Re: [PATCH bpf-next v2 2/7] bpf: Add fd-based tcx multi-prog infra with link support

[Jakub Kicinski <kuba@kernel.org>]

On Wed,  7 Jun 2023 21:26:20 +0200 Daniel Borkmann wrote:
> +	dev = dev_get_by_index(net, attr->link_create.target_ifindex);
> +	if (!dev)
> +		return -EINVAL;
> +	link = kzalloc(sizeof(*link), GFP_USER);
> +	if (!link) {
> +		err = -ENOMEM;
> +		goto out_put;
> +	}
> +
> +	bpf_link_init(&link->link, BPF_LINK_TYPE_TCX, &tcx_link_lops, prog);
> +	link->location = attr->link_create.attach_type;
> +	link->flags = attr->link_create.flags & (BPF_F_FIRST | BPF_F_LAST);
> +	link->dev = dev;
> +
> +	err = bpf_link_prime(&link->link, &link_primer);
> +	if (err) {
> +		kfree(link);
> +		goto out_put;
> +	}
> +	rtnl_lock();

How does this work vs device unregistering? 

Best I can tell (and it is a large patch :() the device may have passed
dev_tcx_uninstall() by the time we take the lock.

> +	err = tcx_link_prog_attach(&link->link, attr->link_create.flags,
> +				   attr->link_create.tcx.relative_fd,
> +				   attr->link_create.tcx.expected_revision);
> +	if (!err)
> +		fd = bpf_link_settle(&link_primer);
> +	rtnl_unlock();