[PATCH net 14/14] batman-adv: tp_meter: directly shut down timer on cleanup

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

batadv_tp_sender_cleanup() was calling timer_delete_sync() followed by
timer_delete() to guard against the timer handler re-arming itself between
the two calls. This double-deletion hack relied on the sending status being
set to 0 to suppress re-arming.

Replace both calls with a single timer_shutdown_sync(). This function both
waits for any running timer callback to complete (like timer_delete_sync())
and permanently disarms the timer so it cannot be re-armed afterwards,
making re-arming prevention unconditional and self-documenting.

The re-arming property is also required because otherwise:

1. context 0 (batadv_tp_recv_ack()) checks in
   batadv_tp_reset_sender_timer() if sending is still 1 -> it is
2. context 1 changes in batadv_tp_sender_shutdown() sending to 0 and in
   this process forces the kthread to stop timer in
   batadv_tp_sender_cleanup()
3. context 0 continues in batadv_tp_reset_sender_timer() and rearms the
   timer -> but the reference for it is already gone

Cc: stable@kernel.org
Fixes: 33a3bb4a3345 ("batman-adv: throughput meter implementation")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/tp_meter.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/net/batman-adv/tp_meter.c b/net/batman-adv/tp_meter.c
index a3593d104caa5..1fd1526059d8a 100644
--- a/net/batman-adv/tp_meter.c
+++ b/net/batman-adv/tp_meter.c
@@ -401,13 +401,7 @@ static void batadv_tp_sender_cleanup(struct batadv_tp_vars *tp_vars)
 	batadv_tp_list_detach(tp_vars);
 
 	/* kill the timer and remove its reference */
-	timer_delete_sync(&tp_vars->timer);
-	/* the worker might have rearmed itself therefore we kill it again. Note
-	 * that if the worker should run again before invoking the following
-	 * timer_delete(), it would not re-arm itself once again because the status
-	 * is OFF now
-	 */
-	timer_delete(&tp_vars->timer);
+	timer_shutdown_sync(&tp_vars->timer);
 	batadv_tp_vars_put(tp_vars);
 }
 
-- 
2.47.3