely to explode, but it's still broken:
> 
>    destroy_workqueue(wq);
>    /* After this point @wq cannot be touched anymore */
> 
>    ---> timer expires
>          queue_work(wq) <---- Results in a NULl pointer dereference

The last NIT (for now...): s/NULl/NULL

Thanks,

	Anna-Maria
diff mbox series

Patch

--- a/drivers/bluetooth/hci_qca.c
+++ b/drivers/bluetooth/hci_qca.c
@@ -696,9 +696,15 @@  static int qca_close(struct hci_uart *hu
 	skb_queue_purge(&qca->tx_wait_q);
 	skb_queue_purge(&qca->txq);
 	skb_queue_purge(&qca->rx_memdump_q);
+	/*
+	 * Shut the timers down so they can't be rearmed when
+	 * destroy_workqueue() drains pending work which in turn might try
+	 * to arm a timer.  After shutdown rearm attempts are silently
+	 * ignored by the timer core code.
+	 */
+	timer_shutdown_sync(&qca->tx_idle_timer);
+	timer_shutdown_sync(&qca->wake_retrans_timer);
 	destroy_workqueue(qca->workqueue);
-	del_timer_sync(&qca->tx_idle_timer);
-	del_timer_sync(&qca->wake_retrans_timer);
 	qca->hu = NULL;
 
 	kfree_skb(qca->rx_skb);