linux-kernel - Re: [PATCH v5 net-next 01/15] net: bridge: mst: Multiple Spanning Tree (MST) mode

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Date:   Mon, 9 Jan 2023 10:05:53 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     davem@...emloft.net, kuba@...nel.org,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Petr Machata <petrm@...dia.com>,
        Ido Schimmel <idosch@...dia.com>,
        Matt Johnston <matt@...econstruct.com.au>,
        Cooper Lees <me@...perlees.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH v5 net-next 01/15] net: bridge: mst: Multiple Spanning
 Tree (MST) mode

On Wed, Mar 16, 2022 at 04:08:43PM +0100, Tobias Waldekranz wrote:
> +DEFINE_STATIC_KEY_FALSE(br_mst_used);

[...]

> +int br_mst_set_enabled(struct net_bridge *br, bool on,
> +		       struct netlink_ext_ack *extack)
> +{
> +	struct net_bridge_vlan_group *vg;
> +	struct net_bridge_port *p;
> +
> +	list_for_each_entry(p, &br->port_list, list) {
> +		vg = nbp_vlan_group(p);
> +
> +		if (!vg->num_vlans)
> +			continue;
> +
> +		NL_SET_ERR_MSG(extack,
> +			       "MST mode can't be changed while VLANs exist");
> +		return -EBUSY;
> +	}
> +
> +	if (br_opt_get(br, BROPT_MST_ENABLED) == on)
> +		return 0;
> +
> +	if (on)
> +		static_branch_enable(&br_mst_used);
> +	else
> +		static_branch_disable(&br_mst_used);
> +
> +	br_opt_toggle(br, BROPT_MST_ENABLED, on);
> +	return 0;
> +}

Hi,

I'm not actually using MST, but I ran into this code and was wondering
if the static key usage is correct. The static key is global (not
per-bridge), so what happens when two bridges have MST enabled and then
it is disabled on one? I believe it would be disabled for both. If so,
maybe use static_branch_inc() / static_branch_dec() instead?

Thanks