Subject: Re: [patch net-next] net: sched: move block device tracking into tcf_block_get/put_ext()

From: Ido Schimmel <[email-masked]>
Date: Wed, 10 Jan 2024 14:09:55 +0200

On Thu, Jan 04, 2024 at 01:58:44PM +0100, Jiri Pirko wrote:
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index adf5de1ff773..253b26f2eddd 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -1428,6 +1428,7 @@ int tcf_block_get_ext(struct tcf_block **p_block, struct Qdisc *q,
>  		      struct tcf_block_ext_info *ei,
>  		      struct netlink_ext_ack *extack)
>  {
> +	struct net_device *dev = qdisc_dev(q);
>  	struct net *net = qdisc_net(q);
>  	struct tcf_block *block = NULL;
>  	int err;
> @@ -1461,9 +1462,18 @@ int tcf_block_get_ext(struct tcf_block **p_block, struct Qdisc *q,
>  	if (err)
>  		goto err_block_offload_bind;
>  
> +	if (tcf_block_shared(block)) {
> +		err = xa_insert(&block->ports, dev->ifindex, dev, GFP_KERNEL);
> +		if (err) {
> +			NL_SET_ERR_MSG(extack, "block dev insert failed");
> +			goto err_dev_insert;
> +		}
> +	}

While this patch fixes the original issue, it creates another one:

# ip link add name swp1 type dummy
# tc qdisc replace dev swp1 root handle 10: prio bands 8 priomap 7 6 5 4 3 2 1
# tc qdisc add dev swp1 parent 10:8 handle 108: red limit 1000000 min 200000 max 200001 probability 1.0 avpkt 8000 burst 38 qevent early_drop block 10
RED: set bandwidth to 10Mbit
# tc qdisc add dev swp1 parent 10:7 handle 107: red limit 1000000 min 500000 max 500001 probability 1.0 avpkt 8000 burst 63 qevent early_drop block 10
RED: set bandwidth to 10Mbit
Error: block dev insert failed.

The reproducer does not fail if I revert this patch and apply Victor's
[1] instead.

[1] https://lore.kernel.org/netdev/[email-masked]/

> +
>  	*p_block = block;
>  	return 0;
>  
> +err_dev_insert:
>  err_block_offload_bind:
>  	tcf_chain0_head_change_cb_del(block, ei);
>  err_chain0_head_change_cb_add: