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Date: Mon, 9 Jan 2023 10:05:53 +0200
From: Ido Schimmel <idosch@idosch.org>
Message-ID: <Y7vK4T18pOZ9KAKE@shredder>
References: <20220316150857.2442916-1-tobias@waldekranz.com>
 <20220316150857.2442916-2-tobias@waldekranz.com>
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Subject: Re: [Bridge] [PATCH v5 net-next 01/15] net: bridge: mst: Multiple
 Spanning Tree (MST) mode
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To: Tobias Waldekranz <tobias@waldekranz.com>
Cc: Ivan Vecera <ivecera@redhat.com>, Andrew Lunn <andrew@lunn.ch>, Florian Fainelli <f.fainelli@gmail.com>, Jiri Pirko <jiri@resnulli.us>, Petr Machata <petrm@nvidia.com>, Nikolay Aleksandrov <razor@blackwall.org>, bridge@lists.linux-foundation.org, Russell King <linux@armlinux.org.uk>, Vivien Didelot <vivien.didelot@gmail.com>, Ido Schimmel <idosch@nvidia.com>, netdev@vger.kernel.org, Cooper Lees <me@cooperlees.com>, Roopa Prabhu <roopa@nvidia.com>, kuba@kernel.org, Matt Johnston <matt@codeconstruct.com.au>, Vladimir Oltean <olteanv@gmail.com>, davem@davemloft.net, linux-kernel@vger.kernel.org

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