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

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Date:   Mon, 9 Jan 2023 13:51:41 +0200
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Ido Schimmel <idosch@...sch.org>,
        Vladimir Oltean <olteanv@...il.com>
Cc:     Tobias Waldekranz <tobias@...dekranz.com>, davem@...emloft.net,
        kuba@...nel.org, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...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 09/01/2023 13:43, Ido Schimmel wrote:
> On Mon, Jan 09, 2023 at 12:02:36PM +0200, Vladimir Oltean wrote:
>> On Mon, Jan 09, 2023 at 10:05:53AM +0200, Ido Schimmel wrote:
>>>> +	if (on)
>>>> +		static_branch_enable(&br_mst_used);
>>>> +	else
>>>> +		static_branch_disable(&br_mst_used);
>>>
>>> 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?
>>
>> Sounds about right. FWIW, br_switchdev_tx_fwd_offload does use
>> static_branch_inc() / static_branch_dec().
> 
> OK, thanks for confirming. Will send a patch later this week if Tobias
> won't take care of it by then. First patch will probably be [1] to make
> sure we dump the correct MST state to user space. It will also make it
> easier to show the problem and validate the fix.
> 
> [1]
> diff --git a/net/bridge/br.c b/net/bridge/br.c
> index 4f5098d33a46..f02a1ad589de 100644
> --- a/net/bridge/br.c
> +++ b/net/bridge/br.c
> @@ -286,7 +286,7 @@ int br_boolopt_get(const struct net_bridge *br, enum br_boolopt_id opt)
>  	case BR_BOOLOPT_MCAST_VLAN_SNOOPING:
>  		return br_opt_get(br, BROPT_MCAST_VLAN_SNOOPING_ENABLED);
>  	case BR_BOOLOPT_MST_ENABLE:
> -		return br_opt_get(br, BROPT_MST_ENABLED);
> +		return br_mst_is_enabled(br);
>  	default:
>  		/* shouldn't be called with unsupported options */
>  		WARN_ON(1);
> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> index 75aff9bbf17e..7f0475f62d45 100644
> --- a/net/bridge/br_private.h
> +++ b/net/bridge/br_private.h
> @@ -1827,7 +1827,7 @@ static inline bool br_vlan_state_allowed(u8 state, bool learn_allow)
>  /* br_mst.c */
>  #ifdef CONFIG_BRIDGE_VLAN_FILTERING
>  DECLARE_STATIC_KEY_FALSE(br_mst_used);
> -static inline bool br_mst_is_enabled(struct net_bridge *br)
> +static inline bool br_mst_is_enabled(const struct net_bridge *br)
>  {
>  	return static_branch_unlikely(&br_mst_used) &&
>  		br_opt_get(br, BROPT_MST_ENABLED);
> @@ -1845,7 +1845,7 @@ int br_mst_fill_info(struct sk_buff *skb,
>  int br_mst_process(struct net_bridge_port *p, const struct nlattr *mst_attr,
>  		   struct netlink_ext_ack *extack);
>  #else
> -static inline bool br_mst_is_enabled(struct net_bridge *br)
> +static inline bool br_mst_is_enabled(const struct net_bridge *br)
>  {
>  	return false;
>  }

Ack, good catch. This should've been _inc/_dec indeed.

Thanks,
 Nik