Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting

[Jakub Kicinski]

On Fri,  5 May 2023 17:16:10 -0700 Peilin Ye wrote:
>  		} else {
> -			dev_queue = dev_ingress_queue(dev);
> -			old = dev_graft_qdisc(dev_queue, new);
> +			old = dev_graft_qdisc(dev_queue, NULL);
> +
> +			/* {ingress,clsact}_destroy() "old" before grafting "new" to avoid
> +			 * unprotected concurrent accesses to net_device::miniq_{in,e}gress
> +			 * pointer(s) in mini_qdisc_pair_swap().
> +			 */
> +			qdisc_notify(net, skb, n, classid, old, new, extack);
> +			qdisc_destroy(old);
> +
> +			dev_graft_qdisc(dev_queue, new);

BTW can't @old be NULL here?