[PATCH 5.2 12/94] taprio: Fix kernel panic in taprio_destroy

From: Greg Kroah-Hartman
Date: Sun Sep 08 2019 - 08:51:35 EST

From: Vladimir Oltean <olteanv@xxxxxxxxx>

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@xxxxxxxxx>
Fixes: 7b9eba7ba0c1 ("net/sched: taprio: fix picos_per_byte miscalculation")
Signed-off-by: Vladimir Oltean <olteanv@xxxxxxxxx>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/sched/sch_taprio.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -903,6 +903,10 @@ static int taprio_init(struct Qdisc *sch
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)

@@ -920,10 +924,6 @@ static int taprio_init(struct Qdisc *sch
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;