Subject: Re: [PATCH net 1/3] taprio: Fix kernel panic in taprio_destroy

From: Vinicius Costa Gomes <[email-masked]>
Date: Wed, 28 Aug 2019 09:31:04 -0700

Hi,

Vladimir Oltean <[email-masked]> writes:

> 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.

Good catch.

>
> 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 iterating through the list and removing it only if found.
>
> Signed-off-by: Vladimir Oltean <[email-masked]>
> ---
>  net/sched/sch_taprio.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> index 540bde009ea5..f1eea8c68011 100644
> --- a/net/sched/sch_taprio.c
> +++ b/net/sched/sch_taprio.c
> @@ -1199,12 +1199,17 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
>  
>  static void taprio_destroy(struct Qdisc *sch)
>  {
> -	struct taprio_sched *q = qdisc_priv(sch);
> +	struct taprio_sched *p, *q = qdisc_priv(sch);
>  	struct net_device *dev = qdisc_dev(sch);
> +	struct list_head *pos, *tmp;
>  	unsigned int i;
>  
>  	spin_lock(&taprio_list_lock);
> -	list_del(&q->taprio_list);
> +	list_for_each_safe(pos, tmp, &taprio_list) {
> +		p = list_entry(pos, struct taprio_sched, taprio_list);
> +		if (p == q)
> +			list_del(&q->taprio_list);
> +	}

Personally, I would do things differently, I am thinking: adding the
taprio instance earlier to the list in taprio_init(), and keeping
taprio_destroy() the way it is now. But take this more as a suggestion
:-)

Cheers,
--
Vinicius