taprio: Fix kernel panic in taprio_destroy

taprio_init may fail earlier than this line:

	list_add(&q->taprio_list, &taprio_list);

i.e. due to the net device not being multi queue.

Attempting to remove q from the global taprio_list when it is not part
of it will result in a kernel panic.

Fix it by matching list_add and list_del better to one another in the
order of operations. This way we can keep the deletion unconditional
and with lower complexity - O(1).

Cc: Leandro Dorileo <leandro.maciel.dorileo@intel.com>
Fixes: 3deb56c37c94 ("net/sched: taprio: fix picos_per_byte miscalculation")
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index e25d414ae12fdd9a7c4b8ea1903293e36e4ae12a..8c85f61e98ddad826868b7a81f527cbfb7e2fdb1 100644 (file)
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1249,6 +1249,10 @@ static int taprio_init(struct Qdisc *sch, struct nlattr *opt,
         */
        q->clockid = -1;
 
+       spin_lock(&taprio_list_lock);
+       list_add(&q->taprio_list, &taprio_list);
+       spin_unlock(&taprio_list_lock);
+
        if (sch->parent != TC_H_ROOT)
                return -EOPNOTSUPP;
 
@@ -1266,10 +1270,6 @@ static int taprio_init(struct Qdisc *sch, struct nlattr *opt,
        if (!opt)
                return -EINVAL;
 
-       spin_lock(&taprio_list_lock);
-       list_add(&q->taprio_list, &taprio_list);
-       spin_unlock(&taprio_list_lock);
-
        for (i = 0; i < dev->num_tx_queues; i++) {
                struct netdev_queue *dev_queue;
                struct Qdisc *qdisc;